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dart / sdk / 69a4f203479952c45c729d5fffaf0cea5edf5c78 / . / pkg / compiler / lib / src / ssa / optimize.dart
blob: e5842105ef60418b8166192d282c58ea2a081e51 [file] [log] [blame]
// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import '../common.dart';
import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
import '../common/names.dart' show Selectors;
import '../common/tasks.dart' show CompilerTask;
import '../compiler.dart' show Compiler;
import '../constants/constant_system.dart' as constant_system;
import '../constants/values.dart';
import '../common_elements.dart' show JCommonElements;
import '../elements/entities.dart';
import '../elements/types.dart';
import '../inferrer/abstract_value_domain.dart';
import '../inferrer/types.dart';
import '../js_backend/field_analysis.dart'
show FieldAnalysisData, JFieldAnalysis;
import '../js_backend/backend.dart';
import '../js_backend/native_data.dart' show NativeData;
import '../js_backend/runtime_types.dart';
import '../native/behavior.dart';
import '../options.dart';
import '../universe/selector.dart' show Selector;
import '../universe/side_effects.dart' show SideEffects;
import '../universe/use.dart' show StaticUse;
import '../util/util.dart';
import '../world.dart' show JClosedWorld;
import 'interceptor_simplifier.dart';
import 'logging.dart';
import 'nodes.dart';
import 'types.dart';
import 'types_propagation.dart';
import 'value_range_analyzer.dart';
import 'value_set.dart';
abstract class OptimizationPhase {
String get name;
void visitGraph(HGraph graph);
}
class SsaOptimizerTask extends CompilerTask {
final JavaScriptBackend _backend;
Map<HInstruction, Range> ranges = <HInstruction, Range>{};
Map<MemberEntity, OptimizationTestLog> loggersForTesting;
SsaOptimizerTask(this._backend) : super(_backend.compiler.measurer);
@override
String get name => 'SSA optimizer';
Compiler get _compiler => _backend.compiler;
CompilerOptions get _options => _compiler.options;
RuntimeTypesSubstitutions get _rtiSubstitutions => _backend.rtiSubstitutions;
void optimize(CodegenWorkItem work, HGraph graph, JClosedWorld closedWorld,
GlobalTypeInferenceResults globalInferenceResults) {
void runPhase(OptimizationPhase phase) {
measureSubtask(phase.name, () => phase.visitGraph(graph));
_backend.tracer.traceGraph(phase.name, graph);
assert(graph.isValid(), 'Graph not valid after ${phase.name}');
}
bool trustPrimitives = _options.trustPrimitives;
CodegenRegistry registry = work.registry;
Set<HInstruction> boundsChecked = new Set<HInstruction>();
SsaCodeMotion codeMotion;
SsaLoadElimination loadElimination;
OptimizationTestLog log;
if (retainDataForTesting) {
loggersForTesting ??= {};
loggersForTesting[work.element] = log = new OptimizationTestLog();
}
measure(() {
List<OptimizationPhase> phases = <OptimizationPhase>[
// Run trivial instruction simplification first to optimize
// some patterns useful for type conversion.
new SsaInstructionSimplifier(globalInferenceResults, _options,
_rtiSubstitutions, closedWorld, registry, log),
new SsaTypeConversionInserter(closedWorld),
new SsaRedundantPhiEliminator(),
new SsaDeadPhiEliminator(),
new SsaTypePropagator(globalInferenceResults, _options,
closedWorld.commonElements, closedWorld, log),
// After type propagation, more instructions can be
// simplified.
new SsaInstructionSimplifier(globalInferenceResults, _options,
_rtiSubstitutions, closedWorld, registry, log),
new SsaCheckInserter(trustPrimitives, closedWorld, boundsChecked),
new SsaInstructionSimplifier(globalInferenceResults, _options,
_rtiSubstitutions, closedWorld, registry, log),
new SsaCheckInserter(trustPrimitives, closedWorld, boundsChecked),
new SsaTypePropagator(globalInferenceResults, _options,
closedWorld.commonElements, closedWorld, log),
// Run a dead code eliminator before LICM because dead
// interceptors are often in the way of LICM'able instructions.
new SsaDeadCodeEliminator(closedWorld, this),
new SsaGlobalValueNumberer(closedWorld.abstractValueDomain),
// After GVN, some instructions might need their type to be
// updated because they now have different inputs.
new SsaTypePropagator(globalInferenceResults, _options,
closedWorld.commonElements, closedWorld, log),
codeMotion = new SsaCodeMotion(closedWorld.abstractValueDomain),
loadElimination = new SsaLoadElimination(_compiler, closedWorld),
new SsaRedundantPhiEliminator(),
new SsaDeadPhiEliminator(),
// After GVN and load elimination the same value may be used in code
// controlled by a test on the value, so redo 'conversion insertion' to
// learn from the refined type.
new SsaTypeConversionInserter(closedWorld),
new SsaTypePropagator(globalInferenceResults, _options,
closedWorld.commonElements, closedWorld, log),
new SsaValueRangeAnalyzer(closedWorld, this),
// Previous optimizations may have generated new
// opportunities for instruction simplification.
new SsaInstructionSimplifier(globalInferenceResults, _options,
_rtiSubstitutions, closedWorld, registry, log),
new SsaCheckInserter(trustPrimitives, closedWorld, boundsChecked),
];
phases.forEach(runPhase);
// Simplifying interceptors is not strictly just an optimization, it is
// required for implementation correctness because the code generator
// assumes it is always performed.
runPhase(new SsaSimplifyInterceptors(
closedWorld, work.element.enclosingClass));
SsaDeadCodeEliminator dce = new SsaDeadCodeEliminator(closedWorld, this);
runPhase(dce);
if (codeMotion.movedCode ||
dce.eliminatedSideEffects ||
loadElimination.newGvnCandidates) {
phases = <OptimizationPhase>[
new SsaTypePropagator(globalInferenceResults, _options,
closedWorld.commonElements, closedWorld, log),
new SsaGlobalValueNumberer(closedWorld.abstractValueDomain),
new SsaCodeMotion(closedWorld.abstractValueDomain),
new SsaValueRangeAnalyzer(closedWorld, this),
new SsaInstructionSimplifier(globalInferenceResults, _options,
_rtiSubstitutions, closedWorld, registry, log),
new SsaCheckInserter(trustPrimitives, closedWorld, boundsChecked),
new SsaSimplifyInterceptors(closedWorld, work.element.enclosingClass),
new SsaDeadCodeEliminator(closedWorld, this),
];
} else {
phases = <OptimizationPhase>[
new SsaTypePropagator(globalInferenceResults, _options,
closedWorld.commonElements, closedWorld, log),
// Run the simplifier to remove unneeded type checks inserted by
// type propagation.
new SsaInstructionSimplifier(globalInferenceResults, _options,
_rtiSubstitutions, closedWorld, registry, log),
];
}
phases.forEach(runPhase);
});
}
}
/// Returns `true` if [mask] represents only types that have a length that
/// cannot change. The current implementation is conservative for the purpose
/// of identifying gvn-able lengths and mis-identifies some unions of fixed
/// length indexables (see TODO) as not fixed length.
bool isFixedLength(AbstractValue mask, JClosedWorld closedWorld) {
AbstractValueDomain abstractValueDomain = closedWorld.abstractValueDomain;
if (abstractValueDomain.isContainer(mask) &&
abstractValueDomain.getContainerLength(mask) != null) {
// A container on which we have inferred the length.
return true;
}
// TODO(sra): Recognize any combination of fixed length indexables.
if (abstractValueDomain.isFixedArray(mask).isDefinitelyTrue ||
abstractValueDomain.isStringOrNull(mask).isDefinitelyTrue ||
abstractValueDomain.isTypedArray(mask).isDefinitelyTrue) {
return true;
}
return false;
}
/// If both inputs to known operations are available execute the operation at
/// compile-time.
class SsaInstructionSimplifier extends HBaseVisitor
implements OptimizationPhase {
// We don't produce constant-folded strings longer than this unless they have
// a single use. This protects against exponentially large constant folded
// strings.
static const MAX_SHARED_CONSTANT_FOLDED_STRING_LENGTH = 512;
@override
final String name = "SsaInstructionSimplifier";
final GlobalTypeInferenceResults _globalInferenceResults;
final CompilerOptions _options;
final RuntimeTypesSubstitutions _rtiSubstitutions;
final JClosedWorld _closedWorld;
final CodegenRegistry _registry;
final OptimizationTestLog _log;
HGraph _graph;
SsaInstructionSimplifier(this._globalInferenceResults, this._options,
this._rtiSubstitutions, this._closedWorld, this._registry, this._log);
JCommonElements get commonElements => _closedWorld.commonElements;
AbstractValueDomain get _abstractValueDomain =>
_closedWorld.abstractValueDomain;
NativeData get _nativeData => _closedWorld.nativeData;
@override
void visitGraph(HGraph visitee) {
_graph = visitee;
visitDominatorTree(visitee);
}
@override
visitBasicBlock(HBasicBlock block) {
simplifyPhis(block);
HInstruction instruction = block.first;
while (instruction != null) {
HInstruction next = instruction.next;
HInstruction replacement = instruction.accept(this);
if (replacement != instruction) {
block.rewrite(instruction, replacement);
// The intersection of double and int return conflicting, and
// because of our number implementation for JavaScript, it
// might be that an operation thought to return double, can be
// simplified to an int. For example:
// `2.5 * 10`.
if (!(replacement
.isNumberOrNull(_abstractValueDomain)
.isDefinitelyTrue &&
instruction
.isNumberOrNull(_abstractValueDomain)
.isDefinitelyTrue)) {
// If we can replace [instruction] with [replacement], then
// [replacement]'s type can be narrowed.
AbstractValue newType = _abstractValueDomain.intersection(
replacement.instructionType, instruction.instructionType);
replacement.instructionType = newType;
}
// If the replacement instruction does not know its
// source element, use the source element of the
// instruction.
replacement.sourceElement ??= instruction.sourceElement;
replacement.sourceInformation ??= instruction.sourceInformation;
if (!replacement.isInBasicBlock()) {
// The constant folding can return an instruction that is already
// part of the graph (like an input), so we only add the replacement
// if necessary.
block.addAfter(instruction, replacement);
// Visit the replacement as the next instruction in case it
// can also be constant folded away.
next = replacement;
}
block.remove(instruction);
}
instruction = next;
}
}
// Simplify some CFG diamonds to equivalent expressions.
simplifyPhis(HBasicBlock block) {
// Is [block] the join point for a simple diamond that generates a single
// phi node?
if (block.phis.isEmpty) return;
HPhi phi = block.phis.first;
if (phi.next != null) return;
if (block.predecessors.length != 2) return;
assert(phi.inputs.length == 2);
HBasicBlock b1 = block.predecessors[0];
HBasicBlock b2 = block.predecessors[1];
HBasicBlock dominator = block.dominator;
if (!(b1.dominator == dominator && b2.dominator == dominator)) return;
// Extract the controlling condition.
HInstruction controlFlow = dominator.last;
if (controlFlow is! HIf) return;
HInstruction test = controlFlow.inputs.single;
if (test.usedBy.length > 1) return;
bool negated = false;
while (test is HNot) {
test = test.inputs.single;
if (test.usedBy.length > 1) return;
negated = !negated;
}
if (test is! HIdentity) return;
HInstruction tested;
if (test.inputs[0].isNull(_abstractValueDomain).isDefinitelyTrue) {
tested = test.inputs[1];
} else if (test.inputs[1].isNull(_abstractValueDomain).isDefinitelyTrue) {
tested = test.inputs[0];
} else {
return;
}
HInstruction whenNullValue = phi.inputs[negated ? 1 : 0];
HInstruction whenNotNullValue = phi.inputs[negated ? 0 : 1];
HBasicBlock whenNullBlock = block.predecessors[negated ? 1 : 0];
HBasicBlock whenNotNullBlock = block.predecessors[negated ? 0 : 1];
// If 'x' is nullable boolean,
//
// x == null ? false : x ---> x == true
//
// This ofen comes from the dart code `x ?? false`.
if (_sameOrRefinementOf(tested, whenNotNullValue) &&
_isBoolConstant(whenNullValue, false) &&
whenNotNullValue
.isBooleanOrNull(_abstractValueDomain)
.isDefinitelyTrue &&
_mostlyEmpty(whenNullBlock) &&
_mostlyEmpty(whenNotNullBlock)) {
HInstruction trueConstant = _graph.addConstantBool(true, _closedWorld);
HInstruction replacement = new HIdentity(
tested, trueConstant, null, _abstractValueDomain.boolType)
..sourceElement = phi.sourceElement
..sourceInformation = phi.sourceInformation;
block.rewrite(phi, replacement);
block.addAtEntry(replacement);
block.removePhi(phi);
return;
}
// If 'x'is nullable boolean,
//
// x == null ? true : x ---> !(x == false)
//
// This ofen comes from the dart code `x ?? true`.
if (_sameOrRefinementOf(tested, whenNotNullValue) &&
_isBoolConstant(whenNullValue, true) &&
whenNotNullValue
.isBooleanOrNull(_abstractValueDomain)
.isDefinitelyTrue &&
_mostlyEmpty(whenNullBlock) &&
_mostlyEmpty(whenNotNullBlock)) {
HInstruction falseConstant = _graph.addConstantBool(false, _closedWorld);
HInstruction compare = new HIdentity(
tested, falseConstant, null, _abstractValueDomain.boolType);
block.addAtEntry(compare);
HInstruction replacement =
new HNot(compare, _abstractValueDomain.boolType)
..sourceElement = phi.sourceElement
..sourceInformation = phi.sourceInformation;
block.rewrite(phi, replacement);
block.addAfter(compare, replacement);
block.removePhi(phi);
return;
}
// TODO(sra): Consider other simple diamonds, e.g. with the addition of a special instruction,
//
// s == null ? "" : s ---> s || "".
return;
}
bool _isBoolConstant(HInstruction node, bool value) {
if (node is HConstant) {
ConstantValue c = node.constant;
if (c is BoolConstantValue) {
return c.boolValue == value;
}
}
return false;
}
bool _sameOrRefinementOf(HInstruction base, HInstruction insn) {
if (base == insn) return true;
if (insn is HTypeKnown) return _sameOrRefinementOf(base, insn.checkedInput);
return false;
}
bool _mostlyEmpty(HBasicBlock block) {
for (HInstruction insn = block.first; insn != null; insn = insn.next) {
if (insn is HTypeKnown) continue;
if (insn is HGoto) return true;
return false;
}
return true;
}
@override
HInstruction visitInstruction(HInstruction node) {
return node;
}
ConstantValue getConstantFromType(HInstruction node) {
if (node.isValue(_abstractValueDomain) &&
node.isNull(_abstractValueDomain).isDefinitelyFalse) {
ConstantValue value =
_abstractValueDomain.getPrimitiveValue(node.instructionType);
if (value.isBool) {
return value;
}
// TODO(het): consider supporting other values (short strings?)
}
return null;
}
void propagateConstantValueToUses(HInstruction node) {
if (node.usedBy.isEmpty) return;
ConstantValue value = getConstantFromType(node);
if (value != null) {
HConstant constant = _graph.addConstant(value, _closedWorld);
for (HInstruction user in node.usedBy.toList()) {
user.changeUse(node, constant);
}
}
}
@override
HInstruction visitParameterValue(HParameterValue node) {
// [HParameterValue]s are either the value of the parameter (in fully SSA
// converted code), or the mutable variable containing the value (in
// incompletely SSA converted code, e.g. methods containing exceptions).
//
// If the parameter is used as a mutable variable we cannot replace the
// variable with a value.
//
// If the parameter is used as a mutable variable but never written, first
// convert to a value parameter.
if (node.usedAsVariable()) {
if (!node.usedBy.every((user) => user is HLocalGet)) return node;
// Trivial SSA-conversion. Replace all HLocalGet instructions with the
// parameter.
for (HLocalGet user in node.usedBy.toList()) {
user.block.rewrite(user, node);
user.block.remove(user);
}
}
propagateConstantValueToUses(node);
return node;
}
@override
HInstruction visitBoolify(HBoolify node) {
List<HInstruction> inputs = node.inputs;
assert(inputs.length == 1);
HInstruction input = inputs[0];
if (input.isBoolean(_abstractValueDomain).isDefinitelyTrue) {
return input;
}
// If the code is unreachable, remove the HBoolify. This can happen when
// there is a throw expression in a short-circuit conditional. Removing the
// unreachable HBoolify makes it easier to reconstruct the short-circuit
// operation.
if (_abstractValueDomain.isEmpty(input.instructionType).isDefinitelyTrue) {
return input;
}
// All values that cannot be 'true' are boolified to false.
AbstractValue mask = input.instructionType;
if (_abstractValueDomain
.containsType(mask, commonElements.jsBoolClass)
.isPotentiallyFalse) {
return _graph.addConstantBool(false, _closedWorld);
}
return node;
}
@override
HInstruction visitNot(HNot node) {
List<HInstruction> inputs = node.inputs;
assert(inputs.length == 1);
HInstruction input = inputs[0];
if (input is HConstant) {
HConstant constant = input;
bool isTrue = constant.constant.isTrue;
return _graph.addConstantBool(!isTrue, _closedWorld);
} else if (input is HNot) {
return input.inputs[0];
}
return node;
}
@override
HInstruction visitInvokeUnary(HInvokeUnary node) {
HInstruction folded = foldUnary(node.operation(), node.operand);
return folded != null ? folded : node;
}
HInstruction foldUnary(
constant_system.UnaryOperation operation, HInstruction operand) {
if (operand is HConstant) {
HConstant receiver = operand;
ConstantValue folded = operation.fold(receiver.constant);
if (folded != null) return _graph.addConstant(folded, _closedWorld);
}
return null;
}
HInstruction tryOptimizeLengthInterceptedGetter(HInvokeDynamic node) {
HInstruction actualReceiver = node.inputs[1];
if (actualReceiver
.isIndexablePrimitive(_abstractValueDomain)
.isDefinitelyTrue) {
if (actualReceiver.isConstantString()) {
HConstant constantInput = actualReceiver;
StringConstantValue constant = constantInput.constant;
return _graph.addConstantInt(constant.length, _closedWorld);
} else if (actualReceiver.isConstantList()) {
HConstant constantInput = actualReceiver;
ListConstantValue constant = constantInput.constant;
return _graph.addConstantInt(constant.length, _closedWorld);
}
bool isFixed =
isFixedLength(actualReceiver.instructionType, _closedWorld);
AbstractValue actualType = node.instructionType;
AbstractValue resultType = _abstractValueDomain.positiveIntType;
// If we already have computed a more specific type, keep that type.
if (_abstractValueDomain
.isInstanceOfOrNull(actualType, commonElements.jsUInt31Class)
.isDefinitelyTrue) {
resultType = _abstractValueDomain.uint31Type;
} else if (_abstractValueDomain
.isInstanceOfOrNull(actualType, commonElements.jsUInt32Class)
.isDefinitelyTrue) {
resultType = _abstractValueDomain.uint32Type;
}
HGetLength result =
new HGetLength(actualReceiver, resultType, isAssignable: !isFixed);
return result;
} else if (actualReceiver.isConstantMap()) {
HConstant constantInput = actualReceiver;
MapConstantValue constant = constantInput.constant;
return _graph.addConstantInt(constant.length, _closedWorld);
}
return null;
}
HInstruction handleInterceptedCall(HInvokeDynamic node) {
// Try constant folding the instruction.
constant_system.Operation operation = node.specializer.operation();
if (operation != null) {
HInstruction instruction = node.inputs.length == 2
? foldUnary(operation, node.inputs[1])
: foldBinary(operation, node.inputs[1], node.inputs[2]);
if (instruction != null) return instruction;
}
// Try converting the instruction to a builtin instruction.
HInstruction instruction = node.specializer.tryConvertToBuiltin(
node,
_graph,
_globalInferenceResults,
_options,
commonElements,
_closedWorld,
_log);
if (instruction != null) {
return instruction;
}
Selector selector = node.selector;
AbstractValue mask = node.mask;
HInstruction input = node.inputs[1];
bool applies(MemberEntity element) {
return selector.applies(element) &&
(mask == null ||
_abstractValueDomain
.isTargetingMember(mask, element, selector.memberName)
.isPotentiallyTrue);
}
if (selector.isCall || selector.isOperator) {
FunctionEntity target;
if (input.isExtendableArray(_abstractValueDomain).isDefinitelyTrue) {
if (applies(commonElements.jsArrayRemoveLast)) {
target = commonElements.jsArrayRemoveLast;
} else if (applies(commonElements.jsArrayAdd)) {
// The codegen special cases array calls, but does not
// inline argument type checks.
if (!_options.parameterCheckPolicy.isEmitted ||
input is HLiteralList) {
target = commonElements.jsArrayAdd;
}
}
} else if (input.isStringOrNull(_abstractValueDomain).isDefinitelyTrue) {
if (commonElements.appliesToJsStringSplit(
selector, mask, _abstractValueDomain)) {
return handleStringSplit(node);
} else if (applies(commonElements.jsStringOperatorAdd)) {
// `operator+` is turned into a JavaScript '+' so we need to
// make sure the receiver and the argument are not null.
// TODO(sra): Do this via [node.specializer].
HInstruction argument = node.inputs[2];
if (argument.isString(_abstractValueDomain).isDefinitelyTrue &&
input.isNull(_abstractValueDomain).isDefinitelyFalse) {
return new HStringConcat(input, argument, node.instructionType);
}
} else if (applies(commonElements.jsStringToString) &&
input.isNull(_abstractValueDomain).isDefinitelyFalse) {
return input;
}
}
if (target != null) {
// TODO(ngeoffray): There is a strong dependency between codegen
// and this optimization that the dynamic invoke does not need an
// interceptor. We currently need to keep a
// HInvokeDynamicMethod and not create a HForeign because
// HForeign is too opaque for the SsaCheckInserter (that adds a
// bounds check on removeLast). Once we start inlining, the
// bounds check will become explicit, so we won't need this
// optimization.
HInvokeDynamicMethod result = new HInvokeDynamicMethod(
node.selector,
node.mask,
node.inputs.sublist(1), // Drop interceptor.
node.instructionType,
node.typeArguments,
node.sourceInformation,
isIntercepted: false);
result.element = target;
return result;
}
} else if (selector.isGetter) {
if (commonElements.appliesToJsIndexableLength(selector)) {
HInstruction optimized = tryOptimizeLengthInterceptedGetter(node);
if (optimized != null) return optimized;
}
}
return node;
}
HInstruction handleStringSplit(HInvokeDynamic node) {
HInstruction argument = node.inputs[2];
if (!argument.isString(_abstractValueDomain).isDefinitelyTrue) {
return node;
}
// Replace `s.split$1(pattern)` with
//
// t1 = s.split(pattern);
// t2 = String;
// t3 = JSArray<t2>;
// t4 = setRuntimeTypeInfo(t1, t3);
//
AbstractValue resultMask = _abstractValueDomain.growableListType;
HInvokeDynamicMethod splitInstruction = new HInvokeDynamicMethod(
node.selector,
node.mask,
node.inputs.sublist(1), // Drop interceptor.
resultMask,
const <DartType>[],
node.sourceInformation,
isIntercepted: false)
..element = commonElements.jsStringSplit
..setAllocation(true);
if (!_closedWorld.rtiNeed
.classNeedsTypeArguments(commonElements.jsArrayClass)) {
return splitInstruction;
}
node.block.addBefore(node, splitInstruction);
HInstruction stringTypeInfo = new HTypeInfoExpression(
TypeInfoExpressionKind.COMPLETE,
_closedWorld.elementEnvironment.getThisType(commonElements.stringClass),
<HInstruction>[],
_abstractValueDomain.dynamicType);
node.block.addBefore(node, stringTypeInfo);
HInstruction typeInfo = new HTypeInfoExpression(
TypeInfoExpressionKind.INSTANCE,
_closedWorld.elementEnvironment
.getThisType(commonElements.jsArrayClass),
<HInstruction>[stringTypeInfo],
_abstractValueDomain.dynamicType);
node.block.addBefore(node, typeInfo);
HInvokeStatic tagInstruction = new HInvokeStatic(
commonElements.setRuntimeTypeInfo,
<HInstruction>[splitInstruction, typeInfo],
resultMask,
const <DartType>[]);
// 'Linear typing' trick: [tagInstruction] is the only use of the
// [splitInstruction], so it becomes the sole alias.
// TODO(sra): Build this knowledge into alias analysis.
tagInstruction.setAllocation(true);
return tagInstruction;
}
@override
HInstruction visitInvokeDynamicMethod(HInvokeDynamicMethod node) {
propagateConstantValueToUses(node);
if (node.isInterceptedCall) {
HInstruction folded = handleInterceptedCall(node);
if (folded != node) return folded;
}
HInstruction receiver = node.getDartReceiver(_closedWorld);
AbstractValue receiverType = receiver.instructionType;
MemberEntity element =
_closedWorld.locateSingleMember(node.selector, receiverType);
// TODO(ngeoffray): Also fold if it's a getter or variable.
if (element != null &&
element.isFunction &&
// If we found out that the only target is an implicitly called
// [:noSuchMethod:] we just ignore it.
node.selector.applies(element)) {
FunctionEntity method = element;
if (_nativeData.isNativeMember(method)) {
HInstruction folded = tryInlineNativeMethod(node, method);
if (folded != null) return folded;
} else {
// TODO(ngeoffray): If the method has optional parameters,
// we should pass the default values.
ParameterStructure parameters = method.parameterStructure;
if (parameters.totalParameters == node.selector.argumentCount &&
parameters.typeParameters ==
node.selector.callStructure.typeArgumentCount) {
node.element = method;
}
}
return node;
}
// Replace method calls through fields with a closure call on the value of
// the field. This usually removes the demand for the call-through stub and
// makes the field load available to further optimization, e.g. LICM.
if (element != null &&
element.isField &&
element.name == node.selector.name) {
FieldEntity field = element;
if (!_nativeData.isNativeMember(field) &&
!node.isCallOnInterceptor(_closedWorld)) {
// Insertion point for the closure call.
HInstruction insertionPoint = node;
HInstruction load;
FieldAnalysisData fieldData =
_closedWorld.fieldAnalysis.getFieldData(field);
if (fieldData.isEffectivelyConstant) {
// The field is elided and replace it with its constant value.
if (_abstractValueDomain.isNull(receiverType).isPotentiallyTrue) {
// The receiver is potentially `null` so we insert a null receiver
// guard to trigger a null pointer exception.
//
// This could be inserted unconditionally and removed by later
// optimizations if unnecessary, but performance we do it
// conditionally here.
// TODO(35996): Replace with null receiver guard instruction.
HInstruction dummyGet = new HFieldGet(null, receiver,
_abstractValueDomain.dynamicType, node.sourceInformation,
isAssignable: false);
_log?.registerFieldCall(node, dummyGet);
node.block.addBefore(node, dummyGet);
insertionPoint = dummyGet;
}
ConstantValue value = fieldData.constantValue;
load = _graph.addConstant(value, _closedWorld,
sourceInformation: node.sourceInformation);
_log?.registerConstantFieldCall(node, field, load);
} else {
AbstractValue type = AbstractValueFactory.inferredTypeForMember(
field, _globalInferenceResults);
load = new HFieldGet(field, receiver, type, node.sourceInformation);
_log?.registerFieldCall(node, load);
node.block.addBefore(node, load);
insertionPoint = load;
}
Selector callSelector = new Selector.callClosureFrom(node.selector);
List<HInstruction> inputs = <HInstruction>[load]
..addAll(node.inputs.skip(node.isInterceptedCall ? 2 : 1));
HInstruction closureCall = new HInvokeClosure(
callSelector, inputs, node.instructionType, node.typeArguments)
..sourceInformation = node.sourceInformation;
node.block.addAfter(insertionPoint, closureCall);
return closureCall;
}
}
return node;
}
HInstruction tryInlineNativeMethod(
HInvokeDynamicMethod node, FunctionEntity method) {
// We can replace the call to the native class interceptor method (target)
// if the target does no conversions or useful type checks.
if (_options.disableInlining) return null;
if (_closedWorld.annotationsData.hasNoInline(method)) {
return null;
}
if (!node.isInterceptedCall) return null;
FunctionType type = _closedWorld.elementEnvironment.getFunctionType(method);
if (type.namedParameters.isNotEmpty) return null;
// The call site might omit optional arguments. The inlined code must
// preserve the number of arguments, so check only the actual arguments.
bool canInline = true;
List<HInstruction> inputs = node.inputs;
int inputPosition = 2; // Skip interceptor and receiver.
void checkParameterType(DartType parameterType) {
if (!canInline) return;
if (inputPosition >= inputs.length) return;
HInstruction input = inputs[inputPosition++];
if (parameterType.unaliased.isFunctionType) {
// Must call the target since it contains a function conversion.
canInline = false;
return;
}
// If the target has no checks don't let a bad type stop us inlining.
if (!_options.parameterCheckPolicy.isEmitted) return;
AbstractValue parameterAbstractValue = _abstractValueDomain
.getAbstractValueForNativeMethodParameterType(parameterType);
if (parameterAbstractValue == null ||
_abstractValueDomain
.isIn(input.instructionType, parameterAbstractValue)
.isPotentiallyFalse) {
canInline = false;
return;
}
}
type.parameterTypes.forEach(checkParameterType);
type.optionalParameterTypes.forEach(checkParameterType);
assert(type.namedParameterTypes.isEmpty);
if (!canInline) return null;
// Strengthen instruction type from annotations to help optimize
// dependent instructions.
NativeBehavior nativeBehavior = _nativeData.getNativeMethodBehavior(method);
AbstractValue returnType =
AbstractValueFactory.fromNativeBehavior(nativeBehavior, _closedWorld);
HInvokeDynamicMethod result = new HInvokeDynamicMethod(
node.selector,
node.mask,
inputs.sublist(1), // Drop interceptor.
returnType,
node.typeArguments,
node.sourceInformation);
result.element = method;
_registry.registerStaticUse(new StaticUse.methodInlining(method, null));
return result;
}
@override
HInstruction visitBoundsCheck(HBoundsCheck node) {
HInstruction index = node.index;
if (index.isInteger(_abstractValueDomain).isDefinitelyTrue) {
return node;
}
if (index.isConstant()) {
HConstant constantInstruction = index;
assert(!constantInstruction.constant.isInt);
if (!constant_system.isInt(constantInstruction.constant)) {
// -0.0 is a double but will pass the runtime integer check.
node.staticChecks = HBoundsCheck.ALWAYS_FALSE;
}
}
return node;
}
HInstruction foldBinary(constant_system.BinaryOperation operation,
HInstruction left, HInstruction right) {
if (left is HConstant && right is HConstant) {
HConstant op1 = left;
HConstant op2 = right;
ConstantValue folded = operation.fold(op1.constant, op2.constant);
if (folded != null) return _graph.addConstant(folded, _closedWorld);
}
return null;
}
@override
HInstruction visitAdd(HAdd node) {
HInstruction left = node.left;
HInstruction right = node.right;
// We can only perform this rewriting on Integer, as it is not
// valid for -0.0.
if (left.isInteger(_abstractValueDomain).isDefinitelyTrue &&
right.isInteger(_abstractValueDomain).isDefinitelyTrue) {
if (left is HConstant && left.constant.isZero) return right;
if (right is HConstant && right.constant.isZero) return left;
}
return super.visitAdd(node);
}
@override
HInstruction visitMultiply(HMultiply node) {
HInstruction left = node.left;
HInstruction right = node.right;
if (left.isNumber(_abstractValueDomain).isDefinitelyTrue &&
right.isNumber(_abstractValueDomain).isDefinitelyTrue) {
if (left is HConstant && left.constant.isOne) return right;
if (right is HConstant && right.constant.isOne) return left;
}
return super.visitMultiply(node);
}
@override
HInstruction visitInvokeBinary(HInvokeBinary node) {
HInstruction left = node.left;
HInstruction right = node.right;
constant_system.BinaryOperation operation = node.operation();
HConstant folded = foldBinary(operation, left, right);
if (folded != null) return folded;
return node;
}
bool allUsersAreBoolifies(HInstruction instruction) {
List<HInstruction> users = instruction.usedBy;
int length = users.length;
for (int i = 0; i < length; i++) {
if (users[i] is! HBoolify) return false;
}
return true;
}
@override
HInstruction visitRelational(HRelational node) {
if (allUsersAreBoolifies(node)) {
// TODO(ngeoffray): Call a boolified selector.
// This node stays the same, but the Boolify node will go away.
}
// Note that we still have to call [super] to make sure that we end up
// in the remaining optimizations.
return super.visitRelational(node);
}
HInstruction handleIdentityCheck(HRelational node) {
HInstruction left = node.left;
HInstruction right = node.right;
AbstractValue leftType = left.instructionType;
AbstractValue rightType = right.instructionType;
HInstruction makeTrue() => _graph.addConstantBool(true, _closedWorld);
HInstruction makeFalse() => _graph.addConstantBool(false, _closedWorld);
// Intersection of int and double return conflicting, so
// we don't optimize on numbers to preserve the runtime semantics.
if (!(left.isNumberOrNull(_abstractValueDomain).isDefinitelyTrue &&
right.isNumberOrNull(_abstractValueDomain).isDefinitelyTrue)) {
if (_abstractValueDomain
.areDisjoint(leftType, rightType)
.isDefinitelyTrue) {
return makeFalse();
}
}
if (left.isNull(_abstractValueDomain).isDefinitelyTrue &&
right.isNull(_abstractValueDomain).isDefinitelyTrue) {
return makeTrue();
}
HInstruction compareConstant(HConstant constant, HInstruction input) {
if (constant.constant.isTrue) {
return input;
} else {
return new HNot(input, _abstractValueDomain.boolType);
}
}
if (left.isConstantBoolean() &&
right.isBoolean(_abstractValueDomain).isDefinitelyTrue) {
return compareConstant(left, right);
}
if (right.isConstantBoolean() &&
left.isBoolean(_abstractValueDomain).isDefinitelyTrue) {
return compareConstant(right, left);
}
if (identical(left.nonCheck(), right.nonCheck())) {
// Avoid constant-folding `identical(x, x)` when `x` might be double. The
// dart2js runtime has not always been consistent with the Dart
// specification (section 16.0.1), which makes distinctions on NaNs and
// -0.0 that are hard to implement efficiently.
if (left.isIntegerOrNull(_abstractValueDomain).isDefinitelyTrue) {
return makeTrue();
}
if (left.isPrimitiveNumber(_abstractValueDomain).isDefinitelyFalse) {
return makeTrue();
}
}
return null;
}
@override
HInstruction visitIdentity(HIdentity node) {
HInstruction newInstruction = handleIdentityCheck(node);
return newInstruction == null ? super.visitIdentity(node) : newInstruction;
}
void simplifyCondition(
HBasicBlock block, HInstruction condition, bool value) {
// `excludePhiOutEdges: true` prevents replacing a partially dominated phi
// node input with a constant. This tends to add unnecessary assignments, by
// transforming the following, which has phi(false, x),
//
// if (x) { init(); x = false; }
//
// into this, which has phi(false, false)
//
// if (x) { init(); x = false; } else { x = false; }
//
// which is further simplified to:
//
// if (x) { init(); }
// ...
// x = false;
//
// This is mostly harmless (if a little confusing) but does cause a lot of
// `x = false;` copies to be inserted when a loop body has many continue
// statements or ends with a switch.
DominatedUses uses =
DominatedUses.of(condition, block.first, excludePhiOutEdges: true);
if (uses.isEmpty) return;
uses.replaceWith(_graph.addConstantBool(value, _closedWorld));
}
@override
HInstruction visitIf(HIf node) {
HInstruction condition = node.condition;
if (condition.isConstant()) return node;
bool isNegated = condition is HNot;
if (isNegated) {
condition = condition.inputs[0];
} else {
// It is possible for LICM to move a negated version of the
// condition out of the loop where it used. We still want to
// simplify the nested use of the condition in that case, so
// we look for all dominating negated conditions and replace
// nested uses of them with true or false.
Iterable<HInstruction> dominating = condition.usedBy
.where((user) => user is HNot && user.dominates(node));
dominating.forEach((hoisted) {
simplifyCondition(node.thenBlock, hoisted, false);
simplifyCondition(node.elseBlock, hoisted, true);
});
}
simplifyCondition(node.thenBlock, condition, !isNegated);
simplifyCondition(node.elseBlock, condition, isNegated);
return node;
}
@override
HInstruction visitIs(HIs node) {
DartType type = node.typeExpression;
if (!node.isRawCheck) {
return node;
} else if (type.isTypedef) {
return node;
} else if (type.isFunctionType) {
return node;
} else if (type.isFutureOr) {
return node;
}
if (type == commonElements.objectType || type.treatAsDynamic) {
return _graph.addConstantBool(true, _closedWorld);
}
InterfaceType interfaceType = type;
ClassEntity element = interfaceType.element;
HInstruction expression = node.expression;
if (expression.isInteger(_abstractValueDomain).isDefinitelyTrue) {
if (element == commonElements.intClass ||
element == commonElements.numClass ||
commonElements.isNumberOrStringSupertype(element)) {
return _graph.addConstantBool(true, _closedWorld);
} else if (element == commonElements.doubleClass) {
// We let the JS semantics decide for that check. Currently
// the code we emit will always return true.
return node;
} else {
return _graph.addConstantBool(false, _closedWorld);
}
} else if (expression.isDouble(_abstractValueDomain).isDefinitelyTrue) {
if (element == commonElements.doubleClass ||
element == commonElements.numClass ||
commonElements.isNumberOrStringSupertype(element)) {
return _graph.addConstantBool(true, _closedWorld);
} else if (element == commonElements.intClass) {
// We let the JS semantics decide for that check. Currently
// the code we emit will return true for a double that can be
// represented as a 31-bit integer and for -0.0.
return node;
} else {
return _graph.addConstantBool(false, _closedWorld);
}
} else if (expression.isNumber(_abstractValueDomain).isDefinitelyTrue) {
if (element == commonElements.numClass) {
return _graph.addConstantBool(true, _closedWorld);
} else {
// We cannot just return false, because the expression may be of
// type int or double.
}
} else if (expression
.isPrimitiveNumber(_abstractValueDomain)
.isPotentiallyTrue &&
element == commonElements.intClass) {
// We let the JS semantics decide for that check.
return node;
// We need the [:hasTypeArguments:] check because we don't have
// the notion of generics in the backend. For example, [:this:] in
// a class [:A<T>:], is currently always considered to have the
// raw type.
} else if (!RuntimeTypesSubstitutions.hasTypeArguments(type)) {
AbstractValue expressionMask = expression.instructionType;
AbstractBool isInstanceOf =
_abstractValueDomain.isInstanceOf(expressionMask, element);
if (isInstanceOf.isDefinitelyTrue) {
return _graph.addConstantBool(true, _closedWorld);
} else if (isInstanceOf.isDefinitelyFalse) {
return _graph.addConstantBool(false, _closedWorld);
}
}
return node;
}
@override
HInstruction visitTypeConversion(HTypeConversion node) {
if (node.isRedundant(_closedWorld)) return node.checkedInput;
// Simplify 'as T' where T is a simple type.
DartType checkedType = node.typeExpression;
if (checkedType is TypeVariableType && node.inputs.length == 2) {
HInstruction rep = node.typeRepresentation;
if (rep is HTypeInfoExpression &&
rep.kind == TypeInfoExpressionKind.COMPLETE &&
rep.inputs.isEmpty) {
DartType type = rep.dartType;
if (type.isInterfaceType && type.treatAsRaw) {
return node.checkedInput.convertType(_closedWorld, type, node.kind)
..sourceInformation = node.sourceInformation;
}
}
}
return node;
}
@override
HInstruction visitTypeKnown(HTypeKnown node) {
return node.isRedundant(_closedWorld) ? node.checkedInput : node;
}
FieldEntity findConcreteFieldForDynamicAccess(
HInvokeDynamicField node, HInstruction receiver) {
AbstractValue receiverType = receiver.instructionType;
MemberEntity member = node.element is FieldEntity
? node.element
: _closedWorld.locateSingleMember(node.selector, receiverType);
return member is FieldEntity ? member : null;
}
@override
HInstruction visitFieldGet(HFieldGet node) {
if (node.isNullCheck) return node;
var receiver = node.receiver;
// HFieldGet of a constructed constant can be replaced with the constant's
// field.
if (receiver is HConstant) {
ConstantValue constant = receiver.constant;
if (constant.isConstructedObject) {
ConstructedConstantValue constructedConstant = constant;
Map<FieldEntity, ConstantValue> fields = constructedConstant.fields;
ConstantValue value = fields[node.element];
if (value != null) {
return _graph.addConstant(value, _closedWorld);
}
}
}
return node;
}
@override
HInstruction visitGetLength(HGetLength node) {
HInstruction receiver = node.receiver;
if (_graph.allocatedFixedLists.contains(receiver)) {
// TODO(ngeoffray): checking if the second input is an integer
// should not be necessary but it currently makes it easier for
// other optimizations to reason about a fixed length constructor
// that we know takes an int.
if (receiver.inputs[0].isInteger(_abstractValueDomain).isDefinitelyTrue) {
return receiver.inputs[0];
}
} else if (receiver.isConstantList()) {
HConstant constantReceiver = receiver;
ListConstantValue constant = constantReceiver.constant;
return _graph.addConstantInt(constant.length, _closedWorld);
} else if (receiver.isConstantString()) {
HConstant constantReceiver = receiver;
StringConstantValue constant = constantReceiver.constant;
return _graph.addConstantInt(constant.length, _closedWorld);
} else {
AbstractValue type = receiver.instructionType;
if (_abstractValueDomain.isContainer(type) &&
_abstractValueDomain.getContainerLength(type) != null) {
HInstruction constant = _graph.addConstantInt(
_abstractValueDomain.getContainerLength(type), _closedWorld);
if (_abstractValueDomain.isNull(type).isPotentiallyTrue) {
// If the container can be null, we update all uses of the length
// access to use the constant instead, but keep the length access in
// the graph, to ensure we still have a null check.
node.block.rewrite(node, constant);
return node;
} else {
return constant;
}
}
}
if (node.isAssignable &&
isFixedLength(receiver.instructionType, _closedWorld)) {
// The input type has changed to fixed-length so change to an unassignable
// HGetLength to allow more GVN optimizations.
return new HGetLength(receiver, node.instructionType,
isAssignable: false);
}
return node;
}
@override
HInstruction visitIndex(HIndex node) {
if (node.receiver.isConstantList() && node.index.isConstantInteger()) {
HConstant instruction = node.receiver;
ListConstantValue list = instruction.constant;
List<ConstantValue> entries = list.entries;
HConstant indexInstruction = node.index;
IntConstantValue indexConstant = indexInstruction.constant;
int index = indexConstant.intValue.toInt();
if (index >= 0 && index < entries.length) {
return _graph.addConstant(entries[index], _closedWorld);
}
}
return node;
}
@override
HInstruction visitInvokeDynamicGetter(HInvokeDynamicGetter node) {
propagateConstantValueToUses(node);
if (node.isInterceptedCall) {
HInstruction folded = handleInterceptedCall(node);
if (folded != node) return folded;
}
HInstruction receiver = node.getDartReceiver(_closedWorld);
AbstractValue receiverType = receiver.instructionType;
FieldEntity field = node.element is FieldEntity
? node.element
: findConcreteFieldForDynamicAccess(node, receiver);
if (field != null) {
FieldAnalysisData fieldData =
_closedWorld.fieldAnalysis.getFieldData(field);
if (fieldData.isEffectivelyConstant) {
// The field is elided and replace it with its constant value.
if (_abstractValueDomain.isNull(receiverType).isPotentiallyTrue) {
// The receiver is potentially `null` so we insert a null receiver
// guard to trigger a null pointer exception.
//
// This could be inserted unconditionally and removed by later
// optimizations if unnecessary, but performance we do it
// conditionally here.
// TODO(35996): Replace with null receiver guard instruction.
HInstruction dummyGet = new HFieldGet(null, receiver,
_abstractValueDomain.dynamicType, node.sourceInformation,
isAssignable: false);
_log?.registerFieldGet(node, dummyGet);
node.block.addBefore(node, dummyGet);
}
ConstantValue constant = fieldData.constantValue;
HConstant result = _graph.addConstant(constant, _closedWorld,
sourceInformation: node.sourceInformation);
_log?.registerConstantFieldGet(node, field, result);
return result;
} else {
HFieldGet result = _directFieldGet(receiver, field, node);
_log?.registerFieldGet(node, result);
return result;
}
}
node.element ??=
_closedWorld.locateSingleMember(node.selector, receiverType);
if (node.element != null &&
node.element.name == node.selector.name &&
node.element.isFunction) {
// A property extraction getter, aka a tear-off.
node.sideEffects.clearAllDependencies();
node.sideEffects.clearAllSideEffects();
node.setUseGvn(); // We don't care about identity of tear-offs.
}
return node;
}
HInstruction _directFieldGet(
HInstruction receiver, FieldEntity field, HInstruction node) {
bool isAssignable = !_closedWorld.fieldNeverChanges(field);
AbstractValue type;
if (_nativeData.isNativeClass(field.enclosingClass)) {
type = AbstractValueFactory.fromNativeBehavior(
_nativeData.getNativeFieldLoadBehavior(field), _closedWorld);
} else {
// TODO(johnniwinther): Use the potentially more precise type of the
// node + find a test that shows its usefulness.
// type = _abstractValueDomain.intersection(
// node.instructionType,
// AbstractValueFactory.inferredTypeForMember(
// field, _globalInferenceResults));
type = AbstractValueFactory.inferredTypeForMember(
field, _globalInferenceResults);
}
return new HFieldGet(field, receiver, type, node.sourceInformation,
isAssignable: isAssignable);
}
@override
HInstruction visitInvokeDynamicSetter(HInvokeDynamicSetter node) {
if (node.isInterceptedCall) {
HInstruction folded = handleInterceptedCall(node);
if (folded != node) return folded;
}
HInstruction receiver = node.getDartReceiver(_closedWorld);
FieldEntity field = findConcreteFieldForDynamicAccess(node, receiver);
if (field == null || !field.isAssignable) return node;
// Use `node.inputs.last` in case the call follows the interceptor calling
// convention, but is not a call on an interceptor.
HInstruction value = node.inputs.last;
if (_options.parameterCheckPolicy.isEmitted) {
DartType type = _closedWorld.elementEnvironment.getFieldType(field);
if (!type.treatAsRaw ||
type.isTypeVariable ||
type.unaliased.isFunctionType ||
type.unaliased.isFutureOr) {
// We cannot generate the correct type representation here, so don't
// inline this access.
// TODO(sra): If the input is such that we don't need a type check, we
// can skip the test an generate the HFieldSet.
node.needsCheck = true;
return node;
}
HInstruction other = value.convertType(
_closedWorld, type, HTypeConversion.CHECKED_MODE_CHECK);
if (other != value) {
node.block.addBefore(node, other);
value = other;
}
}
if (_closedWorld.fieldAnalysis.getFieldData(field).isElided) {
_log?.registerFieldSet(node);
return value;
} else {
HFieldSet result =
new HFieldSet(_abstractValueDomain, field, receiver, value)
..sourceInformation = node.sourceInformation;
_log?.registerFieldSet(node, result);
return result;
}
}
@override
HInstruction visitInvokeClosure(HInvokeClosure node) {
HInstruction closure = node.getDartReceiver(_closedWorld);
// Replace indirect call to static method tear-off closure with direct call
// to static method.
if (closure is HConstant) {
ConstantValue constant = closure.constant;
if (constant is FunctionConstantValue) {
FunctionEntity target = constant.element;
ParameterStructure parameterStructure = target.parameterStructure;
if (parameterStructure.callStructure == node.selector.callStructure) {
// TODO(sra): Handle adding optional arguments default values.
assert(!node.isInterceptedCall);
return new HInvokeStatic(target, node.inputs.skip(1).toList(),
node.instructionType, node.typeArguments)
..sourceInformation = node.sourceInformation;
}
}
}
return node;
}
@override
HInstruction visitInvokeStatic(HInvokeStatic node) {
propagateConstantValueToUses(node);
MemberEntity element = node.element;
if (element == commonElements.identicalFunction) {
if (node.inputs.length == 2) {
return new HIdentity(
node.inputs[0], node.inputs[1], null, _abstractValueDomain.boolType)
..sourceInformation = node.sourceInformation;
}
} else if (element == commonElements.setRuntimeTypeInfo) {
if (node.inputs.length == 2) {
return handleArrayTypeInfo(node);
}
} else if (element == commonElements.checkConcurrentModificationError) {
if (node.inputs.length == 2) {
HInstruction firstArgument = node.inputs[0];
if (firstArgument is HConstant) {
HConstant constant = firstArgument;
if (constant.constant.isTrue) return constant;
}
}
} else if (commonElements.isCheckInt(element)) {
if (node.inputs.length == 1) {
HInstruction argument = node.inputs[0];
if (argument.isInteger(_abstractValueDomain).isDefinitelyTrue) {
return argument;
}
}
} else if (commonElements.isCheckNum(element)) {
if (node.inputs.length == 1) {
HInstruction argument = node.inputs[0];
if (argument.isNumber(_abstractValueDomain).isDefinitelyTrue) {
return argument;
}
}
} else if (commonElements.isCheckString(element)) {
if (node.inputs.length == 1) {
HInstruction argument = node.inputs[0];
if (argument.isString(_abstractValueDomain).isDefinitelyTrue) {
return argument;
}
}
} else if (element == commonElements.assertHelper ||
element == commonElements.assertTest) {
if (node.inputs.length == 1) {
HInstruction argument = node.inputs[0];
if (argument is HConstant) {
ConstantValue constant = argument.constant;
if (constant.isBool) {
bool value = constant.isTrue;
if (element == commonElements.assertTest) {
// `assertTest(argument)` effectively negates the argument.
return _graph.addConstantBool(!value, _closedWorld);
}
// `assertHelper(true)` is a no-op, other values throw.
if (value) return argument;
}
}
}
}
return node;
}
HInstruction handleArrayTypeInfo(HInvokeStatic node) {
// If type information is not needed, use the raw Array.
HInstruction source = node.inputs[0];
if (source.usedBy.length != 1) return node;
if (source.isArray(_abstractValueDomain).isPotentiallyFalse) {
return node;
}
for (HInstruction user in node.usedBy) {
if (user is HGetLength) continue;
if (user is HIndex) continue;
// Bounds check escapes the array, but we don't care.
if (user is HBoundsCheck) continue;
// Interceptor only escapes the Array if array passed to an intercepted
// method.
if (user is HInterceptor) continue;
if (user is HInvokeStatic) {
MemberEntity element = user.element;
if (element == commonElements.checkConcurrentModificationError) {
// CME check escapes the array, but we don't care.
continue;
}
}
if (user is HInvokeDynamicGetter) {
String name = user.selector.name;
// These getters don't use the Array type.
if (name == 'last') continue;
if (name == 'first') continue;
}
// TODO(sra): Implement a more general algorithm - many methods don't use
// the element type.
return node;
}
return source;
}
@override
HInstruction visitStringConcat(HStringConcat node) {
// Simplify string concat:
//
// "" + R -> R
// L + "" -> L
// "L" + "R" -> "LR"
// (prefix + "L") + "R" -> prefix + "LR"
//
StringConstantValue getString(HInstruction instruction) {
if (!instruction.isConstantString()) return null;
HConstant constant = instruction;
return constant.constant;
}
StringConstantValue leftString = getString(node.left);
if (leftString != null && leftString.stringValue.length == 0) {
return node.right;
}
StringConstantValue rightString = getString(node.right);
if (rightString == null) return node;
if (rightString.stringValue.length == 0) return node.left;
HInstruction prefix = null;
if (leftString == null) {
if (node.left is! HStringConcat) return node;
HStringConcat leftConcat = node.left;
// Don't undo CSE.
if (leftConcat.usedBy.length != 1) return node;
prefix = leftConcat.left;
leftString = getString(leftConcat.right);
if (leftString == null) return node;
}
if (leftString.stringValue.length + rightString.stringValue.length >
MAX_SHARED_CONSTANT_FOLDED_STRING_LENGTH) {
if (node.usedBy.length > 1) return node;
}
HInstruction folded = _graph.addConstant(
constant_system
.createString(leftString.stringValue + rightString.stringValue),
_closedWorld);
if (prefix == null) return folded;
return new HStringConcat(prefix, folded, _abstractValueDomain.stringType);
}
@override
HInstruction visitStringify(HStringify node) {
HInstruction input = node.inputs[0];
if (input.isString(_abstractValueDomain).isDefinitelyTrue) {
return input;
}
HInstruction asString(String string) =>
_graph.addConstant(constant_system.createString(string), _closedWorld);
HInstruction tryConstant() {
if (!input.isConstant()) return null;
HConstant constant = input;
if (!constant.constant.isPrimitive) return null;
PrimitiveConstantValue value = constant.constant;
if (value is IntConstantValue) {
// Only constant-fold int.toString() when Dart and JS results the same.
// TODO(18103): We should be able to remove this work-around when issue
// 18103 is resolved by providing the correct string.
if (!value.isUInt32()) return null;
return asString('${value.intValue}');
}
if (value is BoolConstantValue) {
return asString(value.boolValue ? 'true' : 'false');
}
if (value is NullConstantValue) {
return asString('null');
}
if (value is DoubleConstantValue) {
// TODO(sra): It seems unlikely that all dart2js host implementations
// produce exactly the same characters as all JavaScript targets.
return asString('${value.doubleValue}');
}
return null;
}
HInstruction tryToString() {
// If the `toString` method is guaranteed to return a string we can call
// it directly. Keep the stringifier for primitives (since they have fast
// path code in the stringifier) and for classes requiring interceptors
// (since SsaInstructionSimplifier runs after SsaSimplifyInterceptors).
if (input.isPrimitive(_abstractValueDomain).isPotentiallyTrue) {
return null;
}
if (input.isNull(_abstractValueDomain).isPotentiallyTrue) {
return null;
}
Selector selector = Selectors.toString_;
AbstractValue toStringType = AbstractValueFactory.inferredTypeForSelector(
selector, input.instructionType, _globalInferenceResults);
if (_abstractValueDomain
.containsOnlyType(
toStringType, _closedWorld.commonElements.jsStringClass)
.isPotentiallyFalse) {
return null;
}
// All intercepted classes extend `Interceptor`, so if the receiver can't
// be a class extending `Interceptor` then it can be called directly.
if (_abstractValueDomain
.isInterceptor(input.instructionType)
.isDefinitelyFalse) {
var inputs = <HInstruction>[input, input]; // [interceptor, receiver].
HInstruction result = new HInvokeDynamicMethod(
selector,
input.instructionType, // receiver mask.
inputs,
toStringType,
const <DartType>[],
node.sourceInformation,
isIntercepted: true);
return result;
}
return null;
}
return tryConstant() ?? tryToString() ?? node;
}
@override
HInstruction visitOneShotInterceptor(HOneShotInterceptor node) {
return handleInterceptedCall(node);
}
bool needsSubstitutionForTypeVariableAccess(ClassEntity cls) {
if (_closedWorld.isUsedAsMixin(cls)) return true;
return _closedWorld.classHierarchy.anyStrictSubclassOf(cls,
(ClassEntity subclass) {
return !_rtiSubstitutions.isTrivialSubstitution(subclass, cls);
});
}
@override
HInstruction visitTypeInfoExpression(HTypeInfoExpression node) {
// Identify the case where the type info expression would be of the form:
//
// [getTypeArgumentByIndex(this, 0), .., getTypeArgumentByIndex(this, k)]
//
// and k is the number of type arguments of 'this'. We can simply copy the
// list from 'this'.
HInstruction tryCopyInfo() {
if (node.kind != TypeInfoExpressionKind.INSTANCE) return null;
HInstruction source;
int expectedIndex = 0;
for (HInstruction argument in node.inputs) {
if (argument is HTypeInfoReadVariable) {
HInstruction nextSource = argument.object;
if (nextSource is HThis) {
if (source == null) {
source = nextSource;
ClassEntity contextClass =
nextSource.sourceElement.enclosingClass;
if (node.inputs.length !=
_closedWorld.elementEnvironment
.getThisType(contextClass)
.typeArguments
.length) {
return null;
}
if (needsSubstitutionForTypeVariableAccess(contextClass)) {
return null;
}
}
if (nextSource != source) return null;
// Check that the index is the one we expect.
int index = argument.variable.element.index;
if (index != expectedIndex++) return null;
} else {
// TODO(sra): Handle non-this cases (i.e. inlined code). Some
// non-this cases will have a TypeMask that does not need
// substitution, even though the general case does, e.g. inlining a
// method on an exact class.
return null;
}
} else {
return null;
}
}
if (source == null) return null;
return new HTypeInfoReadRaw(source, _abstractValueDomain.dynamicType);
}
// TODO(sra): Consider fusing type expression trees with no type variables,
// as these could be represented like constants.
return tryCopyInfo() ?? node;
}
@override
HInstruction visitTypeInfoReadVariable(HTypeInfoReadVariable node) {
TypeVariableType variable = node.variable;
ClassEntity contextClass = variable.element.typeDeclaration;
HInstruction object = node.object;
HInstruction finishGroundType(InterfaceType groundType) {
InterfaceType typeAtVariable =
_closedWorld.dartTypes.asInstanceOf(groundType, contextClass);
if (typeAtVariable != null) {
int index = variable.element.index;
DartType typeArgument = typeAtVariable.typeArguments[index];
HInstruction replacement = new HTypeInfoExpression(
TypeInfoExpressionKind.COMPLETE,
typeArgument,
const <HInstruction>[],
_abstractValueDomain.dynamicType,
isTypeVariableReplacement: true);
return replacement;
}
return node;
}
/// Read the type variable from an allocation of type [createdClass], where
/// [selectTypeArgumentFromObjectCreation] extracts the type argument from
/// the allocation for factory constructor call.
HInstruction finishSubstituted(ClassEntity createdClass,
HInstruction selectTypeArgumentFromObjectCreation(int index)) {
InterfaceType thisType = _closedWorld.dartTypes.getThisType(createdClass);
HInstruction instructionForTypeVariable(TypeVariableType tv) {
return selectTypeArgumentFromObjectCreation(
thisType.typeArguments.indexOf(tv));
}
DartType type = _closedWorld.dartTypes
.asInstanceOf(thisType, contextClass)
.typeArguments[variable.element.index];
if (type is TypeVariableType) {
return instructionForTypeVariable(type);
}
List<HInstruction> arguments = <HInstruction>[];
type.forEachTypeVariable((v) {
arguments.add(instructionForTypeVariable(v));
});
HInstruction replacement = new HTypeInfoExpression(
TypeInfoExpressionKind.COMPLETE,
type,
arguments,
_abstractValueDomain.dynamicType,
isTypeVariableReplacement: true);
return replacement;
}
// Type variable evaluated in the context of a constant can be replaced with
// a ground term type.
if (object is HConstant) {
ConstantValue value = object.constant;
if (value is ConstructedConstantValue) {
return finishGroundType(value.type);
}
return node;
}
// Look for an allocation with type information and re-write type variable
// as a function of the type parameters of the allocation. This effectively
// store-forwards a type variable read through an allocation.
// Match:
//
// HCreate(ClassElement,
// [arg_i,
// ...,
// HTypeInfoExpression(t_0, t_1, t_2, ...)]);
//
// The `t_i` are the values of the type parameters of ClassElement.
if (object is HCreate) {
void registerInstantiations() {
// Forwarding the type variable references might cause the HCreate to
// become dead. This breaks the algorithm for generating the per-type
// runtime type information, so we instantiate them here in case the
// HCreate becomes dead.
object.instantiatedTypes?.forEach(_registry.registerInstantiation);
}
if (object.hasRtiInput) {
HInstruction typeInfo = object.rtiInput;
if (typeInfo is HTypeInfoExpression) {
registerInstantiations();
return finishSubstituted(
object.element, (int index) => typeInfo.inputs[index]);
}
} else {
// Non-generic type (which extends or mixes in a generic type, for
// example CodeUnits extends UnmodifiableListBase<int>). Also used for
// raw-type when the type parameters are elided.
registerInstantiations();
return finishSubstituted(
object.element,
// If there are type arguments, all type arguments are 'dynamic'.
(int i) => _graph.addConstantNull(_closedWorld));
}
}
// TODO(sra): Factory constructors pass type arguments after the value
// arguments. The [selectTypeArgumentFromObjectCreation] argument of
// [finishSubstituted] indexes into these type arguments.
// Try to remove the interceptor. The interceptor is used for accessing the
// substitution methods.
if (node.isIntercepted) {
// If we don't need the substitution methods then we don't need the
// interceptor to access them.
if (!needsSubstitutionForTypeVariableAccess(contextClass)) {
return new HTypeInfoReadVariable.noInterceptor(
variable, object, node.instructionType);
}
// All intercepted classes extend `Interceptor`, so if the receiver can't
// be a class extending `Interceptor` then the substitution methods can be
// called directly. (We don't care about Null since contexts reading class
// type variables originate from instance methods.)
if (_abstractValueDomain
.isInterceptor(object.instructionType)
.isDefinitelyFalse) {
return new HTypeInfoReadVariable.noInterceptor(
variable, object, node.instructionType);
}
}
return node;
}
}
class SsaCheckInserter extends HBaseVisitor implements OptimizationPhase {
final Set<HInstruction> boundsChecked;
final bool trustPrimitives;
final JClosedWorld closedWorld;
@override
final String name = "SsaCheckInserter";
HGraph graph;
SsaCheckInserter(this.trustPrimitives, this.closedWorld, this.boundsChecked);
AbstractValueDomain get _abstractValueDomain =>
closedWorld.abstractValueDomain;
@override
void visitGraph(HGraph graph) {
this.graph = graph;
// In --trust-primitives mode we don't add bounds checks. This is better
// than trying to remove them later as the limit expression would become
// dead and require DCE.
if (trustPrimitives) return;
visitDominatorTree(graph);
}
@override
void visitBasicBlock(HBasicBlock block) {
HInstruction instruction = block.first;
while (instruction != null) {
HInstruction next = instruction.next;
instruction = instruction.accept(this);
instruction = next;
}
}
HBoundsCheck insertBoundsCheck(
HInstruction indexNode, HInstruction array, HInstruction indexArgument) {
HGetLength length = new HGetLength(
array, closedWorld.abstractValueDomain.positiveIntType,
isAssignable: !isFixedLength(array.instructionType, closedWorld));
indexNode.block.addBefore(indexNode, length);
AbstractValue type =
indexArgument.isPositiveInteger(_abstractValueDomain).isDefinitelyTrue
? indexArgument.instructionType
: closedWorld.abstractValueDomain.positiveIntType;
HBoundsCheck check = new HBoundsCheck(indexArgument, length, array, type)
..sourceInformation = indexNode.sourceInformation;
indexNode.block.addBefore(indexNode, check);
// If the index input to the bounds check was not known to be an integer
// then we replace its uses with the bounds check, which is known to be an
// integer. However, if the input was already an integer we don't do this
// because putting in a check instruction might obscure the real nature of
// the index eg. if it is a constant. The range information from the
// BoundsCheck instruction is attached to the input directly by
// visitBoundsCheck in the SsaValueRangeAnalyzer.
if (indexArgument.isInteger(_abstractValueDomain).isPotentiallyFalse) {
indexArgument.replaceAllUsersDominatedBy(indexNode, check);
}
boundsChecked.add(indexNode);
return check;
}
@override
void visitIndex(HIndex node) {
if (boundsChecked.contains(node)) return;
HInstruction index = node.index;
index = insertBoundsCheck(node, node.receiver, index);
}
@override
void visitIndexAssign(HIndexAssign node) {
if (boundsChecked.contains(node)) return;
HInstruction index = node.index;
index = insertBoundsCheck(node, node.receiver, index);
}
@override
void visitInvokeDynamicMethod(HInvokeDynamicMethod node) {
MemberEntity element = node.element;
if (node.isInterceptedCall) return;
if (element != closedWorld.commonElements.jsArrayRemoveLast) return;
if (boundsChecked.contains(node)) return;
// `0` is the index we want to check, but we want to report `-1`, as if we
// executed `a[a.length-1]`
HBoundsCheck check = insertBoundsCheck(
node, node.receiver, graph.addConstantInt(0, closedWorld));
HInstruction minusOne = graph.addConstantInt(-1, closedWorld);
check.inputs.add(minusOne);
minusOne.usedBy.add(check);
}
}
class SsaDeadCodeEliminator extends HGraphVisitor implements OptimizationPhase {
@override
final String name = "SsaDeadCodeEliminator";
final JClosedWorld closedWorld;
final SsaOptimizerTask optimizer;
HGraph _graph;
SsaLiveBlockAnalyzer analyzer;
Map<HInstruction, bool> trivialDeadStoreReceivers =
new Maplet<HInstruction, bool>();
bool eliminatedSideEffects = false;
SsaDeadCodeEliminator(this.closedWorld, this.optimizer);
AbstractValueDomain get _abstractValueDomain =>
closedWorld.abstractValueDomain;
HInstruction zapInstructionCache;
HInstruction get zapInstruction {
if (zapInstructionCache == null) {
// A constant with no type does not pollute types at phi nodes.
ConstantValue constant = new SyntheticConstantValue(
SyntheticConstantKind.EMPTY_VALUE, _abstractValueDomain.emptyType);
zapInstructionCache = analyzer.graph.addConstant(constant, closedWorld);
}
return zapInstructionCache;
}
/// Returns true of [foreign] will throw an noSuchMethod error if
/// receiver is `null` before having any other side-effects.
bool templateThrowsNSMonNull(HForeignCode foreign, HInstruction receiver) {
if (foreign.inputs.length < 1) return false;
if (foreign.inputs.first != receiver) return false;
if (foreign.throwBehavior.isNullNSMGuard) return true;
return false;
}
/// Returns whether the next throwing instruction that may have side
/// effects after [instruction], throws [NoSuchMethodError] on the
/// same receiver of [instruction].
bool hasFollowingThrowingNSM(HInstruction instruction) {
HInstruction receiver = instruction.getDartReceiver(closedWorld);
HInstruction current = instruction.next;
do {
if ((current.getDartReceiver(closedWorld) == receiver) &&
current.canThrow(_abstractValueDomain)) {
return true;
}
if (current is HForeignCode &&
templateThrowsNSMonNull(current, receiver)) {
return true;
}
if (current.canThrow(_abstractValueDomain) ||
current.sideEffects.hasSideEffects()) {
return false;
}
HInstruction next = current.next;
if (next == null) {
// We do not merge blocks in our SSA graph, so if this block just jumps
// to a single successor, visit the successor, avoiding back-edges.
HBasicBlock successor;
if (current is HGoto) {
successor = current.block.successors.single;
} else if (current is HIf) {
// We also leave HIf nodes in place when one branch is dead.
HInstruction condition = current.inputs.first;
if (condition is HConstant) {
bool isTrue = condition.constant.isTrue;
successor = isTrue ? current.thenBlock : current.elseBlock;
assert(!analyzer.isDeadBlock(successor));
}
}
if (successor != null && successor.id > current.block.id) {
next = successor.first;
}
}
current = next;
} while (current != null);
return false;
}
bool isTrivialDeadStoreReceiver(HInstruction instruction) {
// For an allocation, if all the loads are dead (awaiting removal after
// SsaLoadElimination) and the only other uses are stores, then the
// allocation does not escape which makes all the stores dead too.
bool isDeadUse(HInstruction use) {
if (use is HFieldSet) {
// The use must be the receiver. Even if the use is also the argument,
// i.e. a.x = a, the store is still dead if all other uses are dead.
if (use.getDartReceiver(closedWorld) == instruction) return true;
} else if (use is HFieldGet) {
assert(use.getDartReceiver(closedWorld) == instruction);
if (isDeadCode(use)) return true;
}
return false;
}
return instruction.isAllocation(_abstractValueDomain) &&
instruction.isPure(_abstractValueDomain) &&
trivialDeadStoreReceivers.putIfAbsent(
instruction, () => instruction.usedBy.every(isDeadUse));
}
bool isTrivialDeadStore(HInstruction instruction) {
return instruction is HFieldSet &&
isTrivialDeadStoreReceiver(instruction.getDartReceiver(closedWorld));
}
bool isDeadCode(HInstruction instruction) {
if (!instruction.usedBy.isEmpty) return false;
if (isTrivialDeadStore(instruction)) return true;
if (instruction.sideEffects.hasSideEffects()) return false;
if (instruction.canThrow(_abstractValueDomain)) {
if (instruction.onlyThrowsNSM() && hasFollowingThrowingNSM(instruction)) {
// [instruction] is a null reciever guard that is followed by an
// instruction that fails the same way (by accessing a property of
// `null` or `undefined`).
return true;
}
return false;
}
if (instruction is HParameterValue) return false;
if (instruction is HLocalSet) return false;
return true;
}
@override
void visitGraph(HGraph graph) {
_graph = graph;
analyzer = new SsaLiveBlockAnalyzer(graph, closedWorld, optimizer);
analyzer.analyze();
visitPostDominatorTree(graph);
cleanPhis();
}
@override
void visitBasicBlock(HBasicBlock block) {
bool isDeadBlock = analyzer.isDeadBlock(block);
block.isLive = !isDeadBlock;
simplifyControlFlow(block);
// Start from the last non-control flow instruction in the block.
HInstruction instruction = block.last.previous;
while (instruction != null) {
var previous = instruction.previous;
if (isDeadBlock) {
eliminatedSideEffects =
eliminatedSideEffects || instruction.sideEffects.hasSideEffects();
removeUsers(instruction);
block.remove(instruction);
} else if (isDeadCode(instruction)) {
block.remove(instruction);
}
instruction = previous;
}
block.forEachPhi(simplifyPhi);
evacuateTakenBranch(block);
}
void simplifyPhi(HPhi phi) {
// If the phi is of the form `phi(x, HTypeKnown(x))`, it does not strengthen
// `x`. We can replace the phi with `x` to potentially make the HTypeKnown
// refinement node dead and potentially make a HIf control no HPhis.
// TODO(sra): Implement version of this test that works for a subgraph of
// HPhi nodes.
HInstruction base = null;
bool seenUnrefinedBase = false;
for (HInstruction input in phi.inputs) {
HInstruction value = input;
while (value is HTypeKnown) {
HTypeKnown refinement = value;
value = refinement.checkedInput;
}
if (value == input) seenUnrefinedBase = true;
base ??= value;
if (base != value) return;
}
if (seenUnrefinedBase) {
HBasicBlock block = phi.block;
block.rewrite(phi, base);
block.removePhi(phi);
}
}
void simplifyControlFlow(HBasicBlock block) {
HControlFlow instruction = block.last;
if (instruction is HIf) {
HInstruction condition = instruction.condition;
if (condition.isConstant()) return;
// We want to remove an if-then-else diamond when the then- and else-
// branches are empty and the condition does not control a HPhi. We cannot
// change the CFG structure so we replace the HIf condition with a
// constant. This may leave the original condition unused. i.e. a
// candidate for being dead code.
List<HBasicBlock> dominated = block.dominatedBlocks;
// Diamond-like control flow dominates the then-, else- and join- blocks.
if (dominated.length != 3) return;
HBasicBlock join = dominated.last;
if (!join.phis.isEmpty) return; // condition controls a phi.
// Ignore exit block - usually the join in `if (...) return ...`
if (join.isExitBlock()) return;
int thenSize = measureEmptyInterval(instruction.thenBlock, join);
if (thenSize == null) return;
int elseSize = measureEmptyInterval(instruction.elseBlock, join);
if (elseSize == null) return;
// Pick the 'live' branch to be the smallest subgraph.
bool value = thenSize <= elseSize;
HInstruction newCondition = _graph.addConstantBool(value, closedWorld);
instruction.inputs[0] = newCondition;
condition.usedBy.remove(instruction);
newCondition.usedBy.add(instruction);
}
}
/// Returns the number of blocks from [start] up to but not including [end].
/// Returns `null` if any of the blocks is non-empty (other than control
/// flow). Returns `null` if there is an exit from the region other than
/// [end] or via control flow other than HGoto and HIf.
int measureEmptyInterval(HBasicBlock start, HBasicBlock end) {
if (start.first != start.last) return null; // start is not empty.
// Do a simple single-block region test first.
if (start.last is HGoto &&
start.successors.length == 1 &&
start.successors.single == end) {
return 1;
}
// TODO(sra): Implement fuller test.
return null;
}
/// If [block] is an always-taken branch, move the code from the taken branch
/// into [block]. This has the effect of making the instructions available for
/// further optimizations by moving them to a position that dominates the join
/// point of the if-then-else.
// TODO(29475): Delete dead blocks instead.
void evacuateTakenBranch(HBasicBlock block) {
if (!block.isLive) return;
HControlFlow branch = block.last;
if (branch is HIf) {
if (branch.thenBlock.isLive == branch.elseBlock.isLive) return;
assert(branch.condition.isConstant());
HBasicBlock target =
branch.thenBlock.isLive ? branch.thenBlock : branch.elseBlock;
HInstruction instruction = target.first;
while (!instruction.isControlFlow()) {
HInstruction next = instruction.next;
if (instruction is HTypeKnown && instruction.isPinned) break;
instruction.block.detach(instruction);
block.moveAtExit(instruction);
instruction = next;
}
}
}
void cleanPhis() {
L:
for (HBasicBlock block in _graph.blocks) {
List<HBasicBlock> predecessors = block.predecessors;
// Zap all inputs to phis that correspond to dead blocks.
block.forEachPhi((HPhi phi) {
for (int i = 0; i < phi.inputs.length; ++i) {
if (!predecessors[i].isLive && phi.inputs[i] != zapInstruction) {
replaceInput(i, phi, zapInstruction);
}
}
});
if (predecessors.length < 2) continue L;
// Find the index of the single live predecessor if it exists.
int indexOfLive = -1;
for (int i = 0; i < predecessors.length; i++) {
if (predecessors[i].isLive) {
if (indexOfLive >= 0) continue L;
indexOfLive = i;
}
}
// Run through the phis of the block and replace them with their input
// that comes from the only live predecessor if that dominates the phi.
//
// TODO(sra): If the input is directly in the only live predecessor, it
// might be possible to move it into [block] (e.g. all its inputs are
// dominating.)
block.forEachPhi((HPhi phi) {
HInstruction replacement =
(indexOfLive >= 0) ? phi.inputs[indexOfLive] : zapInstruction;
if (replacement.dominates(phi)) {
block.rewrite(phi, replacement);
block.removePhi(phi);
if (replacement.sourceElement == null &&
phi.sourceElement != null &&
replacement is! HThis) {
replacement.sourceElement = phi.sourceElement;
}
}
});
}
}
void replaceInput(int i, HInstruction from, HInstruction by) {
from.inputs[i].usedBy.remove(from);
from.inputs[i] = by;
by.usedBy.add(from);
}
void removeUsers(HInstruction instruction) {
instruction.usedBy.forEach((user) {
removeInput(user, instruction);
});
instruction.usedBy.clear();
}
void removeInput(HInstruction user, HInstruction input) {
List<HInstruction> inputs = user.inputs;
for (int i = 0, length = inputs.length; i < length; i++) {
if (input == inputs[i]) {
user.inputs[i] = zapInstruction;
zapInstruction.usedBy.add(user);
}
}
}
}
class SsaLiveBlockAnalyzer extends HBaseVisitor {
final HGraph graph;
final Set<HBasicBlock> live = new Set<HBasicBlock>();
final List<HBasicBlock> worklist = <HBasicBlock>[];
final SsaOptimizerTask optimizer;
final JClosedWorld closedWorld;
SsaLiveBlockAnalyzer(this.graph, this.closedWorld, this.optimizer);
AbstractValueDomain get _abstractValueDomain =>
closedWorld.abstractValueDomain;
Map<HInstruction, Range> get ranges => optimizer.ranges;
bool isDeadBlock(HBasicBlock block) => !live.contains(block);
void analyze() {
markBlockLive(graph.entry);
while (!worklist.isEmpty) {
HBasicBlock live = worklist.removeLast();
live.last.accept(this);
}
}
void markBlockLive(HBasicBlock block) {
if (!live.contains(block)) {
worklist.add(block);
live.add(block);
}
}
@override
void visitControlFlow(HControlFlow instruction) {
instruction.block.successors.forEach(markBlockLive);
}
@override
void visitIf(HIf instruction) {
HInstruction condition = instruction.condition;
if (condition.isConstant()) {
if (condition.isConstantTrue()) {
markBlockLive(instruction.thenBlock);
} else {
markBlockLive(instruction.elseBlock);
}
} else {
visitControlFlow(instruction);
}
}
@override
void visitSwitch(HSwitch node) {
if (node.expression.isInteger(_abstractValueDomain).isDefinitelyTrue) {
Range switchRange = ranges[node.expression];
if (switchRange != null &&
switchRange.lower is IntValue &&
switchRange.upper is IntValue) {
IntValue lowerValue = switchRange.lower;
IntValue upperValue = switchRange.upper;
BigInt lower = lowerValue.value;
BigInt upper = upperValue.value;
Set<BigInt> liveLabels = new Set<BigInt>();
for (int pos = 1; pos < node.inputs.length; pos++) {
HConstant input = node.inputs[pos];
if (!input.isConstantInteger()) continue;
IntConstantValue constant = input.constant;
BigInt label = constant.intValue;
if (!liveLabels.contains(label) && label <= upper && label >= lower) {
markBlockLive(node.block.successors[pos - 1]);
liveLabels.add(label);
}
}
if (new BigInt.from(liveLabels.length) != upper - lower + BigInt.one) {
markBlockLive(node.defaultTarget);
}
return;
}
}
visitControlFlow(node);
}
}
class SsaDeadPhiEliminator implements OptimizationPhase {
@override
final String name = "SsaDeadPhiEliminator";
@override
void visitGraph(HGraph graph) {
final List<HPhi> worklist = <HPhi>[];
// A set to keep track of the live phis that we found.
final Set<HPhi> livePhis = new Set<HPhi>();
// Add to the worklist all live phis: phis referenced by non-phi
// instructions.
for (final block in graph.blocks) {
block.forEachPhi((HPhi phi) {
for (final user in phi.usedBy) {
if (user is! HPhi) {
worklist.add(phi);
livePhis.add(phi);
break;
}
}
});
}
// Process the worklist by propagating liveness to phi inputs.
while (!worklist.isEmpty) {
HPhi phi = worklist.removeLast();
for (final input in phi.inputs) {
if (input is HPhi && !livePhis.contains(input)) {
worklist.add(input);
livePhis.add(input);
}
}
}
// Remove phis that are not live.
// Traverse in reverse order to remove phis with no uses before the
// phis that they might use.
// NOTICE: Doesn't handle circular references, but we don't currently
// create any.
List<HBasicBlock> blocks = graph.blocks;
for (int i = blocks.length - 1; i >= 0; i--) {
HBasicBlock block = blocks[i];
HPhi current = block.phis.first;
HPhi next = null;
while (current != null) {
next = current.next;
if (!livePhis.contains(current)
// TODO(ahe): Not sure the following is correct.
&&
current.usedBy.isEmpty) {
block.removePhi(current);
}
current = next;
}
}
}
}
class SsaRedundantPhiEliminator implements OptimizationPhase {
@override
final String name = "SsaRedundantPhiEliminator";
@override
void visitGraph(HGraph graph) {
final List<HPhi> worklist = <HPhi>[];
// Add all phis in the worklist.
for (final block in graph.blocks) {
block.forEachPhi((HPhi phi) => worklist.add(phi));
}
while (!worklist.isEmpty) {
HPhi phi = worklist.removeLast();
// If the phi has already been processed, continue.
if (!phi.isInBasicBlock()) continue;
// Find if the inputs of the phi are the same instruction.
// The builder ensures that phi.inputs[0] cannot be the phi
// itself.
assert(!identical(phi.inputs[0], phi));
HInstruction candidate = phi.inputs[0];
for (int i = 1; i < phi.inputs.length; i++) {
HInstruction input = phi.inputs[i];
// If the input is the phi, the phi is still candidate for
// elimination.
if (!identical(input, candidate) && !identical(input, phi)) {
candidate = null;
break;
}
}
// If the inputs are not the same, continue.
if (candidate == null) continue;
// Because we're updating the users of this phi, we may have new
// phis candidate for elimination. Add phis that used this phi
// to the worklist.
for (final user in phi.usedBy) {
if (user is HPhi) worklist.add(user);
}
phi.block.rewrite(phi, candidate);
phi.block.removePhi(phi);
if (candidate.sourceElement == null &&
phi.sourceElement != null &&
candidate is! HThis) {
candidate.sourceElement = phi.sourceElement;
}
}
}
}
class GvnWorkItem {
final HBasicBlock block;
final ValueSet valueSet;
GvnWorkItem(this.block, this.valueSet);
}
class SsaGlobalValueNumberer implements OptimizationPhase {
final AbstractValueDomain _abstractValueDomain;
@override
final String name = "SsaGlobalValueNumberer";
final Set<int> visited;
List<int> blockChangesFlags;
List<int> loopChangesFlags;
SsaGlobalValueNumberer(this._abstractValueDomain) : visited = new Set<int>();
@override
void visitGraph(HGraph graph) {
computeChangesFlags(graph);
moveLoopInvariantCode(graph);
List<GvnWorkItem> workQueue = <GvnWorkItem>[
new GvnWorkItem(graph.entry, new ValueSet())
];
do {
GvnWorkItem item = workQueue.removeLast();
visitBasicBlock(item.block, item.valueSet, workQueue);
} while (!workQueue.isEmpty);
}
void moveLoopInvariantCode(HGraph graph) {
for (int i = graph.blocks.length - 1; i >= 0; i--) {
HBasicBlock block = graph.blocks[i];
if (block.isLoopHeader()) {
int changesFlags = loopChangesFlags[block.id];
HLoopInformation info = block.loopInformation;
// Iterate over all blocks of this loop. Note that blocks in
// inner loops are not visited here, but we know they
// were visited before because we are iterating in post-order.
// So instructions that are GVN'ed in an inner loop are in their
// loop entry, and [info.blocks] contains this loop entry.
moveLoopInvariantCodeFromBlock(block, block, changesFlags);
for (HBasicBlock other in info.blocks) {
moveLoopInvariantCodeFromBlock(other, block, changesFlags);
}
}
}
}
void moveLoopInvariantCodeFromBlock(
HBasicBlock block, HBasicBlock loopHeader, int changesFlags) {
assert(block.parentLoopHeader == loopHeader || block == loopHeader);
HBasicBlock preheader = loopHeader.predecessors[0];
int dependsFlags = SideEffects.computeDependsOnFlags(changesFlags);
HInstruction instruction = block.first;
bool isLoopAlwaysTaken() {
HInstruction instruction = loopHeader.last;
assert(instruction is HGoto || instruction is HLoopBranch);
return instruction is HGoto || instruction.inputs[0].isConstantTrue();
}
bool firstInstructionInLoop = block == loopHeader
// Compensate for lack of code motion.
||
(blockChangesFlags[loopHeader.id] == 0 &&
isLoopAlwaysTaken() &&
loopHeader.successors[0] == block);
while (instruction != null) {
HInstruction next = instruction.next;
if (instruction.useGvn() &&
instruction.isMovable &&
(!instruction.canThrow(_abstractValueDomain) ||
firstInstructionInLoop) &&
!instruction.sideEffects.dependsOn(dependsFlags)) {
bool loopInvariantInputs = true;
List<HInstruction> inputs = instruction.inputs;
for (int i = 0, length = inputs.length; i < length; i++) {
if (isInputDefinedAfterDominator(inputs[i], preheader)) {
loopInvariantInputs = false;
break;
}
}
// If the inputs are loop invariant, we can move the
// instruction from the current block to the pre-header block.
if (loopInvariantInputs) {
block.detach(instruction);
preheader.moveAtExit(instruction);
} else {
firstInstructionInLoop = false;
}
}
int oldChangesFlags = changesFlags;
changesFlags |= instruction.sideEffects.getChangesFlags();
if (oldChangesFlags != changesFlags) {
dependsFlags = SideEffects.computeDependsOnFlags(changesFlags);
}
instruction = next;
}
}
bool isInputDefinedAfterDominator(HInstruction input, HBasicBlock dominator) {
return input.block.id > dominator.id;
}
void visitBasicBlock(
HBasicBlock block, ValueSet values, List<GvnWorkItem> workQueue) {
HInstruction instruction = block.first;
if (block.isLoopHeader()) {
int flags = loopChangesFlags[block.id];
values.kill(flags);
}
while (instruction != null) {
HInstruction next = instruction.next;
int flags = instruction.sideEffects.getChangesFlags();
assert(flags == 0 || !instruction.useGvn());
values.kill(flags);
if (instruction.useGvn()) {
HInstruction other = values.lookup(instruction);
if (other != null) {
assert(other.gvnEquals(instruction) && instruction.gvnEquals(other));
block.rewriteWithBetterUser(instruction, other);
block.remove(instruction);
} else {
values.add(instruction);
}
}
instruction = next;
}
List<HBasicBlock> dominatedBlocks = block.dominatedBlocks;
for (int i = 0, length = dominatedBlocks.length; i < length; i++) {
HBasicBlock dominated = dominatedBlocks[i];
// No need to copy the value set for the last child.
ValueSet successorValues = (i == length - 1) ? values : values.copy();
// If we have no values in our set, we do not have to kill
// anything. Also, if the range of block ids from the current
// block to the dominated block is empty, there is no blocks on
// any path from the current block to the dominated block so we
// don't have to do anything either.
assert(block.id < dominated.id);
if (!successorValues.isEmpty && block.id + 1 < dominated.id) {
visited.clear();
List<HBasicBlock> workQueue = <HBasicBlock>[dominated];
int changesFlags = 0;
do {
HBasicBlock current = workQueue.removeLast();
changesFlags |=
getChangesFlagsForDominatedBlock(block, current, workQueue);
} while (!workQueue.isEmpty);
successorValues.kill(changesFlags);
}
workQueue.add(new GvnWorkItem(dominated, successorValues));
}
}
void computeChangesFlags(HGraph graph) {
// Create the changes flags lists. Make sure to initialize the
// loop changes flags list to zero so we can use bitwise or when
// propagating loop changes upwards.
final int length = graph.blocks.length;
blockChangesFlags = new List<int>(length);
loopChangesFlags = new List<int>(length);
for (int i = 0; i < length; i++) loopChangesFlags[i] = 0;
// Run through all the basic blocks in the graph and fill in the
// changes flags lists.
for (int i = length - 1; i >= 0; i--) {
final HBasicBlock block = graph.blocks[i];
final int id = block.id;
// Compute block changes flags for the block.
int changesFlags = 0;
HInstruction instruction = block.first;
while (instruction != null) {
changesFlags |= instruction.sideEffects.getChangesFlags();
instruction = instruction.next;
}
assert(blockChangesFlags[id] == null);
blockChangesFlags[id] = changesFlags;
// Loop headers are part of their loop, so update the loop
// changes flags accordingly.
if (block.isLoopHeader()) {
loopChangesFlags[id] |= changesFlags;
}
// Propagate loop changes flags upwards.
HBasicBlock parentLoopHeader = block.parentLoopHeader;
if (parentLoopHeader != null) {
loopChangesFlags[parentLoopHeader.id] |=
(block.isLoopHeader()) ? loopChangesFlags[id] : changesFlags;
}
}
}
int getChangesFlagsForDominatedBlock(HBasicBlock dominator,
HBasicBlock dominated, List<HBasicBlock> workQueue) {
int changesFlags = 0;
List<HBasicBlock> predecessors = dominated.predecessors;
for (int i = 0, length = predecessors.length; i < length; i++) {
HBasicBlock block = predecessors[i];
int id = block.id;
// If the current predecessor block is on the path from the
// dominator to the dominated, it must have an id that is in the
// range from the dominator to the dominated.
if (dominator.id < id && id < dominated.id && !visited.contains(id)) {
visited.add(id);
changesFlags |= blockChangesFlags[id];
// Loop bodies might not be on the path from dominator to dominated,
// but they can invalidate values.
changesFlags |= loopChangesFlags[id];
workQueue.add(block);
}
}
return changesFlags;
}
}
// This phase merges equivalent instructions on different paths into
// one instruction in a dominator block. It runs through the graph
// post dominator order and computes a ValueSet for each block of
// instructions that can be moved to a dominator block. These
// instructions are the ones that:
// 1) can be used for GVN, and
// 2) do not use definitions of their own block.
//
// A basic block looks at its sucessors and finds the intersection of
// these computed ValueSet. It moves all instructions of the
// intersection into its own list of instructions.
class SsaCodeMotion extends HBaseVisitor implements OptimizationPhase {
final AbstractValueDomain _abstractValueDomain;
@override
final String name = "SsaCodeMotion";
bool movedCode = false;
List<ValueSet> values;
SsaCodeMotion(this._abstractValueDomain);
@override
void visitGraph(HGraph graph) {
values = new List<ValueSet>(graph.blocks.length);
for (int i = 0; i < graph.blocks.length; i++) {
values[graph.blocks[i].id] = new ValueSet();
}
visitPostDominatorTree(graph);
}
@override
void visitBasicBlock(HBasicBlock block) {
List<HBasicBlock> successors = block.successors;
// Phase 1: get the ValueSet of all successors (if there are more than one),
// compute the intersection and move the instructions of the intersection
// into this block.
if (successors.length > 1) {
ValueSet instructions = values[successors[0].id];
for (int i = 1; i < successors.length; i++) {
ValueSet other = values[successors[i].id];
instructions = instructions.intersection(other);
}
if (!instructions.isEmpty) {
List<HInstruction> list = instructions.toList();
// Sort by instruction 'id' for more stable ordering under changes to
// unrelated source code. 'id' is a function of the operations of
// compiling the current method, whereas the ValueSet order is dependent
// hashCodes that are a function of the whole program.
list.sort((insn1, insn2) => insn1.id.compareTo(insn2.id));
for (HInstruction instruction in list) {
// Move the instruction to the current block.
instruction.block.detach(instruction);
block.moveAtExit(instruction);
// Go through all successors and rewrite their instruction
// to the shared one.
for (final successor in successors) {
HInstruction toRewrite = values[successor.id].lookup(instruction);
if (toRewrite != instruction) {
successor.rewriteWithBetterUser(toRewrite, instruction);
successor.remove(toRewrite);
movedCode = true;
}
}
}
}
// TODO(sra): There are some non-gvn-able instructions that we could move,
// e.g. allocations. We should probably not move instructions that can
// directly or indirectly throw since the reported location might be in
// the 'wrong' branch.
}
// Don't try to merge instructions to a dominator if we have
// multiple predecessors.
if (block.predecessors.length != 1) return;
// Phase 2: Go through all instructions of this block and find
// which instructions can be moved to a dominator block.
ValueSet set_ = values[block.id];
HInstruction instruction = block.first;
int flags = 0;
while (instruction != null) {
int dependsFlags = SideEffects.computeDependsOnFlags(flags);
flags |= instruction.sideEffects.getChangesFlags();
HInstruction current = instruction;
instruction = instruction.next;
if (!current.useGvn() || !current.isMovable) continue;
// TODO(sra): We could move throwing instructions provided we keep the
// exceptions in the same order. This requires they are in the same order
// in all successors, which is not tracked by the ValueSet.
if (current.canThrow(_abstractValueDomain)) continue;
if (current.sideEffects.dependsOn(dependsFlags)) continue;
bool canBeMoved = true;
for (final HInstruction input in current.inputs) {
if (input.block == block) {
canBeMoved = false;
break;
// TODO(sra): We could move trees of instructions provided we move the
// roots before the leaves.
}
}
if (!canBeMoved) continue;
HInstruction existing = set_.lookup(current);
if (existing == null) {
set_.add(current);
} else {
block.rewriteWithBetterUser(current, existing);
block.remove(current);
movedCode = true;
}
}
}
}
class SsaTypeConversionInserter extends HBaseVisitor
implements OptimizationPhase {
@override
final String name = "SsaTypeconversionInserter";
final JClosedWorld closedWorld;
SsaTypeConversionInserter(this.closedWorld);
AbstractValueDomain get _abstractValueDomain =>
closedWorld.abstractValueDomain;
@override
void visitGraph(HGraph graph) {
visitDominatorTree(graph);
}
// Update users of [input] that are dominated by [:dominator.first:]
// to use [TypeKnown] of [input] instead. As the type information depends
// on the control flow, we mark the inserted [HTypeKnown] nodes as
// non-movable.
void insertTypePropagationForDominatedUsers(
HBasicBlock dominator, HInstruction input, AbstractValue convertedType) {
DominatedUses dominatedUses = DominatedUses.of(input, dominator.first);
if (dominatedUses.isEmpty) return;
// Check to avoid adding a duplicate HTypeKnown node.
if (dominatedUses.isSingleton) {
HInstruction user = dominatedUses.single;
if (user is HTypeKnown &&
user.isPinned &&
user.knownType == convertedType &&
user.checkedInput == input) {
return;
}
}
HTypeKnown newInput = new HTypeKnown.pinned(convertedType, input);
dominator.addBefore(dominator.first, newInput);
dominatedUses.replaceWith(newInput);
}
@override
void visitIs(HIs instruction) {
DartType type = instruction.typeExpression;
if (!instruction.isRawCheck) {
return;
} else if (type.isTypedef) {
return;
} else if (type.isFutureOr) {
return;
}
InterfaceType interfaceType = type;
ClassEntity cls = interfaceType.element;
List<HBasicBlock> trueTargets = <HBasicBlock>[];
List<HBasicBlock> falseTargets = <HBasicBlock>[];
collectTargets(instruction, trueTargets, falseTargets);
if (trueTargets.isEmpty && falseTargets.isEmpty) return;
AbstractValue convertedType =
_abstractValueDomain.createNonNullSubtype(cls);
HInstruction input = instruction.expression;
for (HBasicBlock block in trueTargets) {
insertTypePropagationForDominatedUsers(block, input, convertedType);
}
// TODO(sra): Also strengthen uses for when the condition is known
// false. Avoid strengthening to `null`.
}
@override
void visitIdentity(HIdentity instruction) {
// At HIf(HIdentity(x, null)) strengthens x to non-null on else branch.
HInstruction left = instruction.left;
HInstruction right = instruction.right;
HInstruction input;
if (left.isConstantNull()) {
input = right;
} else if (right.isConstantNull()) {
input = left;
} else {
return;
}
if (_abstractValueDomain.isNull(input.instructionType).isDefinitelyFalse) {
return;
}
List<HBasicBlock> trueTargets = <HBasicBlock>[];
List<HBasicBlock> falseTargets = <HBasicBlock>[];
collectTargets(instruction, trueTargets, falseTargets);
if (trueTargets.isEmpty && falseTargets.isEmpty) return;
AbstractValue nonNullType =
_abstractValueDomain.excludeNull(input.instructionType);
for (HBasicBlock block in falseTargets) {
insertTypePropagationForDominatedUsers(block, input, nonNullType);
}
// We don't strengthen the known-true references. It doesn't happen often
// and we don't want "if (x==null) return x;" to convert between JavaScript
// 'null' and 'undefined'.
}
collectTargets(HInstruction instruction, List<HBasicBlock> trueTargets,
List<HBasicBlock> falseTargets) {
for (HInstruction user in instruction.usedBy) {
if (user is HIf) {
trueTargets?.add(user.thenBlock);
falseTargets?.add(user.elseBlock);
} else if (user is HLoopBranch) {
trueTargets?.add(user.block.successors.first);
// Don't insert refinements on else-branch - may be a critical edge
// block which we currently need to keep empty (except for phis).
} else if (user is HNot) {
collectTargets(user, falseTargets, trueTargets);
} else if (user is HPhi) {
List<HInstruction> inputs = user.inputs;
if (inputs.length == 2) {
assert(inputs.contains(instruction));
HInstruction other = inputs[(inputs[0] == instruction) ? 1 : 0];
if (other.isConstantTrue()) {
// The condition flows to a HPhi(true, user), which means that a
// downstream HIf has true-branch control flow that does not depend
// on the original instruction, so stop collecting [trueTargets].
collectTargets(user, null, falseTargets);
} else if (other.isConstantFalse()) {
// Ditto for false.
collectTargets(user, trueTargets, null);
}
}
} else if (user is HBoolify) {
// We collect targets for strictly boolean operations so HBoolify cannot
// change the result.
collectTargets(user, trueTargets, falseTargets);
}
}
}
}
/// Optimization phase that tries to eliminate memory loads (for example
/// [HFieldGet]), when it knows the value stored in that memory location, and
/// stores that overwrite with the same value.
class SsaLoadElimination extends HBaseVisitor implements OptimizationPhase {
final Compiler compiler;
final JClosedWorld closedWorld;
final JFieldAnalysis _fieldAnalysis;
@override
final String name = "SsaLoadElimination";
MemorySet memorySet;
List<MemorySet> memories;
bool newGvnCandidates = false;
HGraph _graph;
SsaLoadElimination(this.compiler, this.closedWorld)
: _fieldAnalysis = closedWorld.fieldAnalysis;
AbstractValueDomain get _abstractValueDomain =>
closedWorld.abstractValueDomain;
@override
void visitGraph(HGraph graph) {
_graph = graph;
memories = new List<MemorySet>(graph.blocks.length);
List<HBasicBlock> blocks = graph.blocks;
for (int i = 0; i < blocks.length; i++) {
HBasicBlock block = blocks[i];
visitBasicBlock(block);
if (block.successors.isNotEmpty && block.successors[0].isLoopHeader()) {
// We've reached the ending block of a loop. Iterate over the
// blocks of the loop again to take values that flow from that
// ending block into account.
for (int j = block.successors[0].id; j <= block.id; j++) {
visitBasicBlock(blocks[j]);
}
}
}
}
@override
void visitBasicBlock(HBasicBlock block) {
if (block.predecessors.length == 0) {
// Entry block.
memorySet = new MemorySet(closedWorld);
} else if (block.predecessors.length == 1 &&
block.predecessors[0].successors.length == 1) {
// No need to clone, there is no other successor for
// `block.predecessors[0]`, and this block has only one
// predecessor. Since we are not going to visit
// `block.predecessors[0]` again, we can just re-use its
// [memorySet].
memorySet = memories[block.predecessors[0].id];
} else if (block.predecessors.length == 1) {
// Clone the memorySet of the predecessor, because it is also used
// by other successors of it.
memorySet = memories[block.predecessors[0].id].clone();
} else {
// Compute the intersection of all predecessors.
memorySet = memories[block.predecessors[0].id];
for (int i = 1; i < block.predecessors.length; i++) {
memorySet = memorySet.intersectionFor(
memories[block.predecessors[i].id], block, i);
}
}
memories[block.id] = memorySet;
HInstruction instruction = block.first;
while (instruction != null) {
HInstruction next = instruction.next;
instruction.accept(this);
instruction = next;
}
}
void checkNewGvnCandidates(HInstruction instruction, HInstruction existing) {
if (newGvnCandidates) return;
bool hasUseGvn(HInstruction insn) => insn.nonCheck().useGvn();
if (instruction.usedBy.any(hasUseGvn) && existing.usedBy.any(hasUseGvn)) {
newGvnCandidates = true;
}
}
@override
void visitFieldGet(HFieldGet instruction) {
if (instruction.isNullCheck) return;
FieldEntity element = instruction.element;
HInstruction receiver = instruction.getDartReceiver(closedWorld).nonCheck();
_visitFieldGet(element, receiver, instruction);
}
@override
void visitGetLength(HGetLength instruction) {
HInstruction receiver = instruction.receiver.nonCheck();
HInstruction existing =
memorySet.lookupFieldValue(MemoryFeature.length, receiver);
if (existing != null) {
checkNewGvnCandidates(instruction, existing);
instruction.block.rewriteWithBetterUser(instruction, existing);
instruction.block.remove(instruction);
} else {
memorySet.registerFieldValue(MemoryFeature.length, receiver, instruction);
}
}
void _visitFieldGet(
FieldEntity element, HInstruction receiver, HInstruction instruction) {
HInstruction existing = memorySet.lookupFieldValue(element, receiver);
if (existing != null) {
checkNewGvnCandidates(instruction, existing);
instruction.block.rewriteWithBetterUser(instruction, existing);
instruction.block.remove(instruction);
} else {
memorySet.registerFieldValue(element, receiver, instruction);
}
}
@override
void visitFieldSet(HFieldSet instruction) {
FieldEntity element = instruction.element;
HInstruction receiver = instruction.getDartReceiver(closedWorld).nonCheck();
if (memorySet.registerFieldValueUpdate(
element, receiver, instruction.value)) {
instruction.block.remove(instruction);
}
}
@override
void visitCreate(HCreate instruction) {
memorySet.registerAllocation(instruction);
if (shouldTrackInitialValues(instruction)) {
int argumentIndex = 0;
compiler.codegenWorldBuilder.forEachInstanceField(instruction.element,
(_, FieldEntity member, {bool isElided}) {
if (isElided) return;
if (compiler.elementHasCompileTimeError(
// ignore: UNNECESSARY_CAST
member as Entity)) return;
FieldAnalysisData fieldData = _fieldAnalysis.getFieldData(member);
if (fieldData.isInitializedInAllocator) {
// TODO(sra): Can we avoid calling HGraph.addConstant?
ConstantValue value = fieldData.initialValue;
HConstant constant = _graph.addConstant(value, closedWorld);
memorySet.registerFieldValue(member, instruction, constant);
} else {
memorySet.registerFieldValue(
member, instruction, instruction.inputs[argumentIndex++]);
}
});
}
// In case this instruction has as input non-escaping objects, we
// need to mark these objects as escaping.
memorySet.killAffectedBy(instruction);
}
bool shouldTrackInitialValues(HCreate instruction) {
// Don't track initial field values of an allocation that are
// unprofitable. We search the chain of single uses in allocations for a
// limited depth.
const MAX_HEAP_DEPTH = 5;
bool interestingUse(HInstruction instruction, int heapDepth) {
// Heuristic: if the allocation is too deep in heap it is unlikely we will
// recover a field by load-elimination.
// TODO(sra): We can measure this depth by looking at load chains.
if (heapDepth == MAX_HEAP_DEPTH) return false;
// There are multiple uses so do the full store analysis.
if (instruction.usedBy.length != 1) return true;
HInstruction use = instruction.usedBy.single;
// When the only use is an allocation, the allocation becomes the only
// heap alias for the current instruction.
if (use is HCreate) return interestingUse(use, heapDepth + 1);
if (use is HLiteralList) return interestingUse(use, heapDepth + 1);
if (use is HInvokeStatic) {
// Assume the argument escapes. All we do with our initial allocation is
// have it escape or store it into an object that escapes.
return false;
// TODO(sra): Handle library functions that we know do not modify or
// leak the inputs. For example `setRuntimeTypeInfo` is used to mark
// list literals with type information.
}
if (use is HPhi) {
// The initial allocation (it's only alias) gets merged out of the model
// of the heap before load.
return false;
}
return true;
}
return interestingUse(instruction, 0);
}
@override
void visitInstruction(HInstruction instruction) {
if (instruction.isAllocation(_abstractValueDomain)) {
memorySet.registerAllocation(instruction);
}
memorySet.killAffectedBy(instruction);
}
@override
void visitLazyStatic(HLazyStatic instruction) {
FieldEntity field = instruction.element;
handleStaticLoad(field, instruction);
}
void handleStaticLoad(MemberEntity element, HInstruction instruction) {
HInstruction existing = memorySet.lookupFieldValue(element, null);
if (existing != null) {
checkNewGvnCandidates(instruction, existing);
instruction.block.rewriteWithBetterUser(instruction, existing);
instruction.block.remove(instruction);
} else {
memorySet.registerFieldValue(element, null, instruction);
}
}
@override
void visitStatic(HStatic instruction) {
handleStaticLoad(instruction.element, instruction);
}
@override
void visitStaticStore(HStaticStore instruction) {
if (memorySet.registerFieldValueUpdate(
instruction.element, null, instruction.inputs.last)) {
instruction.block.remove(instruction);
}
}
@override
void visitLiteralList(HLiteralList instruction) {
memorySet.registerAllocation(instruction);
memorySet.killAffectedBy(instruction);
// TODO(sra): Set initial keyed values.
// TODO(sra): Set initial length.
}
@override
void visitIndex(HIndex instruction) {
HInstruction receiver = instruction.receiver.nonCheck();
HInstruction existing =
memorySet.lookupKeyedValue(receiver, instruction.index);
if (existing != null) {
checkNewGvnCandidates(instruction, existing);
instruction.block.rewriteWithBetterUser(instruction, existing);
instruction.block.remove(instruction);
} else {
memorySet.registerKeyedValue(receiver, instruction.index, instruction);
}
}
@override
void visitIndexAssign(HIndexAssign instruction) {
HInstruction receiver = instruction.receiver.nonCheck();
memorySet.registerKeyedValueUpdate(
receiver, instruction.index, instruction.value);
}
// Pure operations that do not escape their inputs.
@override
void visitBinaryArithmetic(HBinaryArithmetic instruction) {}
@override
void visitBoundsCheck(HBoundsCheck instruction) {}
@override
void visitConstant(HConstant instruction) {}
@override
void visitIf(HIf instruction) {}
@override
void visitInterceptor(HInterceptor instruction) {}
@override
void visitIs(HIs instruction) {}
@override
void visitIsViaInterceptor(HIsViaInterceptor instruction) {}
@override
void visitNot(HNot instruction) {}
@override
void visitParameterValue(HParameterValue instruction) {}
@override
void visitRelational(HRelational instruction) {}
@override
void visitStringConcat(HStringConcat instruction) {}
@override
void visitTypeKnown(HTypeKnown instruction) {}
@override
void visitTypeInfoReadRaw(HTypeInfoReadRaw instruction) {}
@override
void visitTypeInfoReadVariable(HTypeInfoReadVariable instruction) {}
@override
void visitTypeInfoExpression(HTypeInfoExpression instruction) {}
}
/// A non-field based feature of an object.
enum MemoryFeature {
// Access to the `length` property of a `JSIndexable`.
length,
}
/// Holds values of memory places.
///
/// Generally, values that name a place (a receiver) have type refinements and
/// other checks removed to ensure that checks and type refinements do not
/// confuse aliasing. Values stored into a memory place keep the type
/// refinements to help further optimizations.
class MemorySet {
final JClosedWorld closedWorld;
/// Maps a field to a map of receivers to their current field values.
///
/// The field is either a [FieldEntity], a [FunctionEntity] in case of
/// instance methods, or a [MemoryFeature] for `length` access on
/// `JSIndexable`.
///
// TODO(25544): Split length effects from other effects and model lengths
// separately.
final Map<Object /*MemberEntity|MemoryFeature*/,
Map<HInstruction, HInstruction>>
fieldValues = <Object, Map<HInstruction, HInstruction>>{};
/// Maps a receiver to a map of keys to value.
final Map<HInstruction, Map<HInstruction, HInstruction>> keyedValues =
<HInstruction, Map<HInstruction, HInstruction>>{};
/// Set of objects that we know don't escape the current function.
final Setlet<HInstruction> nonEscapingReceivers = new Setlet<HInstruction>();
MemorySet(this.closedWorld);
AbstractValueDomain get _abstractValueDomain =>
closedWorld.abstractValueDomain;
/// Returns whether [first] and [second] always alias to the same object.
bool mustAlias(HInstruction first, HInstruction second) {
return first == second;
}
/// Returns whether [first] and [second] may alias to the same object.
bool mayAlias(HInstruction first, HInstruction second) {
if (mustAlias(first, second)) return true;
if (isConcrete(first) && isConcrete(second)) return false;
if (nonEscapingReceivers.contains(first)) return false;
if (nonEscapingReceivers.contains(second)) return false;
// Typed arrays of different types might have a shared buffer.
if (couldBeTypedArray(first) && couldBeTypedArray(second)) return true;
return _abstractValueDomain
.areDisjoint(first.instructionType, second.instructionType)
.isPotentiallyFalse;
}
bool isFinal(Object element) {
return element is MemberEntity && closedWorld.fieldNeverChanges(element);
}
bool isConcrete(HInstruction instruction) {
return instruction is HCreate ||
instruction is HConstant ||
instruction is HLiteralList;
}
bool couldBeTypedArray(HInstruction receiver) {
return closedWorld.abstractValueDomain
.couldBeTypedArray(receiver.instructionType)
.isPotentiallyTrue;
}
/// Returns whether [receiver] escapes the current function.
bool escapes(HInstruction receiver) {
assert(receiver == null || receiver == receiver.nonCheck());
return !nonEscapingReceivers.contains(receiver);
}
void registerAllocation(HInstruction instruction) {
assert(instruction == instruction.nonCheck());
nonEscapingReceivers.add(instruction);
}
/// Sets the [field] on [receiver] to contain [value]. Kills all potential
/// places that may be affected by this update. Returns `true` if the update
/// is redundant.
bool registerFieldValueUpdate(
Object field, HInstruction receiver, HInstruction value) {
assert(field is MemberEntity || field is MemoryFeature,
"Unexpected member/feature: $field");
assert(receiver == null || receiver == receiver.nonCheck());
if (closedWorld.nativeData.isNativeMember(field)) {
return false; // TODO(14955): Remove this restriction?
}
// [value] is being set in some place in memory, we remove it from the
// non-escaping set.
nonEscapingReceivers.remove(value.nonCheck());
Map<HInstruction, HInstruction> map =
fieldValues.putIfAbsent(field, () => <HInstruction, HInstruction>{});
bool isRedundant = map[receiver] == value;
map.forEach((key, value) {
if (mayAlias(receiver, key)) map[key] = null;
});
map[receiver] = value;
return isRedundant;
}
/// Registers that the [field] on [receiver] is now [value].
void registerFieldValue(
Object field, HInstruction receiver, HInstruction value) {
assert(field is MemberEntity || field is MemoryFeature,
"Unexpected member/feature: $field");
assert(receiver == null || receiver == receiver.nonCheck());
if (field is MemberEntity && closedWorld.nativeData.isNativeMember(field)) {
return; // TODO(14955): Remove this restriction?
}
Map<HInstruction, HInstruction> map =
fieldValues.putIfAbsent(field, () => <HInstruction, HInstruction>{});
map[receiver] = value;
}
/// Returns the value stored for [field] on [receiver]. Returns `null` if we
/// don't know.
HInstruction lookupFieldValue(Object field, HInstruction receiver) {
assert(field is MemberEntity || field is MemoryFeature,
"Unexpected member/feature: $field");
assert(receiver == null || receiver == receiver.nonCheck());
Map<HInstruction, HInstruction> map = fieldValues[field];
return (map == null) ? null : map[receiver];
}
/// Kill all places that may be affected by this [instruction]. Also update
/// the set of non-escaping objects in case [instruction] has non-escaping
/// objects in its inputs.
void killAffectedBy(HInstruction instruction) {
// Even if [instruction] does not have side effects, it may use non-escaping
// objects and store them in a new object, which make these objects
// escaping.
instruction.inputs.forEach((input) {
nonEscapingReceivers.remove(input.nonCheck());
});
if (instruction.sideEffects.changesInstanceProperty() ||
instruction.sideEffects.changesStaticProperty()) {
List<HInstruction> receiversToRemove = <HInstruction>[];
List<Object> fieldsToRemove;
fieldValues.forEach((Object element, map) {
if (isFinal(element)) return;
map.forEach((receiver, value) {
if (escapes(receiver)) {
receiversToRemove.add(receiver);
}
});
if (receiversToRemove.length == map.length) {
// Remove them all by removing the entire map.
(fieldsToRemove ??= <Object>[]).add(element);
} else {
receiversToRemove.forEach(map.remove);
}
receiversToRemove.clear();
});
fieldsToRemove?.forEach(fieldValues.remove);
}
if (instruction.sideEffects.changesIndex()) {
keyedValues.forEach((receiver, map) {
if (escapes(receiver)) {
map.forEach((index, value) {
map[index] = null;
});
}
});
}
}
/// Returns the value stored in `receiver[index]`. Returns null if we don't
/// know.
HInstruction lookupKeyedValue(HInstruction receiver, HInstruction index) {
Map<HInstruction, HInstruction> map = keyedValues[receiver];
return (map == null) ? null : map[index];
}
/// Registers that `receiver[index]` is now [value].
void registerKeyedValue(
HInstruction receiver, HInstruction index, HInstruction value) {
Map<HInstruction, HInstruction> map =
keyedValues.putIfAbsent(receiver, () => <HInstruction, HInstruction>{});
map[index] = value;
}
/// Sets `receiver[index]` to contain [value]. Kills all potential places that
/// may be affected by this update.
void registerKeyedValueUpdate(
HInstruction receiver, HInstruction index, HInstruction value) {
nonEscapingReceivers.remove(value.nonCheck());
keyedValues.forEach((key, values) {
if (mayAlias(receiver, key)) {
// Typed arrays that are views of the same buffer may have different
// offsets or element sizes, unless they are the same typed array.
bool weakIndex = couldBeTypedArray(key) && !mustAlias(receiver, key);
values.forEach((otherIndex, otherValue) {
if (weakIndex || mayAlias(index, otherIndex)) {
values[otherIndex] = null;
}
});
}
});
// Typed arrays may narrow incoming values.
if (couldBeTypedArray(receiver)) return;
Map<HInstruction, HInstruction> map =
keyedValues.putIfAbsent(receiver, () => <HInstruction, HInstruction>{});
map[index] = value;
}
/// Returns a common instruction for [first] and [second].
///
/// Returns `null` if either [first] or [second] is null. Returns [first] if
/// [first] and [second] are equal. Otherwise creates or re-uses a phi in
/// [block] that holds [first] and [second].
HInstruction findCommonInstruction(HInstruction first, HInstruction second,
HBasicBlock block, int predecessorIndex) {
if (first == null || second == null) return null;
if (first == second) return first;
if (second is HGetLength) {
// Don't always create phis for HGetLength. The phi confuses array bounds
// check elimination and the resulting variable-heavy code probably is
// confusing for JavaScript VMs. In practice, this mostly affects the
// expansion of for-in loops on Arrays, so we match the expression
//
// checkConcurrentModificationError(array.length == _end, array)
//
// starting with the HGetLength of the `array.length`, in the case where
// `array.length` is not used elsewhere (i.e. not already optimized to use
// a previous use, in the loop condition).
//
// TODO(sra): Figure out a better way ensure 'nice' loop code.
// TODO(22407): The phi would not be so bad if it did not confuse bounds
// check elimination.
// TODO(25437): We could add a phi if we undid the harmful cases.
if (second.usedBy.length == 1) {
var user = second.usedBy.single;
if (user is HIdentity && user.usedBy.length == 1) {
HInstruction user2 = user.usedBy.single;
if (user2 is HInvokeStatic &&
user2.element ==
closedWorld.commonElements.checkConcurrentModificationError) {
return null;
}
}
}
}
AbstractValue phiType = _abstractValueDomain.union(
second.instructionType, first.instructionType);
if (first is HPhi && first.block == block) {
HPhi phi = first;
phi.addInput(second);
phi.instructionType = phiType;
return phi;
} else {
HPhi phi = new HPhi.noInputs(null, phiType);
block.addPhi(phi);
// Previous predecessors had the same input. A phi must have
// the same number of inputs as its block has predecessors.
for (int i = 0; i < predecessorIndex; i++) {
phi.addInput(first);
}
phi.addInput(second);
return phi;
}
}
/// Returns the intersection between [this] and the [other] memory set.
MemorySet intersectionFor(
MemorySet other, HBasicBlock block, int predecessorIndex) {
MemorySet result = new MemorySet(closedWorld);
if (other == null) {
// This is the first visit to a loop header ([other] is `null` because we
// have not visited the back edge). Copy the nonEscapingReceivers that are
// guaranteed to survive the loop because they are not escaped before
// method exit.
// TODO(sra): We should do a proper dataflow to find the maximal
// nonEscapingReceivers (a variant of Available-Expressions), which must
// converge before we edit the program in [findCommonInstruction].
for (HInstruction instruction in nonEscapingReceivers) {
bool isNonEscapingUse(HInstruction use) {
if (use is HReturn) return true; // Escapes, but so does control.
if (use is HFieldGet) return true;
if (use is HFieldSet) {
return use.value.nonCheck() != instruction;
}
if (use is HTypeInfoReadVariable) return true;
if (use is HGetLength) return true;
if (use is HBoundsCheck) return true;
if (use is HIndex) return true;
if (use is HIndexAssign) {
return use.value.nonCheck() != instruction;
}
if (use is HInterceptor) return true;
if (use is HInvokeDynamicMethod) {
MemberEntity element = use.element;
if (element != null) {
if (element == closedWorld.commonElements.jsArrayAdd) {
return use.inputs.last != instruction;
}
}
}
if (use is HInvokeStatic) {
if (use.element ==
closedWorld.commonElements.checkConcurrentModificationError)
return true;
}
return false;
}
if (instruction.usedBy.every(isNonEscapingUse)) {
result.nonEscapingReceivers.add(instruction);
}
}
return result;
}
fieldValues.forEach((element, values) {
var otherValues = other.fieldValues[element];
if (otherValues == null) return;
values.forEach((receiver, value) {
HInstruction instruction = findCommonInstruction(
value, otherValues[receiver], block, predecessorIndex);
if (instruction != null) {
result.registerFieldValue(element, receiver, instruction);
}
});
});
keyedValues.forEach((receiver, values) {
var otherValues = other.keyedValues[receiver];
if (otherValues == null) return;
values.forEach((index, value) {
HInstruction instruction = findCommonInstruction(
value, otherValues[index], block, predecessorIndex);
if (instruction != null) {
result.registerKeyedValue(receiver, index, instruction);
}
});
});
nonEscapingReceivers.forEach((receiver) {
if (other.nonEscapingReceivers.contains(receiver)) {
result.nonEscapingReceivers.add(receiver);
}
});
return result;
}
/// Returns a copy of [this] memory set.
MemorySet clone() {
MemorySet result = new MemorySet(closedWorld);
fieldValues.forEach((element, values) {
result.fieldValues[element] =
new Map<HInstruction, HInstruction>.from(values);
});
keyedValues.forEach((receiver, values) {
result.keyedValues[receiver] =
new Map<HInstruction, HInstruction>.from(values);
});
result.nonEscapingReceivers.addAll(nonEscapingReceivers);
return result;
}
}