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// 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.
#include "vm/compiler/backend/flow_graph.h"
#include "vm/compiler/backend/il.h"
namespace dart {
// Sparse conditional constant propagation and unreachable code elimination.
// Assumes that use lists are computed and preserves them.
class ConstantPropagator : public FlowGraphVisitor {
ConstantPropagator(FlowGraph* graph,
const GrowableArray<BlockEntryInstr*>& ignored);
static void Optimize(FlowGraph* graph);
// (1) Visit branches to optimize away unreachable blocks discovered by range
// analysis.
// (2) Eliminate branches that have the same true- and false-target: For
// example, this occurs after expressions like
// if (a == null || b == null) {
// ...
// }
// where b is known to be null.
static void OptimizeBranches(FlowGraph* graph);
// Used to initialize the abstract value of definitions.
static RawObject* Unknown() { return Object::unknown_constant().raw(); }
void Analyze();
void Transform();
void EliminateRedundantBranches();
void SetReachable(BlockEntryInstr* block);
bool SetValue(Definition* definition, const Object& value);
Definition* UnwrapPhi(Definition* defn);
void MarkPhi(Definition* defn);
// Assign the join (least upper bound) of a pair of abstract values to the
// first one.
void Join(Object* left, const Object& right);
bool IsUnknown(const Object& value) { return value.raw() == unknown_.raw(); }
bool IsNonConstant(const Object& value) {
return value.raw() == non_constant_.raw();
bool IsConstant(const Object& value) {
return !IsNonConstant(value) && !IsUnknown(value);
void VisitBinaryIntegerOp(BinaryIntegerOpInstr* binary_op);
void VisitUnaryIntegerOp(UnaryIntegerOpInstr* unary_op);
virtual void VisitBlocks() { UNREACHABLE(); }
#define DECLARE_VISIT(type, attrs) virtual void Visit##type(type##Instr* instr);
Isolate* isolate() const { return graph_->isolate(); }
FlowGraph* graph_;
// Sentinels for unknown constant and non-constant values.
const Object& unknown_;
const Object& non_constant_;
// Analysis results. For each block, a reachability bit. Indexed by
// preorder number.
BitVector* reachable_;
BitVector* marked_phis_;
// Worklists of blocks and definitions.
GrowableArray<BlockEntryInstr*> block_worklist_;
DefinitionWorklist definition_worklist_;
} // namespace dart