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dart / sdk.git / 3c2d1ddd0c4569a266410e9ef4936c7a876cbf77 / . / runtime / vm / flow_graph_allocator.cc
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// Copyright (c) 2013, 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/flow_graph_allocator.h"
#include "vm/bit_vector.h"
#include "vm/intermediate_language.h"
#include "vm/il_printer.h"
#include "vm/flow_graph.h"
#include "vm/flow_graph_compiler.h"
#include "vm/log.h"
#include "vm/parser.h"
namespace dart {
DEFINE_FLAG(bool, print_ssa_liveness, false,
"Print liveness for ssa variables.");
DEFINE_FLAG(bool, trace_ssa_allocator, false,
"Trace register allocation over SSA.");
DEFINE_FLAG(bool, print_ssa_liveranges, false,
"Print live ranges after allocation.");
#if defined(DEBUG)
#define TRACE_ALLOC(statement) \
do { \
if (FLAG_trace_ssa_allocator) statement; \
} while (0)
#else
#define TRACE_ALLOC(statement)
#endif
static const intptr_t kNoVirtualRegister = -1;
static const intptr_t kTempVirtualRegister = -2;
static const intptr_t kIllegalPosition = -1;
static const intptr_t kMaxPosition = 0x7FFFFFFF;
static const intptr_t kPairVirtualRegisterOffset = 1;
// Definitions which have pair representations
// (kPairOfTagged or kPairOfUnboxedDouble) use two virtual register names.
// At SSA index allocation time each definition reserves two SSA indexes,
// the second index is only used for pairs. This function maps from the first
// SSA index to the second.
static intptr_t ToSecondPairVreg(intptr_t vreg) {
// Map vreg to its pair vreg.
return vreg + kPairVirtualRegisterOffset;
}
static intptr_t MinPosition(intptr_t a, intptr_t b) {
return (a < b) ? a : b;
}
static bool IsInstructionStartPosition(intptr_t pos) {
return (pos & 1) == 0;
}
static bool IsInstructionEndPosition(intptr_t pos) {
return (pos & 1) == 1;
}
static intptr_t ToInstructionStart(intptr_t pos) {
return (pos & ~1);
}
static intptr_t ToInstructionEnd(intptr_t pos) {
return (pos | 1);
}
FlowGraphAllocator::FlowGraphAllocator(const FlowGraph& flow_graph,
bool intrinsic_mode)
: flow_graph_(flow_graph),
reaching_defs_(flow_graph),
value_representations_(flow_graph.max_virtual_register_number()),
block_order_(flow_graph.reverse_postorder()),
postorder_(flow_graph.postorder()),
liveness_(flow_graph),
vreg_count_(flow_graph.max_virtual_register_number()),
live_ranges_(flow_graph.max_virtual_register_number()),
cpu_regs_(),
fpu_regs_(),
blocked_cpu_registers_(),
blocked_fpu_registers_(),
number_of_registers_(0),
registers_(),
blocked_registers_(),
cpu_spill_slot_count_(0),
intrinsic_mode_(intrinsic_mode) {
for (intptr_t i = 0; i < vreg_count_; i++) {
live_ranges_.Add(NULL);
}
for (intptr_t i = 0; i < vreg_count_; i++) {
value_representations_.Add(kNoRepresentation);
}
// All registers are marked as "not blocked" (array initialized to false).
// Mark the unavailable ones as "blocked" (true).
for (intptr_t i = 0; i < kFirstFreeCpuRegister; i++) {
blocked_cpu_registers_[i] = true;
}
for (intptr_t i = kLastFreeCpuRegister + 1; i < kNumberOfCpuRegisters; i++) {
blocked_cpu_registers_[i] = true;
}
if (TMP != kNoRegister) {
blocked_cpu_registers_[TMP] = true;
}
if (TMP2 != kNoRegister) {
blocked_cpu_registers_[TMP2] = true;
}
if (PP != kNoRegister) {
blocked_cpu_registers_[PP] = true;
}
blocked_cpu_registers_[SPREG] = true;
blocked_cpu_registers_[FPREG] = true;
blocked_cpu_registers_[THR] = true;
// FpuTMP is used as scratch by optimized code and parallel move resolver.
blocked_fpu_registers_[FpuTMP] = true;
// Block additional registers needed preserved when generating intrinsics.
// TODO(fschneider): Handle saving and restoring these registers when
// generating intrinsic code.
if (intrinsic_mode) {
blocked_cpu_registers_[ARGS_DESC_REG] = true;
}
}
static void DeepLiveness(MaterializeObjectInstr* mat, BitVector* live_in) {
if (mat->was_visited_for_liveness()) {
return;
}
mat->mark_visited_for_liveness();
for (intptr_t i = 0; i < mat->InputCount(); i++) {
if (!mat->InputAt(i)->BindsToConstant()) {
Definition* defn = mat->InputAt(i)->definition();
MaterializeObjectInstr* inner_mat = defn->AsMaterializeObject();
if (inner_mat != NULL) {
DeepLiveness(inner_mat, live_in);
} else {
intptr_t idx = defn->ssa_temp_index();
live_in->Add(idx);
}
}
}
}
void SSALivenessAnalysis::ComputeInitialSets() {
const intptr_t block_count = postorder_.length();
for (intptr_t i = 0; i < block_count; i++) {
BlockEntryInstr* block = postorder_[i];
BitVector* kill = kill_[i];
BitVector* live_in = live_in_[i];
// Iterate backwards starting at the last instruction.
for (BackwardInstructionIterator it(block); !it.Done(); it.Advance()) {
Instruction* current = it.Current();
// Initialize location summary for instruction.
current->InitializeLocationSummary(zone(), true); // opt
LocationSummary* locs = current->locs();
#if defined(DEBUG)
locs->DiscoverWritableInputs();
#endif
// Handle definitions.
Definition* current_def = current->AsDefinition();
if ((current_def != NULL) && current_def->HasSSATemp()) {
kill->Add(current_def->ssa_temp_index());
live_in->Remove(current_def->ssa_temp_index());
if (current_def->HasPairRepresentation()) {
kill->Add(ToSecondPairVreg(current_def->ssa_temp_index()));
live_in->Remove(ToSecondPairVreg(current_def->ssa_temp_index()));
}
}
// Handle uses.
ASSERT(locs->input_count() == current->InputCount());
for (intptr_t j = 0; j < current->InputCount(); j++) {
Value* input = current->InputAt(j);
ASSERT(!locs->in(j).IsConstant() || input->BindsToConstant());
if (locs->in(j).IsConstant()) continue;
live_in->Add(input->definition()->ssa_temp_index());
if (input->definition()->HasPairRepresentation()) {
live_in->Add(ToSecondPairVreg(input->definition()->ssa_temp_index()));
}
}
// Add non-argument uses from the deoptimization environment (pushed
// arguments are not allocated by the register allocator).
if (current->env() != NULL) {
for (Environment::DeepIterator env_it(current->env());
!env_it.Done();
env_it.Advance()) {
Definition* defn = env_it.CurrentValue()->definition();
if (defn->IsMaterializeObject()) {
// MaterializeObject instruction is not in the graph.
// Treat its inputs as part of the environment.
DeepLiveness(defn->AsMaterializeObject(), live_in);
} else if (!defn->IsPushArgument() && !defn->IsConstant()) {
live_in->Add(defn->ssa_temp_index());
if (defn->HasPairRepresentation()) {
live_in->Add(ToSecondPairVreg(defn->ssa_temp_index()));
}
}
}
}
}
// Handle phis.
if (block->IsJoinEntry()) {
JoinEntryInstr* join = block->AsJoinEntry();
for (PhiIterator it(join); !it.Done(); it.Advance()) {
PhiInstr* phi = it.Current();
ASSERT(phi != NULL);
kill->Add(phi->ssa_temp_index());
live_in->Remove(phi->ssa_temp_index());
if (phi->HasPairRepresentation()) {
kill->Add(ToSecondPairVreg(phi->ssa_temp_index()));
live_in->Remove(ToSecondPairVreg(phi->ssa_temp_index()));
}
// If a phi input is not defined by the corresponding predecessor it
// must be marked live-in for that predecessor.
for (intptr_t k = 0; k < phi->InputCount(); k++) {
Value* val = phi->InputAt(k);
if (val->BindsToConstant()) continue;
BlockEntryInstr* pred = block->PredecessorAt(k);
const intptr_t use = val->definition()->ssa_temp_index();
if (!kill_[pred->postorder_number()]->Contains(use)) {
live_in_[pred->postorder_number()]->Add(use);
}
if (phi->HasPairRepresentation()) {
const intptr_t second_use = ToSecondPairVreg(use);
if (!kill_[pred->postorder_number()]->Contains(second_use)) {
live_in_[pred->postorder_number()]->Add(second_use);
}
}
}
}
} else if (block->IsCatchBlockEntry()) {
// Process initial definitions.
CatchBlockEntryInstr* catch_entry = block->AsCatchBlockEntry();
for (intptr_t i = 0;
i < catch_entry->initial_definitions()->length();
i++) {
Definition* def = (*catch_entry->initial_definitions())[i];
const intptr_t vreg = def->ssa_temp_index();
kill_[catch_entry->postorder_number()]->Add(vreg);
live_in_[catch_entry->postorder_number()]->Remove(vreg);
}
}
}
// Process initial definitions, ie, constants and incoming parameters.
for (intptr_t i = 0; i < graph_entry_->initial_definitions()->length(); i++) {
Definition* def = (*graph_entry_->initial_definitions())[i];
const intptr_t vreg = def->ssa_temp_index();
kill_[graph_entry_->postorder_number()]->Add(vreg);
live_in_[graph_entry_->postorder_number()]->Remove(vreg);
}
}
UsePosition* LiveRange::AddUse(intptr_t pos, Location* location_slot) {
ASSERT(location_slot != NULL);
ASSERT((first_use_interval_->start_ <= pos) &&
(pos <= first_use_interval_->end_));
if (uses_ != NULL) {
if ((uses_->pos() == pos) &&
(uses_->location_slot() == location_slot)) {
return uses_;
} else if (uses_->pos() < pos) {
// If an instruction at position P is using the same value both as
// a fixed register input and a non-fixed input (in this order) we will
// add uses both at position P-1 and *then* P which will make
// uses_ unsorted unless we account for it here.
UsePosition* insert_after = uses_;
while ((insert_after->next() != NULL) &&
(insert_after->next()->pos() < pos)) {
insert_after = insert_after->next();
}
UsePosition* insert_before = insert_after->next();
while (insert_before != NULL && (insert_before->pos() == pos)) {
if (insert_before->location_slot() == location_slot) {
return insert_before;
}
insert_before = insert_before->next();
}
insert_after->set_next(
new UsePosition(pos, insert_after->next(), location_slot));
return insert_after->next();
}
}
uses_ = new UsePosition(pos, uses_, location_slot);
return uses_;
}
void LiveRange::AddSafepoint(intptr_t pos, LocationSummary* locs) {
ASSERT(IsInstructionStartPosition(pos));
SafepointPosition* safepoint =
new SafepointPosition(ToInstructionEnd(pos), locs);
if (first_safepoint_ == NULL) {
ASSERT(last_safepoint_ == NULL);
first_safepoint_ = last_safepoint_ = safepoint;
} else {
ASSERT(last_safepoint_ != NULL);
// We assume that safepoints list is sorted by position and that
// safepoints are added in this order.
ASSERT(last_safepoint_->pos() < pos);
last_safepoint_->set_next(safepoint);
last_safepoint_ = safepoint;
}
}
void LiveRange::AddHintedUse(intptr_t pos,
Location* location_slot,
Location* hint) {
ASSERT(hint != NULL);
AddUse(pos, location_slot)->set_hint(hint);
}
void LiveRange::AddUseInterval(intptr_t start, intptr_t end) {
ASSERT(start < end);
// Live ranges are being build by visiting instructions in post-order.
// This implies that use intervals will be prepended in a monotonically
// decreasing order.
if (first_use_interval() != NULL) {
// If the first use interval and the use interval we are adding
// touch then we can just extend the first interval to cover their
// union.
if (start > first_use_interval()->start()) {
// The only case when we can add intervals with start greater than
// start of an already created interval is BlockLocation.
ASSERT(vreg() == kNoVirtualRegister);
ASSERT(end <= first_use_interval()->end());
return;
} else if (start == first_use_interval()->start()) {
// Grow first interval if necessary.
if (end <= first_use_interval()->end()) return;
first_use_interval_->end_ = end;
return;
} else if (end == first_use_interval()->start()) {
first_use_interval()->start_ = start;
return;
}
ASSERT(end < first_use_interval()->start());
}
first_use_interval_ = new UseInterval(start, end, first_use_interval_);
if (last_use_interval_ == NULL) {
ASSERT(first_use_interval_->next() == NULL);
last_use_interval_ = first_use_interval_;
}
}
void LiveRange::DefineAt(intptr_t pos) {
// Live ranges are being build by visiting instructions in post-order.
// This implies that use intervals will be prepended in a monotonically
// decreasing order.
// When we encounter a use of a value inside a block we optimistically
// expand the first use interval to cover the block from the start
// to the last use in the block and then we shrink it if we encounter
// definition of the value inside the same block.
if (first_use_interval_ == NULL) {
// Definition without a use.
first_use_interval_ = new UseInterval(pos, pos + 1, NULL);
last_use_interval_ = first_use_interval_;
} else {
// Shrink the first use interval. It was optimistically expanded to
// cover the the block from the start to the last use in the block.
ASSERT(first_use_interval_->start_ <= pos);
first_use_interval_->start_ = pos;
}
}
LiveRange* FlowGraphAllocator::GetLiveRange(intptr_t vreg) {
if (live_ranges_[vreg] == NULL) {
Representation rep = value_representations_[vreg];
ASSERT(rep != kNoRepresentation);
live_ranges_[vreg] = new LiveRange(vreg, rep);
}
return live_ranges_[vreg];
}
LiveRange* FlowGraphAllocator::MakeLiveRangeForTemporary() {
// Representation does not matter for temps.
Representation ignored = kNoRepresentation;
LiveRange* range = new LiveRange(kTempVirtualRegister, ignored);
#if defined(DEBUG)
temporaries_.Add(range);
#endif
return range;
}
void FlowGraphAllocator::BlockRegisterLocation(Location loc,
intptr_t from,
intptr_t to,
bool* blocked_registers,
LiveRange** blocking_ranges) {
if (blocked_registers[loc.register_code()]) {
return;
}
if (blocking_ranges[loc.register_code()] == NULL) {
Representation ignored = kNoRepresentation;
LiveRange* range = new LiveRange(kNoVirtualRegister, ignored);
blocking_ranges[loc.register_code()] = range;
range->set_assigned_location(loc);
#if defined(DEBUG)
temporaries_.Add(range);
#endif
}
blocking_ranges[loc.register_code()]->AddUseInterval(from, to);
}
// Block location from the start of the instruction to its end.
void FlowGraphAllocator::BlockLocation(Location loc,
intptr_t from,
intptr_t to) {
if (loc.IsRegister()) {
BlockRegisterLocation(loc, from, to, blocked_cpu_registers_, cpu_regs_);
} else if (loc.IsFpuRegister()) {
BlockRegisterLocation(loc, from, to, blocked_fpu_registers_, fpu_regs_);
} else {
UNREACHABLE();
}
}
void LiveRange::Print() {
if (first_use_interval() == NULL) {
return;
}
THR_Print(" live range v%" Pd " [%" Pd ", %" Pd ") in ", vreg(),
Start(),
End());
assigned_location().Print();
if (spill_slot_.HasStackIndex()) {
intptr_t stack_slot = spill_slot_.stack_index();
THR_Print(" allocated spill slot: %" Pd "", stack_slot);
}
THR_Print("\n");
SafepointPosition* safepoint = first_safepoint();
while (safepoint != NULL) {
THR_Print(" Safepoint [%" Pd "]: ", safepoint->pos());
safepoint->locs()->stack_bitmap()->Print();
THR_Print("\n");
safepoint = safepoint->next();
}
UsePosition* use_pos = uses_;
for (UseInterval* interval = first_use_interval_;
interval != NULL;
interval = interval->next()) {
THR_Print(" use interval [%" Pd ", %" Pd ")\n",
interval->start(),
interval->end());
while ((use_pos != NULL) && (use_pos->pos() <= interval->end())) {
THR_Print(" use at %" Pd "", use_pos->pos());
if (use_pos->location_slot() != NULL) {
THR_Print(" as ");
use_pos->location_slot()->Print();
}
THR_Print("\n");
use_pos = use_pos->next();
}
}
if (next_sibling() != NULL) {
next_sibling()->Print();
}
}
void FlowGraphAllocator::PrintLiveRanges() {
#if defined(DEBUG)
for (intptr_t i = 0; i < temporaries_.length(); i++) {
temporaries_[i]->Print();
}
#endif
for (intptr_t i = 0; i < live_ranges_.length(); i++) {
if (live_ranges_[i] != NULL) {
live_ranges_[i]->Print();
}
}
}
// Returns true if all uses of the given range inside the given loop
// have Any allocation policy.
static bool HasOnlyUnconstrainedUsesInLoop(LiveRange* range,
BlockInfo* loop_header) {
const intptr_t boundary = loop_header->last_block()->end_pos();
UsePosition* use = range->first_use();
while ((use != NULL) && (use->pos() < boundary)) {
if (!use->location_slot()->Equals(Location::Any())) {
return false;
}
use = use->next();
}
return true;
}
// Returns true if all uses of the given range have Any allocation policy.
static bool HasOnlyUnconstrainedUses(LiveRange* range) {
UsePosition* use = range->first_use();
while (use != NULL) {
if (!use->location_slot()->Equals(Location::Any())) {
return false;
}
use = use->next();
}
return true;
}
void FlowGraphAllocator::BuildLiveRanges() {
const intptr_t block_count = postorder_.length();
ASSERT(postorder_.Last()->IsGraphEntry());
BitVector* current_interference_set = NULL;
Zone* zone = flow_graph_.zone();
for (intptr_t i = 0; i < (block_count - 1); i++) {
BlockEntryInstr* block = postorder_[i];
BlockInfo* block_info = BlockInfoAt(block->start_pos());
// For every SSA value that is live out of this block, create an interval
// that covers the whole block. It will be shortened if we encounter a
// definition of this value in this block.
for (BitVector::Iterator it(liveness_.GetLiveOutSetAt(i));
!it.Done();
it.Advance()) {
LiveRange* range = GetLiveRange(it.Current());
range->AddUseInterval(block->start_pos(), block->end_pos());
}
BlockInfo* loop_header = block_info->loop_header();
if ((loop_header != NULL) && (loop_header->last_block() == block)) {
current_interference_set = new(zone) BitVector(
zone, flow_graph_.max_virtual_register_number());
ASSERT(loop_header->backedge_interference() == NULL);
// All values flowing into the loop header are live at the back-edge and
// can interfere with phi moves.
current_interference_set->AddAll(
liveness_.GetLiveInSet(loop_header->entry()));
loop_header->set_backedge_interference(
current_interference_set);
}
// Connect outgoing phi-moves that were created in NumberInstructions
// and find last instruction that contributes to liveness.
Instruction* current = ConnectOutgoingPhiMoves(block,
current_interference_set);
// Now process all instructions in reverse order.
while (current != block) {
// Skip parallel moves that we insert while processing instructions.
if (!current->IsParallelMove()) {
ProcessOneInstruction(block, current, current_interference_set);
}
current = current->previous();
}
// Check if any values live into the loop can be spilled for free.
if (block_info->is_loop_header()) {
current_interference_set = NULL;
for (BitVector::Iterator it(liveness_.GetLiveInSetAt(i));
!it.Done();
it.Advance()) {
LiveRange* range = GetLiveRange(it.Current());
if (HasOnlyUnconstrainedUsesInLoop(range, block_info)) {
range->MarkHasOnlyUnconstrainedUsesInLoop(block_info->loop_id());
}
}
}
if (block->IsJoinEntry()) {
ConnectIncomingPhiMoves(block->AsJoinEntry());
} else if (block->IsCatchBlockEntry()) {
// Process initial definitions.
CatchBlockEntryInstr* catch_entry = block->AsCatchBlockEntry();
for (intptr_t i = 0;
i < catch_entry->initial_definitions()->length();
i++) {
Definition* defn = (*catch_entry->initial_definitions())[i];
LiveRange* range = GetLiveRange(defn->ssa_temp_index());
range->DefineAt(catch_entry->start_pos()); // Defined at block entry.
ProcessInitialDefinition(defn, range, catch_entry);
}
// Block the two fixed registers used by CatchBlockEntryInstr from the
// block start to until the end of the instruction so that they are
// preserved.
intptr_t start = catch_entry->start_pos();
BlockLocation(Location::RegisterLocation(kExceptionObjectReg),
start,
ToInstructionEnd(start));
BlockLocation(Location::RegisterLocation(kStackTraceObjectReg),
start,
ToInstructionEnd(start));
}
}
// Process incoming parameters and constants. Do this after all other
// instructions so that safepoints for all calls have already been found.
GraphEntryInstr* graph_entry = flow_graph_.graph_entry();
for (intptr_t i = 0; i < graph_entry->initial_definitions()->length(); i++) {
Definition* defn = (*graph_entry->initial_definitions())[i];
ASSERT(!defn->HasPairRepresentation());
LiveRange* range = GetLiveRange(defn->ssa_temp_index());
range->AddUseInterval(graph_entry->start_pos(), graph_entry->end_pos());
range->DefineAt(graph_entry->start_pos());
ProcessInitialDefinition(defn, range, graph_entry);
}
}
void FlowGraphAllocator::ProcessInitialDefinition(Definition* defn,
LiveRange* range,
BlockEntryInstr* block) {
// Save the range end because it may change below.
intptr_t range_end = range->End();
if (defn->IsParameter()) {
ParameterInstr* param = defn->AsParameter();
// Assert that copied and non-copied parameters are mutually exclusive.
// This might change in the future and, if so, the index will be wrong.
ASSERT((flow_graph_.num_copied_params() == 0) ||
(flow_graph_.num_non_copied_params() == 0));
intptr_t slot_index = param->index();
ASSERT((param->base_reg() == FPREG) || (param->base_reg() == SPREG));
if (param->base_reg() == FPREG) {
// Slot index for the leftmost copied parameter is 0.
// Slot index for the rightmost fixed parameter is -1.
slot_index -= flow_graph_.num_non_copied_params();
}
range->set_assigned_location(Location::StackSlot(slot_index,
param->base_reg()));
range->set_spill_slot(Location::StackSlot(slot_index,
param->base_reg()));
} else if (defn->IsCurrentContext()) {
AssignSafepoints(defn, range);
range->finger()->Initialize(range);
range->set_assigned_location(Location::RegisterLocation(CTX));
if (range->End() > kNormalEntryPos) {
LiveRange* tail = range->SplitAt(kNormalEntryPos);
CompleteRange(tail, Location::kRegister);
}
ConvertAllUses(range);
return;
} else {
ConstantInstr* constant = defn->AsConstant();
ASSERT(constant != NULL);
range->set_assigned_location(Location::Constant(constant));
range->set_spill_slot(Location::Constant(constant));
}
AssignSafepoints(defn, range);
range->finger()->Initialize(range);
UsePosition* use =
range->finger()->FirstRegisterBeneficialUse(block->start_pos());
if (use != NULL) {
LiveRange* tail =
SplitBetween(range, block->start_pos(), use->pos());
// Parameters and constants are tagged, so allocated to CPU registers.
CompleteRange(tail, Location::kRegister);
}
ConvertAllUses(range);
if (defn->IsParameter() && (range->spill_slot().stack_index() >= 0)) {
// Parameters above the frame pointer consume spill slots and are marked
// in stack maps.
spill_slots_.Add(range_end);
quad_spill_slots_.Add(false);
untagged_spill_slots_.Add(false);
// Note, all incoming parameters are assumed to be tagged.
MarkAsObjectAtSafepoints(range);
} else if (defn->IsConstant() && block->IsCatchBlockEntry()) {
// Constants at catch block entries consume spill slots.
spill_slots_.Add(range_end);
quad_spill_slots_.Add(false);
untagged_spill_slots_.Add(false);
}
}
static Location::Kind RegisterKindFromPolicy(Location loc) {
if (loc.policy() == Location::kRequiresFpuRegister) {
return Location::kFpuRegister;
} else {
return Location::kRegister;
}
}
static Location::Kind RegisterKindForResult(Instruction* instr) {
if ((instr->representation() == kUnboxedDouble) ||
(instr->representation() == kUnboxedFloat32x4) ||
(instr->representation() == kUnboxedInt32x4) ||
(instr->representation() == kUnboxedFloat64x2) ||
(instr->representation() == kPairOfUnboxedDouble)) {
return Location::kFpuRegister;
} else {
return Location::kRegister;
}
}
//
// When describing shape of live ranges in comments below we are going to use
// the following notation:
//
// B block entry
// g g' start and end of goto instruction
// i i' start and end of any other instruction
// j j' start and end of any other instruction
// - body of a use interval
// [ start of a use interval
// ) end of a use interval
// * use
//
// For example diagram
//
// i i'
// value --*--)
//
// can be read as: use interval for value starts somewhere before instruction
// and extends until currently processed instruction, there is a use of value
// at the start of the instruction.
//
Instruction* FlowGraphAllocator::ConnectOutgoingPhiMoves(
BlockEntryInstr* block, BitVector* interfere_at_backedge) {
Instruction* last = block->last_instruction();
GotoInstr* goto_instr = last->AsGoto();
if (goto_instr == NULL) return last;
// If we have a parallel move here then the successor block must be a
// join with phis. The phi inputs contribute uses to each predecessor
// block (and the phi outputs contribute definitions in the successor
// block).
if (!goto_instr->HasParallelMove()) return goto_instr->previous();
ParallelMoveInstr* parallel_move = goto_instr->parallel_move();
// All uses are recorded at the position of parallel move preceding goto.
const intptr_t pos = goto_instr->lifetime_position();
JoinEntryInstr* join = goto_instr->successor();
ASSERT(join != NULL);
// Search for the index of the current block in the predecessors of
// the join.
const intptr_t pred_index = join->IndexOfPredecessor(block);
// Record the corresponding phi input use for each phi.
intptr_t move_index = 0;
for (PhiIterator it(join); !it.Done(); it.Advance()) {
PhiInstr* phi = it.Current();
Value* val = phi->InputAt(pred_index);
MoveOperands* move = parallel_move->MoveOperandsAt(move_index++);
ConstantInstr* constant = val->definition()->AsConstant();
if (constant != NULL) {
move->set_src(Location::Constant(constant));
continue;
}
// Expected shape of live ranges:
//
// g g'
// value --*
//
intptr_t vreg = val->definition()->ssa_temp_index();
LiveRange* range = GetLiveRange(vreg);
if (interfere_at_backedge != NULL) interfere_at_backedge->Add(vreg);
range->AddUseInterval(block->start_pos(), pos);
range->AddHintedUse(
pos,
move->src_slot(),
GetLiveRange(phi->ssa_temp_index())->assigned_location_slot());
move->set_src(Location::PrefersRegister());
if (val->definition()->HasPairRepresentation()) {
move = parallel_move->MoveOperandsAt(move_index++);
vreg = ToSecondPairVreg(vreg);
range = GetLiveRange(vreg);
if (interfere_at_backedge != NULL) {
interfere_at_backedge->Add(vreg);
}
range->AddUseInterval(block->start_pos(), pos);
range->AddHintedUse(
pos,
move->src_slot(),
GetLiveRange(ToSecondPairVreg(
phi->ssa_temp_index()))->assigned_location_slot());
move->set_src(Location::PrefersRegister());
}
}
// Begin backward iteration with the instruction before the parallel
// move.
return goto_instr->previous();
}
void FlowGraphAllocator::ConnectIncomingPhiMoves(JoinEntryInstr* join) {
// For join blocks we need to add destinations of phi resolution moves
// to phi's live range so that register allocator will fill them with moves.
// All uses are recorded at the start position in the block.
const intptr_t pos = join->start_pos();
const bool is_loop_header = BlockInfoAt(join->start_pos())->is_loop_header();
intptr_t move_idx = 0;
for (PhiIterator it(join); !it.Done(); it.Advance()) {
PhiInstr* phi = it.Current();
ASSERT(phi != NULL);
const intptr_t vreg = phi->ssa_temp_index();
ASSERT(vreg >= 0);
const bool is_pair_phi = phi->HasPairRepresentation();
// Expected shape of live range:
//
// B
// phi [--------
//
LiveRange* range = GetLiveRange(vreg);
range->DefineAt(pos); // Shorten live range.
if (is_loop_header) range->mark_loop_phi();
if (is_pair_phi) {
LiveRange* second_range = GetLiveRange(ToSecondPairVreg(vreg));
second_range->DefineAt(pos); // Shorten live range.
if (is_loop_header) second_range->mark_loop_phi();
}
for (intptr_t pred_idx = 0; pred_idx < phi->InputCount(); pred_idx++) {
BlockEntryInstr* pred = join->PredecessorAt(pred_idx);
GotoInstr* goto_instr = pred->last_instruction()->AsGoto();
ASSERT((goto_instr != NULL) && (goto_instr->HasParallelMove()));
MoveOperands* move =
goto_instr->parallel_move()->MoveOperandsAt(move_idx);
move->set_dest(Location::PrefersRegister());
range->AddUse(pos, move->dest_slot());
if (is_pair_phi) {
LiveRange* second_range = GetLiveRange(ToSecondPairVreg(vreg));
MoveOperands* second_move =
goto_instr->parallel_move()->MoveOperandsAt(move_idx + 1);
second_move->set_dest(Location::PrefersRegister());
second_range->AddUse(pos, second_move->dest_slot());
}
}
// All phi resolution moves are connected. Phi's live range is
// complete.
AssignSafepoints(phi, range);
CompleteRange(range, RegisterKindForResult(phi));
if (is_pair_phi) {
LiveRange* second_range = GetLiveRange(ToSecondPairVreg(vreg));
AssignSafepoints(phi, second_range);
CompleteRange(second_range, RegisterKindForResult(phi));
}
move_idx += is_pair_phi ? 2 : 1;
}
}
void FlowGraphAllocator::ProcessEnvironmentUses(BlockEntryInstr* block,
Instruction* current) {
ASSERT(current->env() != NULL);
Environment* env = current->env();
while (env != NULL) {
// Any value mentioned in the deoptimization environment should survive
// until the end of instruction but it does not need to be in the register.
// Expected shape of live range:
//
// i i'
// value -----*
//
if (env->Length() == 0) {
env = env->outer();
continue;
}
const intptr_t block_start_pos = block->start_pos();
const intptr_t use_pos = current->lifetime_position() + 1;
Location* locations = flow_graph_.zone()->Alloc<Location>(env->Length());
for (intptr_t i = 0; i < env->Length(); ++i) {
Value* value = env->ValueAt(i);
Definition* def = value->definition();
if (def->HasPairRepresentation()) {
locations[i] = Location::Pair(Location::Any(), Location::Any());
} else {
locations[i] = Location::Any();
}
if (def->IsPushArgument()) {
// Frame size is unknown until after allocation.
locations[i] = Location::NoLocation();
continue;
}
ConstantInstr* constant = def->AsConstant();
if (constant != NULL) {
locations[i] = Location::Constant(constant);
continue;
}
MaterializeObjectInstr* mat = def->AsMaterializeObject();
if (mat != NULL) {
// MaterializeObject itself produces no value. But its uses
// are treated as part of the environment: allocated locations
// will be used when building deoptimization data.
locations[i] = Location::NoLocation();
ProcessMaterializationUses(block, block_start_pos, use_pos, mat);
continue;
}
if (def->HasPairRepresentation()) {
PairLocation* location_pair = locations[i].AsPairLocation();
{
// First live range.
LiveRange* range = GetLiveRange(def->ssa_temp_index());
range->AddUseInterval(block_start_pos, use_pos);
range->AddUse(use_pos, location_pair->SlotAt(0));
}
{
// Second live range.
LiveRange* range =
GetLiveRange(ToSecondPairVreg(def->ssa_temp_index()));
range->AddUseInterval(block_start_pos, use_pos);
range->AddUse(use_pos, location_pair->SlotAt(1));
}
} else {
LiveRange* range = GetLiveRange(def->ssa_temp_index());
range->AddUseInterval(block_start_pos, use_pos);
range->AddUse(use_pos, &locations[i]);
}
}
env->set_locations(locations);
env = env->outer();
}
}
void FlowGraphAllocator::ProcessMaterializationUses(
BlockEntryInstr* block,
const intptr_t block_start_pos,
const intptr_t use_pos,
MaterializeObjectInstr* mat) {
// Materialization can occur several times in the same environment.
// Check if we already processed this one.
if (mat->locations() != NULL) {
return; // Already processed.
}
// Initialize location for every input of the MaterializeObject instruction.
Location* locations = flow_graph_.zone()->Alloc<Location>(mat->InputCount());
mat->set_locations(locations);
for (intptr_t i = 0; i < mat->InputCount(); ++i) {
Definition* def = mat->InputAt(i)->definition();
ConstantInstr* constant = def->AsConstant();
if (constant != NULL) {
locations[i] = Location::Constant(constant);
continue;
}
if (def->HasPairRepresentation()) {
locations[i] = Location::Pair(Location::Any(), Location::Any());
PairLocation* location_pair = locations[i].AsPairLocation();
{
// First live range.
LiveRange* range = GetLiveRange(def->ssa_temp_index());
range->AddUseInterval(block_start_pos, use_pos);
range->AddUse(use_pos, location_pair->SlotAt(0));
}
{
// Second live range.
LiveRange* range =
GetLiveRange(ToSecondPairVreg(def->ssa_temp_index()));
range->AddUseInterval(block_start_pos, use_pos);
range->AddUse(use_pos, location_pair->SlotAt(1));
}
} else if (def->IsMaterializeObject()) {
locations[i] = Location::NoLocation();
ProcessMaterializationUses(
block, block_start_pos, use_pos, def->AsMaterializeObject());
} else {
locations[i] = Location::Any();
LiveRange* range = GetLiveRange(def->ssa_temp_index());
range->AddUseInterval(block_start_pos, use_pos);
range->AddUse(use_pos, &locations[i]);
}
}
}
void FlowGraphAllocator::ProcessOneInput(BlockEntryInstr* block,
intptr_t pos,
Location* in_ref,
Value* input,
intptr_t vreg,
RegisterSet* live_registers) {
ASSERT(in_ref != NULL);
ASSERT(!in_ref->IsPairLocation());
ASSERT(input != NULL);
ASSERT(block != NULL);
LiveRange* range = GetLiveRange(vreg);
if (in_ref->IsMachineRegister()) {
// Input is expected in a fixed register. Expected shape of
// live ranges:
//
// j' i i'
// value --*
// register [-----)
//
if (live_registers != NULL) {
live_registers->Add(*in_ref, range->representation());
}
MoveOperands* move =
AddMoveAt(pos - 1, *in_ref, Location::Any());
BlockLocation(*in_ref, pos - 1, pos + 1);
range->AddUseInterval(block->start_pos(), pos - 1);
range->AddHintedUse(pos - 1, move->src_slot(), in_ref);
} else if (in_ref->IsUnallocated()) {
if (in_ref->policy() == Location::kWritableRegister) {
// Writable unallocated input. Expected shape of
// live ranges:
//
// i i'
// value --*
// temp [--)
MoveOperands* move = AddMoveAt(pos,
Location::RequiresRegister(),
Location::PrefersRegister());
// Add uses to the live range of the input.
range->AddUseInterval(block->start_pos(), pos);
range->AddUse(pos, move->src_slot());
// Create live range for the temporary.
LiveRange* temp = MakeLiveRangeForTemporary();
temp->AddUseInterval(pos, pos + 1);
temp->AddHintedUse(pos, in_ref, move->src_slot());
temp->AddUse(pos, move->dest_slot());
*in_ref = Location::RequiresRegister();
CompleteRange(temp, RegisterKindFromPolicy(*in_ref));
} else {
// Normal unallocated input. Expected shape of
// live ranges:
//
// i i'
// value -----*
//
range->AddUseInterval(block->start_pos(), pos + 1);
range->AddUse(pos + 1, in_ref);
}
} else {
ASSERT(in_ref->IsConstant());
}
}
void FlowGraphAllocator::ProcessOneOutput(BlockEntryInstr* block,
intptr_t pos,
Location* out,
Definition* def,
intptr_t vreg,
bool output_same_as_first_input,
Location* in_ref,
Definition* input,
intptr_t input_vreg,
BitVector* interference_set) {
ASSERT(out != NULL);
ASSERT(!out->IsPairLocation());
ASSERT(def != NULL);
ASSERT(block != NULL);
LiveRange* range = vreg >= 0 ?
GetLiveRange(vreg) : MakeLiveRangeForTemporary();
// Process output and finalize its liverange.
if (out->IsMachineRegister()) {
// Fixed output location. Expected shape of live range:
//
// i i' j j'
// register [--)
// output [-------
//
BlockLocation(*out, pos, pos + 1);
if (range->vreg() == kTempVirtualRegister) return;
// We need to emit move connecting fixed register with another location
// that will be allocated for this output's live range.
// Special case: fixed output followed by a fixed input last use.
UsePosition* use = range->first_use();
// If the value has no uses we don't need to allocate it.
if (use == NULL) return;
if (use->pos() == (pos + 1)) {
ASSERT(use->location_slot()->IsUnallocated());
*(use->location_slot()) = *out;
// Remove first use. It was allocated.
range->set_first_use(range->first_use()->next());
}
// Shorten live range to the point of definition, this might make the range
// empty (if the only use immediately follows). If range is not empty add
// move from a fixed register to an unallocated location.
range->DefineAt(pos + 1);
if (range->Start() == range->End()) return;
MoveOperands* move = AddMoveAt(pos + 1, Location::Any(), *out);
range->AddHintedUse(pos + 1, move->dest_slot(), out);
} else if (output_same_as_first_input) {
ASSERT(in_ref != NULL);
ASSERT(input != NULL);
// Output register will contain a value of the first input at instruction's
// start. Expected shape of live ranges:
//
// i i'
// input #0 --*
// output [----
//
ASSERT(in_ref->Equals(Location::RequiresRegister()) ||
in_ref->Equals(Location::RequiresFpuRegister()));
*out = *in_ref;
// Create move that will copy value between input and output.
MoveOperands* move = AddMoveAt(pos,
Location::RequiresRegister(),
Location::Any());
// Add uses to the live range of the input.
LiveRange* input_range = GetLiveRange(input_vreg);
input_range->AddUseInterval(block->start_pos(), pos);
input_range->AddUse(pos, move->src_slot());
// Shorten output live range to the point of definition and add both input
// and output uses slots to be filled by allocator.
range->DefineAt(pos);
range->AddHintedUse(pos, out, move->src_slot());
range->AddUse(pos, move->dest_slot());
range->AddUse(pos, in_ref);
if ((interference_set != NULL) &&
(range->vreg() >= 0) &&
interference_set->Contains(range->vreg())) {
interference_set->Add(input->ssa_temp_index());
}
} else {
// Normal unallocated location that requires a register. Expected shape of
// live range:
//
// i i'
// output [-------
//
ASSERT(out->Equals(Location::RequiresRegister()) ||
out->Equals(Location::RequiresFpuRegister()));
// Shorten live range to the point of definition and add use to be filled by
// allocator.
range->DefineAt(pos);
range->AddUse(pos, out);
}
AssignSafepoints(def, range);
CompleteRange(range, RegisterKindForResult(def));
}
// Create and update live ranges corresponding to instruction's inputs,
// temporaries and output.
void FlowGraphAllocator::ProcessOneInstruction(BlockEntryInstr* block,
Instruction* current,
BitVector* interference_set) {
LocationSummary* locs = current->locs();
Definition* def = current->AsDefinition();
if ((def != NULL) && (def->AsConstant() != NULL)) {
ASSERT(!def->HasPairRepresentation());
LiveRange* range = (def->ssa_temp_index() != -1) ?
GetLiveRange(def->ssa_temp_index()) : NULL;
// Drop definitions of constants that have no uses.
if ((range == NULL) || (range->first_use() == NULL)) {
locs->set_out(0, Location::NoLocation());
return;
}
// If this constant has only unconstrained uses convert them all
// to use the constant directly and drop this definition.
// TODO(vegorov): improve allocation when we have enough registers to keep
// constants used in the loop in them.
if (HasOnlyUnconstrainedUses(range)) {
ConstantInstr* constant_instr = def->AsConstant();
range->set_assigned_location(Location::Constant(constant_instr));
range->set_spill_slot(Location::Constant(constant_instr));
range->finger()->Initialize(range);
ConvertAllUses(range);
locs->set_out(0, Location::NoLocation());
return;
}
}
const intptr_t pos = current->lifetime_position();
ASSERT(IsInstructionStartPosition(pos));
ASSERT(locs->input_count() == current->InputCount());
// Normalize same-as-first-input output if input is specified as
// fixed register.
if (locs->out(0).IsUnallocated() &&
(locs->out(0).policy() == Location::kSameAsFirstInput)) {
if (locs->in(0).IsPairLocation()) {
// Pair input, pair output.
PairLocation* in_pair = locs->in(0).AsPairLocation();
ASSERT(in_pair->At(0).IsMachineRegister() ==
in_pair->At(1).IsMachineRegister());
if (in_pair->At(0).IsMachineRegister() &&
in_pair->At(1).IsMachineRegister()) {
locs->set_out(0, Location::Pair(in_pair->At(0), in_pair->At(1)));
}
} else if (locs->in(0).IsMachineRegister()) {
// Single input, single output.
locs->set_out(0, locs->in(0));
}
}
const bool output_same_as_first_input =
locs->out(0).IsUnallocated() &&
(locs->out(0).policy() == Location::kSameAsFirstInput);
// Output is same as first input which is a pair.
if (output_same_as_first_input && locs->in(0).IsPairLocation()) {
// Make out into a PairLocation.
locs->set_out(0, Location::Pair(Location::RequiresRegister(),
Location::RequiresRegister()));
}
// Add uses from the deoptimization environment.
if (current->env() != NULL) ProcessEnvironmentUses(block, current);
// Process inputs.
// Skip the first input if output is specified with kSameAsFirstInput policy,
// they will be processed together at the very end.
{
for (intptr_t j = output_same_as_first_input ? 1 : 0;
j < locs->input_count();
j++) {
// Determine if we are dealing with a value pair, and if so, whether
// the location is the first register or second register.
Value* input = current->InputAt(j);
Location* in_ref = locs->in_slot(j);
RegisterSet* live_registers = NULL;
if (locs->HasCallOnSlowPath()) {
live_registers = locs->live_registers();
}
if (in_ref->IsPairLocation()) {
ASSERT(input->definition()->HasPairRepresentation());
PairLocation* pair = in_ref->AsPairLocation();
const intptr_t vreg = input->definition()->ssa_temp_index();
// Each element of the pair is assigned it's own virtual register number
// and is allocated its own LiveRange.
ProcessOneInput(block, pos, pair->SlotAt(0),
input, vreg, live_registers);
ProcessOneInput(block, pos, pair->SlotAt(1), input,
ToSecondPairVreg(vreg), live_registers);
} else {
ProcessOneInput(block, pos, in_ref, input,
input->definition()->ssa_temp_index(), live_registers);
}
}
}
// Process temps.
for (intptr_t j = 0; j < locs->temp_count(); j++) {
// Expected shape of live range:
//
// i i'
// [--)
//
Location temp = locs->temp(j);
// We do not support pair locations for temporaries.
ASSERT(!temp.IsPairLocation());
if (temp.IsMachineRegister()) {
BlockLocation(temp, pos, pos + 1);
} else if (temp.IsUnallocated()) {
LiveRange* range = MakeLiveRangeForTemporary();
range->AddUseInterval(pos, pos + 1);
range->AddUse(pos, locs->temp_slot(j));
CompleteRange(range, RegisterKindFromPolicy(temp));
} else {
UNREACHABLE();
}
}
// Block all allocatable registers for calls and record the stack bitmap.
if (locs->always_calls()) {
// Expected shape of live range:
//
// i i'
// [--)
//
// The stack bitmap describes the position i.
for (intptr_t reg = 0; reg < kNumberOfCpuRegisters; reg++) {
BlockLocation(Location::RegisterLocation(static_cast<Register>(reg)),
pos,
pos + 1);
}
for (intptr_t reg = 0; reg < kNumberOfFpuRegisters; reg++) {
BlockLocation(
Location::FpuRegisterLocation(static_cast<FpuRegister>(reg)),
pos,
pos + 1);
}
#if defined(DEBUG)
// Verify that temps, inputs and output were specified as fixed
// locations. Every register is blocked now so attempt to
// allocate will not succeed.
for (intptr_t j = 0; j < locs->temp_count(); j++) {
ASSERT(!locs->temp(j).IsPairLocation());
ASSERT(!locs->temp(j).IsUnallocated());
}
for (intptr_t j = 0; j < locs->input_count(); j++) {
if (locs->in(j).IsPairLocation()) {
PairLocation* pair = locs->in_slot(j)->AsPairLocation();
ASSERT(!pair->At(0).IsUnallocated());
ASSERT(!pair->At(1).IsUnallocated());
} else {
ASSERT(!locs->in(j).IsUnallocated());
}
}
if (locs->out(0).IsPairLocation()) {
PairLocation* pair = locs->out_slot(0)->AsPairLocation();
ASSERT(!pair->At(0).IsUnallocated());
ASSERT(!pair->At(1).IsUnallocated());
} else {
ASSERT(!locs->out(0).IsUnallocated());
}
#endif
}
if (locs->can_call()) {
safepoints_.Add(current);
}
if (def == NULL) {
ASSERT(locs->out(0).IsInvalid());
return;
}
if (locs->out(0).IsInvalid()) {
ASSERT(def->ssa_temp_index() < 0);
return;
}
ASSERT(locs->output_count() == 1);
Location* out = locs->out_slot(0);
if (out->IsPairLocation()) {
ASSERT(def->HasPairRepresentation());
PairLocation* pair = out->AsPairLocation();
if (output_same_as_first_input) {
ASSERT(locs->in_slot(0)->IsPairLocation());
PairLocation* in_pair = locs->in_slot(0)->AsPairLocation();
Definition* input = current->InputAt(0)->definition();
ASSERT(input->HasPairRepresentation());
// Each element of the pair is assigned it's own virtual register number
// and is allocated its own LiveRange.
ProcessOneOutput(block, pos, // BlockEntry, seq.
pair->SlotAt(0), def, // (output) Location, Definition.
def->ssa_temp_index(), // (output) virtual register.
true, // output mapped to first input.
in_pair->SlotAt(0), input, // (input) Location, Def.
input->ssa_temp_index(), // (input) virtual register.
interference_set);
ProcessOneOutput(block, pos,
pair->SlotAt(1), def,
ToSecondPairVreg(def->ssa_temp_index()),
true,
in_pair->SlotAt(1), input,
ToSecondPairVreg(input->ssa_temp_index()),
interference_set);
} else {
// Each element of the pair is assigned it's own virtual register number
// and is allocated its own LiveRange.
ProcessOneOutput(block, pos,
pair->SlotAt(0), def,
def->ssa_temp_index(),
false, // output is not mapped to first input.
NULL, NULL, -1, // First input not needed.
interference_set);
ProcessOneOutput(block, pos,
pair->SlotAt(1), def,
ToSecondPairVreg(def->ssa_temp_index()),
false,
NULL, NULL, -1,
interference_set);
}
} else {
if (output_same_as_first_input) {
Location* in_ref = locs->in_slot(0);
Definition* input = current->InputAt(0)->definition();
ASSERT(!in_ref->IsPairLocation());
ProcessOneOutput(block, pos, // BlockEntry, Instruction, seq.
out, def, // (output) Location, Definition.
def->ssa_temp_index(), // (output) virtual register.
true, // output mapped to first input.
in_ref, input, // (input) Location, Def.
input->ssa_temp_index(), // (input) virtual register.
interference_set);
} else {
ProcessOneOutput(block, pos,
out, def,
def->ssa_temp_index(),
false, // output is not mapped to first input.
NULL, NULL, -1, // First input not needed.
interference_set);
}
}
}
static ParallelMoveInstr* CreateParallelMoveBefore(Instruction* instr,
intptr_t pos) {
ASSERT(pos > 0);
Instruction* prev = instr->previous();
ParallelMoveInstr* move = prev->AsParallelMove();
if ((move == NULL) || (move->lifetime_position() != pos)) {
move = new ParallelMoveInstr();
prev->LinkTo(move);
move->LinkTo(instr);
move->set_lifetime_position(pos);
}
return move;
}
static ParallelMoveInstr* CreateParallelMoveAfter(Instruction* instr,
intptr_t pos) {
Instruction* next = instr->next();
if (next->IsParallelMove() && (next->lifetime_position() == pos)) {
return next->AsParallelMove();
}
return CreateParallelMoveBefore(next, pos);
}
// Linearize the control flow graph. The chosen order will be used by the
// linear-scan register allocator. Number most instructions with a pair of
// numbers representing lifetime positions. Introduce explicit parallel
// move instructions in the predecessors of join nodes. The moves are used
// for phi resolution.
void FlowGraphAllocator::NumberInstructions() {
intptr_t pos = 0;
// The basic block order is reverse postorder.
const intptr_t block_count = postorder_.length();
for (intptr_t i = block_count - 1; i >= 0; i--) {
BlockEntryInstr* block = postorder_[i];
BlockInfo* info = new BlockInfo(block);
instructions_.Add(block);
block_info_.Add(info);
block->set_start_pos(pos);
block->set_lifetime_position(pos);
pos += 2;
for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
Instruction* current = it.Current();
// Do not assign numbers to parallel move instructions.
if (!current->IsParallelMove()) {
instructions_.Add(current);
block_info_.Add(info);
current->set_lifetime_position(pos);
pos += 2;
}
}
block->set_end_pos(pos);
}
// Create parallel moves in join predecessors. This must be done after
// all instructions are numbered.
for (intptr_t i = block_count - 1; i >= 0; i--) {
BlockEntryInstr* block = postorder_[i];
// For join entry predecessors create phi resolution moves if
// necessary. They will be populated by the register allocator.
JoinEntryInstr* join = block->AsJoinEntry();
if (join != NULL) {
intptr_t move_count = 0;
for (PhiIterator it(join); !it.Done(); it.Advance()) {
move_count += it.Current()->HasPairRepresentation() ? 2 : 1;
}
for (intptr_t i = 0; i < block->PredecessorCount(); i++) {
// Insert the move between the last two instructions of the
// predecessor block (all such blocks have at least two instructions:
// the block entry and goto instructions.)
Instruction* last = block->PredecessorAt(i)->last_instruction();
ASSERT(last->IsGoto());
ParallelMoveInstr* move = last->AsGoto()->GetParallelMove();
// Populate the ParallelMove with empty moves.
for (intptr_t j = 0; j < move_count; j++) {
move->AddMove(Location::NoLocation(), Location::NoLocation());
}
}
}
}
}
// Discover structural (reducible) loops nesting structure.
void FlowGraphAllocator::DiscoverLoops() {
// This algorithm relies on the assumption that we emit blocks in reverse
// postorder, so postorder number can be used to identify loop nesting.
//
// TODO(vegorov): consider using a generic algorithm to correctly discover
// both headers of reducible and irreducible loops.
BlockInfo* current_loop = NULL;
intptr_t loop_id = 0; // All loop headers have a unique id.
const intptr_t block_count = postorder_.length();
for (intptr_t i = 0; i < block_count; i++) {
BlockEntryInstr* block = postorder_[i];
GotoInstr* goto_instr = block->last_instruction()->AsGoto();
if (goto_instr != NULL) {
JoinEntryInstr* successor = goto_instr->successor();
if (successor->postorder_number() > i) {
// This is back-edge.
BlockInfo* successor_info = BlockInfoAt(successor->lifetime_position());
ASSERT(successor_info->entry() == successor);
if (!successor_info->is_loop_header() &&
((current_loop == NULL) ||
(current_loop->entry()->postorder_number() >
successor_info->entry()->postorder_number()))) {
ASSERT(successor_info != current_loop);
successor_info->mark_loop_header();
successor_info->set_loop_id(loop_id++);
successor_info->set_last_block(block);
// For loop header loop information points to the outer loop.
successor_info->set_loop(current_loop);
current_loop = successor_info;
}
}
}
if (current_loop != NULL) {
BlockInfo* current_info = BlockInfoAt(block->lifetime_position());
if (current_info == current_loop) {
ASSERT(current_loop->is_loop_header());
current_loop = current_info->loop();
} else {
current_info->set_loop(current_loop);
}
}
}
}
Instruction* FlowGraphAllocator::InstructionAt(intptr_t pos) const {
return instructions_[pos / 2];
}
BlockInfo* FlowGraphAllocator::BlockInfoAt(intptr_t pos) const {
return block_info_[pos / 2];
}
bool FlowGraphAllocator::IsBlockEntry(intptr_t pos) const {
return IsInstructionStartPosition(pos) && InstructionAt(pos)->IsBlockEntry();
}
void AllocationFinger::Initialize(LiveRange* range) {
first_pending_use_interval_ = range->first_use_interval();
first_register_use_ = range->first_use();
first_register_beneficial_use_ = range->first_use();
first_hinted_use_ = range->first_use();
}
bool AllocationFinger::Advance(const intptr_t start) {
UseInterval* a = first_pending_use_interval_;
while (a != NULL && a->end() <= start) a = a->next();
first_pending_use_interval_ = a;
return (first_pending_use_interval_ == NULL);
}
Location AllocationFinger::FirstHint() {
UsePosition* use = first_hinted_use_;
while (use != NULL) {
if (use->HasHint()) return use->hint();
use = use->next();
}
return Location::NoLocation();
}
static UsePosition* FirstUseAfter(UsePosition* use, intptr_t after) {
while ((use != NULL) && (use->pos() < after)) {
use = use->next();
}
return use;
}
UsePosition* AllocationFinger::FirstRegisterUse(intptr_t after) {
for (UsePosition* use = FirstUseAfter(first_register_use_, after);
use != NULL;
use = use->next()) {
Location* loc = use->location_slot();
if (loc->IsUnallocated() &&
((loc->policy() == Location::kRequiresRegister) ||
(loc->policy() == Location::kRequiresFpuRegister))) {
first_register_use_ = use;
return use;
}
}
return NULL;
}
UsePosition* AllocationFinger::FirstRegisterBeneficialUse(intptr_t after) {
for (UsePosition* use = FirstUseAfter(first_register_beneficial_use_, after);
use != NULL;
use = use->next()) {
Location* loc = use->location_slot();
if (loc->IsUnallocated() && loc->IsRegisterBeneficial()) {
first_register_beneficial_use_ = use;
return use;
}
}
return NULL;
}
UsePosition* AllocationFinger::FirstInterferingUse(intptr_t after) {
if (IsInstructionEndPosition(after)) {
// If after is a position at the end of the instruction disregard
// any use occuring at it.
after += 1;
}
return FirstRegisterUse(after);
}
void AllocationFinger::UpdateAfterSplit(intptr_t first_use_after_split_pos) {
if ((first_register_use_ != NULL) &&
(first_register_use_->pos() >= first_use_after_split_pos)) {
first_register_use_ = NULL;
}
if ((first_register_beneficial_use_ != NULL) &&
(first_register_beneficial_use_->pos() >= first_use_after_split_pos)) {
first_register_beneficial_use_ = NULL;
}
}
intptr_t UseInterval::Intersect(UseInterval* other) {
if (this->start() <= other->start()) {
if (other->start() < this->end()) return other->start();
} else if (this->start() < other->end()) {
return this->start();
}
return kIllegalPosition;
}
static intptr_t FirstIntersection(UseInterval* a, UseInterval* u) {
while (a != NULL && u != NULL) {
const intptr_t pos = a->Intersect(u);
if (pos != kIllegalPosition) return pos;
if (a->start() < u->start()) {
a = a->next();
} else {
u = u->next();
}
}
return kMaxPosition;
}
template<typename PositionType>
PositionType* SplitListOfPositions(PositionType** head,
intptr_t split_pos,
bool split_at_start) {
PositionType* last_before_split = NULL;
PositionType* pos = *head;
if (split_at_start) {
while ((pos != NULL) && (pos->pos() < split_pos)) {
last_before_split = pos;
pos = pos->next();
}
} else {
while ((pos != NULL) && (pos->pos() <= split_pos)) {
last_before_split = pos;
pos = pos->next();
}
}
if (last_before_split == NULL) {
*head = NULL;
} else {
last_before_split->set_next(NULL);
}
return pos;
}
LiveRange* LiveRange::SplitAt(intptr_t split_pos) {
if (Start() == split_pos) return this;
UseInterval* interval = finger_.first_pending_use_interval();
if (interval == NULL) {
finger_.Initialize(this);
interval = finger_.first_pending_use_interval();
}
ASSERT(split_pos < End());
// Corner case. Split position can be inside the a lifetime hole or at its
// end. We need to start over to find the previous interval.
if (split_pos <= interval->start()) interval = first_use_interval_;
UseInterval* last_before_split = NULL;
while (interval->end() <= split_pos) {
last_before_split = interval;
interval = interval->next();
}
const bool split_at_start = (interval->start() == split_pos);
UseInterval* first_after_split = interval;
if (!split_at_start && interval->Contains(split_pos)) {
first_after_split = new UseInterval(split_pos,
interval->end(),
interval->next());
interval->end_ = split_pos;
interval->next_ = first_after_split;
last_before_split = interval;
}
ASSERT(last_before_split != NULL);
ASSERT(last_before_split->next() == first_after_split);
ASSERT(last_before_split->end() <= split_pos);
ASSERT(split_pos <= first_after_split->start());
UsePosition* first_use_after_split =
SplitListOfPositions(&uses_, split_pos, split_at_start);
SafepointPosition* first_safepoint_after_split =
SplitListOfPositions(&first_safepoint_, split_pos, split_at_start);
UseInterval* last_use_interval = (last_before_split == last_use_interval_) ?
first_after_split : last_use_interval_;
next_sibling_ = new LiveRange(vreg(),
representation(),
first_use_after_split,
first_after_split,
last_use_interval,
first_safepoint_after_split,
next_sibling_);
TRACE_ALLOC(THR_Print(" split sibling [%" Pd ", %" Pd ")\n",
next_sibling_->Start(), next_sibling_->End()));
last_use_interval_ = last_before_split;
last_use_interval_->next_ = NULL;
if (first_use_after_split != NULL) {
finger_.UpdateAfterSplit(first_use_after_split->pos());
}
return next_sibling_;
}
LiveRange* FlowGraphAllocator::SplitBetween(LiveRange* range,
intptr_t from,
intptr_t to) {
TRACE_ALLOC(THR_Print("split v%" Pd " [%" Pd ", %" Pd
") between [%" Pd ", %" Pd ")\n",
range->vreg(), range->Start(), range->End(), from, to));
intptr_t split_pos = kIllegalPosition;
BlockInfo* split_block = BlockInfoAt(to);
if (from < split_block->entry()->lifetime_position()) {
// Interval [from, to) spans multiple blocks.
// If last block is inside a loop prefer splitting at outermost loop's
// header.
BlockInfo* loop_header = split_block->loop();
while ((loop_header != NULL) &&
(from < loop_header->entry()->lifetime_position())) {
split_block = loop_header;
loop_header = loop_header->loop();
}
// Split at block's start.
split_pos = split_block->entry()->lifetime_position();
} else {
// Interval [from, to) is contained inside a single block.
// Split at position corresponding to the end of the previous
// instruction.
split_pos = ToInstructionStart(to) - 1;
}
ASSERT(split_pos != kIllegalPosition);
ASSERT(from < split_pos);
return range->SplitAt(split_pos);
}
void FlowGraphAllocator::SpillBetween(LiveRange* range,
intptr_t from,
intptr_t to) {
ASSERT(from < to);
TRACE_ALLOC(THR_Print("spill v%" Pd " [%" Pd ", %" Pd ") "
"between [%" Pd ", %" Pd ")\n",
range->vreg(), range->Start(), range->End(), from, to));
LiveRange* tail = range->SplitAt(from);
if (tail->Start() < to) {
// There is an intersection of tail and [from, to).
LiveRange* tail_tail = SplitBetween(tail, tail->Start(), to);
Spill(tail);
AddToUnallocated(tail_tail);
} else {
// No intersection between tail and [from, to).
AddToUnallocated(tail);
}
}
void FlowGraphAllocator::SpillAfter(LiveRange* range, intptr_t from) {
TRACE_ALLOC(THR_Print("spill v%" Pd " [%" Pd ", %" Pd ") after %" Pd "\n",
range->vreg(), range->Start(), range->End(), from));
// When spilling the value inside the loop check if this spill can
// be moved outside.
BlockInfo* block_info = BlockInfoAt(from);
if (block_info->is_loop_header() || (block_info->loop() != NULL)) {
BlockInfo* loop_header =
block_info->is_loop_header() ? block_info : block_info->loop();
if ((range->Start() <= loop_header->entry()->start_pos()) &&
RangeHasOnlyUnconstrainedUsesInLoop(range, loop_header->loop_id())) {
ASSERT(loop_header->entry()->start_pos() <= from);
from = loop_header->entry()->start_pos();
TRACE_ALLOC(THR_Print(" moved spill position to loop header %" Pd "\n",
from));
}
}
LiveRange* tail = range->SplitAt(from);
Spill(tail);
}
void FlowGraphAllocator::AllocateSpillSlotFor(LiveRange* range) {
ASSERT(range->spill_slot().IsInvalid());
// Compute range start and end.
LiveRange* last_sibling = range;
while (last_sibling->next_sibling() != NULL) {
last_sibling = last_sibling->next_sibling();
}
const intptr_t start = range->Start();
const intptr_t end = last_sibling->End();
// During fpu register allocation spill slot indices are computed in terms of
// double (64bit) stack slots. We treat quad stack slot (128bit) as a
// consecutive pair of two double spill slots.
// Special care is taken to never allocate the same index to both
// double and quad spill slots as it complicates disambiguation during
// parallel move resolution.
const bool need_quad = (register_kind_ == Location::kFpuRegister) &&
((range->representation() == kUnboxedFloat32x4) ||
(range->representation() == kUnboxedInt32x4) ||
(range->representation() == kUnboxedFloat64x2));
const bool need_untagged = (register_kind_ == Location::kRegister) &&
((range->representation() == kUntagged));
// Search for a free spill slot among allocated: the value in it should be
// dead and its type should match (e.g. it should not be a part of the quad if
// we are allocating normal double slot).
// For CPU registers we need to take reserved slots for try-catch into
// account.
intptr_t idx = register_kind_ == Location::kRegister
? flow_graph_.graph_entry()->fixed_slot_count()
: 0;
for (; idx < spill_slots_.length(); idx++) {
if ((need_quad == quad_spill_slots_[idx]) &&
(need_untagged == untagged_spill_slots_[idx]) &&
(spill_slots_[idx] <= start)) {
break;
}
}
if (idx == spill_slots_.length()) {
// No free spill slot found. Allocate a new one.
spill_slots_.Add(0);
quad_spill_slots_.Add(need_quad);
untagged_spill_slots_.Add(need_untagged);
if (need_quad) { // Allocate two double stack slots if we need quad slot.
spill_slots_.Add(0);
quad_spill_slots_.Add(need_quad);
untagged_spill_slots_.Add(need_untagged);
}
}
// Set spill slot expiration boundary to the live range's end.
spill_slots_[idx] = end;
if (need_quad) {
ASSERT(quad_spill_slots_[idx] && quad_spill_slots_[idx + 1]);
idx++; // Use the higher index it corresponds to the lower stack address.
spill_slots_[idx] = end;
} else {
ASSERT(!quad_spill_slots_[idx]);
}
// Assign spill slot to the range.
if (register_kind_ == Location::kRegister) {
range->set_spill_slot(Location::StackSlot(idx));
} else {
// We use the index of the slot with the lowest address as an index for the
// FPU register spill slot. In terms of indexes this relation is inverted:
// so we have to take the highest index.
const intptr_t slot_idx = cpu_spill_slot_count_ +
idx * kDoubleSpillFactor + (kDoubleSpillFactor - 1);
Location location;
if ((range->representation() == kUnboxedFloat32x4) ||
(range->representation() == kUnboxedInt32x4) ||
(range->representation() == kUnboxedFloat64x2)) {
ASSERT(need_quad);
location = Location::QuadStackSlot(slot_idx);
} else {
ASSERT((range->representation() == kUnboxedDouble));
location = Location::DoubleStackSlot(slot_idx);
}
range->set_spill_slot(location);
}
spilled_.Add(range);
}
void FlowGraphAllocator::MarkAsObjectAtSafepoints(LiveRange* range) {
intptr_t stack_index = range->spill_slot().stack_index();
ASSERT(stack_index >= 0);
while (range != NULL) {
for (SafepointPosition* safepoint = range->first_safepoint();
safepoint != NULL;
safepoint = safepoint->next()) {
// Mark the stack slot as having an object.
safepoint->locs()->SetStackBit(stack_index);
}
range = range->next_sibling();
}
}
void FlowGraphAllocator::Spill(LiveRange* range) {
LiveRange* parent = GetLiveRange(range->vreg());
if (parent->spill_slot().IsInvalid()) {
AllocateSpillSlotFor(parent);
if (range->representation() == kTagged) {
MarkAsObjectAtSafepoints(parent);
}
}
range->set_assigned_location(parent->spill_slot());
ConvertAllUses(range);
}
intptr_t FlowGraphAllocator::FirstIntersectionWithAllocated(
intptr_t reg, LiveRange* unallocated) {
intptr_t intersection = kMaxPosition;
for (intptr_t i = 0; i < registers_[reg]->length(); i++) {
LiveRange* allocated = (*registers_[reg])[i];
if (allocated == NULL) continue;
UseInterval* allocated_head =
allocated->finger()->first_pending_use_interval();
if (allocated_head->start() >= intersection) continue;
const intptr_t pos = FirstIntersection(
unallocated->finger()->first_pending_use_interval(),
allocated_head);
if (pos < intersection) intersection = pos;
}
return intersection;
}
void ReachingDefs::AddPhi(PhiInstr* phi) {
if (phi->reaching_defs() == NULL) {
Zone* zone = flow_graph_.zone();
phi->set_reaching_defs(new(zone) BitVector(
zone, flow_graph_.max_virtual_register_number()));
// Compute initial set reaching defs set.
bool depends_on_phi = false;
for (intptr_t i = 0; i < phi->InputCount(); i++) {
Definition* input = phi->InputAt(i)->definition();
if (input->IsPhi()) {
depends_on_phi = true;
}
phi->reaching_defs()->Add(input->ssa_temp_index());
if (phi->HasPairRepresentation()) {
phi->reaching_defs()->Add(ToSecondPairVreg(input->ssa_temp_index()));
}
}
// If this phi depends on another phi then we need fix point iteration.
if (depends_on_phi) phis_.Add(phi);
}
}
void ReachingDefs::Compute() {
// Transitively collect all phis that are used by the given phi.
for (intptr_t i = 0; i < phis_.length(); i++) {
PhiInstr* phi = phis_[i];
// Add all phis that affect this phi to the list.
for (intptr_t i = 0; i < phi->InputCount(); i++) {
PhiInstr* input_phi = phi->InputAt(i)->definition()->AsPhi();
if (input_phi != NULL) {
AddPhi(input_phi);
}
}
}
// Propagate values until fix point is reached.
bool changed;
do {
changed = false;
for (intptr_t i = 0; i < phis_.length(); i++) {
PhiInstr* phi = phis_[i];
for (intptr_t i = 0; i < phi->InputCount(); i++) {
PhiInstr* input_phi = phi->InputAt(i)->definition()->AsPhi();
if (input_phi != NULL) {
if (phi->reaching_defs()->AddAll(input_phi->reaching_defs())) {
changed = true;
}
}
}
}
} while (changed);
phis_.Clear();
}
BitVector* ReachingDefs::Get(PhiInstr* phi) {
if (phi->reaching_defs() == NULL) {
ASSERT(phis_.is_empty());
AddPhi(phi);
Compute();
}
return phi->reaching_defs();
}
bool FlowGraphAllocator::AllocateFreeRegister(LiveRange* unallocated) {
intptr_t candidate = kNoRegister;
intptr_t free_until = 0;
// If hint is available try hint first.
// TODO(vegorov): ensure that phis are hinted on the back edge.
Location hint = unallocated->finger()->FirstHint();
if (hint.IsMachineRegister()) {
if (!blocked_registers_[hint.register_code()]) {
free_until = FirstIntersectionWithAllocated(hint.register_code(),
unallocated);
candidate = hint.register_code();
}
TRACE_ALLOC(THR_Print("found hint %s for v%" Pd ": free until %" Pd "\n",
hint.Name(),
unallocated->vreg(),
free_until));
} else {
for (intptr_t reg = 0; reg < NumberOfRegisters(); ++reg) {
if (!blocked_registers_[reg] && (registers_[reg]->length() == 0)) {
candidate = reg;
free_until = kMaxPosition;
break;
}
}
}
ASSERT(0 <= kMaxPosition);
if (free_until != kMaxPosition) {
for (intptr_t reg = 0; reg < NumberOfRegisters(); ++reg) {
if (blocked_registers_[reg] || (reg == candidate)) continue;
const intptr_t intersection =
FirstIntersectionWithAllocated(reg, unallocated);
if (intersection > free_until) {
candidate = reg;
free_until = intersection;
if (free_until == kMaxPosition) break;
}
}
}
// All registers are blocked by active ranges.
if (free_until <= unallocated->Start()) return false;
// We have a very good candidate (either hinted to us or completely free).
// If we are in a loop try to reduce number of moves on the back edge by
// searching for a candidate that does not interfere with phis on the back
// edge.
BlockInfo* loop_header = BlockInfoAt(unallocated->Start())->loop_header();
if ((unallocated->vreg() >= 0) &&
(loop_header != NULL) &&
(free_until >= loop_header->last_block()->end_pos()) &&
loop_header->backedge_interference()->Contains(unallocated->vreg())) {
GrowableArray<bool> used_on_backedge(number_of_registers_);
for (intptr_t i = 0; i < number_of_registers_; i++) {
used_on_backedge.Add(false);
}
for (PhiIterator it(loop_header->entry()->AsJoinEntry());
!it.Done();
it.Advance()) {
PhiInstr* phi = it.Current();
ASSERT(phi->is_alive());
const intptr_t phi_vreg = phi->ssa_temp_index();
LiveRange* range = GetLiveRange(phi_vreg);
if (range->assigned_location().kind() == register_kind_) {
const intptr_t reg = range->assigned_location().register_code();
if (!reaching_defs_.Get(phi)->Contains(unallocated->vreg())) {
used_on_backedge[reg] = true;
}
}
if (phi->HasPairRepresentation()) {
const intptr_t second_phi_vreg = ToSecondPairVreg(phi_vreg);
LiveRange* second_range = GetLiveRange(second_phi_vreg);
if (second_range->assigned_location().kind() == register_kind_) {
const intptr_t reg =
second_range->assigned_location().register_code();
if (!reaching_defs_.Get(phi)->Contains(unallocated->vreg())) {
used_on_backedge[reg] = true;
}
}
}
}
if (used_on_backedge[candidate]) {
TRACE_ALLOC(THR_Print(
"considering %s for v%" Pd ": has interference on the back edge"
" {loop [%" Pd ", %" Pd ")}\n",
MakeRegisterLocation(candidate).Name(),
unallocated->vreg(),
loop_header->entry()->start_pos(),
loop_header->last_block()->end_pos()));
for (intptr_t reg = 0; reg < NumberOfRegisters(); ++reg) {
if (blocked_registers_[reg] ||
(reg == candidate) ||
used_on_backedge[reg]) {
continue;
}
const intptr_t intersection =
FirstIntersectionWithAllocated(reg, unallocated);
if (intersection >= free_until) {
candidate = reg;
free_until = intersection;
TRACE_ALLOC(THR_Print(
"found %s for v%" Pd " with no interference on the back edge\n",
MakeRegisterLocation(candidate).Name(),
candidate));
break;
}
}
}
}
TRACE_ALLOC(THR_Print("assigning free register "));
TRACE_ALLOC(MakeRegisterLocation(candidate).Print());
TRACE_ALLOC(THR_Print(" to v%" Pd "\n", unallocated->vreg()));
if (free_until != kMaxPosition) {
// There was an intersection. Split unallocated.
TRACE_ALLOC(THR_Print(" splitting at %" Pd "\n", free_until));
LiveRange* tail = unallocated->SplitAt(free_until);
AddToUnallocated(tail);
}
registers_[candidate]->Add(unallocated);
unallocated->set_assigned_location(MakeRegisterLocation(candidate));
return true;
}
bool FlowGraphAllocator::RangeHasOnlyUnconstrainedUsesInLoop(LiveRange* range,
intptr_t loop_id) {
if (range->vreg() >= 0) {
LiveRange* parent = GetLiveRange(range->vreg());
return parent->HasOnlyUnconstrainedUsesInLoop(loop_id);
}
return false;
}
bool FlowGraphAllocator::IsCheapToEvictRegisterInLoop(BlockInfo* loop,
intptr_t reg) {
const intptr_t loop_start = loop->entry()->start_pos();
const intptr_t loop_end = loop->last_block()->end_pos();
for (intptr_t i = 0; i < registers_[reg]->length(); i++) {
LiveRange* allocated = (*registers_[reg])[i];
UseInterval* interval = allocated->finger()->first_pending_use_interval();
if (interval->Contains(loop_start)) {
if (!RangeHasOnlyUnconstrainedUsesInLoop(allocated, loop->loop_id())) {
return false;
}
} else if (interval->start() < loop_end) {
return false;
}
}
return true;
}
bool FlowGraphAllocator::HasCheapEvictionCandidate(LiveRange* phi_range) {
ASSERT(phi_range->is_loop_phi());
BlockInfo* loop_header = BlockInfoAt(phi_range->Start());
ASSERT(loop_header->is_loop_header());
ASSERT(phi_range->Start() == loop_header->entry()->start_pos());
for (intptr_t reg = 0; reg < NumberOfRegisters(); ++reg) {
if (blocked_registers_[reg]) continue;
if (IsCheapToEvictRegisterInLoop(loop_header, reg)) {
return true;
}
}
return false;
}
void FlowGraphAllocator::AllocateAnyRegister(LiveRange* unallocated) {
// If a loop phi has no register uses we might still want to allocate it
// to the register to reduce amount of memory moves on the back edge.
// This is possible if there is a register blocked by a range that can be
// cheaply evicted i.e. it has no register beneficial uses inside the
// loop.
UsePosition* register_use =
unallocated->finger()->FirstRegisterUse(unallocated->Start());
if ((register_use == NULL) &&
!(unallocated->is_loop_phi() && HasCheapEvictionCandidate(unallocated))) {
Spill(unallocated);
return;
}
intptr_t candidate = kNoRegister;
intptr_t free_until = 0;
intptr_t blocked_at = kMaxPosition;
for (int reg = 0; reg < NumberOfRegisters(); ++reg) {
if (blocked_registers_[reg]) continue;
if (UpdateFreeUntil(reg, unallocated, &free_until, &blocked_at)) {
candidate = reg;
}
}
const intptr_t register_use_pos =
(register_use != NULL) ? register_use->pos()
: unallocated->Start();
if (free_until < register_use_pos) {
// Can't acquire free register. Spill until we really need one.
ASSERT(unallocated->Start() < ToInstructionStart(register_use_pos));
SpillBetween(unallocated, unallocated->Start(), register_use->pos());
return;
}
ASSERT(candidate != kNoRegister);
TRACE_ALLOC(THR_Print("assigning blocked register "));
TRACE_ALLOC(MakeRegisterLocation(candidate).Print());
TRACE_ALLOC(THR_Print(" to live range v%" Pd " until %" Pd "\n",
unallocated->vreg(), blocked_at));
if (blocked_at < unallocated->End()) {
// Register is blocked before the end of the live range. Split the range
// at latest at blocked_at position.
LiveRange* tail = SplitBetween(unallocated,
unallocated->Start(),
blocked_at + 1);
AddToUnallocated(tail);
}
AssignNonFreeRegister(unallocated, candidate);
}
bool FlowGraphAllocator::UpdateFreeUntil(intptr_t reg,
LiveRange* unallocated,
intptr_t* cur_free_until,
intptr_t* cur_blocked_at) {
intptr_t free_until = kMaxPosition;
intptr_t blocked_at = kMaxPosition;
const intptr_t start = unallocated->Start();
for (intptr_t i = 0; i < registers_[reg]->length(); i++) {
LiveRange* allocated = (*registers_[reg])[i];
UseInterval* first_pending_use_interval =
allocated->finger()->first_pending_use_interval();
if (first_pending_use_interval->Contains(start)) {
// This is an active interval.
if (allocated->vreg() < 0) {
// This register blocked by an interval that
// can't be spilled.
return false;
}
UsePosition* use =
allocated->finger()->FirstInterferingUse(start);
if ((use != NULL) && ((ToInstructionStart(use->pos()) - start) <= 1)) {
// This register is blocked by interval that is used
// as register in the current instruction and can't
// be spilled.
return false;
}
const intptr_t use_pos = (use != NULL) ? use->pos()
: allocated->End();
if (use_pos < free_until) free_until = use_pos;
} else {
// This is inactive interval.
const intptr_t intersection = FirstIntersection(
first_pending_use_interval, unallocated->first_use_interval());
if (intersection != kMaxPosition) {
if (intersection < free_until) free_until = intersection;
if (allocated->vreg() == kNoVirtualRegister) blocked_at = intersection;
}
}
if (free_until <= *cur_free_until) {
return false;
}
}
ASSERT(free_until > *cur_free_until);
*cur_free_until = free_until;
*cur_blocked_at = blocked_at;
return true;
}
void FlowGraphAllocator::RemoveEvicted(intptr_t reg, intptr_t first_evicted) {
intptr_t to = first_evicted;
intptr_t from = first_evicted + 1;
while (from < registers_[reg]->length()) {
LiveRange* allocated = (*registers_[reg])[from++];
if (allocated != NULL) (*registers_[reg])[to++] = allocated;
}
registers_[reg]->TruncateTo(to);
}
void FlowGraphAllocator::AssignNonFreeRegister(LiveRange* unallocated,
intptr_t reg) {
intptr_t first_evicted = -1;
for (intptr_t i = registers_[reg]->length() - 1; i >= 0; i--) {
LiveRange* allocated = (*registers_[reg])[i];
if (allocated->vreg() < 0) continue; // Can't be evicted.
if (EvictIntersection(allocated, unallocated)) {
// If allocated was not spilled convert all pending uses.
if (allocated->assigned_location().IsMachineRegister()) {
ASSERT(allocated->End() <= unallocated->Start());
ConvertAllUses(allocated);
}
(*registers_[reg])[i] = NULL;
first_evicted = i;
}
}
// Remove evicted ranges from the array.
if (first_evicted != -1) RemoveEvicted(reg, first_evicted);
registers_[reg]->Add(unallocated);
unallocated->set_assigned_location(MakeRegisterLocation(reg));
}
bool FlowGraphAllocator::EvictIntersection(LiveRange* allocated,
LiveRange* unallocated) {
UseInterval* first_unallocated =
unallocated->finger()->first_pending_use_interval();
const intptr_t intersection = FirstIntersection(
allocated->finger()->first_pending_use_interval(),
first_unallocated);
if (intersection == kMaxPosition) return false;
const intptr_t spill_position = first_unallocated->start();
UsePosition* use = allocated->finger()->FirstInterferingUse(spill_position);
if (use == NULL) {
// No register uses after this point.
SpillAfter(allocated, spill_position);
} else {
const intptr_t restore_position =
(spill_position < intersection) ? MinPosition(intersection, use->pos())
: use->pos();
SpillBetween(allocated, spill_position, restore_position);
}
return true;
}
MoveOperands* FlowGraphAllocator::AddMoveAt(intptr_t pos,
Location to,
Location from) {
ASSERT(!IsBlockEntry(pos));
if (pos < kNormalEntryPos) {
ASSERT(pos > 0);
// Parallel moves added to the GraphEntry (B0) will be added at the start
// of the normal entry (B1)
BlockEntryInstr* entry = InstructionAt(kNormalEntryPos)->AsBlockEntry();
return entry->GetParallelMove()->AddMove(to, from);
}
Instruction* instr = InstructionAt(pos);
ParallelMoveInstr* parallel_move = NULL;
if (IsInstructionStartPosition(pos)) {
parallel_move = CreateParallelMoveBefore(instr, pos);
} else {
parallel_move = CreateParallelMoveAfter(instr, pos);
}
return parallel_move->AddMove(to, from);
}
void FlowGraphAllocator::ConvertUseTo(UsePosition* use, Location loc) {
ASSERT(!loc.IsPairLocation());
ASSERT(use->location_slot() != NULL);
Location* slot = use->location_slot();
ASSERT(slot->IsUnallocated());
TRACE_ALLOC(THR_Print(" use at %" Pd " converted to ", use->pos()));
TRACE_ALLOC(loc.Print());
TRACE_ALLOC(THR_Print("\n"));
*slot = loc;
}
void FlowGraphAllocator::ConvertAllUses(LiveRange* range) {
if (range->vreg() == kNoVirtualRegister) return;
const Location loc = range->assigned_location();
ASSERT(!loc.IsInvalid());
TRACE_ALLOC(THR_Print("range [%" Pd ", %" Pd ") "
"for v%" Pd " has been allocated to ",
range->Start(), range->End(), range->vreg()));
TRACE_ALLOC(loc.Print());
TRACE_ALLOC(THR_Print(":\n"));
for (UsePosition* use = range->first_use(); use != NULL; use = use->next()) {
ConvertUseTo(use, loc);
}
// Add live registers at all safepoints for instructions with slow-path
// code.
if (loc.IsMachineRegister()) {
for (SafepointPosition* safepoint = range->first_safepoint();
safepoint != NULL;
safepoint = safepoint->next()) {
if (!safepoint->locs()->always_calls()) {
ASSERT(safepoint->locs()->can_call());
safepoint->locs()->live_registers()->Add(loc, range->representation());
}
}
}
}
void FlowGraphAllocator::AdvanceActiveIntervals(const intptr_t start) {
for (intptr_t reg = 0; reg < NumberOfRegisters(); reg++) {
if (registers_[reg]->is_empty()) continue;
intptr_t first_evicted = -1;
for (intptr_t i = registers_[reg]->length() - 1; i >= 0; i--) {
LiveRange* range = (*registers_[reg])[i];
if (range->finger()->Advance(start)) {
ConvertAllUses(range);
(*registers_[reg])[i] = NULL;
first_evicted = i;
}
}
if (first_evicted != -1) RemoveEvicted(reg, first_evicted);
}
}
bool LiveRange::Contains(intptr_t pos) const {
if (!CanCover(pos)) return false;
for (UseInterval* interval = first_use_interval_;
interval != NULL;
interval = interval->next()) {
if (interval->Contains(pos)) {
return true;
}
}
return false;
}
void FlowGraphAllocator::AssignSafepoints(Definition* defn,
LiveRange* range) {
for (intptr_t i = safepoints_.length() - 1; i >= 0; i--) {
Instruction* safepoint_instr = safepoints_[i];
if (safepoint_instr == defn) {
// The value is not live until after the definition is fully executed,
// don't assign the safepoint inside the definition itself to
// definition's liverange.
continue;
}
const intptr_t pos = safepoint_instr->lifetime_position();
if (range->End() <= pos) break;
if (range->Contains(pos)) {
range->AddSafepoint(pos, safepoint_instr->locs());
}
}
}
static inline bool ShouldBeAllocatedBefore(LiveRange* a, LiveRange* b) {
// TODO(vegorov): consider first hint position when ordering live ranges.
return a->Start() <= b->Start();
}
static void AddToSortedListOfRanges(GrowableArray<LiveRange*>* list,
LiveRange* range) {
range->finger()->Initialize(range);
if (list->is_empty()) {
list->Add(range);
return;
}
for (intptr_t i = list->length() - 1; i >= 0; i--) {
if (ShouldBeAllocatedBefore(range, (*list)[i])) {
list->InsertAt(i + 1, range);
return;
}
}
list->InsertAt(0, range);
}
void FlowGraphAllocator::AddToUnallocated(LiveRange* range) {
AddToSortedListOfRanges(&unallocated_, range);
}
void FlowGraphAllocator::CompleteRange(LiveRange* range, Location::Kind kind) {
switch (kind) {
case Location::kRegister:
AddToSortedListOfRanges(&unallocated_cpu_, range);
break;
case Location::kFpuRegister:
AddToSortedListOfRanges(&unallocated_xmm_, range);
break;
default:
UNREACHABLE();
}
}
#if defined(DEBUG)
bool FlowGraphAllocator::UnallocatedIsSorted() {
for (intptr_t i = unallocated_.length() - 1; i >= 1; i--) {
LiveRange* a = unallocated_[i];
LiveRange* b = unallocated_[i - 1];
if (!ShouldBeAllocatedBefore(a, b)) {
UNREACHABLE();
return false;
}
}
return true;
}
#endif
void FlowGraphAllocator::PrepareForAllocation(
Location::Kind register_kind,
intptr_t number_of_registers,
const GrowableArray<LiveRange*>& unallocated,
LiveRange** blocking_ranges,
bool* blocked_registers) {
register_kind_ = register_kind;
number_of_registers_ = number_of_registers;
blocked_registers_.Clear();
registers_.Clear();
for (intptr_t i = 0; i < number_of_registers_; i++) {
blocked_registers_.Add(false);
registers_.Add(new ZoneGrowableArray<LiveRange*>);
}
ASSERT(unallocated_.is_empty());
unallocated_.AddArray(unallocated);
for (intptr_t reg = 0; reg < number_of_registers; reg++) {
blocked_registers_[reg] = blocked_registers[reg];
ASSERT(registers_[reg]->is_empty());
LiveRange* range = blocking_ranges[reg];
if (range != NULL) {
range->finger()->Initialize(range);
registers_[reg]->Add(range);
}
}
}
void FlowGraphAllocator::AllocateUnallocatedRanges() {
#if defined(DEBUG)
ASSERT(UnallocatedIsSorted());
#endif
while (!unallocated_.is_empty()) {
LiveRange* range = unallocated_.RemoveLast();
const intptr_t start = range->Start();
TRACE_ALLOC(THR_Print("Processing live range for v%" Pd " "
"starting at %" Pd "\n",
range->vreg(),
start));
// TODO(vegorov): eagerly spill liveranges without register uses.
AdvanceActiveIntervals(start);
if (!AllocateFreeRegister(range)) {
if (intrinsic_mode_) {
// No spilling when compiling intrinsics.
// TODO(fschneider): Handle spilling in intrinsics. For now, the
// IR has to be built so that there are enough free registers.
UNREACHABLE();
}
AllocateAnyRegister(range);
}
}
// All allocation decisions were done.
ASSERT(unallocated_.is_empty());
// Finish allocation.
AdvanceActiveIntervals(kMaxPosition);
TRACE_ALLOC(THR_Print("Allocation completed\n"));
}
bool FlowGraphAllocator::TargetLocationIsSpillSlot(LiveRange* range,
Location target) {
if (target.IsStackSlot() ||
target.IsDoubleStackSlot() ||
target.IsConstant()) {
ASSERT(GetLiveRange(range->vreg())->spill_slot().Equals(target));
return true;
}
return false;
}
void FlowGraphAllocator::ConnectSplitSiblings(LiveRange* parent,
BlockEntryInstr* source_block,
BlockEntryInstr* target_block) {
TRACE_ALLOC(THR_Print("Connect v%" Pd " on the edge B%" Pd " -> B%" Pd "\n",
parent->vreg(),
source_block->block_id(),
target_block->block_id()));
if (parent->next_sibling() == NULL) {
// Nothing to connect. The whole range was allocated to the same location.
TRACE_ALLOC(THR_Print("range v%" Pd " has no siblings\n", parent->vreg()));
return;
}
const intptr_t source_pos = source_block->end_pos() - 1;
ASSERT(IsInstructionEndPosition(source_pos));
const intptr_t target_pos = target_block->start_pos();
Location target;
Location source;
#if defined(DEBUG)
LiveRange* source_cover = NULL;
LiveRange* target_cover = NULL;
#endif
LiveRange* range = parent;
while ((range != NULL) && (source.IsInvalid() || target.IsInvalid())) {
if (range->CanCover(source_pos)) {
ASSERT(source.IsInvalid());
source = range->assigned_location();
#if defined(DEBUG)
source_cover = range;
#endif
}
if (range->CanCover(target_pos)) {
ASSERT(target.IsInvalid());
target = range->assigned_location();
#if defined(DEBUG)
target_cover = range;
#endif
}
range = range->next_sibling();
}
TRACE_ALLOC(THR_Print("connecting v%" Pd " between [%" Pd ", %" Pd ") {%s} "
"to [%" Pd ", %" Pd ") {%s}\n",
parent->vreg(),
source_cover->Start(),
source_cover->End(),
source.Name(),
target_cover->Start(),
target_cover->End(),
target.Name()));
// Siblings were allocated to the same register.
if (source.Equals(target)) return;
// Values are eagerly spilled. Spill slot already contains appropriate value.
if (TargetLocationIsSpillSlot(parent, target)) {
return;
}
Instruction* last = source_block->last_instruction();
if ((last->SuccessorCount() == 1) && !source_block->IsGraphEntry()) {
ASSERT(last->IsGoto());
last->AsGoto()->GetParallelMove()->AddMove(target, source);
} else {
target_block->GetParallelMove()->AddMove(target, source);
}