/*
* Copyright (C) 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "register_allocator_linear_scan.h"
#include <iostream>
#include <sstream>
#include "base/bit_vector-inl.h"
#include "base/enums.h"
#include "code_generator.h"
#include "linear_order.h"
#include "register_allocation_resolver.h"
#include "ssa_liveness_analysis.h"
namespace art {
static constexpr size_t kMaxLifetimePosition = -1;
static constexpr size_t kDefaultNumberOfSpillSlots = 4;
// For simplicity, we implement register pairs as (reg, reg + 1).
// Note that this is a requirement for double registers on ARM, since we
// allocate SRegister.
static int GetHighForLowRegister(int reg) { return reg + 1; }
static bool IsLowRegister(int reg) { return (reg & 1) == 0; }
static bool IsLowOfUnalignedPairInterval(LiveInterval* low) {
return GetHighForLowRegister(low->GetRegister()) != low->GetHighInterval()->GetRegister();
}
RegisterAllocatorLinearScan::RegisterAllocatorLinearScan(ArenaAllocator* allocator,
CodeGenerator* codegen,
const SsaLivenessAnalysis& liveness)
: RegisterAllocator(allocator, codegen, liveness),
unhandled_core_intervals_(allocator->Adapter(kArenaAllocRegisterAllocator)),
unhandled_fp_intervals_(allocator->Adapter(kArenaAllocRegisterAllocator)),
unhandled_(nullptr),
handled_(allocator->Adapter(kArenaAllocRegisterAllocator)),
active_(allocator->Adapter(kArenaAllocRegisterAllocator)),
inactive_(allocator->Adapter(kArenaAllocRegisterAllocator)),
physical_core_register_intervals_(allocator->Adapter(kArenaAllocRegisterAllocator)),
physical_fp_register_intervals_(allocator->Adapter(kArenaAllocRegisterAllocator)),
temp_intervals_(allocator->Adapter(kArenaAllocRegisterAllocator)),
int_spill_slots_(allocator->Adapter(kArenaAllocRegisterAllocator)),
long_spill_slots_(allocator->Adapter(kArenaAllocRegisterAllocator)),
float_spill_slots_(allocator->Adapter(kArenaAllocRegisterAllocator)),
double_spill_slots_(allocator->Adapter(kArenaAllocRegisterAllocator)),
catch_phi_spill_slots_(0),
safepoints_(allocator->Adapter(kArenaAllocRegisterAllocator)),
processing_core_registers_(false),
number_of_registers_(-1),
registers_array_(nullptr),
blocked_core_registers_(codegen->GetBlockedCoreRegisters()),
blocked_fp_registers_(codegen->GetBlockedFloatingPointRegisters()),
reserved_out_slots_(0) {
temp_intervals_.reserve(4);
int_spill_slots_.reserve(kDefaultNumberOfSpillSlots);
long_spill_slots_.reserve(kDefaultNumberOfSpillSlots);
float_spill_slots_.reserve(kDefaultNumberOfSpillSlots);
double_spill_slots_.reserve(kDefaultNumberOfSpillSlots);
codegen->SetupBlockedRegisters();
physical_core_register_intervals_.resize(codegen->GetNumberOfCoreRegisters(), nullptr);
physical_fp_register_intervals_.resize(codegen->GetNumberOfFloatingPointRegisters(), nullptr);
// Always reserve for the current method and the graph's max out registers.
// TODO: compute it instead.
// ArtMethod* takes 2 vregs for 64 bits.
size_t ptr_size = static_cast<size_t>(InstructionSetPointerSize(codegen->GetInstructionSet()));
reserved_out_slots_ = ptr_size / kVRegSize + codegen->GetGraph()->GetMaximumNumberOfOutVRegs();
}
static bool ShouldProcess(bool processing_core_registers, LiveInterval* interval) {
if (interval == nullptr) return false;
bool is_core_register = (interval->GetType() != Primitive::kPrimDouble)
&& (interval->GetType() != Primitive::kPrimFloat);
return processing_core_registers == is_core_register;
}
void RegisterAllocatorLinearScan::AllocateRegisters() {
AllocateRegistersInternal();
RegisterAllocationResolver(allocator_, codegen_, liveness_)
.Resolve(ArrayRef<HInstruction* const>(safepoints_),
reserved_out_slots_,
int_spill_slots_.size(),
long_spill_slots_.size(),
float_spill_slots_.size(),
double_spill_slots_.size(),
catch_phi_spill_slots_,
temp_intervals_);
if (kIsDebugBuild) {
processing_core_registers_ = true;
ValidateInternal(true);
processing_core_registers_ = false;
ValidateInternal(true);
// Check that the linear order is still correct with regards to lifetime positions.
// Since only parallel moves have been inserted during the register allocation,
// these checks are mostly for making sure these moves have been added correctly.
size_t current_liveness = 0;
for (HBasicBlock* block : codegen_->GetGraph()->GetLinearOrder()) {
for (HInstructionIterator inst_it(block->GetPhis()); !inst_it.Done(); inst_it.Advance()) {
HInstruction* instruction = inst_it.Current();
DCHECK_LE(current_liveness, instruction->GetLifetimePosition());
current_liveness = instruction->GetLifetimePosition();
}
for (HInstructionIterator inst_it(block->GetInstructions());
!inst_it.Done();
inst_it.Advance()) {
HInstruction* instruction = inst_it.Current();
DCHECK_LE(current_liveness, instruction->GetLifetimePosition()) << instruction->DebugName();
current_liveness = instruction->GetLifetimePosition();
}
}
}
}
void RegisterAllocatorLinearScan::BlockRegister(Location location, size_t start, size_t end) {
int reg = location.reg();
DCHECK(location.IsRegister() || location.IsFpuRegister());
LiveInterval* interval = location.IsRegister()
? physical_core_register_intervals_[reg]
: physical_fp_register_intervals_[reg];
Primitive::Type type = location.IsRegister()
? Primitive::kPrimInt
: Primitive::kPrimFloat;
if (interval == nullptr) {
interval = LiveInterval::MakeFixedInterval(allocator_, reg, type);
if (location.IsRegister()) {
physical_core_register_intervals_[reg] = interval;
} else {
physical_fp_register_intervals_[reg] = interval;
}
}
DCHECK(interval->GetRegister() == reg);
interval->AddRange(start, end);
}
void RegisterAllocatorLinearScan::BlockRegisters(size_t start, size_t end, bool caller_save_only) {
for (size_t i = 0; i < codegen_->GetNumberOfCoreRegisters(); ++i) {
if (!caller_save_only || !codegen_->IsCoreCalleeSaveRegister(i)) {
BlockRegister(Location::RegisterLocation(i), start, end);
}
}
for (size_t i = 0; i < codegen_->GetNumberOfFloatingPointRegisters(); ++i) {
if (!caller_save_only || !codegen_->IsFloatingPointCalleeSaveRegister(i)) {
BlockRegister(Location::FpuRegisterLocation(i), start, end);
}
}
}
void RegisterAllocatorLinearScan::AllocateRegistersInternal() {
// Iterate post-order, to ensure the list is sorted, and the last added interval
// is the one with the lowest start position.
for (HBasicBlock* block : codegen_->GetGraph()->GetLinearPostOrder()) {
for (HBackwardInstructionIterator back_it(block->GetInstructions()); !back_it.Done();
back_it.Advance()) {
ProcessInstruction(back_it.Current());
}
for (HInstructionIterator inst_it(block->GetPhis()); !inst_it.Done(); inst_it.Advance()) {
ProcessInstruction(inst_it.Current());
}
if (block->IsCatchBlock() ||
(block->IsLoopHeader() && block->GetLoopInformation()->IsIrreducible())) {
// By blocking all registers at the top of each catch block or irreducible loop, we force
// intervals belonging to the live-in set of the catch/header block to be spilled.
// TODO(ngeoffray): Phis in this block could be allocated in register.
size_t position = block->GetLifetimeStart();
BlockRegisters(position, position + 1);
}
}
number_of_registers_ = codegen_->GetNumberOfCoreRegisters();
registers_array_ = allocator_->AllocArray<size_t>(number_of_registers_,
kArenaAllocRegisterAllocator);
processing_core_registers_ = true;
unhandled_ = &unhandled_core_intervals_;
for (LiveInterval* fixed : physical_core_register_intervals_) {
if (fixed != nullptr) {
// Fixed interval is added to inactive_ instead of unhandled_.
// It's also the only type of inactive interval whose start position
// can be after the current interval during linear scan.
// Fixed interval is never split and never moves to unhandled_.
inactive_.push_back(fixed);
}
}
LinearScan();
inactive_.clear();
active_.clear();
handled_.clear();
number_of_registers_ = codegen_->GetNumberOfFloatingPointRegisters();
registers_array_ = allocator_->AllocArray<size_t>(number_of_registers_,
kArenaAllocRegisterAllocator);
processing_core_registers_ = false;
unhandled_ = &unhandled_fp_intervals_;
for (LiveInterval* fixed : physical_fp_register_intervals_) {
if (fixed != nullptr) {
// Fixed interval is added to inactive_ instead of unhandled_.
// It's also the only type of inactive interval whose start position
// can be after the current interval during linear scan.
// Fixed interval is never split and never moves to unhandled_.
inactive_.push_back(fixed);
}
}
LinearScan();
}
void RegisterAllocatorLinearScan::ProcessInstruction(HInstruction* instruction) {
LocationSummary* locations = instruction->GetLocations();
size_t position = instruction->GetLifetimePosition();
if (locations == nullptr) return;
// Create synthesized intervals for temporaries.
for (size_t i = 0; i < locations->GetTempCount(); ++i) {
Location temp = locations->GetTemp(i);
if (temp.IsRegister() || temp.IsFpuRegister()) {
BlockRegister(temp, position, position + 1);
// Ensure that an explicit temporary register is marked as being allocated.
codegen_->AddAllocatedRegister(temp);
} else {
DCHECK(temp.IsUnallocated());
switch (temp.GetPolicy()) {
case Location::kRequiresRegister: {
LiveInterval* interval =
LiveInterval::MakeTempInterval(allocator_, Primitive::kPrimInt);
temp_intervals_.push_back(interval);
interval->AddTempUse(instruction, i);
unhandled_core_intervals_.push_back(interval);
break;
}
case Location::kRequiresFpuRegister: {
LiveInterval* interval =
LiveInterval::MakeTempInterval(allocator_, Primitive::kPrimDouble);
temp_intervals_.push_back(interval);
interval->AddTempUse(instruction, i);
if (codegen_->NeedsTwoRegisters(Primitive::kPrimDouble)) {
interval->AddHighInterval(/* is_temp */ true);
LiveInterval* high = interval->GetHighInterval();
temp_intervals_.push_back(high);
unhandled_fp_intervals_.push_back(high);
}
unhandled_fp_intervals_.push_back(interval);
break;
}
default:
LOG(FATAL) << "Unexpected policy for temporary location "
<< temp.GetPolicy();
}
}
}
bool core_register = (instruction->GetType() != Primitive::kPrimDouble)
&& (instruction->GetType() != Primitive::kPrimFloat);
if (locations->NeedsSafepoint()) {
if (codegen_->IsLeafMethod()) {
// TODO: We do this here because we do not want the suspend check to artificially
// create live registers. We should find another place, but this is currently the
// simplest.
DCHECK(instruction->IsSuspendCheckEntry());
instruction->GetBlock()->RemoveInstruction(instruction);
return;
}
safepoints_.push_back(instruction);
}
if (locations->WillCall()) {
BlockRegisters(position, position + 1, /* caller_save_only */ true);
}
for (size_t i = 0; i < locations->GetInputCount(); ++i) {
Location input = locations->InAt(i);
if (input.IsRegister() || input.IsFpuRegister()) {
BlockRegister(input, position, position + 1);
} else if (input.IsPair()) {
BlockRegister(input.ToLow(), position, position + 1);
BlockRegister(input.ToHigh(), position, position + 1);
}
}
LiveInterval* current = instruction->GetLiveInterval();
if (current == nullptr) return;
ArenaVector<LiveInterval*>& unhandled = core_register
? unhandled_core_intervals_
: unhandled_fp_intervals_;
DCHECK(unhandled.empty() || current->StartsBeforeOrAt(unhandled.back()));
if (codegen_->NeedsTwoRegisters(current->GetType())) {
current->AddHighInterval();
}
for (size_t safepoint_index = safepoints_.size(); safepoint_index > 0; --safepoint_index) {
HInstruction* safepoint = safepoints_[safepoint_index - 1u];
size_t safepoint_position = safepoint->GetLifetimePosition();
// Test that safepoints are ordered in the optimal way.
DCHECK(safepoint_index == safepoints_.size() ||
safepoints_[safepoint_index]->GetLifetimePosition() < safepoint_position);
if (safepoint_position == current->GetStart()) {
// The safepoint is for this instruction, so the location of the instruction
// does not need to be saved.
DCHECK_EQ(safepoint_index, safepoints_.size());
DCHECK_EQ(safepoint, instruction);
continue;
} else if (current->IsDeadAt(safepoint_position)) {
break;
} else if (!current->Covers(safepoint_position)) {
// Hole in the interval.
continue;
}
current->AddSafepoint(safepoint);
}
current->ResetSearchCache();
// Some instructions define their output in fixed register/stack slot. We need
// to ensure we know these locations before doing register allocation. For a
// given register, we create an interval that covers these locations. The register
// will be unavailable at these locations when trying to allocate one for an
// interval.
//
// The backwards walking ensures the ranges are ordered on increasing start positions.
Location output = locations->Out();
if (output.IsUnallocated() && output.GetPolicy() == Location::kSameAsFirstInput) {
Location first = locations->InAt(0);
if (first.IsRegister() || first.IsFpuRegister()) {
current->SetFrom(position + 1);
current->SetRegister(first.reg());
} else if (first.IsPair()) {
current->SetFrom(position + 1);
current->SetRegister(first.low());
LiveInterval* high = current->GetHighInterval();
high->SetRegister(first.high());
high->SetFrom(position + 1);
}
} else if (output.IsRegister() || output.IsFpuRegister()) {
// Shift the interval's start by one to account for the blocked register.
current->SetFrom(position + 1);
current->SetRegister(output.reg());
BlockRegister(output, position, position + 1);
} else if (output.IsPair()) {
current->SetFrom(position + 1);
current->SetRegister(output.low());
LiveInterval* high = current->GetHighInterval();
high->SetRegister(output.high());
high->SetFrom(position + 1);
BlockRegister(output.ToLow(), position, position + 1);
BlockRegister(output.ToHigh(), position, position + 1);
} else if (output.IsStackSlot() || output.IsDoubleStackSlot()) {
current->SetSpillSlot(output.GetStackIndex());
} else {
DCHECK(output.IsUnallocated() || output.IsConstant());
}
if (instruction->IsPhi() && instruction->AsPhi()->IsCatchPhi()) {
AllocateSpillSlotForCatchPhi(instruction->AsPhi());
}
// If needed, add interval to the list of unhandled intervals.
if (current->HasSpillSlot() || instruction->IsConstant()) {
// Split just before first register use.
size_t first_register_use = current->FirstRegisterUse();
if (first_register_use != kNoLifetime) {
LiveInterval* split = SplitBetween(current, current->GetStart(), first_register_use - 1);
// Don't add directly to `unhandled`, it needs to be sorted and the start
// of this new interval might be after intervals already in the list.
AddSorted(&unhandled, split);
} else {
// Nothing to do, we won't allocate a register for this value.
}
} else {
// Don't add directly to `unhandled`, temp or safepoint intervals
// for this instruction may have been added, and those can be
// processed first.
AddSorted(&unhandled, current);
}
}
class AllRangesIterator : public ValueObject {
public:
explicit AllRangesIterator(LiveInterval* interval)
: current_interval_(interval),
current_range_(interval->GetFirstRange()) {}
bool Done() const { return current_interval_ == nullptr; }
LiveRange* CurrentRange() const { return current_range_; }
LiveInterval* CurrentInterval() const { return current_interval_; }
void Advance() {
current_range_ = current_range_->GetNext();
if (current_range_ == nullptr) {
current_interval_ = current_interval_->GetNextSibling();
if (current_interval_ != nullptr) {
current_range_ = current_interval_->GetFirstRange();
}
}
}
private:
LiveInterval* current_interval_;
LiveRange* current_range_;
DISALLOW_COPY_AND_ASSIGN(AllRangesIterator);
};
bool RegisterAllocatorLinearScan::ValidateInternal(bool log_fatal_on_failure) const {
// To simplify unit testing, we eagerly create the array of intervals, and
// call the helper method.
ArenaVector<LiveInterval*> intervals(allocator_->Adapter(kArenaAllocRegisterAllocatorValidate));
for (size_t i = 0; i < liveness_.GetNumberOfSsaValues(); ++i) {
HInstruction* instruction = liveness_.GetInstructionFromSsaIndex(i);
if (ShouldProcess(processing_core_registers_, instruction->GetLiveInterval())) {
intervals.push_back(instruction->GetLiveInterval());
}
}
const ArenaVector<LiveInterval*>* physical_register_intervals = processing_core_registers_
? &physical_core_register_intervals_
: &physical_fp_register_intervals_;
for (LiveInterval* fixed : *physical_register_intervals) {
if (fixed != nullptr) {
intervals.push_back(fixed);
}
}
for (LiveInterval* temp : temp_intervals_) {
if (ShouldProcess(processing_core_registers_, temp)) {
intervals.push_back(temp);
}
}
return ValidateIntervals(intervals, GetNumberOfSpillSlots(), reserved_out_slots_, *codegen_,
allocator_, processing_core_registers_, log_fatal_on_failure);
}
void RegisterAllocatorLinearScan::DumpInterval(std::ostream& stream, LiveInterval* interval) const {
interval->Dump(stream);
stream << ": ";
if (interval->HasRegister()) {
if (interval->IsFloatingPoint()) {
codegen_->DumpFloatingPointRegister(stream, interval->GetRegister());
} else {
codegen_->DumpCoreRegister(stream, interval->GetRegister());
}
} else {
stream << "spilled";
}
stream << std::endl;
}
void RegisterAllocatorLinearScan::DumpAllIntervals(std::ostream& stream) const {
stream << "inactive: " << std::endl;
for (LiveInterval* inactive_interval : inactive_) {
DumpInterval(stream, inactive_interval);
}
stream << "active: " << std::endl;
for (LiveInterval* active_interval : active_) {
DumpInterval(stream, active_interval);
}
stream << "unhandled: " << std::endl;
auto unhandled = (unhandled_ != nullptr) ?
unhandled_ : &unhandled_core_intervals_;
for (LiveInterval* unhandled_interval : *unhandled) {
DumpInterval(stream, unhandled_interval);
}
stream << "handled: " << std::endl;
for (LiveInterval* handled_interval : handled_) {
DumpInterval(stream, handled_interval);
}
}
// By the book implementation of a linear scan register allocator.
void RegisterAllocatorLinearScan::LinearScan() {
while (!unhandled_->empty()) {
// (1) Remove interval with the lowest start position from unhandled.
LiveInterval* current = unhandled_->back();
unhandled_->pop_back();
// Make sure the interval is an expected state.
DCHECK(!current->IsFixed() && !current->HasSpillSlot());
// Make sure we are going in the right order.
DCHECK(unhandled_->empty() || unhandled_->back()->GetStart() >= current->GetStart());
// Make sure a low interval is always with a high.
DCHECK(!current->IsLowInterval() || unhandled_->back()->IsHighInterval());
// Make sure a high interval is always with a low.
DCHECK(current->IsLowInterval() ||
unhandled_->empty() ||
!unhandled_->back()->IsHighInterval());
size_t position = current->GetStart();
// Remember the inactive_ size here since the ones moved to inactive_ from
// active_ below shouldn't need to be re-checked.
size_t inactive_intervals_to_handle = inactive_.size();
// (2) Remove currently active intervals that are dead at this position.
// Move active intervals that have a lifetime hole at this position
// to inactive.
auto active_kept_end = std::remove_if(
active_.begin(),
active_.end(),
[this, position](LiveInterval* interval) {
if (interval->IsDeadAt(position)) {
handled_.push_back(interval);
return true;
} else if (!interval->Covers(position)) {
inactive_.push_back(interval);
return true;
} else {
return false; // Keep this interval.
}
});
active_.erase(active_kept_end, active_.end());
// (3) Remove currently inactive intervals that are dead at this position.
// Move inactive intervals that cover this position to active.
auto inactive_to_handle_end = inactive_.begin() + inactive_intervals_to_handle;
auto inactive_kept_end = std::remove_if(
inactive_.begin(),
inactive_to_handle_end,
[this, position](LiveInterval* interval) {
DCHECK(interval->GetStart() < position || interval->IsFixed());
if (interval->IsDeadAt(position)) {
handled_.push_back(interval);
return true;
} else if (interval->Covers(position)) {
active_.push_back(interval);
return true;
} else {
return false; // Keep this interval.
}
});
inactive_.erase(inactive_kept_end, inactive_to_handle_end);
if (current->IsHighInterval() && !current->GetLowInterval()->HasRegister()) {
DCHECK(!current->HasRegister());
// Allocating the low part was unsucessful. The splitted interval for the high part
// will be handled next (it is in the `unhandled_` list).
continue;
}
// (4) Try to find an available register.
bool success = TryAllocateFreeReg(current);
// (5) If no register could be found, we need to spill.
if (!success) {
success = AllocateBlockedReg(current);
}
// (6) If the interval had a register allocated, add it to the list of active
// intervals.
if (success) {
codegen_->AddAllocatedRegister(processing_core_registers_
? Location::RegisterLocation(current->GetRegister())
: Location::FpuRegisterLocation(current->GetRegister()));
active_.push_back(current);
if (current->HasHighInterval() && !current->GetHighInterval()->HasRegister()) {
current->GetHighInterval()->SetRegister(GetHighForLowRegister(current->GetRegister()));
}
}
}
}
static void FreeIfNotCoverAt(LiveInterval* interval, size_t position, size_t* free_until) {
DCHECK(!interval->IsHighInterval());
// Note that the same instruction may occur multiple times in the input list,
// so `free_until` may have changed already.
// Since `position` is not the current scan position, we need to use CoversSlow.
if (interval->IsDeadAt(position)) {
// Set the register to be free. Note that inactive intervals might later
// update this.
free_until[interval->GetRegister()] = kMaxLifetimePosition;
if (interval->HasHighInterval()) {
DCHECK(interval->GetHighInterval()->IsDeadAt(position));
free_until[interval->GetHighInterval()->GetRegister()] = kMaxLifetimePosition;
}
} else if (!interval->CoversSlow(position)) {
// The interval becomes inactive at `defined_by`. We make its register
// available only until the next use strictly after `defined_by`.
free_until[interval->GetRegister()] = interval->FirstUseAfter(position);
if (interval->HasHighInterval()) {
DCHECK(!interval->GetHighInterval()->CoversSlow(position));
free_until[interval->GetHighInterval()->GetRegister()] = free_until[interval->GetRegister()];
}
}
}
// Find a free register. If multiple are found, pick the register that
// is free the longest.
bool RegisterAllocatorLinearScan::TryAllocateFreeReg(LiveInterval* current) {
size_t* free_until = registers_array_;
// First set all registers to be free.
for (size_t i = 0; i < number_of_registers_; ++i) {
free_until[i] = kMaxLifetimePosition;
}
// For each active interval, set its register to not free.
for (LiveInterval* interval : active_) {
DCHECK(interval->HasRegister());
free_until[interval->GetRegister()] = 0;
}
// An interval that starts an instruction (that is, it is not split), may
// re-use the registers used by the inputs of that instruciton, based on the
// location summary.
HInstruction* defined_by = current->GetDefinedBy();
if (defined_by != nullptr && !current->IsSplit()) {
LocationSummary* locations = defined_by->GetLocations();
if (!locations->OutputCanOverlapWithInputs() && locations->Out().IsUnallocated()) {
HInputsRef inputs = defined_by->GetInputs();
for (size_t i = 0; i < inputs.size(); ++i) {
if (locations->InAt(i).IsValid()) {
// Take the last interval of the input. It is the location of that interval
// that will be used at `defined_by`.
LiveInterval* interval = inputs[i]->GetLiveInterval()->GetLastSibling();
// Note that interval may have not been processed yet.
// TODO: Handle non-split intervals last in the work list.
if (interval->HasRegister() && interval->SameRegisterKind(*current)) {
// The input must be live until the end of `defined_by`, to comply to
// the linear scan algorithm. So we use `defined_by`'s end lifetime
// position to check whether the input is dead or is inactive after
// `defined_by`.
DCHECK(interval->CoversSlow(defined_by->GetLifetimePosition()));
size_t position = defined_by->GetLifetimePosition() + 1;
FreeIfNotCoverAt(interval, position, free_until);
}
}
}
}
}
// For each inactive interval, set its register to be free until
// the next intersection with `current`.
for (LiveInterval* inactive : inactive_) {
// Temp/Slow-path-safepoint interval has no holes.
DCHECK(!inactive->IsTemp());
if (!current->IsSplit() && !inactive->IsFixed()) {
// Neither current nor inactive are fixed.
// Thanks to SSA, a non-split interval starting in a hole of an
// inactive interval should never intersect with that inactive interval.
// Only if it's not fixed though, because fixed intervals don't come from SSA.
DCHECK_EQ(inactive->FirstIntersectionWith(current), kNoLifetime);
continue;
}
DCHECK(inactive->HasRegister());
if (free_until[inactive->GetRegister()] == 0) {
// Already used by some active interval. No need to intersect.
continue;
}
size_t next_intersection = inactive->FirstIntersectionWith(current);
if (next_intersection != kNoLifetime) {
free_until[inactive->GetRegister()] =
std::min(free_until[inactive->GetRegister()], next_intersection);
}
}
int reg = kNoRegister;
if (current->HasRegister()) {
// Some instructions have a fixed register output.
reg = current->GetRegister();
if (free_until[reg] == 0) {
DCHECK(current->IsHighInterval());
// AllocateBlockedReg will spill the holder of the register.
return false;
}
} else {
DCHECK(!current->IsHighInterval());
int hint = current->FindFirstRegisterHint(free_until, liveness_);
if ((hint != kNoRegister)
// For simplicity, if the hint we are getting for a pair cannot be used,
// we are just going to allocate a new pair.
&& !(current->IsLowInterval() && IsBlocked(GetHighForLowRegister(hint)))) {
DCHECK(!IsBlocked(hint));
reg = hint;
} else if (current->IsLowInterval()) {
reg = FindAvailableRegisterPair(free_until, current->GetStart());
} else {
reg = FindAvailableRegister(free_until, current);
}
}
DCHECK_NE(reg, kNoRegister);
// If we could not find a register, we need to spill.
if (free_until[reg] == 0) {
return false;
}
if (current->IsLowInterval()) {
// If the high register of this interval is not available, we need to spill.
int high_reg = current->GetHighInterval()->GetRegister();
if (high_reg == kNoRegister) {
high_reg = GetHighForLowRegister(reg);
}
if (free_until[high_reg] == 0) {
return false;
}
}
current->SetRegister(reg);
if (!current->IsDeadAt(free_until[reg])) {
// If the register is only available for a subset of live ranges
// covered by `current`, split `current` before the position where
// the register is not available anymore.
LiveInterval* split = SplitBetween(current, current->GetStart(), free_until[reg]);
DCHECK(split != nullptr);
AddSorted(unhandled_, split);
}
return true;
}
bool RegisterAllocatorLinearScan::IsBlocked(int reg) const {
return processing_core_registers_
? blocked_core_registers_[reg]
: blocked_fp_registers_[reg];
}
int RegisterAllocatorLinearScan::FindAvailableRegisterPair(size_t* next_use, size_t starting_at) const {
int reg = kNoRegister;
// Pick the register pair that is used the last.
for (size_t i = 0; i < number_of_registers_; ++i) {
if (IsBlocked(i)) continue;
if (!IsLowRegister(i)) continue;
int high_register = GetHighForLowRegister(i);
if (IsBlocked(high_register)) continue;
int existing_high_register = GetHighForLowRegister(reg);
if ((reg == kNoRegister) || (next_use[i] >= next_use[reg]
&& next_use[high_register] >= next_use[existing_high_register])) {
reg = i;
if (next_use[i] == kMaxLifetimePosition
&& next_use[high_register] == kMaxLifetimePosition) {
break;
}
} else if (next_use[reg] <= starting_at || next_use[existing_high_register] <= starting_at) {
// If one of the current register is known to be unavailable, just unconditionally
// try a new one.
reg = i;
}
}
return reg;
}
bool RegisterAllocatorLinearScan::IsCallerSaveRegister(int reg) const {
return processing_core_registers_
? !codegen_->IsCoreCalleeSaveRegister(reg)
: !codegen_->IsFloatingPointCalleeSaveRegister(reg);
}
int RegisterAllocatorLinearScan::FindAvailableRegister(size_t* next_use, LiveInterval* current) const {
// We special case intervals that do not span a safepoint to try to find a caller-save
// register if one is available. We iterate from 0 to the number of registers,
// so if there are caller-save registers available at the end, we continue the iteration.
bool prefers_caller_save = !current->HasWillCallSafepoint();
int reg = kNoRegister;
for (size_t i = 0; i < number_of_registers_; ++i) {
if (IsBlocked(i)) {
// Register cannot be used. Continue.
continue;
}
// Best case: we found a register fully available.
if (next_use[i] == kMaxLifetimePosition) {
if (prefers_caller_save && !IsCallerSaveRegister(i)) {
// We can get shorter encodings on some platforms by using
// small register numbers. So only update the candidate if the previous
// one was not available for the whole method.
if (reg == kNoRegister || next_use[reg] != kMaxLifetimePosition) {
reg = i;
}
// Continue the iteration in the hope of finding a caller save register.
continue;
} else {
reg = i;
// We know the register is good enough. Return it.
break;
}
}
// If we had no register before, take this one as a reference.
if (reg == kNoRegister) {
reg = i;
continue;
}
// Pick the register that is used the last.
if (next_use[i] > next_use[reg]) {
reg = i;
continue;
}
}
return reg;
}
// Remove interval and its other half if any. Return iterator to the following element.
static ArenaVector<LiveInterval*>::iterator RemoveIntervalAndPotentialOtherHalf(
ArenaVector<LiveInterval*>* intervals, ArenaVector<LiveInterval*>::iterator pos) {
DCHECK(intervals->begin() <= pos && pos < intervals->end());
LiveInterval* interval = *pos;
if (interval->IsLowInterval()) {
DCHECK(pos + 1 < intervals->end());
DCHECK_EQ(*(pos + 1), interval->GetHighInterval());
return intervals->erase(pos, pos + 2);
} else if (interval->IsHighInterval()) {
DCHECK(intervals->begin() < pos);
DCHECK_EQ(*(pos - 1), interval->GetLowInterval());
return intervals->erase(pos - 1, pos + 1);
} else {
return intervals->erase(pos);
}
}
bool RegisterAllocatorLinearScan::TrySplitNonPairOrUnalignedPairIntervalAt(size_t position,
size_t first_register_use,
size_t* next_use) {
for (auto it = active_.begin(), end = active_.end(); it != end; ++it) {
LiveInterval* active = *it;
DCHECK(active->HasRegister());
if (active->IsFixed()) continue;
if (active->IsHighInterval()) continue;
if (first_register_use > next_use[active->GetRegister()]) continue;
// Split the first interval found that is either:
// 1) A non-pair interval.
// 2) A pair interval whose high is not low + 1.
// 3) A pair interval whose low is not even.
if (!active->IsLowInterval() ||
IsLowOfUnalignedPairInterval(active) ||
!IsLowRegister(active->GetRegister())) {
LiveInterval* split = Split(active, position);
if (split != active) {
handled_.push_back(active);
}
RemoveIntervalAndPotentialOtherHalf(&active_, it);
AddSorted(unhandled_, split);
return true;
}
}
return false;
}
// Find the register that is used the last, and spill the interval
// that holds it. If the first use of `current` is after that register
// we spill `current` instead.
bool RegisterAllocatorLinearScan::AllocateBlockedReg(LiveInterval* current) {
size_t first_register_use = current->FirstRegisterUse();
if (current->HasRegister()) {
DCHECK(current->IsHighInterval());
// The low interval has allocated the register for the high interval. In
// case the low interval had to split both intervals, we may end up in a
// situation where the high interval does not have a register use anymore.
// We must still proceed in order to split currently active and inactive
// uses of the high interval's register, and put the high interval in the
// active set.
DCHECK(first_register_use != kNoLifetime || (current->GetNextSibling() != nullptr));
} else if (first_register_use == kNoLifetime) {
AllocateSpillSlotFor(current);
return false;
}
// First set all registers as not being used.
size_t* next_use = registers_array_;
for (size_t i = 0; i < number_of_registers_; ++i) {
next_use[i] = kMaxLifetimePosition;
}
// For each active interval, find the next use of its register after the
// start of current.
for (LiveInterval* active : active_) {
DCHECK(active->HasRegister());
if (active->IsFixed()) {
next_use[active->GetRegister()] = current->GetStart();
} else {
size_t use = active->FirstRegisterUseAfter(current->GetStart());
if (use != kNoLifetime) {
next_use[active->GetRegister()] = use;
}
}
}
// For each inactive interval, find the next use of its register after the
// start of current.
for (LiveInterval* inactive : inactive_) {
// Temp/Slow-path-safepoint interval has no holes.
DCHECK(!inactive->IsTemp());
if (!current->IsSplit() && !inactive->IsFixed()) {
// Neither current nor inactive are fixed.
// Thanks to SSA, a non-split interval starting in a hole of an
// inactive interval should never intersect with that inactive interval.
// Only if it's not fixed though, because fixed intervals don't come from SSA.
DCHECK_EQ(inactive->FirstIntersectionWith(current), kNoLifetime);
continue;
}
DCHECK(inactive->HasRegister());
size_t next_intersection = inactive->FirstIntersectionWith(current);
if (next_intersection != kNoLifetime) {
if (inactive->IsFixed()) {
next_use[inactive->GetRegister()] =
std::min(next_intersection, next_use[inactive->GetRegister()]);
} else {
size_t use = inactive->FirstUseAfter(current->GetStart());
if (use != kNoLifetime) {
next_use[inactive->GetRegister()] = std::min(use, next_use[inactive->GetRegister()]);
}
}
}
}
int reg = kNoRegister;
bool should_spill = false;
if (current->HasRegister()) {
DCHECK(current->IsHighInterval());
reg = current->GetRegister();
// When allocating the low part, we made sure the high register was available.
DCHECK_LT(first_register_use, next_use[reg]);
} else if (current->IsLowInterval()) {
reg = FindAvailableRegisterPair(next_use, first_register_use);
// We should spill if both registers are not available.
should_spill = (first_register_use >= next_use[reg])
|| (first_register_use >= next_use[GetHighForLowRegister(reg)]);
} else {
DCHECK(!current->IsHighInterval());
reg = FindAvailableRegister(next_use, current);
should_spill = (first_register_use >= next_use[reg]);
}
DCHECK_NE(reg, kNoRegister);
if (should_spill) {
DCHECK(!current->IsHighInterval());
bool is_allocation_at_use_site = (current->GetStart() >= (first_register_use - 1));
if (is_allocation_at_use_site) {
if (!current->IsLowInterval()) {
DumpInterval(std::cerr, current);
DumpAllIntervals(std::cerr);
// This situation has the potential to infinite loop, so we make it a non-debug CHECK.
HInstruction* at = liveness_.GetInstructionFromPosition(first_register_use / 2);
CHECK(false) << "There is not enough registers available for "
<< current->GetParent()->GetDefinedBy()->DebugName() << " "
<< current->GetParent()->GetDefinedBy()->GetId()
<< " at " << first_register_use - 1 << " "
<< (at == nullptr ? "" : at->DebugName());
}
// If we're allocating a register for `current` because the instruction at
// that position requires it, but we think we should spill, then there are
// non-pair intervals or unaligned pair intervals blocking the allocation.
// We split the first interval found, and put ourselves first in the
// `unhandled_` list.
bool success = TrySplitNonPairOrUnalignedPairIntervalAt(current->GetStart(),
first_register_use,
next_use);
DCHECK(success);
LiveInterval* existing = unhandled_->back();
DCHECK(existing->IsHighInterval());
DCHECK_EQ(existing->GetLowInterval(), current);
unhandled_->push_back(current);
} else {
// If the first use of that instruction is after the last use of the found
// register, we split this interval just before its first register use.
AllocateSpillSlotFor(current);
LiveInterval* split = SplitBetween(current, current->GetStart(), first_register_use - 1);
DCHECK(current != split);
AddSorted(unhandled_, split);
}
return false;
} else {
// Use this register and spill the active and inactives interval that
// have that register.
current->SetRegister(reg);
for (auto it = active_.begin(), end = active_.end(); it != end; ++it) {
LiveInterval* active = *it;
if (active->GetRegister() == reg) {
DCHECK(!active->IsFixed());
LiveInterval* split = Split(active, current->GetStart());
if (split != active) {
handled_.push_back(active);
}
RemoveIntervalAndPotentialOtherHalf(&active_, it);
AddSorted(unhandled_, split);
break;
}
}
// NOTE: Retrieve end() on each iteration because we're removing elements in the loop body.
for (auto it = inactive_.begin(); it != inactive_.end(); ) {
LiveInterval* inactive = *it;
bool erased = false;
if (inactive->GetRegister() == reg) {
if (!current->IsSplit() && !inactive->IsFixed()) {
// Neither current nor inactive are fixed.
// Thanks to SSA, a non-split interval starting in a hole of an
// inactive interval should never intersect with that inactive interval.
// Only if it's not fixed though, because fixed intervals don't come from SSA.
DCHECK_EQ(inactive->FirstIntersectionWith(current), kNoLifetime);
} else {
size_t next_intersection = inactive->FirstIntersectionWith(current);
if (next_intersection != kNoLifetime) {
if (inactive->IsFixed()) {
LiveInterval* split = Split(current, next_intersection);
DCHECK_NE(split, current);
AddSorted(unhandled_, split);
} else {
// Split at the start of `current`, which will lead to splitting
// at the end of the lifetime hole of `inactive`.
LiveInterval* split = Split(inactive, current->GetStart());
// If it's inactive, it must start before the current interval.
DCHECK_NE(split, inactive);
it = RemoveIntervalAndPotentialOtherHalf(&inactive_, it);
erased = true;
handled_.push_back(inactive);
AddSorted(unhandled_, split);
}
}
}
}
// If we have erased the element, `it` already points to the next element.
// Otherwise we need to move to the next element.
if (!erased) {
++it;
}
}
return true;
}
}
void RegisterAllocatorLinearScan::AddSorted(ArenaVector<LiveInterval*>* array, LiveInterval* interval) {
DCHECK(!interval->IsFixed() && !interval->HasSpillSlot());
size_t insert_at = 0;
for (size_t i = array->size(); i > 0; --i) {
LiveInterval* current = (*array)[i - 1u];
// High intervals must be processed right after their low equivalent.
if (current->StartsAfter(interval) && !current->IsHighInterval()) {
insert_at = i;
break;
}
}
// Insert the high interval before the low, to ensure the low is processed before.
auto insert_pos = array->begin() + insert_at;
if (interval->HasHighInterval()) {
array->insert(insert_pos, { interval->GetHighInterval(), interval });
} else if (interval->HasLowInterval()) {
array->insert(insert_pos, { interval, interval->GetLowInterval() });
} else {
array->insert(insert_pos, interval);
}
}
void RegisterAllocatorLinearScan::AllocateSpillSlotFor(LiveInterval* interval) {
if (interval->IsHighInterval()) {
// The low interval already took care of allocating the spill slot.
DCHECK(!interval->GetLowInterval()->HasRegister());
DCHECK(interval->GetLowInterval()->GetParent()->HasSpillSlot());
return;
}
LiveInterval* parent = interval->GetParent();
// An instruction gets a spill slot for its entire lifetime. If the parent
// of this interval already has a spill slot, there is nothing to do.
if (parent->HasSpillSlot()) {
return;
}
HInstruction* defined_by = parent->GetDefinedBy();
DCHECK(!defined_by->IsPhi() || !defined_by->AsPhi()->IsCatchPhi());
if (defined_by->IsParameterValue()) {
// Parameters have their own stack slot.
parent->SetSpillSlot(codegen_->GetStackSlotOfParameter(defined_by->AsParameterValue()));
return;
}
if (defined_by->IsCurrentMethod()) {
parent->SetSpillSlot(0);
return;
}
if (defined_by->IsConstant()) {
// Constants don't need a spill slot.
return;
}
ArenaVector<size_t>* spill_slots = nullptr;
switch (interval->GetType()) {
case Primitive::kPrimDouble:
spill_slots = &double_spill_slots_;
break;
case Primitive::kPrimLong:
spill_slots = &long_spill_slots_;
break;
case Primitive::kPrimFloat:
spill_slots = &float_spill_slots_;
break;
case Primitive::kPrimNot:
case Primitive::kPrimInt:
case Primitive::kPrimChar:
case Primitive::kPrimByte:
case Primitive::kPrimBoolean:
case Primitive::kPrimShort:
spill_slots = &int_spill_slots_;
break;
case Primitive::kPrimVoid:
LOG(FATAL) << "Unexpected type for interval " << interval->GetType();
}
// Find first available spill slots.
size_t number_of_spill_slots_needed = parent->NumberOfSpillSlotsNeeded();
size_t slot = 0;
for (size_t e = spill_slots->size(); slot < e; ++slot) {
bool found = true;
for (size_t s = slot, u = std::min(slot + number_of_spill_slots_needed, e); s < u; s++) {
if ((*spill_slots)[s] > parent->GetStart()) {
found = false; // failure
break;
}
}
if (found) {
break; // success
}
}
// Need new spill slots?
size_t upper = slot + number_of_spill_slots_needed;
if (upper > spill_slots->size()) {
spill_slots->resize(upper);
}
// Set slots to end.
size_t end = interval->GetLastSibling()->GetEnd();
for (size_t s = slot; s < upper; s++) {
(*spill_slots)[s] = end;
}
// Note that the exact spill slot location will be computed when we resolve,
// that is when we know the number of spill slots for each type.
parent->SetSpillSlot(slot);
}
void RegisterAllocatorLinearScan::AllocateSpillSlotForCatchPhi(HPhi* phi) {
LiveInterval* interval = phi->GetLiveInterval();
HInstruction* previous_phi = phi->GetPrevious();
DCHECK(previous_phi == nullptr ||
previous_phi->AsPhi()->GetRegNumber() <= phi->GetRegNumber())
<< "Phis expected to be sorted by vreg number, so that equivalent phis are adjacent.";
if (phi->IsVRegEquivalentOf(previous_phi)) {
// This is an equivalent of the previous phi. We need to assign the same
// catch phi slot.
DCHECK(previous_phi->GetLiveInterval()->HasSpillSlot());
interval->SetSpillSlot(previous_phi->GetLiveInterval()->GetSpillSlot());
} else {
// Allocate a new spill slot for this catch phi.
// TODO: Reuse spill slots when intervals of phis from different catch
// blocks do not overlap.
interval->SetSpillSlot(catch_phi_spill_slots_);
catch_phi_spill_slots_ += interval->NumberOfSpillSlotsNeeded();
}
}
} // namespace art