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* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include "base/macros.h"
#include "primitive.h"
#include "utils/growable_array.h"
namespace art {
class CodeGenerator;
class HBasicBlock;
class HGraph;
class HInstruction;
class HParallelMove;
class LiveInterval;
class Location;
class SsaLivenessAnalysis;
* An implementation of a linear scan register allocator on an `HGraph` with SSA form.
class RegisterAllocator {
RegisterAllocator(ArenaAllocator* allocator,
CodeGenerator* codegen,
const SsaLivenessAnalysis& analysis);
// Main entry point for the register allocator. Given the liveness analysis,
// allocates registers to live intervals.
void AllocateRegisters();
// Validate that the register allocator did not allocate the same register to
// intervals that intersect each other. Returns false if it did not.
bool Validate(bool log_fatal_on_failure) {
processing_core_registers_ = true;
if (!ValidateInternal(log_fatal_on_failure)) {
return false;
processing_core_registers_ = false;
return ValidateInternal(log_fatal_on_failure);
// Helper method for validation. Used by unit testing.
static bool ValidateIntervals(const GrowableArray<LiveInterval*>& intervals,
size_t number_of_spill_slots,
size_t number_of_out_slots,
const CodeGenerator& codegen,
ArenaAllocator* allocator,
bool processing_core_registers,
bool log_fatal_on_failure);
static bool CanAllocateRegistersFor(const HGraph& graph, InstructionSet instruction_set);
size_t GetNumberOfSpillSlots() const {
return int_spill_slots_.Size()
+ long_spill_slots_.Size()
+ float_spill_slots_.Size()
+ double_spill_slots_.Size();
static constexpr const char* kRegisterAllocatorPassName = "register";
// Main methods of the allocator.
void LinearScan();
bool TryAllocateFreeReg(LiveInterval* interval);
bool AllocateBlockedReg(LiveInterval* interval);
void Resolve();
// Add `interval` in the given sorted list.
static void AddSorted(GrowableArray<LiveInterval*>* array, LiveInterval* interval);
// Split `interval` at the position `position`. The new interval starts at `position`.
LiveInterval* Split(LiveInterval* interval, size_t position);
// Split `interval` at a position between `from` and `to`. The method will try
// to find an optimal split position.
LiveInterval* SplitBetween(LiveInterval* interval, size_t from, size_t to);
// Returns whether `reg` is blocked by the code generator.
bool IsBlocked(int reg) const;
// Update the interval for the register in `location` to cover [start, end).
void BlockRegister(Location location, size_t start, size_t end);
// Allocate a spill slot for the given interval.
void AllocateSpillSlotFor(LiveInterval* interval);
// Connect adjacent siblings within blocks.
void ConnectSiblings(LiveInterval* interval);
// Connect siblings between block entries and exits.
void ConnectSplitSiblings(LiveInterval* interval, HBasicBlock* from, HBasicBlock* to) const;
// Helper methods to insert parallel moves in the graph.
void InsertParallelMoveAtExitOf(HBasicBlock* block,
HInstruction* instruction,
Location source,
Location destination) const;
void InsertParallelMoveAtEntryOf(HBasicBlock* block,
HInstruction* instruction,
Location source,
Location destination) const;
void InsertMoveAfter(HInstruction* instruction, Location source, Location destination) const;
void AddInputMoveFor(HInstruction* input,
HInstruction* user,
Location source,
Location destination) const;
void InsertParallelMoveAt(size_t position,
HInstruction* instruction,
Location source,
Location destination) const;
void AddMove(HParallelMove* move,
Location source,
Location destination,
HInstruction* instruction,
Primitive::Type type) const;
// Helper methods.
void AllocateRegistersInternal();
void ProcessInstruction(HInstruction* instruction);
bool ValidateInternal(bool log_fatal_on_failure) const;
void DumpInterval(std::ostream& stream, LiveInterval* interval) const;
void DumpAllIntervals(std::ostream& stream) const;
int FindAvailableRegisterPair(size_t* next_use, size_t starting_at) const;
int FindAvailableRegister(size_t* next_use) const;
// Try splitting an active non-pair or unaligned pair interval at the given `position`.
// Returns whether it was successful at finding such an interval.
bool TrySplitNonPairOrUnalignedPairIntervalAt(size_t position,
size_t first_register_use,
size_t* next_use);
// If `interval` has another half, remove it from the list of `intervals`.
// `index` holds the index at which `interval` is in `intervals`.
// Returns whether there is another half.
bool PotentiallyRemoveOtherHalf(LiveInterval* interval,
GrowableArray<LiveInterval*>* intervals,
size_t index);
ArenaAllocator* const allocator_;
CodeGenerator* const codegen_;
const SsaLivenessAnalysis& liveness_;
// List of intervals for core registers that must be processed, ordered by start
// position. Last entry is the interval that has the lowest start position.
// This list is initially populated before doing the linear scan.
GrowableArray<LiveInterval*> unhandled_core_intervals_;
// List of intervals for floating-point registers. Same comments as above.
GrowableArray<LiveInterval*> unhandled_fp_intervals_;
// Currently processed list of unhandled intervals. Either `unhandled_core_intervals_`
// or `unhandled_fp_intervals_`.
GrowableArray<LiveInterval*>* unhandled_;
// List of intervals that have been processed.
GrowableArray<LiveInterval*> handled_;
// List of intervals that are currently active when processing a new live interval.
// That is, they have a live range that spans the start of the new interval.
GrowableArray<LiveInterval*> active_;
// List of intervals that are currently inactive when processing a new live interval.
// That is, they have a lifetime hole that spans the start of the new interval.
GrowableArray<LiveInterval*> inactive_;
// Fixed intervals for physical registers. Such intervals cover the positions
// where an instruction requires a specific register.
GrowableArray<LiveInterval*> physical_core_register_intervals_;
GrowableArray<LiveInterval*> physical_fp_register_intervals_;
// Intervals for temporaries. Such intervals cover the positions
// where an instruction requires a temporary.
GrowableArray<LiveInterval*> temp_intervals_;
// The spill slots allocated for live intervals. We ensure spill slots
// are typed to avoid (1) doing moves and swaps between two different kinds
// of registers, and (2) swapping between a single stack slot and a double
// stack slot. This simplifies the parallel move resolver.
GrowableArray<size_t> int_spill_slots_;
GrowableArray<size_t> long_spill_slots_;
GrowableArray<size_t> float_spill_slots_;
GrowableArray<size_t> double_spill_slots_;
// Instructions that need a safepoint.
GrowableArray<HInstruction*> safepoints_;
// True if processing core registers. False if processing floating
// point registers.
bool processing_core_registers_;
// Number of registers for the current register kind (core or floating point).
size_t number_of_registers_;
// Temporary array, allocated ahead of time for simplicity.
size_t* registers_array_;
// Blocked registers, as decided by the code generator.
bool* const blocked_core_registers_;
bool* const blocked_fp_registers_;
// Slots reserved for out arguments.
size_t reserved_out_slots_;
// The maximum live core registers at safepoints.
size_t maximum_number_of_live_core_registers_;
// The maximum live FP registers at safepoints.
size_t maximum_number_of_live_fp_registers_;
ART_FRIEND_TEST(RegisterAllocatorTest, FreeUntil);
ART_FRIEND_TEST(RegisterAllocatorTest, SpillInactive);
} // namespace art