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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
*
* 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.
*/
#ifndef ART_COMPILER_OPTIMIZING_SSA_LIVENESS_ANALYSIS_H_
#define ART_COMPILER_OPTIMIZING_SSA_LIVENESS_ANALYSIS_H_
#include "nodes.h"
namespace art {
class BlockInfo : public ArenaObject {
public:
BlockInfo(ArenaAllocator* allocator, const HBasicBlock& block, size_t number_of_ssa_values)
: block_(block),
live_in_(allocator, number_of_ssa_values, false),
live_out_(allocator, number_of_ssa_values, false),
kill_(allocator, number_of_ssa_values, false) {
live_in_.ClearAllBits();
live_out_.ClearAllBits();
kill_.ClearAllBits();
}
private:
const HBasicBlock& block_;
ArenaBitVector live_in_;
ArenaBitVector live_out_;
ArenaBitVector kill_;
friend class SsaLivenessAnalysis;
DISALLOW_COPY_AND_ASSIGN(BlockInfo);
};
/**
* A live range contains the start and end of a range where an instruction
* is live.
*/
class LiveRange : public ValueObject {
public:
LiveRange(size_t start, size_t end) : start_(start), end_(end) {
DCHECK_LT(start, end);
}
size_t GetStart() const { return start_; }
size_t GetEnd() const { return end_; }
private:
size_t start_;
size_t end_;
};
static constexpr int kDefaultNumberOfRanges = 3;
/**
* An interval is a list of disjoint live ranges where an instruction is live.
* Each instruction that has uses gets an interval.
*/
class LiveInterval : public ArenaObject {
public:
explicit LiveInterval(ArenaAllocator* allocator) : ranges_(allocator, kDefaultNumberOfRanges) {}
void AddUse(HInstruction* instruction) {
size_t position = instruction->GetLifetimePosition();
size_t start_block_position = instruction->GetBlock()->GetLifetimeStart();
size_t end_block_position = instruction->GetBlock()->GetLifetimeEnd();
if (ranges_.IsEmpty()) {
// First time we see a use of that interval.
ranges_.Add(LiveRange(start_block_position, position));
} else if (ranges_.Peek().GetStart() == start_block_position) {
// There is a use later in the same block.
DCHECK_LE(position, ranges_.Peek().GetEnd());
} else if (ranges_.Peek().GetStart() == end_block_position + 1) {
// Last use is in a following block.
LiveRange existing = ranges_.Pop();
ranges_.Add(LiveRange(start_block_position, existing.GetEnd()));
} else {
// There is a hole in the interval. Create a new range.
ranges_.Add(LiveRange(start_block_position, position));
}
}
void AddRange(size_t start, size_t end) {
if (ranges_.IsEmpty()) {
ranges_.Add(LiveRange(start, end));
} else if (ranges_.Peek().GetStart() == end + 1) {
// There is a use in the following block.
LiveRange existing = ranges_.Pop();
ranges_.Add(LiveRange(start, existing.GetEnd()));
} else {
// There is a hole in the interval. Create a new range.
ranges_.Add(LiveRange(start, end));
}
}
void AddLoopRange(size_t start, size_t end) {
DCHECK(!ranges_.IsEmpty());
while (!ranges_.IsEmpty() && ranges_.Peek().GetEnd() < end) {
DCHECK_LE(start, ranges_.Peek().GetStart());
ranges_.Pop();
}
if (ranges_.IsEmpty()) {
// Uses are only in the loop.
ranges_.Add(LiveRange(start, end));
} else {
// There are uses after the loop.
LiveRange range = ranges_.Pop();
ranges_.Add(LiveRange(start, range.GetEnd()));
}
}
void SetFrom(size_t from) {
DCHECK(!ranges_.IsEmpty());
LiveRange existing = ranges_.Pop();
ranges_.Add(LiveRange(from, existing.GetEnd()));
}
const GrowableArray<LiveRange>& GetRanges() const { return ranges_; }
private:
GrowableArray<LiveRange> ranges_;
DISALLOW_COPY_AND_ASSIGN(LiveInterval);
};
class SsaLivenessAnalysis : public ValueObject {
public:
explicit SsaLivenessAnalysis(const HGraph& graph)
: graph_(graph),
linear_post_order_(graph.GetArena(), graph.GetBlocks().Size()),
block_infos_(graph.GetArena(), graph.GetBlocks().Size()),
instructions_from_ssa_index_(graph.GetArena(), 0),
number_of_ssa_values_(0) {
block_infos_.SetSize(graph.GetBlocks().Size());
}
void Analyze();
BitVector* GetLiveInSet(const HBasicBlock& block) const {
return &block_infos_.Get(block.GetBlockId())->live_in_;
}
BitVector* GetLiveOutSet(const HBasicBlock& block) const {
return &block_infos_.Get(block.GetBlockId())->live_out_;
}
BitVector* GetKillSet(const HBasicBlock& block) const {
return &block_infos_.Get(block.GetBlockId())->kill_;
}
const GrowableArray<HBasicBlock*>& GetLinearPostOrder() const {
return linear_post_order_;
}
HInstruction* GetInstructionFromSsaIndex(size_t index) {
return instructions_from_ssa_index_.Get(index);
}
private:
// Linearize the graph so that:
// (1): a block is always after its dominator,
// (2): blocks of loops are contiguous.
// This creates a natural and efficient ordering when visualizing live ranges.
void LinearizeGraph();
// Give an SSA number to each instruction that defines a value used by another instruction,
// and setup the lifetime information of each instruction and block.
void NumberInstructions();
// Compute live ranges of instructions, as well as live_in, live_out and kill sets.
void ComputeLiveness();
// Compute the live ranges of instructions, as well as the initial live_in, live_out and
// kill sets, that do not take into account backward branches.
void ComputeLiveRanges();
// After computing the initial sets, this method does a fixed point
// calculation over the live_in and live_out set to take into account
// backwards branches.
void ComputeLiveInAndLiveOutSets();
// Update the live_in set of the block and returns whether it has changed.
bool UpdateLiveIn(const HBasicBlock& block);
// Update the live_out set of the block and returns whether it has changed.
bool UpdateLiveOut(const HBasicBlock& block);
const HGraph& graph_;
GrowableArray<HBasicBlock*> linear_post_order_;
GrowableArray<BlockInfo*> block_infos_;
GrowableArray<HInstruction*> instructions_from_ssa_index_;
size_t number_of_ssa_values_;
DISALLOW_COPY_AND_ASSIGN(SsaLivenessAnalysis);
};
} // namespace art
#endif // ART_COMPILER_OPTIMIZING_SSA_LIVENESS_ANALYSIS_H_
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