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/*
* Copyright (C) 2015-2017 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "AirOptimizeBlockOrder.h"
#if ENABLE(B3_JIT)
#include "AirBlockWorklist.h"
#include "AirCode.h"
#include "AirPhaseScope.h"
#include <wtf/BubbleSort.h>
namespace JSC { namespace B3 { namespace Air {
namespace {
class SortedSuccessors {
public:
SortedSuccessors()
{
}
void append(BasicBlock* block)
{
m_successors.append(block);
}
void process(BlockWorklist& worklist)
{
// We prefer a stable sort, and we don't want it to go off the rails if we see NaN. Also, the number
// of successors is bounded. In fact, it currently cannot be more than 2. :-)
bubbleSort(
m_successors.begin(), m_successors.end(),
[] (BasicBlock* left, BasicBlock* right) {
return left->frequency() < right->frequency();
});
// Pushing the successors in ascending order of frequency ensures that the very next block we visit
// is our highest-frequency successor (unless that successor has already been visited).
for (unsigned i = 0; i < m_successors.size(); ++i)
worklist.push(m_successors[i]);
m_successors.shrink(0);
}
private:
Vector<BasicBlock*, 2> m_successors;
};
} // anonymous namespace
Vector<BasicBlock*> blocksInOptimizedOrder(Code& code)
{
Vector<BasicBlock*> blocksInOrder;
BlockWorklist fastWorklist;
SortedSuccessors sortedSuccessors;
SortedSuccessors sortedSlowSuccessors;
// We expect entrypoint lowering to have already happened.
RELEASE_ASSERT(code.numEntrypoints());
auto appendSuccessor = [&] (const FrequentedBlock& block) {
if (block.isRare())
sortedSlowSuccessors.append(block.block());
else
sortedSuccessors.append(block.block());
};
// For everything but the first entrypoint, we push them in order of frequency and frequency
// class.
for (unsigned i = 1; i < code.numEntrypoints(); ++i)
appendSuccessor(code.entrypoint(i));
// Always push the primary successor last so that it gets highest priority.
fastWorklist.push(code.entrypoint(0).block());
while (BasicBlock* block = fastWorklist.pop()) {
blocksInOrder.append(block);
for (FrequentedBlock& successor : block->successors())
appendSuccessor(successor);
sortedSuccessors.process(fastWorklist);
}
BlockWorklist slowWorklist;
sortedSlowSuccessors.process(slowWorklist);
while (BasicBlock* block = slowWorklist.pop()) {
// We might have already processed this block.
if (fastWorklist.saw(block))
continue;
blocksInOrder.append(block);
for (BasicBlock* successor : block->successorBlocks())
sortedSuccessors.append(successor);
sortedSuccessors.process(slowWorklist);
}
ASSERT(fastWorklist.isEmpty());
ASSERT(slowWorklist.isEmpty());
return blocksInOrder;
}
void optimizeBlockOrder(Code& code)
{
PhaseScope phaseScope(code, "optimizeBlockOrder"_s);
Vector<BasicBlock*> blocksInOrder = blocksInOptimizedOrder(code);
// Place blocks into Code's block list according to the ordering in blocksInOrder. We do this by leaking
// all of the blocks and then readopting them.
for (auto& entry : code.blockList())
entry.release();
code.blockList().shrink(0);
for (unsigned i = 0; i < blocksInOrder.size(); ++i) {
BasicBlock* block = blocksInOrder[i];
block->setIndex(i);
code.blockList().append(std::unique_ptr<BasicBlock>(block));
}
// Finally, flip any branches that we recognize. It's most optimal if the taken successor does not point
// at the next block.
for (BasicBlock* block : code) {
Inst& branch = block->last();
// It's somewhat tempting to just say that if the block has two successors and the first arg is
// invertible, then we can do the optimization. But that's wagging the dog. The fact that an
// instruction happens to have an argument that is invertible doesn't mean it's a branch, even though
// it is true that currently only branches have invertible arguments. It's also tempting to say that
// the /branch flag in AirOpcode.opcodes tells us that something is a branch - except that there,
// /branch also means Jump. The approach taken here means that if you add new branch instructions and
// forget about this phase, then at worst your new instructions won't opt into the inversion
// optimization. You'll probably realize that as soon as you look at the disassembly, and it
// certainly won't cause any correctness issues.
switch (branch.kind.opcode) {
case Branch8:
case Branch32:
case Branch64:
case BranchTest8:
case BranchTest32:
case BranchTest64:
case BranchFloat:
case BranchDouble:
case BranchAdd32:
case BranchAdd64:
case BranchMul32:
case BranchMul64:
case BranchSub32:
case BranchSub64:
case BranchNeg32:
case BranchNeg64:
case BranchAtomicStrongCAS8:
case BranchAtomicStrongCAS16:
case BranchAtomicStrongCAS32:
case BranchAtomicStrongCAS64:
if (code.findNextBlock(block) == block->successorBlock(0) && branch.args[0].isInvertible()) {
std::swap(block->successor(0), block->successor(1));
branch.args[0] = branch.args[0].inverted();
}
break;
default:
break;
}
}
}
} } } // namespace JSC::B3::Air
#endif // ENABLE(B3_JIT)
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