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/*
* Copyright (C) 2016-2019 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 "B3DuplicateTails.h"
#if ENABLE(B3_JIT)
#include "B3BasicBlock.h"
#include "B3BreakCriticalEdges.h"
#include "B3FixSSA.h"
#include "B3InsertionSet.h"
#include "B3PhaseScope.h"
#include "B3Procedure.h"
#include "B3ValueInlines.h"
#include <wtf/IndexSet.h>
namespace JSC { namespace B3 {
namespace {
namespace B3DuplicateTailsInternal {
static constexpr bool verbose = false;
}
class DuplicateTails {
public:
DuplicateTails(Procedure& proc)
: m_proc(proc)
, m_insertionSet(proc)
, m_maxSize(Options::maxB3TailDupBlockSize())
, m_maxSuccessors(Options::maxB3TailDupBlockSuccessors())
{
}
void run()
{
// Breaking critical edges introduces blocks that jump to things. Those Jumps' successors
// become candidates for tail duplication. Prior to critical edge breaking, some of those
// Jumps would have been Branches, and so no tail duplication would have happened.
breakCriticalEdges(m_proc);
// Find blocks that would be candidates for tail duplication. They must be small enough
// and they much not have too many successors.
m_proc.resetValueOwners();
IndexSet<BasicBlock*> candidates;
for (BasicBlock* block : m_proc) {
if (block->size() > m_maxSize)
continue;
if (block->numSuccessors() > m_maxSuccessors)
continue;
if (block->last()->type() != Void) // Demoting doesn't handle terminals with values.
continue;
bool canCopyBlock = true;
for (Value* value : *block) {
if (value->kind().isCloningForbidden()) {
canCopyBlock = false;
break;
}
}
if (canCopyBlock)
candidates.add(block);
}
// Collect the set of values that must be de-SSA'd.
IndexSet<Value*> valuesToDemote;
for (BasicBlock* block : m_proc) {
for (Value* value : *block) {
if (value->opcode() == Phi && candidates.contains(block))
valuesToDemote.add(value);
for (Value* child : value->children()) {
if (child->owner != block && candidates.contains(child->owner))
valuesToDemote.add(child);
}
}
}
demoteValues(m_proc, valuesToDemote);
if (B3DuplicateTailsInternal::verbose) {
dataLog("Procedure after value demotion:\n");
dataLog(m_proc);
}
for (BasicBlock* block : m_proc) {
if (block->last()->opcode() != Jump)
continue;
BasicBlock* tail = block->successorBlock(0);
if (!candidates.contains(tail))
continue;
// Don't tail duplicate a trivial self-loop, because the code below can't handle block and
// tail being the same block.
if (block == tail)
continue;
// We're about to change 'block'. Make sure that nobody duplicates block after this
// point.
candidates.remove(block);
if (B3DuplicateTailsInternal::verbose)
dataLog("Duplicating ", *tail, " into ", *block, "\n");
block->removeLast(m_proc);
UncheckedKeyHashMap<Value*, Value*> map;
for (Value* value : *tail) {
Value* clone = m_proc.clone(value);
for (Value*& child : clone->children()) {
if (Value* replacement = map.get(child))
child = replacement;
}
if (value->type() != Void)
map.add(value, clone);
block->append(clone);
}
block->successors() = tail->successors();
}
m_proc.resetReachability();
m_proc.invalidateCFG();
}
private:
Procedure& m_proc;
InsertionSet m_insertionSet;
unsigned m_maxSize;
unsigned m_maxSuccessors;
};
} // anonymous namespace
void duplicateTails(Procedure& proc)
{
PhaseScope phaseScope(proc, "duplicateTails"_s);
DuplicateTails duplicateTails(proc);
duplicateTails.run();
}
} } // namespace JSC::B3
#endif // ENABLE(B3_JIT)
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