mirror of
https://github.com/classilla/tenfourfox.git
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204 lines
6.9 KiB
C++
204 lines
6.9 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=8 sts=4 et sw=4 tw=99:
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include "jit/EffectiveAddressAnalysis.h"
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#include "jit/MIR.h"
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#include "jit/MIRGraph.h"
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using namespace js;
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using namespace jit;
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#if(0) // bug 881882
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static void
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AnalyzeLsh(TempAllocator& alloc, MLsh* lsh)
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{
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if (lsh->specialization() != MIRType_Int32)
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return;
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if (lsh->isRecoveredOnBailout())
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return;
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MDefinition* index = lsh->lhs();
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MOZ_ASSERT(index->type() == MIRType_Int32);
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MDefinition* shift = lsh->rhs();
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if (!shift->isConstantValue())
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return;
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Value shiftValue = shift->constantValue();
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if (!shiftValue.isInt32() || !IsShiftInScaleRange(shiftValue.toInt32()))
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return;
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Scale scale = ShiftToScale(shiftValue.toInt32());
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int32_t displacement = 0;
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MInstruction* last = lsh;
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MDefinition* base = nullptr;
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while (true) {
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if (!last->hasOneUse())
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break;
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MUseIterator use = last->usesBegin();
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if (!use->consumer()->isDefinition() || !use->consumer()->toDefinition()->isAdd())
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break;
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MAdd* add = use->consumer()->toDefinition()->toAdd();
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if (add->specialization() != MIRType_Int32 || !add->isTruncated())
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break;
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MDefinition* other = add->getOperand(1 - add->indexOf(*use));
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if (other->isConstantValue()) {
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displacement += other->constantValue().toInt32();
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} else {
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if (base)
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break;
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base = other;
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}
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last = add;
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if (last->isRecoveredOnBailout())
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return;
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}
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if (!base) {
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uint32_t elemSize = 1 << ScaleToShift(scale);
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if (displacement % elemSize != 0)
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return;
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if (!last->hasOneUse())
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return;
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MUseIterator use = last->usesBegin();
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if (!use->consumer()->isDefinition() || !use->consumer()->toDefinition()->isBitAnd())
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return;
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MBitAnd* bitAnd = use->consumer()->toDefinition()->toBitAnd();
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if (bitAnd->isRecoveredOnBailout())
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return;
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MDefinition* other = bitAnd->getOperand(1 - bitAnd->indexOf(*use));
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if (!other->isConstantValue() || !other->constantValue().isInt32())
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return;
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uint32_t bitsClearedByShift = elemSize - 1;
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uint32_t bitsClearedByMask = ~uint32_t(other->constantValue().toInt32());
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if ((bitsClearedByShift & bitsClearedByMask) != bitsClearedByMask)
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return;
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bitAnd->replaceAllUsesWith(last);
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return;
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}
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if (base->isRecoveredOnBailout())
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return;
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MEffectiveAddress* eaddr = MEffectiveAddress::New(alloc, base, index, scale, displacement);
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last->replaceAllUsesWith(eaddr);
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last->block()->insertAfter(last, eaddr);
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}
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template<typename MAsmJSHeapAccessType>
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bool
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EffectiveAddressAnalysis::tryAddDisplacement(MAsmJSHeapAccessType* ins, int32_t o)
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{
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// Compute the new offset. Check for overflow and negative. In theory it
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// ought to be possible to support negative offsets, but it'd require
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// more elaborate bounds checking mechanisms than we currently have.
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MOZ_ASSERT(ins->offset() >= 0);
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int32_t newOffset = uint32_t(ins->offset()) + o;
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if (newOffset < 0)
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return false;
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// Compute the new offset to the end of the access. Check for overflow
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// and negative here also.
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int32_t newEnd = uint32_t(newOffset) + ins->byteSize();
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if (newEnd < 0)
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return false;
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MOZ_ASSERT(uint32_t(newEnd) >= uint32_t(newOffset));
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// Determine the range of valid offsets which can be folded into this
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// instruction and check whether our computed offset is within that range.
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size_t range = mir_->foldableOffsetRange(ins);
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if (size_t(newEnd) > range)
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return false;
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// Everything checks out. This is the new offset.
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ins->setOffset(newOffset);
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return true;
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}
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template<typename MAsmJSHeapAccessType>
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void
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EffectiveAddressAnalysis::analyzeAsmHeapAccess(MAsmJSHeapAccessType* ins)
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{
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MDefinition* ptr = ins->ptr();
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if (ptr->isConstantValue()) {
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// Look for heap[i] where i is a constant offset, and fold the offset.
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// By doing the folding now, we simplify the task of codegen; the offset
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// is always the address mode immediate. This also allows it to avoid
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// a situation where the sum of a constant pointer value and a non-zero
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// offset doesn't actually fit into the address mode immediate.
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int32_t imm = ptr->constantValue().toInt32();
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if (imm != 0 && tryAddDisplacement(ins, imm)) {
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MInstruction* zero = MConstant::New(graph_.alloc(), Int32Value(0));
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ins->block()->insertBefore(ins, zero);
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ins->replacePtr(zero);
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}
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} else if (ptr->isAdd()) {
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// Look for heap[a+i] where i is a constant offset, and fold the offset.
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// Alignment masks have already been moved out of the way by the
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// Alignment Mask Analysis pass.
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MDefinition* op0 = ptr->toAdd()->getOperand(0);
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MDefinition* op1 = ptr->toAdd()->getOperand(1);
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if (op0->isConstantValue())
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mozilla::Swap(op0, op1);
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if (op1->isConstantValue()) {
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int32_t imm = op1->constantValue().toInt32();
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if (tryAddDisplacement(ins, imm))
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ins->replacePtr(op0);
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}
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}
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}
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#endif // JS_ASMJS
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// This analysis converts patterns of the form:
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// truncate(x + (y << {0,1,2,3}))
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// truncate(x + (y << {0,1,2,3}) + imm32)
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// into a single lea instruction, and patterns of the form:
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// asmload(x + imm32)
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// asmload(x << {0,1,2,3})
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// asmload((x << {0,1,2,3}) + imm32)
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// asmload((x << {0,1,2,3}) & mask) (where mask is redundant with shift)
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// asmload(((x << {0,1,2,3}) + imm32) & mask) (where mask is redundant with shift + imm32)
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// into a single asmload instruction (and for asmstore too).
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//
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// Additionally, we should consider the general forms:
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// truncate(x + y + imm32)
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// truncate((y << {0,1,2,3}) + imm32)
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bool
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EffectiveAddressAnalysis::analyze()
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{
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#if(0) // bug 881882
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for (ReversePostorderIterator block(graph_.rpoBegin()); block != graph_.rpoEnd(); block++) {
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for (MInstructionIterator i = block->begin(); i != block->end(); i++) {
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// Note that we don't check for MAsmJSCompareExchangeHeap
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// or MAsmJSAtomicBinopHeap, because the backend and the OOB
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// mechanism don't support non-zero offsets for them yet.
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if (i->isLsh())
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AnalyzeLsh(graph_.alloc(), i->toLsh());
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else if (i->isAsmJSLoadHeap())
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analyzeAsmHeapAccess(i->toAsmJSLoadHeap());
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else if (i->isAsmJSStoreHeap())
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analyzeAsmHeapAccess(i->toAsmJSStoreHeap());
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}
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}
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#endif // JS_ASMJS
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return true;
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}
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