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0b8c9a80f2
into their new header subdirectory: include/llvm/IR. This matches the directory structure of lib, and begins to correct a long standing point of file layout clutter in LLVM. There are still more header files to move here, but I wanted to handle them in separate commits to make tracking what files make sense at each layer easier. The only really questionable files here are the target intrinsic tablegen files. But that's a battle I'd rather not fight today. I've updated both CMake and Makefile build systems (I think, and my tests think, but I may have missed something). I've also re-sorted the includes throughout the project. I'll be committing updates to Clang, DragonEgg, and Polly momentarily. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171366 91177308-0d34-0410-b5e6-96231b3b80d8
263 lines
9.8 KiB
C++
263 lines
9.8 KiB
C++
//===-- BypassSlowDivision.cpp - Bypass slow division ---------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file contains an optimization for div and rem on architectures that
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// execute short instructions significantly faster than longer instructions.
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// For example, on Intel Atom 32-bit divides are slow enough that during
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// runtime it is profitable to check the value of the operands, and if they are
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// positive and less than 256 use an unsigned 8-bit divide.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "bypass-slow-division"
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#include "llvm/Transforms/Utils/BypassSlowDivision.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instructions.h"
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using namespace llvm;
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namespace {
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struct DivOpInfo {
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bool SignedOp;
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Value *Dividend;
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Value *Divisor;
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DivOpInfo(bool InSignedOp, Value *InDividend, Value *InDivisor)
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: SignedOp(InSignedOp), Dividend(InDividend), Divisor(InDivisor) {}
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};
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struct DivPhiNodes {
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PHINode *Quotient;
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PHINode *Remainder;
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DivPhiNodes(PHINode *InQuotient, PHINode *InRemainder)
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: Quotient(InQuotient), Remainder(InRemainder) {}
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};
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}
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namespace llvm {
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template<>
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struct DenseMapInfo<DivOpInfo> {
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static bool isEqual(const DivOpInfo &Val1, const DivOpInfo &Val2) {
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return Val1.SignedOp == Val2.SignedOp &&
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Val1.Dividend == Val2.Dividend &&
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Val1.Divisor == Val2.Divisor;
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}
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static DivOpInfo getEmptyKey() {
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return DivOpInfo(false, 0, 0);
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}
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static DivOpInfo getTombstoneKey() {
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return DivOpInfo(true, 0, 0);
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}
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static unsigned getHashValue(const DivOpInfo &Val) {
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return (unsigned)(reinterpret_cast<uintptr_t>(Val.Dividend) ^
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reinterpret_cast<uintptr_t>(Val.Divisor)) ^
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(unsigned)Val.SignedOp;
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}
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};
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typedef DenseMap<DivOpInfo, DivPhiNodes> DivCacheTy;
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}
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// insertFastDiv - Substitutes the div/rem instruction with code that checks the
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// value of the operands and uses a shorter-faster div/rem instruction when
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// possible and the longer-slower div/rem instruction otherwise.
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static bool insertFastDiv(Function &F,
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Function::iterator &I,
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BasicBlock::iterator &J,
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IntegerType *BypassType,
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bool UseDivOp,
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bool UseSignedOp,
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DivCacheTy &PerBBDivCache) {
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// Get instruction operands
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Instruction *Instr = J;
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Value *Dividend = Instr->getOperand(0);
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Value *Divisor = Instr->getOperand(1);
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if (isa<ConstantInt>(Divisor) ||
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(isa<ConstantInt>(Dividend) && isa<ConstantInt>(Divisor))) {
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// Operations with immediate values should have
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// been solved and replaced during compile time.
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return false;
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}
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// Basic Block is split before divide
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BasicBlock *MainBB = I;
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BasicBlock *SuccessorBB = I->splitBasicBlock(J);
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++I; //advance iterator I to successorBB
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// Add new basic block for slow divide operation
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BasicBlock *SlowBB = BasicBlock::Create(F.getContext(), "",
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MainBB->getParent(), SuccessorBB);
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SlowBB->moveBefore(SuccessorBB);
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IRBuilder<> SlowBuilder(SlowBB, SlowBB->begin());
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Value *SlowQuotientV;
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Value *SlowRemainderV;
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if (UseSignedOp) {
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SlowQuotientV = SlowBuilder.CreateSDiv(Dividend, Divisor);
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SlowRemainderV = SlowBuilder.CreateSRem(Dividend, Divisor);
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} else {
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SlowQuotientV = SlowBuilder.CreateUDiv(Dividend, Divisor);
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SlowRemainderV = SlowBuilder.CreateURem(Dividend, Divisor);
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}
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SlowBuilder.CreateBr(SuccessorBB);
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// Add new basic block for fast divide operation
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BasicBlock *FastBB = BasicBlock::Create(F.getContext(), "",
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MainBB->getParent(), SuccessorBB);
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FastBB->moveBefore(SlowBB);
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IRBuilder<> FastBuilder(FastBB, FastBB->begin());
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Value *ShortDivisorV = FastBuilder.CreateCast(Instruction::Trunc, Divisor,
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BypassType);
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Value *ShortDividendV = FastBuilder.CreateCast(Instruction::Trunc, Dividend,
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BypassType);
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// udiv/urem because optimization only handles positive numbers
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Value *ShortQuotientV = FastBuilder.CreateExactUDiv(ShortDividendV,
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ShortDivisorV);
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Value *ShortRemainderV = FastBuilder.CreateURem(ShortDividendV,
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ShortDivisorV);
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Value *FastQuotientV = FastBuilder.CreateCast(Instruction::ZExt,
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ShortQuotientV,
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Dividend->getType());
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Value *FastRemainderV = FastBuilder.CreateCast(Instruction::ZExt,
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ShortRemainderV,
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Dividend->getType());
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FastBuilder.CreateBr(SuccessorBB);
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// Phi nodes for result of div and rem
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IRBuilder<> SuccessorBuilder(SuccessorBB, SuccessorBB->begin());
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PHINode *QuoPhi = SuccessorBuilder.CreatePHI(Instr->getType(), 2);
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QuoPhi->addIncoming(SlowQuotientV, SlowBB);
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QuoPhi->addIncoming(FastQuotientV, FastBB);
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PHINode *RemPhi = SuccessorBuilder.CreatePHI(Instr->getType(), 2);
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RemPhi->addIncoming(SlowRemainderV, SlowBB);
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RemPhi->addIncoming(FastRemainderV, FastBB);
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// Replace Instr with appropriate phi node
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if (UseDivOp)
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Instr->replaceAllUsesWith(QuoPhi);
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else
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Instr->replaceAllUsesWith(RemPhi);
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Instr->eraseFromParent();
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// Combine operands into a single value with OR for value testing below
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MainBB->getInstList().back().eraseFromParent();
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IRBuilder<> MainBuilder(MainBB, MainBB->end());
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Value *OrV = MainBuilder.CreateOr(Dividend, Divisor);
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// BitMask is inverted to check if the operands are
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// larger than the bypass type
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uint64_t BitMask = ~BypassType->getBitMask();
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Value *AndV = MainBuilder.CreateAnd(OrV, BitMask);
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// Compare operand values and branch
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Value *ZeroV = MainBuilder.getInt32(0);
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Value *CmpV = MainBuilder.CreateICmpEQ(AndV, ZeroV);
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MainBuilder.CreateCondBr(CmpV, FastBB, SlowBB);
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// point iterator J at first instruction of successorBB
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J = I->begin();
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// Cache phi nodes to be used later in place of other instances
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// of div or rem with the same sign, dividend, and divisor
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DivOpInfo Key(UseSignedOp, Dividend, Divisor);
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DivPhiNodes Value(QuoPhi, RemPhi);
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PerBBDivCache.insert(std::pair<DivOpInfo, DivPhiNodes>(Key, Value));
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return true;
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}
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// reuseOrInsertFastDiv - Reuses previously computed dividend or remainder if
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// operands and operation are identical. Otherwise call insertFastDiv to perform
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// the optimization and cache the resulting dividend and remainder.
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static bool reuseOrInsertFastDiv(Function &F,
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Function::iterator &I,
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BasicBlock::iterator &J,
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IntegerType *BypassType,
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bool UseDivOp,
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bool UseSignedOp,
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DivCacheTy &PerBBDivCache) {
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// Get instruction operands
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Instruction *Instr = J;
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DivOpInfo Key(UseSignedOp, Instr->getOperand(0), Instr->getOperand(1));
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DivCacheTy::iterator CacheI = PerBBDivCache.find(Key);
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if (CacheI == PerBBDivCache.end()) {
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// If previous instance does not exist, insert fast div
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return insertFastDiv(F, I, J, BypassType, UseDivOp, UseSignedOp,
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PerBBDivCache);
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}
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// Replace operation value with previously generated phi node
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DivPhiNodes &Value = CacheI->second;
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if (UseDivOp) {
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// Replace all uses of div instruction with quotient phi node
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J->replaceAllUsesWith(Value.Quotient);
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} else {
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// Replace all uses of rem instruction with remainder phi node
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J->replaceAllUsesWith(Value.Remainder);
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}
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// Advance to next operation
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++J;
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// Remove redundant operation
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Instr->eraseFromParent();
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return true;
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}
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// bypassSlowDivision - This optimization identifies DIV instructions that can
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// be profitably bypassed and carried out with a shorter, faster divide.
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bool llvm::bypassSlowDivision(Function &F,
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Function::iterator &I,
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const DenseMap<unsigned int, unsigned int> &BypassWidths) {
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DivCacheTy DivCache;
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bool MadeChange = false;
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for (BasicBlock::iterator J = I->begin(); J != I->end(); J++) {
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// Get instruction details
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unsigned Opcode = J->getOpcode();
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bool UseDivOp = Opcode == Instruction::SDiv || Opcode == Instruction::UDiv;
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bool UseRemOp = Opcode == Instruction::SRem || Opcode == Instruction::URem;
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bool UseSignedOp = Opcode == Instruction::SDiv ||
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Opcode == Instruction::SRem;
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// Only optimize div or rem ops
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if (!UseDivOp && !UseRemOp)
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continue;
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// Skip division on vector types, only optimize integer instructions
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if (!J->getType()->isIntegerTy())
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continue;
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// Get bitwidth of div/rem instruction
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IntegerType *T = cast<IntegerType>(J->getType());
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int bitwidth = T->getBitWidth();
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// Continue if bitwidth is not bypassed
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DenseMap<unsigned int, unsigned int>::const_iterator BI = BypassWidths.find(bitwidth);
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if (BI == BypassWidths.end())
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continue;
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// Get type for div/rem instruction with bypass bitwidth
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IntegerType *BT = IntegerType::get(J->getContext(), BI->second);
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MadeChange |= reuseOrInsertFastDiv(F, I, J, BT, UseDivOp,
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UseSignedOp, DivCache);
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}
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return MadeChange;
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}
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