mirror of
https://github.com/c64scene-ar/llvm-6502.git
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56e1394c88
directory. These passes are already defined in the IR library, and it doesn't make any sense to have the headers in Analysis. Long term, I think there is going to be a much better way to divide these matters. The dominators code should be fully separated into the abstract graph algorithm and have that put in Support where it becomes obvious that evn Clang's CFGBlock's can use it. Then the verifier can manually construct dominance information from the Support-driven interface while the Analysis library can provide a pass which both caches, reconstructs, and supports a nice update API. But those are very long term, and so I don't want to leave the really confusing structure until that day arrives. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199082 91177308-0d34-0410-b5e6-96231b3b80d8
474 lines
17 KiB
C++
474 lines
17 KiB
C++
//===-- SimplifyIndVar.cpp - Induction variable simplification ------------===//
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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 implements induction variable simplification. It does
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// not define any actual pass or policy, but provides a single function to
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// simplify a loop's induction variables based on ScalarEvolution.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "indvars"
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#include "llvm/Transforms/Utils/SimplifyIndVar.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/IVUsers.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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STATISTIC(NumElimIdentity, "Number of IV identities eliminated");
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STATISTIC(NumElimOperand, "Number of IV operands folded into a use");
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STATISTIC(NumElimRem , "Number of IV remainder operations eliminated");
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STATISTIC(NumElimCmp , "Number of IV comparisons eliminated");
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namespace {
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/// SimplifyIndvar - This is a utility for simplifying induction variables
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/// based on ScalarEvolution. It is the primary instrument of the
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/// IndvarSimplify pass, but it may also be directly invoked to cleanup after
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/// other loop passes that preserve SCEV.
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class SimplifyIndvar {
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Loop *L;
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LoopInfo *LI;
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ScalarEvolution *SE;
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const DataLayout *TD; // May be NULL
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SmallVectorImpl<WeakVH> &DeadInsts;
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bool Changed;
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public:
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SimplifyIndvar(Loop *Loop, ScalarEvolution *SE, LPPassManager *LPM,
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SmallVectorImpl<WeakVH> &Dead, IVUsers *IVU = NULL) :
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L(Loop),
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LI(LPM->getAnalysisIfAvailable<LoopInfo>()),
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SE(SE),
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TD(LPM->getAnalysisIfAvailable<DataLayout>()),
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DeadInsts(Dead),
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Changed(false) {
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assert(LI && "IV simplification requires LoopInfo");
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}
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bool hasChanged() const { return Changed; }
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/// Iteratively perform simplification on a worklist of users of the
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/// specified induction variable. This is the top-level driver that applies
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/// all simplicitions to users of an IV.
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void simplifyUsers(PHINode *CurrIV, IVVisitor *V = NULL);
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Value *foldIVUser(Instruction *UseInst, Instruction *IVOperand);
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bool eliminateIVUser(Instruction *UseInst, Instruction *IVOperand);
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void eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand);
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void eliminateIVRemainder(BinaryOperator *Rem, Value *IVOperand,
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bool IsSigned);
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Instruction *splitOverflowIntrinsic(Instruction *IVUser,
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const DominatorTree *DT);
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};
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}
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/// foldIVUser - Fold an IV operand into its use. This removes increments of an
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/// aligned IV when used by a instruction that ignores the low bits.
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///
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/// IVOperand is guaranteed SCEVable, but UseInst may not be.
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///
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/// Return the operand of IVOperand for this induction variable if IVOperand can
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/// be folded (in case more folding opportunities have been exposed).
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/// Otherwise return null.
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Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand) {
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Value *IVSrc = 0;
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unsigned OperIdx = 0;
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const SCEV *FoldedExpr = 0;
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switch (UseInst->getOpcode()) {
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default:
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return 0;
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case Instruction::UDiv:
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case Instruction::LShr:
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// We're only interested in the case where we know something about
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// the numerator and have a constant denominator.
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if (IVOperand != UseInst->getOperand(OperIdx) ||
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!isa<ConstantInt>(UseInst->getOperand(1)))
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return 0;
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// Attempt to fold a binary operator with constant operand.
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// e.g. ((I + 1) >> 2) => I >> 2
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if (!isa<BinaryOperator>(IVOperand)
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|| !isa<ConstantInt>(IVOperand->getOperand(1)))
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return 0;
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IVSrc = IVOperand->getOperand(0);
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// IVSrc must be the (SCEVable) IV, since the other operand is const.
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assert(SE->isSCEVable(IVSrc->getType()) && "Expect SCEVable IV operand");
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ConstantInt *D = cast<ConstantInt>(UseInst->getOperand(1));
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if (UseInst->getOpcode() == Instruction::LShr) {
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// Get a constant for the divisor. See createSCEV.
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uint32_t BitWidth = cast<IntegerType>(UseInst->getType())->getBitWidth();
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if (D->getValue().uge(BitWidth))
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return 0;
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D = ConstantInt::get(UseInst->getContext(),
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APInt::getOneBitSet(BitWidth, D->getZExtValue()));
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}
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FoldedExpr = SE->getUDivExpr(SE->getSCEV(IVSrc), SE->getSCEV(D));
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}
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// We have something that might fold it's operand. Compare SCEVs.
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if (!SE->isSCEVable(UseInst->getType()))
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return 0;
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// Bypass the operand if SCEV can prove it has no effect.
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if (SE->getSCEV(UseInst) != FoldedExpr)
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return 0;
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DEBUG(dbgs() << "INDVARS: Eliminated IV operand: " << *IVOperand
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<< " -> " << *UseInst << '\n');
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UseInst->setOperand(OperIdx, IVSrc);
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assert(SE->getSCEV(UseInst) == FoldedExpr && "bad SCEV with folded oper");
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++NumElimOperand;
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Changed = true;
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if (IVOperand->use_empty())
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DeadInsts.push_back(IVOperand);
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return IVSrc;
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}
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/// eliminateIVComparison - SimplifyIVUsers helper for eliminating useless
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/// comparisons against an induction variable.
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void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
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unsigned IVOperIdx = 0;
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ICmpInst::Predicate Pred = ICmp->getPredicate();
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if (IVOperand != ICmp->getOperand(0)) {
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// Swapped
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assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand");
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IVOperIdx = 1;
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Pred = ICmpInst::getSwappedPredicate(Pred);
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}
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// Get the SCEVs for the ICmp operands.
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const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx));
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const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx));
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// Simplify unnecessary loops away.
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const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
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S = SE->getSCEVAtScope(S, ICmpLoop);
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X = SE->getSCEVAtScope(X, ICmpLoop);
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// If the condition is always true or always false, replace it with
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// a constant value.
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if (SE->isKnownPredicate(Pred, S, X))
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ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
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else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
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ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
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else
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return;
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DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
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++NumElimCmp;
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Changed = true;
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DeadInsts.push_back(ICmp);
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}
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/// eliminateIVRemainder - SimplifyIVUsers helper for eliminating useless
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/// remainder operations operating on an induction variable.
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void SimplifyIndvar::eliminateIVRemainder(BinaryOperator *Rem,
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Value *IVOperand,
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bool IsSigned) {
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// We're only interested in the case where we know something about
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// the numerator.
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if (IVOperand != Rem->getOperand(0))
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return;
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// Get the SCEVs for the ICmp operands.
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const SCEV *S = SE->getSCEV(Rem->getOperand(0));
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const SCEV *X = SE->getSCEV(Rem->getOperand(1));
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// Simplify unnecessary loops away.
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const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
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S = SE->getSCEVAtScope(S, ICmpLoop);
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X = SE->getSCEVAtScope(X, ICmpLoop);
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// i % n --> i if i is in [0,n).
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if ((!IsSigned || SE->isKnownNonNegative(S)) &&
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SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
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S, X))
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Rem->replaceAllUsesWith(Rem->getOperand(0));
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else {
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// (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
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const SCEV *LessOne =
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SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1));
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if (IsSigned && !SE->isKnownNonNegative(LessOne))
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return;
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if (!SE->isKnownPredicate(IsSigned ?
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ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
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LessOne, X))
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return;
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ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
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Rem->getOperand(0), Rem->getOperand(1));
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SelectInst *Sel =
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SelectInst::Create(ICmp,
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ConstantInt::get(Rem->getType(), 0),
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Rem->getOperand(0), "tmp", Rem);
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Rem->replaceAllUsesWith(Sel);
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}
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DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
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++NumElimRem;
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Changed = true;
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DeadInsts.push_back(Rem);
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}
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/// eliminateIVUser - Eliminate an operation that consumes a simple IV and has
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/// no observable side-effect given the range of IV values.
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/// IVOperand is guaranteed SCEVable, but UseInst may not be.
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bool SimplifyIndvar::eliminateIVUser(Instruction *UseInst,
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Instruction *IVOperand) {
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if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) {
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eliminateIVComparison(ICmp, IVOperand);
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return true;
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}
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if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) {
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bool IsSigned = Rem->getOpcode() == Instruction::SRem;
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if (IsSigned || Rem->getOpcode() == Instruction::URem) {
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eliminateIVRemainder(Rem, IVOperand, IsSigned);
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return true;
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}
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}
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// Eliminate any operation that SCEV can prove is an identity function.
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if (!SE->isSCEVable(UseInst->getType()) ||
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(UseInst->getType() != IVOperand->getType()) ||
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(SE->getSCEV(UseInst) != SE->getSCEV(IVOperand)))
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return false;
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DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n');
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UseInst->replaceAllUsesWith(IVOperand);
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++NumElimIdentity;
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Changed = true;
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DeadInsts.push_back(UseInst);
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return true;
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}
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/// \brief Split sadd.with.overflow into add + sadd.with.overflow to allow
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/// analysis and optimization.
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///
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/// \return A new value representing the non-overflowing add if possible,
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/// otherwise return the original value.
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Instruction *SimplifyIndvar::splitOverflowIntrinsic(Instruction *IVUser,
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const DominatorTree *DT) {
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IntrinsicInst *II = dyn_cast<IntrinsicInst>(IVUser);
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if (!II || II->getIntrinsicID() != Intrinsic::sadd_with_overflow)
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return IVUser;
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// Find a branch guarded by the overflow check.
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BranchInst *Branch = 0;
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Instruction *AddVal = 0;
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for (Value::use_iterator UI = II->use_begin(), E = II->use_end();
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UI != E; ++UI) {
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if (ExtractValueInst *ExtractInst = dyn_cast<ExtractValueInst>(*UI)) {
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if (ExtractInst->getNumIndices() != 1)
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continue;
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if (ExtractInst->getIndices()[0] == 0)
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AddVal = ExtractInst;
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else if (ExtractInst->getIndices()[0] == 1 && ExtractInst->hasOneUse())
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Branch = dyn_cast<BranchInst>(ExtractInst->use_back());
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}
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}
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if (!AddVal || !Branch)
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return IVUser;
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BasicBlock *ContinueBB = Branch->getSuccessor(1);
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if (llvm::next(pred_begin(ContinueBB)) != pred_end(ContinueBB))
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return IVUser;
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// Check if all users of the add are provably NSW.
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bool AllNSW = true;
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for (Value::use_iterator UI = AddVal->use_begin(), E = AddVal->use_end();
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UI != E; ++UI) {
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if (Instruction *UseInst = dyn_cast<Instruction>(*UI)) {
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BasicBlock *UseBB = UseInst->getParent();
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if (PHINode *PHI = dyn_cast<PHINode>(UseInst))
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UseBB = PHI->getIncomingBlock(UI);
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if (!DT->dominates(ContinueBB, UseBB)) {
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AllNSW = false;
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break;
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}
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}
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}
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if (!AllNSW)
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return IVUser;
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// Go for it...
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IRBuilder<> Builder(IVUser);
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Instruction *AddInst = dyn_cast<Instruction>(
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Builder.CreateNSWAdd(II->getOperand(0), II->getOperand(1)));
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// The caller expects the new add to have the same form as the intrinsic. The
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// IV operand position must be the same.
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assert((AddInst->getOpcode() == Instruction::Add &&
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AddInst->getOperand(0) == II->getOperand(0)) &&
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"Bad add instruction created from overflow intrinsic.");
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AddVal->replaceAllUsesWith(AddInst);
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DeadInsts.push_back(AddVal);
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return AddInst;
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}
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/// pushIVUsers - Add all uses of Def to the current IV's worklist.
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///
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static void pushIVUsers(
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Instruction *Def,
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SmallPtrSet<Instruction*,16> &Simplified,
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SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) {
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for (Value::use_iterator UI = Def->use_begin(), E = Def->use_end();
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UI != E; ++UI) {
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Instruction *User = cast<Instruction>(*UI);
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// Avoid infinite or exponential worklist processing.
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// Also ensure unique worklist users.
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// If Def is a LoopPhi, it may not be in the Simplified set, so check for
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// self edges first.
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if (User != Def && Simplified.insert(User))
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SimpleIVUsers.push_back(std::make_pair(User, Def));
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}
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}
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/// isSimpleIVUser - Return true if this instruction generates a simple SCEV
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/// expression in terms of that IV.
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///
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/// This is similar to IVUsers' isInteresting() but processes each instruction
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/// non-recursively when the operand is already known to be a simpleIVUser.
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///
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static bool isSimpleIVUser(Instruction *I, const Loop *L, ScalarEvolution *SE) {
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if (!SE->isSCEVable(I->getType()))
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return false;
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// Get the symbolic expression for this instruction.
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const SCEV *S = SE->getSCEV(I);
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// Only consider affine recurrences.
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const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S);
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if (AR && AR->getLoop() == L)
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return true;
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return false;
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}
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/// simplifyUsers - Iteratively perform simplification on a worklist of users
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/// of the specified induction variable. Each successive simplification may push
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/// more users which may themselves be candidates for simplification.
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///
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/// This algorithm does not require IVUsers analysis. Instead, it simplifies
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/// instructions in-place during analysis. Rather than rewriting induction
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/// variables bottom-up from their users, it transforms a chain of IVUsers
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/// top-down, updating the IR only when it encouters a clear optimization
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/// opportunitiy.
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///
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/// Once DisableIVRewrite is default, LSR will be the only client of IVUsers.
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///
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void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
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if (!SE->isSCEVable(CurrIV->getType()))
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return;
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// Instructions processed by SimplifyIndvar for CurrIV.
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SmallPtrSet<Instruction*,16> Simplified;
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// Use-def pairs if IV users waiting to be processed for CurrIV.
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SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers;
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// Push users of the current LoopPhi. In rare cases, pushIVUsers may be
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// called multiple times for the same LoopPhi. This is the proper thing to
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// do for loop header phis that use each other.
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pushIVUsers(CurrIV, Simplified, SimpleIVUsers);
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while (!SimpleIVUsers.empty()) {
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std::pair<Instruction*, Instruction*> UseOper =
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SimpleIVUsers.pop_back_val();
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Instruction *UseInst = UseOper.first;
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// Bypass back edges to avoid extra work.
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if (UseInst == CurrIV) continue;
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if (V && V->shouldSplitOverflowInstrinsics()) {
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UseInst = splitOverflowIntrinsic(UseInst, V->getDomTree());
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if (!UseInst)
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continue;
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}
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Instruction *IVOperand = UseOper.second;
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for (unsigned N = 0; IVOperand; ++N) {
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assert(N <= Simplified.size() && "runaway iteration");
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Value *NewOper = foldIVUser(UseOper.first, IVOperand);
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if (!NewOper)
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break; // done folding
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IVOperand = dyn_cast<Instruction>(NewOper);
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}
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if (!IVOperand)
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continue;
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if (eliminateIVUser(UseOper.first, IVOperand)) {
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pushIVUsers(IVOperand, Simplified, SimpleIVUsers);
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continue;
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}
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CastInst *Cast = dyn_cast<CastInst>(UseOper.first);
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if (V && Cast) {
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V->visitCast(Cast);
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continue;
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}
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if (isSimpleIVUser(UseOper.first, L, SE)) {
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pushIVUsers(UseOper.first, Simplified, SimpleIVUsers);
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}
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}
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}
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namespace llvm {
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void IVVisitor::anchor() { }
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/// simplifyUsersOfIV - Simplify instructions that use this induction variable
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/// by using ScalarEvolution to analyze the IV's recurrence.
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bool simplifyUsersOfIV(PHINode *CurrIV, ScalarEvolution *SE, LPPassManager *LPM,
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SmallVectorImpl<WeakVH> &Dead, IVVisitor *V)
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{
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LoopInfo *LI = &LPM->getAnalysis<LoopInfo>();
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SimplifyIndvar SIV(LI->getLoopFor(CurrIV->getParent()), SE, LPM, Dead);
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SIV.simplifyUsers(CurrIV, V);
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return SIV.hasChanged();
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}
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/// simplifyLoopIVs - Simplify users of induction variables within this
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/// loop. This does not actually change or add IVs.
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bool simplifyLoopIVs(Loop *L, ScalarEvolution *SE, LPPassManager *LPM,
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SmallVectorImpl<WeakVH> &Dead) {
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bool Changed = false;
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for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) {
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Changed |= simplifyUsersOfIV(cast<PHINode>(I), SE, LPM, Dead);
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}
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return Changed;
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}
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} // namespace llvm
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