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300 lines
11 KiB
C++
300 lines
11 KiB
C++
//===- LoopVR.cpp - Value Range analysis driven by loop information -------===//
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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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// FIXME: What does this do?
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loopvr"
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#include "llvm/Analysis/LoopVR.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Assembly/Writer.h"
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#include "llvm/Support/CFG.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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char LoopVR::ID = 0;
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static RegisterPass<LoopVR> X("loopvr", "Loop Value Ranges", false, true);
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/// getRange - determine the range for a particular SCEV within a given Loop
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ConstantRange LoopVR::getRange(const SCEV *S, Loop *L, ScalarEvolution &SE) {
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const SCEV *T = SE.getBackedgeTakenCount(L);
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if (isa<SCEVCouldNotCompute>(T))
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return ConstantRange(cast<IntegerType>(S->getType())->getBitWidth(), true);
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T = SE.getTruncateOrZeroExtend(T, S->getType());
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return getRange(S, T, SE);
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}
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/// getRange - determine the range for a particular SCEV with a given trip count
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ConstantRange LoopVR::getRange(const SCEV *S, const SCEV *T, ScalarEvolution &SE){
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if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
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return ConstantRange(C->getValue()->getValue());
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ConstantRange FullSet(cast<IntegerType>(S->getType())->getBitWidth(), true);
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// {x,+,y,+,...z}. We detect overflow by checking the size of the set after
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// summing the upper and lower.
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if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
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ConstantRange X = getRange(Add->getOperand(0), T, SE);
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if (X.isFullSet()) return FullSet;
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for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i) {
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ConstantRange Y = getRange(Add->getOperand(i), T, SE);
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if (Y.isFullSet()) return FullSet;
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APInt Spread_X = X.getSetSize(), Spread_Y = Y.getSetSize();
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APInt NewLower = X.getLower() + Y.getLower();
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APInt NewUpper = X.getUpper() + Y.getUpper() - 1;
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if (NewLower == NewUpper)
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return FullSet;
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X = ConstantRange(NewLower, NewUpper);
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if (X.getSetSize().ult(Spread_X) || X.getSetSize().ult(Spread_Y))
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return FullSet; // we've wrapped, therefore, full set.
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}
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return X;
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}
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// {x,*,y,*,...,z}. In order to detect overflow, we use k*bitwidth where
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// k is the number of terms being multiplied.
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if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
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ConstantRange X = getRange(Mul->getOperand(0), T, SE);
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if (X.isFullSet()) return FullSet;
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const IntegerType *Ty = Context->getIntegerType(X.getBitWidth());
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const IntegerType *ExTy = Context->getIntegerType(X.getBitWidth() *
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Mul->getNumOperands());
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ConstantRange XExt = X.zeroExtend(ExTy->getBitWidth());
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for (unsigned i = 1, e = Mul->getNumOperands(); i != e; ++i) {
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ConstantRange Y = getRange(Mul->getOperand(i), T, SE);
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if (Y.isFullSet()) return FullSet;
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ConstantRange YExt = Y.zeroExtend(ExTy->getBitWidth());
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XExt = ConstantRange(XExt.getLower() * YExt.getLower(),
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((XExt.getUpper()-1) * (YExt.getUpper()-1)) + 1);
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}
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return XExt.truncate(Ty->getBitWidth());
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}
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// X smax Y smax ... Z is: range(smax(X_smin, Y_smin, ..., Z_smin),
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// smax(X_smax, Y_smax, ..., Z_smax))
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// It doesn't matter if one of the SCEVs has FullSet because we're taking
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// a maximum of the minimums across all of them.
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if (const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(S)) {
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ConstantRange X = getRange(SMax->getOperand(0), T, SE);
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if (X.isFullSet()) return FullSet;
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APInt smin = X.getSignedMin(), smax = X.getSignedMax();
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for (unsigned i = 1, e = SMax->getNumOperands(); i != e; ++i) {
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ConstantRange Y = getRange(SMax->getOperand(i), T, SE);
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smin = APIntOps::smax(smin, Y.getSignedMin());
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smax = APIntOps::smax(smax, Y.getSignedMax());
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}
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if (smax + 1 == smin) return FullSet;
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return ConstantRange(smin, smax + 1);
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}
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// X umax Y umax ... Z is: range(umax(X_umin, Y_umin, ..., Z_umin),
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// umax(X_umax, Y_umax, ..., Z_umax))
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// It doesn't matter if one of the SCEVs has FullSet because we're taking
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// a maximum of the minimums across all of them.
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if (const SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(S)) {
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ConstantRange X = getRange(UMax->getOperand(0), T, SE);
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if (X.isFullSet()) return FullSet;
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APInt umin = X.getUnsignedMin(), umax = X.getUnsignedMax();
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for (unsigned i = 1, e = UMax->getNumOperands(); i != e; ++i) {
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ConstantRange Y = getRange(UMax->getOperand(i), T, SE);
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umin = APIntOps::umax(umin, Y.getUnsignedMin());
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umax = APIntOps::umax(umax, Y.getUnsignedMax());
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}
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if (umax + 1 == umin) return FullSet;
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return ConstantRange(umin, umax + 1);
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}
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// L udiv R. Luckily, there's only ever 2 sides to a udiv.
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if (const SCEVUDivExpr *UDiv = dyn_cast<SCEVUDivExpr>(S)) {
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ConstantRange L = getRange(UDiv->getLHS(), T, SE);
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ConstantRange R = getRange(UDiv->getRHS(), T, SE);
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if (L.isFullSet() && R.isFullSet()) return FullSet;
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if (R.getUnsignedMax() == 0) {
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// RHS must be single-element zero. Return an empty set.
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return ConstantRange(R.getBitWidth(), false);
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}
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APInt Lower = L.getUnsignedMin().udiv(R.getUnsignedMax());
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APInt Upper;
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if (R.getUnsignedMin() == 0) {
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// Just because it contains zero, doesn't mean it will also contain one.
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// Use maximalIntersectWith to get the right behaviour.
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ConstantRange NotZero(APInt(L.getBitWidth(), 1),
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APInt::getNullValue(L.getBitWidth()));
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R = R.maximalIntersectWith(NotZero);
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}
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// But, the maximal intersection might still include zero. If it does, then
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// we know it also included one.
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if (R.contains(APInt::getNullValue(L.getBitWidth())))
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Upper = L.getUnsignedMax();
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else
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Upper = L.getUnsignedMax().udiv(R.getUnsignedMin());
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return ConstantRange(Lower, Upper);
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}
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// ConstantRange already implements the cast operators.
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if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S)) {
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T = SE.getTruncateOrZeroExtend(T, ZExt->getOperand()->getType());
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ConstantRange X = getRange(ZExt->getOperand(), T, SE);
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return X.zeroExtend(cast<IntegerType>(ZExt->getType())->getBitWidth());
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}
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if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S)) {
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T = SE.getTruncateOrZeroExtend(T, SExt->getOperand()->getType());
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ConstantRange X = getRange(SExt->getOperand(), T, SE);
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return X.signExtend(cast<IntegerType>(SExt->getType())->getBitWidth());
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}
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if (const SCEVTruncateExpr *Trunc = dyn_cast<SCEVTruncateExpr>(S)) {
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T = SE.getTruncateOrZeroExtend(T, Trunc->getOperand()->getType());
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ConstantRange X = getRange(Trunc->getOperand(), T, SE);
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if (X.isFullSet()) return FullSet;
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return X.truncate(cast<IntegerType>(Trunc->getType())->getBitWidth());
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}
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if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
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const SCEVConstant *Trip = dyn_cast<SCEVConstant>(T);
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if (!Trip) return FullSet;
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if (AddRec->isAffine()) {
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const SCEV *StartHandle = AddRec->getStart();
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const SCEV *StepHandle = AddRec->getOperand(1);
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const SCEVConstant *Step = dyn_cast<SCEVConstant>(StepHandle);
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if (!Step) return FullSet;
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uint32_t ExWidth = 2 * Trip->getValue()->getBitWidth();
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APInt TripExt = Trip->getValue()->getValue(); TripExt.zext(ExWidth);
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APInt StepExt = Step->getValue()->getValue(); StepExt.zext(ExWidth);
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if ((TripExt * StepExt).ugt(APInt::getLowBitsSet(ExWidth, ExWidth >> 1)))
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return FullSet;
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const SCEV *EndHandle = SE.getAddExpr(StartHandle,
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SE.getMulExpr(T, StepHandle));
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const SCEVConstant *Start = dyn_cast<SCEVConstant>(StartHandle);
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const SCEVConstant *End = dyn_cast<SCEVConstant>(EndHandle);
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if (!Start || !End) return FullSet;
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const APInt &StartInt = Start->getValue()->getValue();
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const APInt &EndInt = End->getValue()->getValue();
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const APInt &StepInt = Step->getValue()->getValue();
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if (StepInt.isNegative()) {
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if (EndInt == StartInt + 1) return FullSet;
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return ConstantRange(EndInt, StartInt + 1);
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} else {
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if (StartInt == EndInt + 1) return FullSet;
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return ConstantRange(StartInt, EndInt + 1);
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}
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}
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}
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// TODO: non-affine addrec, udiv, SCEVUnknown (narrowed from elsewhere)?
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return FullSet;
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}
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void LoopVR::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredTransitive<LoopInfo>();
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AU.addRequiredTransitive<ScalarEvolution>();
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AU.setPreservesAll();
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}
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bool LoopVR::runOnFunction(Function &F) { Map.clear(); return false; }
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void LoopVR::print(std::ostream &os, const Module *) const {
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raw_os_ostream OS(os);
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for (std::map<Value *, ConstantRange *>::const_iterator I = Map.begin(),
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E = Map.end(); I != E; ++I) {
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OS << *I->first << ": " << *I->second << '\n';
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}
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}
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void LoopVR::releaseMemory() {
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for (std::map<Value *, ConstantRange *>::iterator I = Map.begin(),
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E = Map.end(); I != E; ++I) {
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delete I->second;
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}
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Map.clear();
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}
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ConstantRange LoopVR::compute(Value *V) {
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if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
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return ConstantRange(CI->getValue());
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I)
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return ConstantRange(cast<IntegerType>(V->getType())->getBitWidth(), false);
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LoopInfo &LI = getAnalysis<LoopInfo>();
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Loop *L = LI.getLoopFor(I->getParent());
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if (!L || L->isLoopInvariant(I))
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return ConstantRange(cast<IntegerType>(V->getType())->getBitWidth(), false);
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ScalarEvolution &SE = getAnalysis<ScalarEvolution>();
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const SCEV *S = SE.getSCEV(I);
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if (isa<SCEVUnknown>(S) || isa<SCEVCouldNotCompute>(S))
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return ConstantRange(cast<IntegerType>(V->getType())->getBitWidth(), false);
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return ConstantRange(getRange(S, L, SE));
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}
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ConstantRange LoopVR::get(Value *V) {
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std::map<Value *, ConstantRange *>::iterator I = Map.find(V);
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if (I == Map.end()) {
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ConstantRange *CR = new ConstantRange(compute(V));
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Map[V] = CR;
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return *CR;
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}
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return *I->second;
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}
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void LoopVR::remove(Value *V) {
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std::map<Value *, ConstantRange *>::iterator I = Map.find(V);
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if (I != Map.end()) {
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delete I->second;
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Map.erase(I);
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}
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}
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void LoopVR::narrow(Value *V, const ConstantRange &CR) {
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if (CR.isFullSet()) return;
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std::map<Value *, ConstantRange *>::iterator I = Map.find(V);
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if (I == Map.end())
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Map[V] = new ConstantRange(CR);
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else
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Map[V] = new ConstantRange(Map[V]->maximalIntersectWith(CR));
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}
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