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simplify CanEvaluateZExtd now that we don't care about the number of
bits known clear in the result and don't care about the # casts eliminated. TD is also dead but keeping it for now. llvm-svn: 93098
This commit is contained in:
Chris Lattner
parent
1106f03886
commit
7314e76078
@ -575,122 +575,60 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
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return 0;
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}
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/// GetLeadingZeros - Compute the number of known-zero leading bits.
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static unsigned GetLeadingZeros(Value *V, const TargetData *TD) {
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unsigned Bits = V->getType()->getScalarSizeInBits();
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APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
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ComputeMaskedBits(V, APInt::getAllOnesValue(Bits), KnownZero, KnownOne, TD);
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return KnownZero.countLeadingOnes();
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}
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/// CanEvaluateZExtd - Determine if the specified value can be computed in the
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/// specified wider type and produce the same low bits. If not, return -1. If
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/// it is possible, return the number of high bits that are known to be zero in
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/// the promoted value.
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static int CanEvaluateZExtd(Value *V, const Type *Ty,unsigned &NumCastsRemoved,
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const TargetData *TD) {
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const Type *OrigTy = V->getType();
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if (isa<Constant>(V)) {
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unsigned Extended = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits();
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// Constants can always be zero ext'd, even if it requires a ConstantExpr.
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if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
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return Extended + CI->getValue().countLeadingZeros();
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return Extended;
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}
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static bool CanEvaluateZExtd(Value *V, const Type *Ty, const TargetData *TD) {
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if (isa<Constant>(V))
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return true;
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I) return -1;
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if (!I) return false;
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// If the input is a truncate from the destination type, we can trivially
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// eliminate it, and this will remove a cast overall.
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if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty) {
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// If the first operand is itself a cast, and is eliminable, do not count
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// this as an eliminable cast. We would prefer to eliminate those two
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// casts first.
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if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse())
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++NumCastsRemoved;
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// Figure out the number of known-zero bits coming in.
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return GetLeadingZeros(I->getOperand(0), TD);
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}
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// eliminate it.
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if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
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return true;
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// We can't extend or shrink something that has multiple uses: doing so would
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// require duplicating the instruction in general, which isn't profitable.
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if (!I->hasOneUse()) return -1;
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if (!I->hasOneUse()) return false;
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int Tmp1, Tmp2;
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unsigned Opc = I->getOpcode();
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switch (Opc) {
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case Instruction::And:
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Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD);
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if (Tmp1 == -1) return -1;
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Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
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if (Tmp2 == -1) return -1;
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return std::max(Tmp1, Tmp2);
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case Instruction::Or:
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case Instruction::Xor:
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Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD);
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if (Tmp1 == -1) return -1;
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Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
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return std::min(Tmp1, Tmp2);
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case Instruction::Add:
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case Instruction::Sub:
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case Instruction::Mul:
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Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD);
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if (Tmp1 == -1) return -1;
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Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
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if (Tmp2 == -1) return -1;
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return 0; // TODO: Could be improved.
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case Instruction::Shl:
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Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD);
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if (Tmp1 == -1) return -1;
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if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1)))
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return Tmp1 - CI->getZExtValue();
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// Variable shift, no known zext bits.
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Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
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if (Tmp2 == -1) return -1;
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return 0;
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return CanEvaluateZExtd(I->getOperand(0), Ty, TD) &&
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CanEvaluateZExtd(I->getOperand(1), Ty, TD);
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//case Instruction::LShr:
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case Instruction::ZExt:
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// zext(zext(x)) -> zext(x). Since we're replacing it, it isn't eliminated.
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Tmp1 = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits();
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return GetLeadingZeros(I, TD)+Tmp1;
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case Instruction::SExt:
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// zext(sext(x)) -> sext(x) with no upper bits known.
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return 0;
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//case Instruction::Trunc: -> Could turn into AND.
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case Instruction::ZExt: // zext(zext(x)) -> zext(x).
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case Instruction::SExt: // zext(sext(x)) -> sext(x).
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return true;
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case Instruction::Select:
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Tmp1 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
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if (Tmp1 == -1) return -1;
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Tmp2 = CanEvaluateZExtd(I->getOperand(2), Ty, NumCastsRemoved, TD);
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return std::min(Tmp1, Tmp2);
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return CanEvaluateZExtd(I->getOperand(1), Ty, TD) &&
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CanEvaluateZExtd(I->getOperand(2), Ty, TD);
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case Instruction::PHI: {
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// We can change a phi if we can change all operands. Note that we never
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// get into trouble with cyclic PHIs here because we only consider
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// instructions with a single use.
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PHINode *PN = cast<PHINode>(I);
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int Result = CanEvaluateZExtd(PN->getIncomingValue(0), Ty,
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NumCastsRemoved, TD);
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for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
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if (Result == -1) return -1;
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Tmp1 = CanEvaluateZExtd(PN->getIncomingValue(i), Ty, NumCastsRemoved, TD);
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Result = std::min(Result, Tmp1);
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}
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return Result;
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if (!CanEvaluateZExtd(PN->getIncomingValue(0), Ty, TD)) return false;
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for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
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if (!CanEvaluateZExtd(PN->getIncomingValue(0), Ty, TD)) return false;
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return true;
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}
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default:
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// TODO: Can handle more cases here.
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return -1;
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return false;
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}
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}
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@ -716,11 +654,8 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
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// type. Only do this if the dest type is a simple type, don't convert the
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// expression tree to something weird like i93 unless the source is also
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// strange.
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if (isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) {
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unsigned NumCastsRemoved = 0;
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int BitsZExt = CanEvaluateZExtd(Src, DestTy, NumCastsRemoved, TD);
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if (BitsZExt == -1) return 0;
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if ((isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) &&
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CanEvaluateZExtd(Src, DestTy, TD)) {
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// Okay, we can transform this! Insert the new expression now.
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DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
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" to avoid zero extend: " << CI);
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@ -731,8 +666,7 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
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// cast with the result.
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uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
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uint32_t DestBitSize = DestTy->getScalarSizeInBits();
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if (unsigned(BitsZExt) >= DestBitSize-SrcBitSize ||
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MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize,
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if (MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize,
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DestBitSize-SrcBitSize)))
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return ReplaceInstUsesWith(CI, Res);
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