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move CannotBeNegativeZero to ValueTracking. Simplify some signbit comparisons.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51864 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-06-02 01:29:46 +00:00
parent 173234a68f
commit 833f25d79e
3 changed files with 59 additions and 54 deletions
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7
include/llvm/Analysis/ValueTracking.h
View File

@ -28,6 +28,9 @@ namespace llvm {
APInt &KnownOne, TargetData *TD = 0,
unsigned Depth = 0);
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. Mask is known to be
/// zero for bits that V cannot have.
bool MaskedValueIsZero(Value *V, const APInt &Mask,
TargetData *TD = 0, unsigned Depth = 0);
@ -43,6 +46,10 @@ namespace llvm {
unsigned ComputeNumSignBits(Value *Op, TargetData *TD = 0,
unsigned Depth = 0);
/// CannotBeNegativeZero - Return true if we can prove that the specified FP
/// value is never equal to -0.0.
///
bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
} // end namespace llvm
#endif

50
lib/Analysis/ValueTracking.cpp
View File

@ -707,3 +707,53 @@ unsigned llvm::ComputeNumSignBits(Value *V, TargetData *TD, unsigned Depth) {
// shifting. We don't want to return '64' as for an i32 "0".
return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
}
/// CannotBeNegativeZero - Return true if we can prove that the specified FP
/// value is never equal to -0.0.
///
/// NOTE: this function will need to be revisited when we support non-default
/// rounding modes!
///
bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegZero();
if (Depth == 6)
return 1; // Limit search depth.
const Instruction *I = dyn_cast<Instruction>(V);
if (I == 0) return false;
// (add x, 0.0) is guaranteed to return +0.0, not -0.0.
if (I->getOpcode() == Instruction::Add &&
isa<ConstantFP>(I->getOperand(1)) &&
cast<ConstantFP>(I->getOperand(1))->isNullValue())
return true;
// sitofp and uitofp turn into +0.0 for zero.
if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
return true;
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
// sqrt(-0.0) = -0.0, no other negative results are possible.
if (II->getIntrinsicID() == Intrinsic::sqrt)
return CannotBeNegativeZero(II->getOperand(1), Depth+1);
if (const CallInst *CI = dyn_cast<CallInst>(I))
if (const Function *F = CI->getCalledFunction()) {
if (F->isDeclaration()) {
switch (F->getNameLen()) {
case 3: // abs(x) != -0.0
if (!strcmp(F->getNameStart(), "abs")) return true;
break;
case 4: // abs[lf](x) != -0.0
if (!strcmp(F->getNameStart(), "absf")) return true;
if (!strcmp(F->getNameStart(), "absl")) return true;
break;
}
}
}
return false;
}

56
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -1839,50 +1839,6 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
}
/// CannotBeNegativeZero - Return true if we can prove that the specified FP
/// value is never equal to -0.0.
///
/// Note that this function will need to be revisited when we support nondefault
/// rounding modes!
///
static bool CannotBeNegativeZero(const Value *V) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegZero();
if (const Instruction *I = dyn_cast<Instruction>(V)) {
// (add x, 0.0) is guaranteed to return +0.0, not -0.0.
if (I->getOpcode() == Instruction::Add &&
isa<ConstantFP>(I->getOperand(1)) &&
cast<ConstantFP>(I->getOperand(1))->isNullValue())
return true;
// sitofp and uitofp turn into +0.0 for zero.
if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
return true;
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
if (II->getIntrinsicID() == Intrinsic::sqrt)
return CannotBeNegativeZero(II->getOperand(1));
if (const CallInst *CI = dyn_cast<CallInst>(I))
if (const Function *F = CI->getCalledFunction()) {
if (F->isDeclaration()) {
switch (F->getNameLen()) {
case 3: // abs(x) != -0.0
if (!strcmp(F->getNameStart(), "abs")) return true;
break;
case 4: // abs[lf](x) != -0.0
if (!strcmp(F->getNameStart(), "absf")) return true;
if (!strcmp(F->getNameStart(), "absl")) return true;
break;
}
}
}
}
return false;
}
/// WillNotOverflowSignedAdd - Return true if we can prove that:
/// (sext (add LHS, RHS)) === (add (sext LHS), (sext RHS))
/// This basically requires proving that the add in the original type would not
@ -2268,13 +2224,6 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
return Changed ? &I : 0;
}
// isSignBit - Return true if the value represented by the constant only has the
// highest order bit set.
static bool isSignBit(ConstantInt *CI) {
uint32_t NumBits = CI->getType()->getPrimitiveSizeInBits();
return CI->getValue() == APInt::getSignBit(NumBits);
}
Instruction *InstCombiner::visitSub(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@ -2460,8 +2409,7 @@ static bool isSignBitCheck(ICmpInst::Predicate pred, ConstantInt *RHS,
case ICmpInst::ICMP_UGE:
// True if LHS u>= RHS and RHS == high-bit-mask (2^7, 2^15, 2^31, etc)
TrueIfSigned = true;
return RHS->getValue() ==
APInt::getSignBit(RHS->getType()->getPrimitiveSizeInBits());
return RHS->getValue().isSignBit();
default:
return false;
}
@ -6124,7 +6072,7 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
Constant::getNullValue(RHS->getType()));
// Replace (and X, (1 << size(X)-1) != 0) with x s< 0
if (isSignBit(BOC)) {
if (BOC->getValue().isSignBit()) {
Value *X = BO->getOperand(0);
Constant *Zero = Constant::getNullValue(X->getType());
ICmpInst::Predicate pred = isICMP_NE ?