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fix a miscompilation of: 

define i32 @test(i32 %X) {
entry:
        %Y = and i32 %X, 4              ; <i32> [#uses=1]
        icmp eq i32 %Y, 0               ; <i1>:0 [#uses=1]
        sext i1 %0 to i32               ; <i32>:1 [#uses=1]
        ret i32 %1
}

by moving code out of commonIntCastTransforms into visitZExt.  Simplify the
APInt gymnastics in it etc.

llvm-svn: 35885
This commit is contained in:
Chris Lattner 2007-04-11 05:45:39 +00:00
parent a6aa0319f1
commit 7ddbff090a
1 changed files with 59 additions and 63 deletions
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122
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -6457,69 +6457,6 @@ Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
}
}
break;
case Instruction::ICmp:
// If we are just checking for a icmp eq of a single bit and casting it
// to an integer, then shift the bit to the appropriate place and then
// cast to integer to avoid the comparison.
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
const APInt& Op1CV = Op1C->getValue();
// cast (X == 0) to int --> X^1 iff X has only the low bit set.
// cast (X == 0) to int --> (X>>1)^1 iff X has only the 2nd bit set.
// cast (X == 1) to int --> X iff X has only the low bit set.
// cast (X == 2) to int --> X>>1 iff X has only the 2nd bit set.
// cast (X != 0) to int --> X iff X has only the low bit set.
// cast (X != 0) to int --> X>>1 iff X has only the 2nd bit set.
// cast (X != 1) to int --> X^1 iff X has only the low bit set.
// cast (X != 2) to int --> (X>>1)^1 iff X has only the 2nd bit set.
if (Op1CV == 0 || Op1CV.isPowerOf2()) {
// If Op1C some other power of two, convert:
uint32_t BitWidth = Op1C->getType()->getBitWidth();
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
APInt TypeMask(APInt::getAllOnesValue(BitWidth));
ComputeMaskedBits(Op0, TypeMask, KnownZero, KnownOne);
// This only works for EQ and NE
ICmpInst::Predicate pred = cast<ICmpInst>(SrcI)->getPredicate();
if (pred != ICmpInst::ICMP_NE && pred != ICmpInst::ICMP_EQ)
break;
APInt KnownZeroMask(KnownZero ^ TypeMask);
if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
bool isNE = pred == ICmpInst::ICMP_NE;
if (Op1CV != 0 && (Op1CV != KnownZeroMask)) {
// (X&4) == 2 --> false
// (X&4) != 2 --> true
Constant *Res = ConstantInt::get(Type::Int1Ty, isNE);
Res = ConstantExpr::getZExt(Res, CI.getType());
return ReplaceInstUsesWith(CI, Res);
}
uint32_t ShiftAmt = KnownZeroMask.logBase2();
Value *In = Op0;
if (ShiftAmt) {
// Perform a logical shr by shiftamt.
// Insert the shift to put the result in the low bit.
In = InsertNewInstBefore(
BinaryOperator::createLShr(In,
ConstantInt::get(In->getType(), ShiftAmt),
In->getName()+".lobit"), CI);
}
if ((Op1CV != 0) == isNE) { // Toggle the low bit.
Constant *One = ConstantInt::get(In->getType(), 1);
In = BinaryOperator::createXor(In, One, "tmp");
InsertNewInstBefore(cast<Instruction>(In), CI);
}
if (CI.getType() == In->getType())
return ReplaceInstUsesWith(CI, In);
else
return CastInst::createIntegerCast(In, CI.getType(), false/*ZExt*/);
}
}
}
break;
}
return 0;
}
@ -6617,6 +6554,65 @@ Instruction *InstCombiner::visitZExt(CastInst &CI) {
}
}
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src)) {
// If we are just checking for a icmp eq of a single bit and zext'ing it
// to an integer, then shift the bit to the appropriate place and then
// cast to integer to avoid the comparison.
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
const APInt& Op1CV = Op1C->getValue();
// cast (X == 0) to int --> X^1 iff X has only the low bit set.
// cast (X == 0) to int --> (X>>1)^1 iff X has only the 2nd bit set.
// cast (X == 1) to int --> X iff X has only the low bit set.
// cast (X == 2) to int --> X>>1 iff X has only the 2nd bit set.
// cast (X != 0) to int --> X iff X has only the low bit set.
// cast (X != 0) to int --> X>>1 iff X has only the 2nd bit set.
// cast (X != 1) to int --> X^1 iff X has only the low bit set.
// cast (X != 2) to int --> (X>>1)^1 iff X has only the 2nd bit set.
if ((Op1CV == 0 || Op1CV.isPowerOf2()) &&
// This only works for EQ and NE
ICI->isEquality()) {
// If Op1C some other power of two, convert:
uint32_t BitWidth = Op1C->getType()->getBitWidth();
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
APInt TypeMask(APInt::getAllOnesValue(BitWidth));
ComputeMaskedBits(ICI->getOperand(0), TypeMask, KnownZero, KnownOne);
APInt KnownZeroMask(~KnownZero);
if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE;
if (Op1CV != 0 && (Op1CV != KnownZeroMask)) {
// (X&4) == 2 --> false
// (X&4) != 2 --> true
Constant *Res = ConstantInt::get(Type::Int1Ty, isNE);
Res = ConstantExpr::getZExt(Res, CI.getType());
return ReplaceInstUsesWith(CI, Res);
}
uint32_t ShiftAmt = KnownZeroMask.logBase2();
Value *In = ICI->getOperand(0);
if (ShiftAmt) {
// Perform a logical shr by shiftamt.
// Insert the shift to put the result in the low bit.
In = InsertNewInstBefore(
BinaryOperator::createLShr(In,
ConstantInt::get(In->getType(), ShiftAmt),
In->getName()+".lobit"), CI);
}
if ((Op1CV != 0) == isNE) { // Toggle the low bit.
Constant *One = ConstantInt::get(In->getType(), 1);
In = BinaryOperator::createXor(In, One, "tmp");
InsertNewInstBefore(cast<Instruction>(In), CI);
}
if (CI.getType() == In->getType())
return ReplaceInstUsesWith(CI, In);
else
return CastInst::createIntegerCast(In, CI.getType(), false/*ZExt*/);
}
}
}
}
return 0;
}