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Simplify some comparisons to arithmetic, this implements:

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Transforms/InstCombine/icmp.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35890 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-04-11 06:53:04 +00:00
parent f6e166b386
commit a2e2c9bbf3
1 changed files with 27 additions and 0 deletions
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27
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -6570,6 +6570,33 @@ Instruction *InstCombiner::visitZExt(CastInst &CI) {
// cast to integer to avoid the comparison.
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
const APInt &Op1CV = Op1C->getValue();
// zext (x <s 0) to i32 --> x>>u31 true if signbit set.
// zext (x >s -1) to i32 --> (x>>u31)^1 true if signbit clear.
if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV == 0) ||
(ICI->getPredicate() == ICmpInst::ICMP_SGT &&Op1CV.isAllOnesValue())){
Value *In = ICI->getOperand(0);
Value *Sh = ConstantInt::get(In->getType(),
In->getType()->getPrimitiveSizeInBits()-1);
In = InsertNewInstBefore(BinaryOperator::createLShr(In, Sh,
In->getName()+".lobit"),
CI);
if (In->getType() != CI.getType())
In = CastInst::createIntegerCast(In, CI.getType(),
false/*ZExt*/, "tmp", &CI);
if (ICI->getPredicate() == ICmpInst::ICMP_SGT) {
Constant *One = ConstantInt::get(In->getType(), 1);
In = InsertNewInstBefore(BinaryOperator::createXor(In, One,
In->getName()+".not"),
CI);
}
return ReplaceInstUsesWith(CI, In);
}
// zext (X == 0) to i32 --> X^1 iff X has only the low bit set.
// zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
// zext (X == 1) to i32 --> X iff X has only the low bit set.