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[InstCombine] make fold for icmp with sext more efficient; NFC

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We were creating 2 instructions and relying on a subsequent fold
to invert a not(icmp). Create the final icmp directly instead.

llvm-svn: 369411
This commit is contained in:
Sanjay Patel 2019-08-20 17:03:22 +00:00
parent a5daa6c00e
commit af3a0f7768
1 changed files with 7 additions and 13 deletions
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20
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -4128,27 +4128,21 @@ Instruction *InstCombiner::foldICmpWithCastOp(ICmpInst &ICmp) {
// The re-extended constant changed, partly changed (in the case of a vector),
// or could not be determined to be equal (in the case of a constant
// expression), so the constant cannot be represented in the shorter type.
// Consequently, we cannot emit a simple comparison.
// All the cases that fold to true or false will have already been handled
// by SimplifyICmpInst, so only deal with the tricky case.
if (isSignedCmp || !isSignedExt || !isa<ConstantInt>(C))
return nullptr;
// Evaluate the comparison for LT (we invert for GT below). LE and GE cases
// should have been folded away previously and not enter in here.
// We're performing an unsigned comp with a sign extended value.
// This is true if the input is >= 0. [aka >s -1]
Constant *NegOne = Constant::getAllOnesValue(SrcTy);
Value *Result = Builder.CreateICmpSGT(Op0Src, NegOne, ICmp.getName());
// Finally, return the value computed.
// Is source op positive?
// icmp ult (sext X), C --> icmp sgt X, -1
if (ICmp.getPredicate() == ICmpInst::ICMP_ULT)
return replaceInstUsesWith(ICmp, Result);
return new ICmpInst(CmpInst::ICMP_SGT, Op0Src,
Constant::getAllOnesValue(SrcTy));
// Is source op negative?
// icmp ugt (sext X), C --> icmp slt X, 0
assert(ICmp.getPredicate() == ICmpInst::ICMP_UGT && "ICmp should be folded!");
return BinaryOperator::CreateNot(Result);
return new ICmpInst(CmpInst::ICMP_SLT, Op0Src, Constant::getNullValue(SrcTy));
}
static bool isNeutralValue(Instruction::BinaryOps BinaryOp, Value *RHS) {