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Add transformation:

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xor (or (icmp, icmp), true) -> and(icmp, icmp)

This is possible because of De Morgan's law.

llvm-svn: 61537
This commit is contained in:
Bill Wendling 2009-01-01 01:18:23 +00:00
parent bf9874fd09
commit efbe8b808c
2 changed files with 43 additions and 1 deletions
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33
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -4871,8 +4871,8 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
// xor (cmp A, B), true = not (cmp A, B) = !cmp A, B
if (RHS == ConstantInt::getTrue() && Op0->hasOneUse()) {
// xor (cmp A, B), true = not (cmp A, B) = !cmp A, B
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Op0))
return new ICmpInst(ICI->getInversePredicate(),
ICI->getOperand(0), ICI->getOperand(1));
@ -4880,6 +4880,37 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
if (FCmpInst *FCI = dyn_cast<FCmpInst>(Op0))
return new FCmpInst(FCI->getInversePredicate(),
FCI->getOperand(0), FCI->getOperand(1));
// xor (or (cmp x,m),(cmp y,n)),true --> and (!cmp x,m),(!cmp y,n)
//
// Proof:
// Let A = (cmp x,m)
// Let B = (cmp y,n)
// Let C = (or A, B)
// C true implies that either A, B, or both are true.
//
// (xor C, true) is true only if C is false. We can the apply de
// Morgan's law. QED.
BinaryOperator *Op0I = dyn_cast<BinaryOperator>(Op0);
if (Op0I) {
Value *A, *B;
if (match(Op0I, m_Or(m_Value(A), m_Value(B)))) {
ICmpInst *AOp = dyn_cast<ICmpInst>(A);
ICmpInst *BOp = dyn_cast<ICmpInst>(B);
if (AOp && BOp) {
ICmpInst *NewA = new ICmpInst(AOp->getInversePredicate(),
AOp->getOperand(0),
AOp->getOperand(1));
InsertNewInstBefore(NewA, I);
ICmpInst *NewB = new ICmpInst(BOp->getInversePredicate(),
BOp->getOperand(0),
BOp->getOperand(1));
InsertNewInstBefore(NewB, I);
return BinaryOperator::CreateAnd(NewA, NewB);
}
}
}
}
// fold (xor(zext(cmp)), 1) and (xor(sext(cmp)), -1) to ext(!cmp).

11
test/Transforms/InstCombine/xor-demorgans.ll Normal file
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@ -0,0 +1,11 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep {= or}
; PR3266
define i1 @foo(i32 %x, i32 %y) nounwind {
.summary:
%0 = icmp sgt i32 %x, 4 ; <i1> [#uses=1]
%1 = icmp sgt i32 %y, 0 ; <i1> [#uses=1]
%.demorgan = or i1 %1, %0 ; <i1> [#uses=1]
%2 = xor i1 %.demorgan, true ; <i1> [#uses=1]
ret i1 %2
}