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InstCombine: Optimize -x s< cst

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Summary:
This gets rid of a sub instruction by moving the negation to the
constant when valid.

Reviewers: nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3773

llvm-svn: 208827
This commit is contained in:
David Majnemer 2014-05-15 00:02:20 +00:00
parent 071f1f0679
commit 809b8a331d
2 changed files with 19 additions and 0 deletions
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10
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2971,6 +2971,16 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
BO0->hasOneUse() && BO1->hasOneUse())
return new ICmpInst(Pred, D, B);
// icmp (0-X) < cst --> x > -cst
if (NoOp0WrapProblem && ICmpInst::isSigned(Pred)) {
Value *X;
if (match(BO0, m_Neg(m_Value(X))))
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1))
if (!RHSC->isMinValue(/*isSigned=*/true))
return new ICmpInst(I.getSwappedPredicate(), X,
ConstantExpr::getNeg(RHSC));
}
BinaryOperator *SRem = nullptr;
// icmp (srem X, Y), Y
if (BO0 && BO0->getOpcode() == Instruction::SRem &&

9
test/Transforms/InstCombine/icmp.ll
View File

@ -1356,3 +1356,12 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32 %b) nounwind {
%z = icmp ne i32 %x, %y
ret i1 %z
}
; CHECK-LABEL: @icmp_neg_cst_slt
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp sgt i32 %a, 10
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_neg_cst_slt(i32 %a) {
%1 = sub nsw i32 0, %a
%2 = icmp slt i32 %1, -10
ret i1 %2
}