[llvm] r208827 - InstCombine: Optimize -x s< cst
David Majnemer
david.majnemer at gmail.com
Wed May 14 17:02:21 PDT 2014
Author: majnemer
Date: Wed May 14 19:02:20 2014
New Revision: 208827
URL: http://llvm.org/viewvc/llvm-project?rev=208827&view=rev
Log:
InstCombine: Optimize -x s< cst
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
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/trunk/test/Transforms/InstCombine/icmp.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=208827&r1=208826&r2=208827&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Wed May 14 19:02:20 2014
@@ -2971,6 +2971,16 @@ Instruction *InstCombiner::visitICmpInst
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 &&
Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=208827&r1=208826&r2=208827&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Wed May 14 19:02:20 2014
@@ -1356,3 +1356,12 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32
%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
+}
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