From 8878b79cfe99e1ef36a265539329cd323e05a40d Mon Sep 17 00:00:00 2001 From: Roman Lebedev Date: Thu, 6 Aug 2020 11:02:29 +0300 Subject: [PATCH] [InstCombine] (-NSW x) ==/!= x --> x ==/!= 0 (PR39480) Name: (-x) == x --> x == 0 %neg_x = sub nsw i8 0, %x ; %x must not be INT_MIN %r = icmp eq i8 %neg_x, %x => %r = icmp eq i8 %x, 0 Name: (-x) != x --> x != 0 %neg_x = sub nsw i8 0, %x ; %x must not be INT_MIN %r = icmp ne i8 %neg_x, %x => %r = icmp ne i8 %x, 0 https://rise4fun.com/Alive/4slH https://bugs.llvm.org/show_bug.cgi?id=39480 --- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp | 6 ++++++ llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll | 6 ++---- 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp index 0032b65..ce75a36 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -3733,6 +3733,12 @@ Instruction *foldICmpXNegX(ICmpInst &I) { NewRHS = Constant::getNullValue(X->getType()); break; + case ICmpInst::ICMP_EQ: + case ICmpInst::ICMP_NE: + NewPred = Pred; + NewRHS = Constant::getNullValue(X->getType()); + break; + default: return nullptr; } diff --git a/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll b/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll index 485e329..a2e39f1 100644 --- a/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll +++ b/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll @@ -118,8 +118,7 @@ define i1 @t7(i8 %x) { define i1 @t8(i8 %x) { ; CHECK-LABEL: @t8( -; CHECK-NEXT: [[NEG_X:%.*]] = sub nsw i8 0, [[X:%.*]] -; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[NEG_X]], [[X]] +; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], 0 ; CHECK-NEXT: ret i1 [[CMP]] ; %neg_x = sub nsw i8 0, %x @@ -129,8 +128,7 @@ define i1 @t8(i8 %x) { define i1 @t9(i8 %x) { ; CHECK-LABEL: @t9( -; CHECK-NEXT: [[NEG_X:%.*]] = sub nsw i8 0, [[X:%.*]] -; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[NEG_X]], [[X]] +; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], 0 ; CHECK-NEXT: ret i1 [[CMP]] ; %neg_x = sub nsw i8 0, %x -- 2.7.4