[llvm] 01a6c4b - [InstCombine] (-NSW x) s< x --> x s> 0 (PR39480)

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2020-08-06T11:50:35+03:00
New Revision: 01a6c4bd26a599e877301568f77eb835d0a6e812

URL: https://github.com/llvm/llvm-project/commit/01a6c4bd26a599e877301568f77eb835d0a6e812
DIFF: https://github.com/llvm/llvm-project/commit/01a6c4bd26a599e877301568f77eb835d0a6e812.diff

LOG: [InstCombine] (-NSW x) s< x  --> x s> 0  (PR39480)

Name: (-x) s< x  -->  x > 0
%neg_x = sub nsw i8 0, %x ; %x must not be INT_MIN
%r = icmp slt i8 %neg_x, %x
  =>
%r = icmp sgt i8 %x, 0

https://rise4fun.com/Alive/3IXb

https://bugs.llvm.org/show_bug.cgi?id=39480

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 13dacd4b0bf3..0a8ed3c198c8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3738,6 +3738,11 @@ Instruction *foldICmpXNegX(ICmpInst &I) {
     NewRHS = Constant::getNullValue(X->getType());
     break;
 
+  case ICmpInst::ICMP_SLT:
+    NewPred = ICmpInst::ICMP_SGT;
+    NewRHS = Constant::getNullValue(X->getType());
+    break;
+
   case ICmpInst::ICMP_EQ:
   case ICmpInst::ICMP_NE:
     NewPred = Pred;

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 0a557a81fa0d..9a32a24d1b1c 100644
--- a/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll
+++ b/llvm/test/Transforms/InstCombine/cmp-x-vs-neg-x.ll
@@ -51,8 +51,7 @@ define i1 @t1(i8 %x) {
 
 define i1 @t2(i8 %x) {
 ; CHECK-LABEL: @t2(
-; CHECK-NEXT:    [[NEG_X:%.*]] = sub nsw i8 0, [[X:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[NEG_X]], [[X]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %neg_x = sub nsw i8 0, %x