[InstCombine] (-NSW x) u<= x --> x s<=0 (PR39480)

Name: (-x) u<= x --> x s<= 0 %neg_x = sub nsw i8 0, %x ; %x must not be INT_MIN %r = icmp ule i8 %neg_x, %x => %r = icmp sle i8 %x, 0 https://rise4fun.com/Alive/V22 https://bugs.llvm.org/show_bug.cgi?id=39480
llvm · Aug 6, 2020 · 1413576 · 1413576
1 parent 132be1f
commit 1413576
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Showing 2 changed files with 6 additions and 2 deletions.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3763,6 +3763,11 @@ Instruction *foldICmpXNegX(ICmpInst &I) {
     NewRHS = Constant::getNullValue(X->getType());
     break;
 
+  case ICmpInst::ICMP_ULE:
+    NewPred = ICmpInst::ICMP_SLE;
+    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
@@ -101,8 +101,7 @@ define i1 @t6(i8 %x) {
 
 define i1 @t7(i8 %x) {
 ; CHECK-LABEL: @t7(
-; CHECK-NEXT:    [[NEG_X:%.*]] = sub nsw i8 0, [[X:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ule i8 [[NEG_X]], [[X]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 1
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %neg_x = sub nsw i8 0, %x