[llvm] [ConstraintElim] Check the other signedness when hasSameSign (PR #128168)

[Ramkumar Ramachandra via llvm-commits]

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@@ -303,3 +303,43 @@ define i1 @ugt_assumed_positive_values(i8 %a, i8 %b) {
 
   ret i1 %result
 }
+
+define i1 @samesign_flipped_signedness_1(i8 %a, i8 %b)  {
+; CHECK-LABEL: @samesign_flipped_signedness_1(
+; CHECK-NEXT:    [[CMP_UGT:%.*]] = icmp ugt i8 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    br i1 [[CMP_UGT]], label [[GREATER:%.*]], label [[EXIT:%.*]]
+; CHECK:       greater:
+; CHECK-NEXT:    ret i1 true
+; CHECK:       exit:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp_ugt = icmp ugt i8 %a, %b
+  br i1 %cmp_ugt, label %greater, label %exit
+
+greater:
+  %cmp_sgt = icmp samesign sgt i8 %a, %b
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artagnon wrote:

Sorry, I think I missed this earlier, but samesign is canonicalized with unsigned predicates.

https://github.com/llvm/llvm-project/pull/128168