[ConstraintElim] Check the other signedness when hasSameSign

Author: citymarina

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -1427,7 +1427,7 @@ static std::optional<bool> checkCondition(CmpInst::Predicate Pred, Value *A,
 }
 
 static bool checkAndReplaceCondition(
-    CmpInst *Cmp, ConstraintInfo &Info, unsigned NumIn, unsigned NumOut,
+    ICmpInst *Cmp, ConstraintInfo &Info, unsigned NumIn, unsigned NumOut,
     Instruction *ContextInst, Module *ReproducerModule,
     ArrayRef<ReproducerEntry> ReproducerCondStack, DominatorTree &DT,
     SmallVectorImpl<Instruction *> &ToRemove) {
@@ -1460,6 +1460,13 @@ static bool checkAndReplaceCondition(
           checkCondition(Cmp->getPredicate(), Cmp->getOperand(0),
                          Cmp->getOperand(1), Cmp, Info))
     return ReplaceCmpWithConstant(Cmp, *ImpliedCondition);
+
+  if (Cmp->hasSameSign())
+    if (auto ImpliedCondition = checkCondition(
+            ICmpInst::getFlippedSignednessPredicate(Cmp->getPredicate()),
+            Cmp->getOperand(0), Cmp->getOperand(1), Cmp, Info))
+      return ReplaceCmpWithConstant(Cmp, *ImpliedCondition);
+
   return false;
 }
 

llvm/test/Transforms/ConstraintElimination/transfer-samesign-facts.ll

@@ -309,8 +309,7 @@ define i1 @samesign_flipped_signedness(i8 %a)  {
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt i8 [[A:%.*]], 0
 ; CHECK-NEXT:    br i1 [[TMP1]], label [[GREATER:%.*]], label [[EXIT:%.*]]
 ; CHECK:       greater:
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp samesign sgt i8 [[A]], 0
-; CHECK-NEXT:    ret i1 [[TMP2]]
+; CHECK-NEXT:    ret i1 true
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret i1 false
 ;