[llvm-reduce] Reduce samesign flag from icmp (#115492)

Author: dtcxzyw

llvm/test/tools/llvm-reduce/reduce-flags.ll

@@ -272,3 +272,19 @@ define i32 @trunc_nsw_keep(i64 %a) {
   %op = trunc nsw i64 %a to i32
   ret i32 %op
 }
+
+; CHECK-LABEL: @icmp_samesign_drop(
+; INTERESTING: = icmp
+; RESULT: icmp ult i32
+define i1 @icmp_samesign_drop(i32 %a) {
+  %op = icmp samesign ult i32 %a, 10
+  ret i1 %op
+}
+
+; CHECK-LABEL: @icmp_samesign_keep(
+; INTERESTING: = icmp samesign
+; RESULT: icmp samesign ult i32
+define i1 @icmp_samesign_keep(i32 %a) {
+  %op = icmp samesign ult i32 %a, 10
+  ret i1 %op
+}

llvm/tools/llvm-reduce/deltas/ReduceInstructionFlags.cpp

@@ -42,6 +42,9 @@ static void reduceFlagsInModule(Oracle &O, ReducerWorkItem &WorkItem) {
       } else if (auto *PDI = dyn_cast<PossiblyDisjointInst>(&I)) {
         if (PDI->isDisjoint() && !O.shouldKeep())
           PDI->setIsDisjoint(false);
+      } else if (auto *ICmp = dyn_cast<ICmpInst>(&I)) {
+        if (ICmp->hasSameSign() && !O.shouldKeep())
+          ICmp->setSameSign(false);
       } else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
         GEPNoWrapFlags NW = GEP->getNoWrapFlags();
         if (NW.isInBounds() && !O.shouldKeep())