[InstCombine] Drop samesign in foldLogOpOfMaskedICmps (#125829)

Alive2: https://alive2.llvm.org/ce/z/6zLAYp

Note: We can also apply this fix to the logic below (`if (Mask &
AMask_NotAllOnes)`), but it seems unreachable.

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -610,8 +610,13 @@ static Value *foldLogOpOfMaskedICmps(Value *LHS, Value *RHS, bool IsAnd,
       APInt NewMask = *ConstB & *ConstD;
       if (NewMask == *ConstB)
         return LHS;
-      if (NewMask == *ConstD)
+      if (NewMask == *ConstD) {
+        if (IsLogical) {
+          if (auto *RHSI = dyn_cast<Instruction>(RHS))
+            RHSI->dropPoisonGeneratingFlags();
+        }
         return RHS;
+      }
     }
 
     if (Mask & AMask_NotAllOnes) {

llvm/test/Transforms/InstCombine/sign-test-and-or.ll

@@ -349,6 +349,29 @@ define i1 @test9_logical(i32 %a) {
   ret i1 %or.cond
 }
 
+define i1 @test9_logical_samesign(i32 %a) {
+; CHECK-LABEL: @test9_logical_samesign(
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp sgt i32 [[A:%.*]], -1
+; CHECK-NEXT:    ret i1 [[CMP2]]
+;
+  %masked = and i32 %a, -1073741825
+  %cmp1 = icmp eq i32 %masked, 0
+  %cmp2 = icmp samesign sgt i32 %a, -1
+  %or.cond = select i1 %cmp1, i1 true, i1 %cmp2
+  ret i1 %or.cond
+}
+
+define i1 @test_logical_or_icmp_icmp_samesign(i32 %a) {
+; CHECK-LABEL: @test_logical_or_icmp_icmp_samesign(
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp sgt i32 [[A:%.*]], -1
+; CHECK-NEXT:    ret i1 [[CMP2]]
+;
+  %cmp1 = icmp eq i32 %a, 0
+  %cmp2 = icmp samesign sgt i32 %a, -1
+  %or = select i1 %cmp1, i1 true, i1 %cmp2
+  ret i1 %or
+}
+
 define i1 @test10(i32 %a) {
 ; CHECK-LABEL: @test10(
 ; CHECK-NEXT:    [[OR_COND:%.*]] = icmp ult i32 [[A:%.*]], 2