[InstCombine] Drop samesign flags in foldLogOpOfMaskedICmps_NotAllZeros_BMask_Mixed

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -464,8 +464,11 @@ static Value *foldLogOpOfMaskedICmps_NotAllZeros_BMask_Mixed(
   // ie. (B & E) != 0, then LHS is subsumed by RHS. For example.
   // (icmp ne (A & 12), 0) & (icmp eq (A & 15), 8) -> (icmp eq (A & 15), 8).
   assert(IsSubSetOrEqual(BCst, DCst) && "Precondition due to above code");
-  if ((*BCst & ECst) != 0)
+  if ((*BCst & ECst) != 0) {
+    // We can't guarantee that samesign hold after this fold.
+    RHS->setSameSign(false);
     return RHS;
+  }
   // Otherwise, LHS and RHS contradict and the whole expression becomes false
   // (or true if negated.) For example,
   // (icmp ne (A & 7), 0) & (icmp eq (A & 15), 8) -> false.

llvm/test/Transforms/InstCombine/icmp-logical.ll

@@ -1915,7 +1915,7 @@ define i1 @pr120361(i8 %x, i8 %y) {
 define i1 @pr120361_v2(i32 %x) {
 ; CHECK-LABEL: @pr120361_v2(
 ; CHECK-NEXT:    [[AND2:%.*]] = and i32 [[X:%.*]], -113
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp samesign eq i32 [[AND2]], 15
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i32 [[AND2]], 15
 ; CHECK-NEXT:    ret i1 [[CMP2]]
 ;
   %and1 = and i32 %x, 15