[IndVarSimplify] Drop samesame flags after narrowing compares

Author: dtcxzyw

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -1530,6 +1530,8 @@ bool IndVarSimplify::canonicalizeExitCondition(Loop *L) {
           L->getLoopPreheader()->getTerminator()->getIterator());
       ICmp->setOperand(Swapped ? 1 : 0, LHSOp);
       ICmp->setOperand(Swapped ? 0 : 1, NewRHS);
+      // Samesign flag cannot be preserved after narrowing the compare.
+      ICmp->setSameSign(false);
       if (LHS->use_empty())
         DeadInsts.push_back(LHS);
     };

llvm/test/Transforms/IndVarSimplify/finite-exit-comparisons.ll

@@ -1064,7 +1064,7 @@ define i8 @test_drop_icmp_samesign(i1 %cond, i32 range(i32 0, 32) %x) {
 ; CHECK-NEXT:    br label [[EXIT:%.*]]
 ; CHECK:       for.body:
 ; CHECK-NEXT:    [[CALL2:%.*]] = call i8 @callee()
-; CHECK-NEXT:    [[COND2:%.*]] = icmp samesign ugt i8 [[TMP0]], [[CALL2]]
+; CHECK-NEXT:    [[COND2:%.*]] = icmp ugt i8 [[TMP0]], [[CALL2]]
 ; CHECK-NEXT:    br i1 [[COND2]], label [[FOR_BODY]], label [[EXIT_LOOPEXIT:%.*]]
 ; CHECK:       exit.loopexit:
 ; CHECK-NEXT:    [[CALL2_LCSSA:%.*]] = phi i8 [ [[CALL2]], [[FOR_BODY]] ]