Sema: show shift result in hexadecimal

Change the output for -Wshift-overflow and
-Wshift-sign-overflow to an unsigned hexadecimal. It makes
more sense for looking at bits than a signed decimal does.
Also, change the diagnostic's wording from "overrides"
to "sets".

This uses a new optional argument in APInt::toString()
that adds the '0x' prefix to hexademical numbers.

This fixes PR 9651.

Patch by nobled@dreamwidth.org!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@133033 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 3 deletions

diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 91821fb4d8..9f9c05244e 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -7394,19 +7394,24 @@ static void DiagnoseBadShiftValues(Sema& S, ExprResult &lex, ExprResult &rex,
   llvm::APSInt Result = Left.extend(ResultBits.getLimitedValue());
   Result = Result.shl(Right);
 
+  // Print the bit representation of the signed integer as an unsigned
+  // hexadecimal number.
+  llvm::SmallString<40> HexResult;
+  Result.toString(HexResult, 16, /*Signed =*/false, /*Literal =*/true);
+
   // If we are only missing a sign bit, this is less likely to result in actual
   // bugs -- if the result is cast back to an unsigned type, it will have the
   // expected value. Thus we place this behind a different warning that can be
   // turned off separately if needed.
   if (LeftBits == ResultBits - 1) {
-    S.Diag(Loc, diag::warn_shift_result_overrides_sign_bit)
-        << Result.toString(10) << LHSTy
+    S.Diag(Loc, diag::warn_shift_result_sets_sign_bit)
+        << HexResult.str() << LHSTy
         << lex.get()->getSourceRange() << rex.get()->getSourceRange();
     return;
   }
 
   S.Diag(Loc, diag::warn_shift_result_gt_typewidth)
-    << Result.toString(10) << Result.getMinSignedBits() << LHSTy
+    << HexResult.str() << Result.getMinSignedBits() << LHSTy
     << Left.getBitWidth() << lex.get()->getSourceRange() << rex.get()->getSourceRange();
 }