================
@@ -11444,9 +11444,12 @@ static void DiagnoseBadShiftValues(Sema& S, ExprResult
&LHS, ExprResult &RHS,
llvm::APSInt Right = RHSResult.Val.getInt();
if (Right.isNegative()) {
- S.DiagRuntimeBehavior(Loc, RHS.get(),
- S.PDiag(diag::warn_shift_negative)
- << RHS.get()->getSourceRange());
+ if (S.ExprEvalContexts.back().isConstantEvaluated())
+ S.Diag(Loc, diag::warn_shift_negative) << RHS.get()->getSourceRange();
+ else
+ S.DiagRuntimeBehavior(Loc, RHS.get(),
+ S.PDiag(diag::warn_shift_negative)
+ << RHS.get()->getSourceRange());
----------------
tbaederr wrote:
The constant interpreter already diagnoses this:
https://github.com/llvm/llvm-project/blob/51089e360e37962c7841fe0a494ba9fb5368bab2/clang/lib/AST/ExprConstant.cpp#L2850-L2851
and for the test case with the `(-1 << 29)` enum value, this is evaluated in
`Sema::VerifyIntegerConstantExpresssion()` and it's also diagnosed here:
https://github.com/llvm/llvm-project/blob/51089e360e37962c7841fe0a494ba9fb5368bab2/clang/lib/Sema/SemaExpr.cpp#L18158-L18159
But the diagnostic doesn't show up. Not sure why. If I modify the constant
interpreter to `return false` in the negative LHS case, I get the expected
diagnostic:
```console
/home/tbaeder/test.cpp:2:9: error: expression is not an integral constant
expression
2 | X = (-1<<29) // expected-warning {{shifting a negative signed value
is undefined}}
| ^~~~~~~~
/home/tbaeder/test.cpp:2:12: note: left shift of negative value -1
2 | X = (-1<<29) // expected-warning {{shifting a negative signed value
is undefined}}
| ^
```
https://github.com/llvm/llvm-project/pull/70307
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