[PATCH] D142867: [Clang] Add machinery to catch overflow in unary minus outside of a constant expression context

[Hubert Tong via Phabricator via cfe-commits]

hubert.reinterpretcast added a comment.

In D142867#4108079 <https://reviews.llvm.org/D142867#4108079>, @eaeltsin wrote:

> The warning now fires even if overflow is prevented with `if constexpr`:
>
>   if constexpr (width <= 64) {
>     if constexpr (width == 64) {
>       return 1;
>     }
>     return -static_cast<int64_t>(uint64_t{1} << (width - 1));
>   }
>
> https://godbolt.org/z/M3xdcKd3M

For reference, actually placing the second return into an `else` block (thus making it a discarded statement) does suppress the diagnostic:
https://godbolt.org/z/Kb6Md5PrK

I also question the focus on `if constexpr`. Replacing with `if (true) { return 1; }` should be as effective in the non-`else`-block case in suppressing the warning in terms of QoI.


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  https://reviews.llvm.org/D142867/new/

https://reviews.llvm.org/D142867