[cfe-users] -Warray-bounds

[David Blaikie via cfe-users]

Supporting the oldest form doesn't seem to be a priority for a warning - if
you have a very old codebase, probably not worth building it with warnings
enabled. Updating code to use more modern/idiomatic forms is within scope
for Clang's warnings, within reason, I think.

- Dave

On Fri, Dec 28, 2018 at 1:26 PM Jay K via cfe-users <
cfe-users at lists.llvm.org> wrote:

> This is an old topic:
>
>
> http://clang-developers.42468.n3.nabble.com/Warray-bounds-seems-over-zealous-on-Clang-td3162669.html
>
> But some points were left not covered.
>
> 1. "code hygiene" I'd say is that, the code should
> just be portable to "all" compilers, and have the same meaning
> with all of them, with a minimum of ifdefs.
>
> 2. Furthermore, regarding "same meaning" to all of them,
> there are these choices:
>
> typedef struct A1 {
>   int a;
>   int b[0];
> } A1;
>
> typedef struct A2 {
>   int a;
>   int b[];
> } A2;
>
> typedef struct A3 {
>   int a;
>   int b[1];
> } A3;
>
> int a1 = sizeof(A1);
> int a2 = sizeof(A2);
> int a3 = sizeof(A3);
>
> They are all valid with clang and probably gcc.
> But they are not likely all valid with additional compilers and through
> time.
> [1] seems like the most portable and oldest form, and might as well just
> keep using it indefinitely.
>
> But it gets a warning.
> If one were to ifdef clang to avoid it, one would lose interopation across
> compilers, as
> the various forms do not have the same meaning.
> Everyone would have to compile with the same compiler/defines.
> Else the types would vary in size.
>
> So I come back to believing that the best choices are either:
>  - do not warn for size=1 at end of aggregate
>  - possibly a separate setting for specifically that
>
> That is what gcc does also it appears (both).
>
> I ran across all this exact situation -- ifdef gnuc/clang in some code,
> with comment that everyone has to compile the same, chosing between 0 and 1
> for zero sized array.
>
>
> Thank you,
>  - Jay
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