Re: [PATCH] adding missing LTO to some warning options (PR 78606)

[Martin Sebor <msebor@gmail.com>]

On 04/30/2017 02:02 PM, Tom de Vries wrote:
> On 01/10/2017 11:16 PM, Martin Sebor wrote:
>> +  __builtin_sprintf (d, "%32s", "x");   /* { dg-warning "directive
>> writing 32 bytes into a region of size 12" "-Wformat-length" { xfail
>> *-*-* } } */
>
> This xpasses for me on an older system:
> ...
> XPASS: gcc.dg/pr78768.c -Wformat-overflow (test for warnings, line 11)
> ...
>
> The mechanism is as follows:
> - the system doesn't have linker plugin support, and sets
>   HAVE_LTO_PLUGIN to 0
> - consequently, opts.c:finish_options() sets x_flag_fat_lto_objects to 1
>   in cc1
> - cgraphunit.c:symbol_table::compile() does not return
>   here:
>   ...
>      /* Do nothing else if any IPA pass found errors or if we are just
>         streaming LTO.  */
>      if (seen_error ()
>         || (!in_lto_p && flag_lto && !flag_fat_lto_objects))
>       {
>         timevar_pop (TV_CGRAPHOPT);
>         return;
>       }
>   ...
>   and ends up calling expand_all_functions, which calls
>   pass_sprintf_length
> - the warning is generated by cc1
>
> Maybe the test needs:
> ...
> /* { dg-require-linker-plugin "" } */
> ...
> ?

That seems possible.  IIUC, without linker plugin support the
pass will run when the ordinary object file is created during
the first stage of compilation.  I don't have a system to confirm
it on but if pr78768.c xfails when you add the directive I'd say
go ahead and commit the fix as obvious.

Thanks
Martin