Re: get_gcov_type() vs. -fprofile-update=atomic

[Sebastian Huber <sebastian.huber@embedded-brains.de>]

On 09/08/2021 08:51, Sebastian Huber wrote:
> Hello,
> 
> I would like to use gcov for a multi-threaded program running on an SMP 
> machine using a 32-bit SPARC/LEON3 target. This target supports 
> HAVE_atomic_compare_and_swapsi but not HAVE_atomic_compare_and_swapdi. 
> Unfortunately we have:
> 
> /* Return the type node for gcov_type.  */
> 
> tree
> get_gcov_type (void)
> {
>    scalar_int_mode mode
>      = smallest_int_mode_for_size (LONG_LONG_TYPE_SIZE > 32 ? 64 : 32);
>    return lang_hooks.types.type_for_mode (mode, false);
> }
> 
> The long long type is 64-bit, the get_gcov_type() returns a 64-bit type. 
> This disables the atomic support in tree_profiling().
> 
> For what is the gcov type used? Could we add an option to force it to 
> 32-bit? What would be the consequences?
> 
> Another option would be to add something like an 
> -fprofile-update=force-atomic option which would resort to libatomic. 
> Which would deliver bad performance, however, correct results in a 
> multi-threaded program I guess.

Here is a proposed patch:

https://gcc.gnu.org/pipermail/gcc-patches/2021-August/576947.html

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