On Wed, Jan 03, 2024 at 11:42:58PM +0800, xndcn wrote:
> Hi, I am new to this, and I really need your advice, thanks.
>
> I noticed PR71716 and I want to enable ATOMIC_COMPARE_EXCHANGE
> internal-fn optimization
>
> for floating type or types contains padding (e.g., long double).
> Please correct me if I happen to
> make any mistakes, Thanks!
>
> Firstly, about the concerns of sNaNs float/doduble value, it seems
> work well and shall have been
> covered by testsuite/gcc.dg/atomic/c11-atomic-exec-5.c
>
> Secondly, since ATOMIC_COMPARE_EXCHANGE is only enabled when expected
> var is only addressable
> because of the call, the padding bits can not be modified by any other
> stmts. So we can save all
> bits after ATOMIC_COMPARE_EXCHANGE call and extract the padding bits.
> After first iteration, the
> extracted padding bits can be mixed with the expected var.
>
> Bootstrapped/regtested on x86_64-linux.
>
> I did some benchmarks, and there is some significant time optimization
> for float/double types,
>
> while there is no regression for long double type.
If anything, this should be using clear_padding_type_may_have_padding_p
and call to __builtin_clear_padding.
Code in that file uses /* ... */ style comments, so please use them instead
of // for consistency, and furthermore comments should be terminated with
a dot and two spaces before */
Also, I don't think this is late stage3 material, so needs to wait for GCC
15.
Jakub
