Wilco Dijkstra <wilco.dijks...@arm.com> writes:
> Hi Richard&Kyrill,
>
>>> I’m in favour of this.
>>
>> Yeah, seems ok to me too. I suppose we ought to update the documentation
>> too:
>
> I've added a note to the documentation. However it is impossible to be
> complete here
> since many targets switch off early scheduling under various circumstances.
Yeah, that's fair. :)
> So I've just mentioned what x86 and AArch64 do (see v2 below).
SGTM. Getting it right for two target is a strict improvement
over the status quo. Wording suggestion below though:
> Cheers,
> Wilco
>
>
> v2: Update documentation
>
> Enable the early scheduler on AArch64 for O3/Ofast. This means GCC15 benefits
> from much faster build times with -O2, but avoids the regressions in lbm which
> is very sensitive to minor scheduling changes due to long FMA chains.
>
> gcc:
> PR target/118351
> * common/config/aarch64/aarch64-common.cc: Enable early scheduling
> with
> -O3 and higher.
> * doc/invoke.texi (-fschedule-insns): Update comment.
>
> ---
>
> diff --git a/gcc/common/config/aarch64/aarch64-common.cc
> b/gcc/common/config/aarch64/aarch64-common.cc
> index
> 3d694f16d1fd84e142254a4880c91a7f053e72aa..3044336923415d9414b6c66e66d872612ead24cd
> 100644
> --- a/gcc/common/config/aarch64/aarch64-common.cc
> +++ b/gcc/common/config/aarch64/aarch64-common.cc
> @@ -54,8 +54,10 @@ static const struct default_options
> aarch_option_optimization_table[] =
> { OPT_LEVELS_FAST, OPT_fomit_frame_pointer, NULL, 1 },
> /* Enable -fsched-pressure by default when optimizing. */
> { OPT_LEVELS_1_PLUS, OPT_fsched_pressure, NULL, 1 },
> - /* Disable early scheduling due to high compile-time overheads. */
> + /* Except for -O3 and higher, disable early scheduling due to high
> + compile-time overheads. */
> { OPT_LEVELS_ALL, OPT_fschedule_insns, NULL, 0 },
> + { OPT_LEVELS_3_PLUS, OPT_fschedule_insns, NULL, 1 },
> /* Enable redundant extension instructions removal at -O2 and higher. */
> { OPT_LEVELS_2_PLUS, OPT_free, NULL, 1 },
> { OPT_LEVELS_2_PLUS, OPT_mearly_ra_, NULL, AARCH64_EARLY_RA_ALL },
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index
> bad49a017cc1bb0922eba9f0b2db80166d409cd7..5eb2e96c483126ad075b427969e8c02ce3f51e7a
> 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -13503,7 +13503,9 @@ helps machines that have slow floating point or
> memory load instructions
> by allowing other instructions to be issued until the result of the load
> or floating-point instruction is required.
>
> -Enabled at levels @option{-O2}, @option{-O3}.
> +Enabled at levels @option{-O2}, @option{-O3}. Many targets use a different
> +default, for example, it is disabled on x86 and enabled only at level
> +@option{-O3} on AArch64.
Very minor, and this is going to be personal taste, but how about:
Conventionally enabled at optimization levels @option{-O2} and @option{-O3}.
However, many targets override this behavior. For example, on x86, it is
disabled at all levels, while on AArch64, it is enabled only at @option{-O3}.
(I'm just trying to avoid the second sentence contradicting the first.)
OK with that change if noone objects in 24hrs.
Thanks,
Richard
