Re: [PATCH] LoongArch: Set 4 * (issue rate) as the default for -falign-functions and -falign-loops

[Lulu Cheng <chenglulu@loongson.cn>]

Hi, ruoyao:

Thank you so much for making this submission. But we are testing the 
impact of these two alignment parameters

(also including -falign-jumps and -falign-lables ) on performance. So 
before the result comes out, this patch will

not be merged into the main branch for the time being.

Thanks!

在 2023/4/18 下午8:17, Xi Ruoyao 写道:
> According to Xuerui's LLVM changeset [1], doing so can make a
> significant performace gain.
>
> Bootstrapped and regtested on loongarch64-linux-gnu.  Ok for GCC 14?
>
> [1]:https://reviews.llvm.org/D148622
>
> gcc/ChangeLog:
>
> 	* config/loongarch/loongarch.cc
> 	(loongarch_option_override_internal): If -falign-functions is
> 	used but the alignment is not explicitly specified, set it to
> 	4 * loongarch_issue_rate ().  Likewise for -falign-loops.
> ---
>   gcc/config/loongarch/loongarch.cc | 11 +++++++++++
>   1 file changed, 11 insertions(+)
>
> diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
> index 06fc1cd0604..6552484de7c 100644
> --- a/gcc/config/loongarch/loongarch.cc
> +++ b/gcc/config/loongarch/loongarch.cc
> @@ -6236,6 +6236,17 @@ loongarch_option_override_internal (struct gcc_options *opts)
>         && !opts->x_optimize_size)
>       opts->x_flag_prefetch_loop_arrays = 1;
>   
> +  /* Align functions and loops to (issue rate) * (insn size) to improve
> +     the throughput of the fetching units.  */
> +  char *align = XNEWVEC (char, 16);
> +  sprintf (align, "%d", loongarch_issue_rate () * 4);
> +
> +  if (opts->x_flag_align_functions && !opts->x_str_align_functions)
> +    opts->x_str_align_functions = align;
> +
> +  if (opts->x_flag_align_loops && !opts->x_str_align_loops)
> +    opts->x_str_align_loops = align;
> +
>     if (TARGET_DIRECT_EXTERN_ACCESS && flag_shlib)
>       error ("%qs cannot be used for compiling a shared library",
>   	   "-mdirect-extern-access");