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

[WANG Xuerui <i@xen0n.name>]

Hi,

Thanks for helping confirming on GCC and porting this! I'd never know 
even GCC lacked this adaptation without someone actually checking... Too 
many things are taken for granted these days.

On 2023/4/18 20:17, Xi Ruoyao wrote:
> 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.  */
What about gating all of these on !opts->x_optimize_size, similar to 
what aarch64 does?
> +  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");
Otherwise LGTM, thanks!