Re: [PATCH] MIPS: don't expand large block move

[Jeff Law <jeffreyalaw@gmail.com>]

On 5/19/23 00:11, YunQiang Su wrote:
> On platform with LWL/LWR, mips_block_move_loop is always used,
> which expand __buildin_memcpy/strcpy to a loop of lwl/lwr/swl/swl etc.
> 
> For short (normally <=64), it has better performance,
> but when the src/dest are long, use memcpy/strcpy lib call may have
> better performance.
> 
> At the same time, lib call may be optimized with SIMD, so,
> on the platform with SIMD, lib call may have much better performace.
> 
> gcc/ChangeLog:
> 	* config/mips/mips.cc (mips_expand_block_move): don't expand
> 	  if length>=64.
> 
> gcc/testsuite/ChangeLog:
> 	* gcc.target/mips/expand-block-move-large.c: New test.
> ---
>   gcc/config/mips/mips.cc                         |  6 ++++++
>   .../gcc.target/mips/expand-block-move-large.c   | 17 +++++++++++++++++
>   2 files changed, 23 insertions(+)
>   create mode 100644 gcc/testsuite/gcc.target/mips/expand-block-move-large.c
> 
> diff --git a/gcc/config/mips/mips.cc b/gcc/config/mips/mips.cc
> index ca491b981a3..00f26d5e923 100644
> --- a/gcc/config/mips/mips.cc
> +++ b/gcc/config/mips/mips.cc
> @@ -8313,6 +8313,12 @@ mips_expand_block_move (rtx dest, rtx src, rtx length)
>   	}
>         else if (optimize)
>   	{
> +	  /* When the length is big enough, the lib call has better performace
> +	     than load/store insns.
> +	     In most platform, the value is about 64-128.
> +	     And in fact lib call may be optimized with SIMD */
> +	  if (INTVAL(length) >= 64)
> +	    return false;
Just a formatting nit.  Space between INTVAL and the open paren for its 
argument list.

OK with that change.

jeff