Re: [PATCH] rs6000: Enable overlapped by-pieces operations

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi,

on 2024/5/8 14:47, HAO CHEN GUI wrote:
> Hi,
>   This patch enables overlapped by-piece operations. On rs6000, default
> move/set/clear ratio is 2. So the overlap is only enabled with compare
> by-pieces.

Thanks for enabling this, did you evaluate if it can help some benchmark?

> 
>   Bootstrapped and tested on powerpc64-linux BE and LE with no
> regressions. Is it OK for the trunk?
> 
> Thanks
> Gui Haochen
> 
> ChangeLog
> rs6000: Enable overlapped by-pieces operations
> 
> This patch enables overlapped by-piece operations by defining
> TARGET_OVERLAP_OP_BY_PIECES_P to true.  On rs6000, default move/set/clear
> ratio is 2.  So the overlap is only enabled with compare by-pieces.
> 
> gcc/
> 	* config/rs6000/rs6000.cc (TARGET_OVERLAP_OP_BY_PIECES_P): Define.
> 
> gcc/testsuite/
> 	* gcc.target/powerpc/block-cmp-9.c: New.
> 
> 
> patch.diff
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index 6b9a40fcc66..2b5f5cf1d86 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -1774,6 +1774,9 @@ static const scoped_attribute_specs *const rs6000_attribute_table[] =
>  #undef TARGET_CONST_ANCHOR
>  #define TARGET_CONST_ANCHOR 0x8000
> 
> +#undef TARGET_OVERLAP_OP_BY_PIECES_P
> +#define TARGET_OVERLAP_OP_BY_PIECES_P hook_bool_void_true
> +
>  \f
> 
>  /* Processor table.  */
> diff --git a/gcc/testsuite/gcc.target/powerpc/block-cmp-9.c b/gcc/testsuite/gcc.target/powerpc/block-cmp-9.c
> new file mode 100644
> index 00000000000..b5f51affbb7
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/block-cmp-9.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -mdejagnu-cpu=power8" } */

Why does it need power8 forced here?

BR,
Kewen

> +/* { dg-final { scan-assembler-not {\ml[hb]z\M} } } */
> +
> +/* Test if by-piece overlap compare is enabled and following case is
> +   implemented by two overlap word loads and compares.  */
> +
> +int foo (const char* s1, const char* s2)
> +{
> +  return __builtin_memcmp (s1, s2, 7) == 0;
> +}