[RFA] Restore combine.c split point for multiply-accumulate instructions

[Segher Boessenkool]

On Wed, May 20, 2015 at 11:38:44PM -0600, Jeff Law wrote:
> I've also verified this is one of the changes ultimately necessary to 
> resolve the code generation regressions caused by Venkat's combine.c 
> change on the PA across my 300+ testfiles for a PA cross compiler.

How much does it help, do you know?

> OK for the trunk?

Yes, please commit.  Thanks.  (One tiny comment below).


Segher


> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index 490386e..250fa0a 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,5 +1,8 @@
>  2015-05-20  Jeff Law  <law@redhat.com>
>  
> +	* combine.c (find_split_point): Handle ASHIFT like MULT to encourage
> +	multiply-accumulate/shift-add insn generation.
> +
>  	* config/pa/pa.c (pa_print_operand): New 'o' output modifier.
>  	(pa_mem_shadd_constant_p): Renamed from pa_shadd_constant_p.
>  	(pa_shadd_constant_p): Allow constants for shadd insns rather
> diff --git a/gcc/combine.c b/gcc/combine.c
> index a90849e..ab6de3a 100644
> --- a/gcc/combine.c
> +++ b/gcc/combine.c
> @@ -5145,7 +5163,9 @@ find_split_point (rtx *loc, rtx_insn *insn, bool set_src)
>        /* Split at a multiply-accumulate instruction.  However if this is
>           the SET_SRC, we likely do not have such an instruction and it's
>           worthless to try this split.  */
> -      if (!set_src && GET_CODE (XEXP (x, 0)) == MULT)
> +      if (!set_src
> +	  && (GET_CODE (XEXP (x, 0)) == MULT
> +	      || GET_CODE (XEXP (x, 0)) == ASHIFT))
>          return loc;

It might be better to also check if it is shifting by a CONST_INT.
I doubt it matters much, but it is closer to the original.


Segher