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Re: LEA-splitting improvement patch.


Uros,

Let me try to explain you why I used such code duplication:

Here we have a common case of LEA with 3 different registers - r0
(target), r1(base), r2(index) and possible offset.
To get the better scheduling we first try to determine what register
is prefirable for inititial setting - r1 or r2 through
find_nearest_reg_def. And then we generate the following sequence of
instructions:
       r0 = r_best;
       r0 = $const, r0
       r0 = r_worse, r0
that can save 2 cycles for Atom since first 2 instructions can be hoisted up.
I could not find better way for coding it.

Below is modified ChangeLog.

2012-08-14  Yuri Rumyantsev  <ysrumyan@gmail.com>

	* config/i386/i386-protos.h (ix86_split_lea_for_addr) : Add
	additional argument.
	* config/i386/i386.md (ix86_split_lea_for_addr) : Add
	additional argument curr_insn.
	* config/i386/i386.c (ix86_split_lea_for_addr): Do instructions
	reodering to get opportunities for better scheduling.
	(ix86_lea_outperforms): Prefer LEA if only split cost exceeds
	AGU stall.
	(find_nearest_reg-def): New function. Find nearest register
	definition used in address.


2012/8/14 Uros Bizjak <ubizjak@gmail.com>:
> On Tue, Aug 14, 2012 at 2:28 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>
>> Thanks  a lot forr your comments.
>>
>> I prepared new patch and ChangeLog. Testing of x32 is in progress.
>>
>> It it OK for trunk?
>>
>> 2012-08-14  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>
>>         * config/i386/i386-protos.h (ix86_split_lea_for_addr) : Add
>>         additional argument.
>>         * config/i386/i386.md (ix86_split_lea_for_addr) : Add
>>         additional argument curr_insn.
>>         * config/i386/i386.c (ix86_split_lea_for_addr): Do instructions
>>         reodering to get opportunities for better scheduling.
>>         (ix86_lea_outperforms): Do more aggressive lea splitting.
>
> You are not doing splitting in ix86_lea_outperforms.
>
>>         (find_nearest_reg-def): New function. Find nearest register
>>         definition used in address.
>
> Just say:
>
> (find_nearest_reg_def): New function.
>
> +             emit_insn (gen_rtx_SET (VOIDmode, target, tmp));
> +              if (parts.disp && parts.disp != const0_rtx)
> +                ix86_emit_binop (PLUS, mode, target, parts.disp);
> +              ix86_emit_binop (PLUS, mode, target, tmp1);
> +             return;
>
> Can you explain, why you have to duplicate this code? Here you
> generate the same sequence as in the code below. Use tmp and tmp1 in
> the way that it will fit existing code.
>
> Uros.


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