0004-Set-pseudos-only-once.patch

[Jeff Law]

On 06/22/10 06:08, Maxim Kuvyrkov wrote:
> On 6/21/10 9:55 PM, Jeff Law wrote:
>> On 06/16/10 09:57, Maxim Kuvyrkov wrote:
>>> IRA and reload has special relationship with pseudos that are set only
>>> once. When such pseudos initialized with constants or instances that
>>> can be considered constant across the function, reload can
>>> rematerialize them instead of spilling or apply other optimizations.
>>>
>>> This patch makes sure that we don't unnecessarily set same pseudo more
>>> than once.
>>>
>>> OK to apply?
>> OK. THanks,
>
> Thank you for reviewing this and other patches.
>
> There is similar code in gcse.c:pre_delete():
>
>         /* Create a pseudo-reg to store the result of reaching
>            expressions into.  Get the mode for the new pseudo from
>            the mode of the original destination pseudo.  */
>         if (expr->reaching_reg == NULL)
>           expr->reaching_reg = gen_reg_rtx_and_attrs (SET_DEST (set));
>
>         gcse_emit_move_after (expr->reaching_reg, SET_DEST (set), insn);
>         delete_insn (insn);
>         occr->deleted_p = 1;
>         changed = 1;
>         gcse_subst_count++;
>
> From quick look at PRE, it seem that creating a new pseudo for PRE is 
> also correct.  Do you know off-hand if this indeed is the case?
Creating a new pseudo for PRE would be good; however, it's not 
immediately clear to me if creating a new pseudo is safe given the way 
deletion & insertion work for our implementation of PRE.

jeff