On 6/2/21 1:51 AM, Richard Biener wrote:
> On Tue, Jun 1, 2021 at 10:37 PM Pat Haugen via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Make sure link reg save MEM has frame alias set, to match other link reg
>> save/restore code.
>>
>> Bootstrap/regtest on powerpc64/powerpc64le with no new regressions. Ok for
>> trunk?
>>
>> -Pat
>>
>>
>> 2021-06-01 Pat Haugen <pthau...@linux.ibm.com>
>>
>> gcc/ChangeLog:
>>
>> * config/rs6000/rs6000-logue.c (rs6000_emit_prologue): Use
>> gen_frame_store.
>>
>>
>>
>> diff --git a/gcc/config/rs6000/rs6000-logue.c
>> b/gcc/config/rs6000/rs6000-logue.c
>> index 13c00e740d6..07337c4836a 100644
>> --- a/gcc/config/rs6000/rs6000-logue.c
>> +++ b/gcc/config/rs6000/rs6000-logue.c
>> @@ -3257,7 +3257,7 @@ rs6000_emit_prologue (void)
>> if (!WORLD_SAVE_P (info) && info->lr_save_p
>> && !cfun->machine->lr_is_wrapped_separately)
>> {
>> - rtx addr, reg, mem;
>> + rtx reg;
>>
>> reg = gen_rtx_REG (Pmode, 0);
>> START_USE (0);
>> @@ -3267,13 +3267,8 @@ rs6000_emit_prologue (void)
>> if (!(strategy & (SAVE_NOINLINE_GPRS_SAVES_LR
>> | SAVE_NOINLINE_FPRS_SAVES_LR)))
>> {
>> - addr = gen_rtx_PLUS (Pmode, frame_reg_rtx,
>> - GEN_INT (info->lr_save_offset + frame_off));
>> - mem = gen_rtx_MEM (Pmode, addr);
>> - /* This should not be of rs6000_sr_alias_set, because of
>> - __builtin_return_address. */
>
> I can't figure what this comment meant - did you? Note the old code
> looks like it would end up with alias-set zero and thus more conservative
> than with using frame-alias-set so this is an optimization?
No, I couldn't figure out the reasoning for the comment/code either. It's been
that way since it was introduced in March 2000 as part of the “Merge in changes
from newppc-branch.” patch. All other places where we save/restore the link reg
use a MEM with frame-alias-set. This change is an optimization as you suspect
in that it allows us to schedule non-aliased loads above the link reg store
(which couldn't happen before due to use of alias-set zero).
-Pat
