On Wed, Jun 2, 2021 at 1:15 PM Pat Haugen <pthau...@linux.ibm.com> wrote:
>
> 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).
So did you check the RTL (and alias-sets) produced by
__builtin_return_address? Test coverage might
be low here and w/o scheduling opportunities to break things.
Richard.
> -Pat
