On 22/01/2024 13:45, Richard Sandiford wrote:
> Alex Coplan <alex.cop...@arm.com> writes:
> > This exposes an interface for users to create new uses in RTL-SSA.
> > This is needed for updating uses after inserting a new store pair insn
> > in the aarch64 load/store pair fusion pass.
> >
> > gcc/ChangeLog:
> >
> > PR target/113070
> > * rtl-ssa/accesses.cc (function_info::create_use): New.
> > * rtl-ssa/changes.cc (function_info::finalize_new_accesses):
> > Handle temporary uses, ensure new uses end up referring to
> > permanent defs.
> > * rtl-ssa/functions.h (function_info::create_use): Declare.
> > ---
> > gcc/rtl-ssa/accesses.cc | 10 ++++++++++
> > gcc/rtl-ssa/changes.cc | 24 +++++++++++++++++++-----
> > gcc/rtl-ssa/functions.h | 5 +++++
> > 3 files changed, 34 insertions(+), 5 deletions(-)
> >
> > diff --git a/gcc/rtl-ssa/accesses.cc b/gcc/rtl-ssa/accesses.cc
> > index ce4a8b8dc00..3f1304fc5bf 100644
> > --- a/gcc/rtl-ssa/accesses.cc
> > +++ b/gcc/rtl-ssa/accesses.cc
> > @@ -1466,6 +1466,16 @@ function_info::create_set (obstack_watermark
> > &watermark,
> > return set;
> > }
> >
> > +use_info *
> > +function_info::create_use (obstack_watermark &watermark,
> > + insn_info *insn,
> > + set_info *set)
> > +{
> > + auto use = change_alloc<use_info> (watermark, insn, set->resource (),
> > set);
> > + use->m_is_temp = true;
> > + return use;
> > +}
> > +
> > // Return true if ACCESS1 can represent ACCESS2 and if ACCESS2 can
> > // represent ACCESS1.
> > static bool
> > diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
> > index e538b637848..ce51d6ccd8d 100644
> > --- a/gcc/rtl-ssa/changes.cc
> > +++ b/gcc/rtl-ssa/changes.cc
> > @@ -538,7 +538,9 @@ function_info::finalize_new_accesses (insn_change
> > &change, insn_info *pos)
> > unsigned int i = 0;
> > for (use_info *use : change.new_uses)
> > {
> > - if (!use->m_has_been_superceded)
> > + if (use->m_is_temp)
> > + use->m_has_been_superceded = true;
> > + else if (!use->m_has_been_superceded)
> > {
>
> Is this part necessary for correctness, or is it just a compile-time
> optimisation? We already have temporary uses via make_uses_available,
> and in principle, it's possible to reuse the uses for multiple changes
> within the same group. E.g. when replacing A with B in multiple
> instructions, it's OK for the associated insn changes to refer to
> A's uses directly, or to uses created for A by make_uses_available.
>
> So IMO it'd better to drop this hunk if we can.
Yeah, I agree it's just a compile-time optimisation and shouldn't be
needed for correctness. I initially thought it might save on memory,
but IIUC the memory allocated with allocate_temp will get freed when we
return from finalize_new_accesses anyway.
So I'll drop that hunk and re-test the series, thanks.
Alex
>
> > use = allocate_temp<use_info> (insn, use->resource (), use->def ());
> > use->m_has_been_superceded = true;
> > @@ -609,15 +611,27 @@ function_info::finalize_new_accesses (insn_change
> > &change, insn_info *pos)
> > m_temp_uses[i] = use = allocate<use_info> (*use);
> > use->m_is_temp = false;
> > set_info *def = use->def ();
> > - // Handle cases in which the value was previously not used
> > - // within the block.
> > - if (def && def->m_is_temp)
> > + if (!def || !def->m_is_temp)
> > + continue;
> > +
> > + if (auto phi = dyn_cast<phi_info *> (def))
> > {
> > - phi_info *phi = as_a<phi_info *> (def);
> > + // Handle cases in which the value was previously not used
> > + // within the block.
> > gcc_assert (phi->is_degenerate ());
> > phi = create_degenerate_phi (phi->ebb (), phi->input_value (0));
> > use->set_def (phi);
> > }
> > + else
> > + {
> > + // The temporary def may also be a set added with this change, in
> > + // which case the permanent set is stored in the last_def link,
> > + // and we need to update the use to refer to the permanent set.
> > + gcc_assert (is_a<set_info *> (def));
> > + auto perm_set = as_a<set_info *> (def->last_def ());
> > + gcc_assert (!perm_set->is_temporary ());
> > + use->set_def (perm_set);
> > + }
> > }
> > }
> >
> > diff --git a/gcc/rtl-ssa/functions.h b/gcc/rtl-ssa/functions.h
> > index 58d0b50ea83..962180e27d6 100644
> > --- a/gcc/rtl-ssa/functions.h
> > +++ b/gcc/rtl-ssa/functions.h
> > @@ -73,6 +73,11 @@ public:
> > insn_info *insn,
> > resource_info resource);
> >
> > + // Create a temporary use.
>
> How about something like:
>
> // Create a temporary use of SET as part of a change to INSN.
> // SET can be a pre-existing definition or one that is being created
> // as part of the same change group.
>
> (Feel free to tweak the wording.)
>
> OK those changes, thanks.
>
> Richard
>
> > + use_info *create_use (obstack_watermark &watermark,
> > + insn_info *insn,
> > + set_info *set);
> > +
> > // Create a temporary insn with code INSN_CODE and pattern PAT.
> > insn_info *create_insn (obstack_watermark &watermark,
> > rtx_code insn_code,
