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.
> 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,
