Alex Coplan <alex.cop...@arm.com> writes:
> N.B. this is just a rebased (but otherwise unchanged) version of the
> same patch already posted here:
>
> https://gcc.gnu.org/pipermail/gcc-patches/2023-October/633348.html
>
> this is the only unreviewed dependency from the previous series, so it
> seemed easier just to re-post it (not least to appease the pre-commit
> CI).
>
> -- >8 --
>
> The upcoming aarch64 load pair pass needs to form store pairs, and can
> re-order stores over loads when alias analysis determines this is safe.
> In the case that both mem defs have uses in the RTL-SSA IR, and both
> stores require re-ordering over their uses, we represent that as
> (tentative) deletion of the original store insns and creation of a new
> insn, to prevent requiring repeated re-parenting of uses during the
> pass. We then update all mem uses that require re-parenting in one go
> at the end of the pass.
>
> To support this, RTL-SSA needs to handle inserting new insns (rather
> than just changing existing ones), so this patch adds support for that.
>
> New insns (and new accesses) are temporaries, allocated above a temporary
> obstack_watermark, such that the user can easily back out of a change without
> awkward bookkeeping.
>
> Bootstrapped/regtested as a series on aarch64-linux-gnu, OK for trunk?
>
> gcc/ChangeLog:
>
> * rtl-ssa/accesses.cc (function_info::create_set): New.
> * rtl-ssa/accesses.h (access_info::is_temporary): New.
> * rtl-ssa/changes.cc (move_insn): Handle new (temporary) insns.
> (function_info::finalize_new_accesses): Handle new/temporary
> user-created accesses.
> (function_info::apply_changes_to_insn): Ensure m_is_temp flag
> on new insns gets cleared.
> (function_info::change_insns): Handle new/temporary insns.
> (function_info::create_insn): New.
> * rtl-ssa/changes.h (class insn_change): Make function_info a
> friend class.
> * rtl-ssa/functions.h (function_info): Declare new entry points:
> create_set, create_insn. Declare new change_alloc helper.
> * rtl-ssa/insns.cc (insn_info::print_full): Identify temporary insns
> in
> dump.
> * rtl-ssa/insns.h (insn_info): Add new m_is_temp flag and accompanying
> is_temporary accessor.
> * rtl-ssa/internals.inl (insn_info::insn_info): Initialize m_is_temp
> to
> false.
> * rtl-ssa/member-fns.inl (function_info::change_alloc): New.
> * rtl-ssa/movement.h (restrict_movement_for_defs_ignoring): Add
> handling for temporary defs.
Looks good, but there were a couple of things I didn't understand:
> ---
> gcc/rtl-ssa/accesses.cc | 10 ++++++
> gcc/rtl-ssa/accesses.h | 4 +++
> gcc/rtl-ssa/changes.cc | 74 +++++++++++++++++++++++++++++++-------
> gcc/rtl-ssa/changes.h | 2 ++
> gcc/rtl-ssa/functions.h | 14 ++++++++
> gcc/rtl-ssa/insns.cc | 5 +++
> gcc/rtl-ssa/insns.h | 7 +++-
> gcc/rtl-ssa/internals.inl | 1 +
> gcc/rtl-ssa/member-fns.inl | 12 +++++++
> gcc/rtl-ssa/movement.h | 8 ++++-
> 10 files changed, 123 insertions(+), 14 deletions(-)
>
> diff --git a/gcc/rtl-ssa/accesses.cc b/gcc/rtl-ssa/accesses.cc
> index 510545a8bad..76d70fd8bd3 100644
> --- a/gcc/rtl-ssa/accesses.cc
> +++ b/gcc/rtl-ssa/accesses.cc
> @@ -1456,6 +1456,16 @@ function_info::make_uses_available (obstack_watermark
> &watermark,
> return use_array (new_uses, num_uses);
> }
>
> +set_info *
> +function_info::create_set (obstack_watermark &watermark,
> + insn_info *insn,
> + resource_info resource)
> +{
> + auto set = change_alloc<set_info> (watermark, insn, resource);
> + set->m_is_temp = true;
> + return set;
> +}
> +
> // Return true if ACCESS1 can represent ACCESS2 and if ACCESS2 can
> // represent ACCESS1.
> static bool
> diff --git a/gcc/rtl-ssa/accesses.h b/gcc/rtl-ssa/accesses.h
> index fce31d46717..7e7a90ece97 100644
> --- a/gcc/rtl-ssa/accesses.h
> +++ b/gcc/rtl-ssa/accesses.h
> @@ -204,6 +204,10 @@ public:
> // in the main instruction pattern.
> bool only_occurs_in_notes () const { return m_only_occurs_in_notes; }
>
> + // Return true if this is a temporary access, e.g. one created for
> + // an insn that is about to be inserted.
> + bool is_temporary () const { return m_is_temp; }
> +
> protected:
> access_info (resource_info, access_kind);
>
> diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
> index aab532b9f26..da2a61d701a 100644
> --- a/gcc/rtl-ssa/changes.cc
> +++ b/gcc/rtl-ssa/changes.cc
> @@ -394,14 +394,20 @@ move_insn (insn_change &change, insn_info *after)
> // At the moment we don't support moving instructions between EBBs,
> // but this would be worth adding if it's useful.
> insn_info *insn = change.insn ();
> - gcc_assert (after->ebb () == insn->ebb ());
> +
> bb_info *bb = after->bb ();
> basic_block cfg_bb = bb->cfg_bb ();
>
> - if (insn->bb () != bb)
> - // Force DF to mark the old block as dirty.
> - df_insn_delete (rtl);
> - ::remove_insn (rtl);
> + if (!insn->is_temporary ())
> + {
> + gcc_assert (after->ebb () == insn->ebb ());
> +
> + if (insn->bb () != bb)
> + // Force DF to mark the old block as dirty.
> + df_insn_delete (rtl);
> + ::remove_insn (rtl);
> + }
> +
> ::add_insn_after (rtl, after_rtl, cfg_bb);
> }
>
> @@ -439,10 +445,15 @@ function_info::finalize_new_accesses (insn_change
> &change, insn_info *pos)
> gcc_assert (def);
> if (def->m_is_temp)
> {
> - // At present, the only temporary instruction definitions we
> - // create are clobbers, such as those added during recog.
> - gcc_assert (is_a<clobber_info *> (def));
> - def = allocate<clobber_info> (change.insn (), ref.regno);
> + if (is_a<clobber_info *> (def))
> + def = allocate<clobber_info> (change.insn (), ref.regno);
> + else if (is_a<set_info *> (def))
> + {
> + def->m_is_temp = false;
> + def = allocate<set_info> (change.insn (), def->resource ());
Why is it necessary to clear is_temp on the old temporary set,
when it wasn't for the temporary clobber?
> + }
> + else
> + gcc_unreachable ();
> }
> else if (!def->m_has_been_superceded)
> {
> @@ -511,7 +522,9 @@ 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)
Where do the temporary uses come from? It doesn't look like this patch
itself provided a new means of creating them.
Thanks,
Richard
> {
> use = allocate_temp<use_info> (insn, use->resource (), use->def ());
> use->m_has_been_superceded = true;
> @@ -645,6 +658,8 @@ function_info::apply_changes_to_insn (insn_change &change)
>
> insn->set_accesses (builder.finish ().begin (), num_defs, num_uses);
> }
> +
> + insn->m_is_temp = false;
> }
>
> // Add a temporary placeholder instruction after AFTER.
> @@ -677,7 +692,8 @@ function_info::change_insns (array_slice<insn_change *>
> changes)
> if (!change->is_deletion ())
> {
> // Remove any notes that are no longer relevant.
> - update_notes (change->rtl ());
> + if (!change->insn ()->m_is_temp)
> + update_notes (change->rtl ());
>
> // Make sure that the placement of this instruction would still
> // leave room for previous instructions.
> @@ -686,6 +702,17 @@ function_info::change_insns (array_slice<insn_change *>
> changes)
> // verify_insn_changes is supposed to make sure that this holds.
> gcc_unreachable ();
> min_insn = later_insn (min_insn, change->move_range.first);
> +
> + if (change->insn ()->m_is_temp)
> + {
> + change->m_insn = allocate<insn_info> (change->insn ()->bb (),
> + change->rtl (),
> + change->insn_uid ());
> +
> + // Set the flag again so subsequent logic is aware.
> + // It will be cleared later on.
> + change->m_insn->m_is_temp = true;
> + }
> }
> }
>
> @@ -784,7 +811,8 @@ function_info::change_insns (array_slice<insn_change *>
> changes)
> // Remove the placeholder first so that we have a wider range of
> // program points when inserting INSN.
> insn_info *after = placeholder->prev_any_insn ();
> - remove_insn (insn);
> + if (!insn->is_temporary ())
> + remove_insn (insn);
> remove_insn (placeholder);
> insn->set_bb (after->bb ());
> add_insn_after (insn, after);
> @@ -1105,6 +1133,28 @@ function_info::perform_pending_updates ()
> return changed_cfg;
> }
>
> +insn_info *
> +function_info::create_insn (obstack_watermark &watermark,
> + rtx_code insn_code,
> + rtx pat)
> +{
> + rtx_insn *rti = nullptr;
> +
> + // TODO: extend, move in to emit-rtl.cc.
> + switch (insn_code)
> + {
> + case INSN:
> + rti = make_insn_raw (pat);
> + break;
> + default:
> + gcc_unreachable ();
> + }
> +
> + auto insn = change_alloc<insn_info> (watermark, nullptr, rti, INSN_UID
> (rti));
> + insn->m_is_temp = true;
> + return insn;
> +}
> +
> // Print a description of CHANGE to PP.
> void
> rtl_ssa::pp_insn_change (pretty_printer *pp, const insn_change &change)
> diff --git a/gcc/rtl-ssa/changes.h b/gcc/rtl-ssa/changes.h
> index d56e3a646e2..d91cf432afe 100644
> --- a/gcc/rtl-ssa/changes.h
> +++ b/gcc/rtl-ssa/changes.h
> @@ -32,6 +32,8 @@ namespace rtl_ssa {
> // something that we might do.
> class insn_change
> {
> + friend class function_info;
> +
> public:
> enum delete_action { DELETE };
>
> diff --git a/gcc/rtl-ssa/functions.h b/gcc/rtl-ssa/functions.h
> index ecb40fdaf57..4ffd3fa44e2 100644
> --- a/gcc/rtl-ssa/functions.h
> +++ b/gcc/rtl-ssa/functions.h
> @@ -68,6 +68,16 @@ public:
> // Return the SSA information for CFG_BB.
> bb_info *bb (basic_block cfg_bb) const { return m_bbs[cfg_bb->index]; }
>
> + // Create a temporary def.
> + set_info *create_set (obstack_watermark &watermark,
> + insn_info *insn,
> + resource_info resource);
> +
> + // Create a temporary insn with code INSN_CODE and pattern PAT.
> + insn_info *create_insn (obstack_watermark &watermark,
> + rtx_code insn_code,
> + rtx pat);
> +
> // Return a list of all the instructions in the function, in reverse
> // postorder. The list includes both real and artificial instructions.
> //
> @@ -195,6 +205,10 @@ public:
> // Print the contents of the function to PP.
> void print (pretty_printer *pp) const;
>
> + // Allocate an object of type T above the obstack watermark WM.
> + template<typename T, typename... Ts>
> + T *change_alloc (obstack_watermark &wm, Ts... args);
> +
> private:
> class bb_phi_info;
> class build_info;
> diff --git a/gcc/rtl-ssa/insns.cc b/gcc/rtl-ssa/insns.cc
> index 5fde3f2bb4b..2fa48e0dacd 100644
> --- a/gcc/rtl-ssa/insns.cc
> +++ b/gcc/rtl-ssa/insns.cc
> @@ -192,6 +192,11 @@ insn_info::print_full (pretty_printer *pp) const
> pp_newline_and_indent (pp, 0);
> pp_string (pp, "has volatile refs");
> }
> + if (m_is_temp)
> + {
> + pp_newline_and_indent (pp, 0);
> + pp_string (pp, "temporary");
> + }
> }
> pp_indentation (pp) -= 2;
> }
> diff --git a/gcc/rtl-ssa/insns.h b/gcc/rtl-ssa/insns.h
> index a604fe295cd..6d0506706ad 100644
> --- a/gcc/rtl-ssa/insns.h
> +++ b/gcc/rtl-ssa/insns.h
> @@ -306,6 +306,8 @@ public:
> // Print a full description of the instruction.
> void print_full (pretty_printer *) const;
>
> + bool is_temporary () const { return m_is_temp; }
> +
> private:
> // The first-order way of representing the order between instructions
> // is to assign "program points", with higher point numbers coming
> @@ -414,8 +416,11 @@ private:
> unsigned int m_has_pre_post_modify : 1;
> unsigned int m_has_volatile_refs : 1;
>
> + // Indicates the insn is a temporary / new user-allocated insn.
> + unsigned int m_is_temp : 1;
> +
> // For future expansion.
> - unsigned int m_spare : 27;
> + unsigned int m_spare : 26;
>
> // The program point at which the instruction occurs.
> //
> diff --git a/gcc/rtl-ssa/internals.inl b/gcc/rtl-ssa/internals.inl
> index e49297c12b3..907c4504352 100644
> --- a/gcc/rtl-ssa/internals.inl
> +++ b/gcc/rtl-ssa/internals.inl
> @@ -415,6 +415,7 @@ inline insn_info::insn_info (bb_info *bb, rtx_insn *rtl,
> int cost_or_uid)
> m_is_asm (false),
> m_has_pre_post_modify (false),
> m_has_volatile_refs (false),
> + m_is_temp (false),
> m_spare (0),
> m_point (0),
> m_cost_or_uid (cost_or_uid),
> diff --git a/gcc/rtl-ssa/member-fns.inl b/gcc/rtl-ssa/member-fns.inl
> index ce2db045b78..b8940ca5566 100644
> --- a/gcc/rtl-ssa/member-fns.inl
> +++ b/gcc/rtl-ssa/member-fns.inl
> @@ -962,4 +962,16 @@ function_info::add_regno_clobber (obstack_watermark
> &watermark,
> return true;
> }
>
> +template<typename T, typename... Ts>
> +inline T *
> +function_info::change_alloc (obstack_watermark &wm, Ts... args)
> +{
> + static_assert (std::is_trivially_destructible<T>::value,
> + "destructor won't be called");
> + static_assert (alignof (T) <= obstack_alignment,
> + "too much alignment required");
> + void *addr = XOBNEW (wm, T);
> + return new (addr) T (std::forward<Ts> (args)...);
> +}
> +
> }
> diff --git a/gcc/rtl-ssa/movement.h b/gcc/rtl-ssa/movement.h
> index ec076db406f..41226dd3666 100644
> --- a/gcc/rtl-ssa/movement.h
> +++ b/gcc/rtl-ssa/movement.h
> @@ -182,6 +182,11 @@ restrict_movement_for_defs_ignoring (insn_range_info
> &move_range,
> {
> for (def_info *def : defs)
> {
> + // Skip fresh defs that are being inserted, as these shouldn't
> + // constrain movement.
> + if (def->is_temporary ())
> + continue;
> +
> // If the definition is a clobber, we can move it with respect
> // to other clobbers.
> //
> @@ -247,7 +252,8 @@ restrict_movement_for_defs_ignoring (insn_range_info
> &move_range,
>
> // Make sure that we don't move stores between basic blocks, since we
> // don't have enough information to tell whether it's safe.
> - if (def_info *def = memory_access (defs))
> + def_info *def = memory_access (defs);
> + if (def && !def->is_temporary ())
> {
> move_range = move_later_than (move_range, def->bb ()->head_insn ());
> move_range = move_earlier_than (move_range, def->bb ()->end_insn ());
