Re: [PATCH 3/4] rtl-ssa: Ensure new defs get inserted [PR113070]

[Richard Sandiford <richard.sandiford@arm.com>]

Alex Coplan <alex.coplan@arm.com> writes:
> In r14-5820-ga49befbd2c783e751dc2110b544fe540eb7e33eb I added support to
> RTL-SSA for inserting new insns, which included support for users
> creating new defs.
>
> However, I missed that apply_changes_to_insn needed updating to ensure
> that the new defs actually got inserted into the main def chain.  This
> meant that when the aarch64 ldp/stp pass inserted a new stp insn, the
> stp would just get skipped over during subsequent alias analysis, as its
> def never got inserted into the memory def chain.  This (unsurprisingly)
> led to wrong code.
>
> This patch fixes the issue by ensuring new user-created defs get
> inserted.  I would have preferred to have used a flag internal to the
> defs instead of a separate data structure to keep track of them, but since
> machine_mode increased to 16 bits we're already at 64 bits in access_info,
> and we can't really reuse m_is_temp as the logic in finalize_new_accesses
> requires it to get cleared.
>
> Bootstrapped/regtested as a series on aarch64-linux-gnu, OK for trunk?
>
> Thanks,
> Alex
>
> gcc/ChangeLog:
>
> 	PR target/113070
> 	* rtl-ssa.h: Include hash-set.h.
> 	* rtl-ssa/changes.cc (function_info::finalize_new_accesses): Add
> 	new_sets parameter and use it to keep track of new user-created sets.
> 	(function_info::apply_changes_to_insn): Also call add_def on new sets.
> 	(function_info::change_insns): Add hash_set to keep track of new
> 	user-created defs.  Plumb it through.
> 	* rtl-ssa/functions.h: Add hash_set parameter to finalize_new_accesses and
> 	apply_changes_to_insn.
> ---
>  gcc/rtl-ssa.h           |  1 +
>  gcc/rtl-ssa/changes.cc  | 28 +++++++++++++++++++++-------
>  gcc/rtl-ssa/functions.h |  6 ++++--
>  3 files changed, 26 insertions(+), 9 deletions(-)
>
> diff --git a/gcc/rtl-ssa.h b/gcc/rtl-ssa.h
> index f0cf656f5ac..17337639ae8 100644
> --- a/gcc/rtl-ssa.h
> +++ b/gcc/rtl-ssa.h
> @@ -50,6 +50,7 @@
>  #include "mux-utils.h"
>  #include "rtlanal.h"
>  #include "cfgbuild.h"
> +#include "hash-set.h"
>  
>  // Provides the global crtl->ssa.
>  #include "memmodel.h"
> diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
> index ce51d6ccd8d..6119ec3535b 100644
> --- a/gcc/rtl-ssa/changes.cc
> +++ b/gcc/rtl-ssa/changes.cc
> @@ -429,7 +429,8 @@ update_insn_in_place (insn_change &change)
>  // POS gives the final position of INSN, which hasn't yet been moved into
>  // place.

The new parameter should be documented.  How about:

  // place.  NEW_SETS contains the new set_infos that are being added as part
  // of this change (as opposed to being moved or repurposed from existing
  // instructions).


>  void
> -function_info::finalize_new_accesses (insn_change &change, insn_info *pos)
> +function_info::finalize_new_accesses (insn_change &change, insn_info *pos,
> +				      hash_set<def_info *> &new_sets)
>  {
>    insn_info *insn = change.insn ();
>  
> @@ -465,6 +466,12 @@ function_info::finalize_new_accesses (insn_change &change, insn_info *pos)
>  		// later in case we see a second write to the same resource.
>  		def_info *perm_def = allocate<set_info> (change.insn (),
>  							 def->resource ());
> +
> +		// Keep track of the new set so we remember to add it to the
> +		// def chain later.
> +		if (new_sets.add (perm_def))
> +		  gcc_unreachable (); // We shouldn't see duplicates here.
> +
>  		def->set_last_def (perm_def);
>  		def = perm_def;
>  	      }
> @@ -647,7 +654,8 @@ function_info::finalize_new_accesses (insn_change &change, insn_info *pos)
>  // Copy information from CHANGE to its underlying insn_info, given that
>  // the insn_info has already been placed appropriately.

Similarly here.

OK with those changes, thanks.

Richard

>  void
> -function_info::apply_changes_to_insn (insn_change &change)
> +function_info::apply_changes_to_insn (insn_change &change,
> +				      hash_set<def_info *> &new_sets)
>  {
>    insn_info *insn = change.insn ();
>    if (change.is_deletion ())
> @@ -659,10 +667,11 @@ function_info::apply_changes_to_insn (insn_change &change)
>    // Copy the cost.
>    insn->set_cost (change.new_cost);
>  
> -  // Add all clobbers.  Sets and call clobbers never move relative to
> -  // other definitions, so are OK as-is.
> +  // Add all clobbers and newly-created sets.  Existing sets and call
> +  // clobbers never move relative to other definitions, so are OK as-is.
>    for (def_info *def : change.new_defs)
> -    if (is_a<clobber_info *> (def) && !def->is_call_clobber ())
> +    if ((is_a<clobber_info *> (def) && !def->is_call_clobber ())
> +	|| (is_a<set_info *> (def) && new_sets.contains (def)))
>        add_def (def);
>  
>    // Add all uses, now that their position is final.
> @@ -793,6 +802,10 @@ function_info::change_insns (array_slice<insn_change *> changes)
>        placeholders[i] = placeholder;
>      }
>  
> +  // We need to keep track of newly-added sets as these need adding to
> +  // the def chain later.
> +  hash_set<def_info *> new_sets;
> +
>    // Finalize the new list of accesses for each change.  Don't install them yet,
>    // so that we still have access to the old lists below.
>    //
> @@ -806,7 +819,8 @@ function_info::change_insns (array_slice<insn_change *> changes)
>        insn_info *placeholder = placeholders[i];
>        if (!change.is_deletion ())
>  	finalize_new_accesses (change,
> -			       placeholder ? placeholder : change.insn ());
> +			       placeholder ? placeholder : change.insn (),
> +			       new_sets);
>      }
>  
>    // Remove all definitions that are no longer needed.  After the above,
> @@ -861,7 +875,7 @@ function_info::change_insns (array_slice<insn_change *> changes)
>  
>    // Apply the changes to the underlying insn_infos.
>    for (insn_change *change : changes)
> -    apply_changes_to_insn (*change);
> +    apply_changes_to_insn (*change, new_sets);
>  
>    // Now that the insns and accesses are up to date, add any REG_UNUSED notes.
>    for (insn_change *change : changes)
> diff --git a/gcc/rtl-ssa/functions.h b/gcc/rtl-ssa/functions.h
> index 962180e27d6..4573453d896 100644
> --- a/gcc/rtl-ssa/functions.h
> +++ b/gcc/rtl-ssa/functions.h
> @@ -299,8 +299,10 @@ private:
>    void process_uses_of_deleted_def (set_info *);
>    insn_info *add_placeholder_after (insn_info *);
>    void possibly_queue_changes (insn_change &);
> -  void finalize_new_accesses (insn_change &, insn_info *);
> -  void apply_changes_to_insn (insn_change &);
> +  void finalize_new_accesses (insn_change &, insn_info *,
> +			      hash_set<def_info *> &);
> +  void apply_changes_to_insn (insn_change &,
> +			      hash_set<def_info *> &);
>  
>    void init_function_data ();
>    void calculate_potential_phi_regs (build_info &);