Re: [PATCH 04/11] rtl-ssa: Support inferring uses of mem in change_insns

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

Alex Coplan <alex.coplan@arm.com> writes:
> Currently, rtl_ssa::change_insns requires all new uses and defs to be
> specified explicitly.  This turns out to be rather inconvenient for
> forming load pairs in the new aarch64 load pair pass, as the pass has to
> determine which mem def the final load pair consumes, and then obtain or
> create a suitable use (i.e. significant bookkeeping, just to keep the
> RTL-SSA IR consistent).  It turns out to be much more convenient to
> allow change_insns to infer which def is consumed and create a suitable
> use of mem itself.  This patch does that.
>
> Bootstrapped/regtested as a series on aarch64-linux-gnu, OK for trunk?
>
> gcc/ChangeLog:
>
> 	* rtl-ssa/changes.cc (function_info::finalize_new_accesses): Add new
> 	parameter to give final insn position, infer use of mem if it isn't
> 	specified explicitly.
> 	(function_info::change_insns): Pass down final insn position to
> 	finalize_new_accesses.
> 	* rtl-ssa/functions.h: Add parameter to finalize_new_accesses.

OK, thanks.

Richard

> ---
>  gcc/rtl-ssa/changes.cc  | 31 ++++++++++++++++++++++++++++---
>  gcc/rtl-ssa/functions.h |  2 +-
>  2 files changed, 29 insertions(+), 4 deletions(-)
>
> diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
> index c48ddd2463c..523ad60d7d8 100644
> --- a/gcc/rtl-ssa/changes.cc
> +++ b/gcc/rtl-ssa/changes.cc
> @@ -370,8 +370,11 @@ update_insn_in_place (insn_change &change)
>  // Finalize the new list of definitions and uses in CHANGE, removing
>  // any uses and definitions that are no longer needed, and converting
>  // pending clobbers into actual definitions.
> +//
> +// POS gives the final position of INSN, which hasn't yet been moved into
> +// place.
>  void
> -function_info::finalize_new_accesses (insn_change &change)
> +function_info::finalize_new_accesses (insn_change &change, insn_info *pos)
>  {
>    insn_info *insn = change.insn ();
>  
> @@ -462,13 +465,34 @@ function_info::finalize_new_accesses (insn_change &change)
>    // Add (possibly temporary) uses to m_temp_uses for each resource.
>    // If there are multiple references to the same resource, aggregate
>    // information in the modes and flags.
> +  use_info *mem_use = nullptr;
>    for (rtx_obj_reference ref : properties.refs ())
>      if (ref.is_read ())
>        {
>  	unsigned int regno = ref.regno;
>  	machine_mode mode = ref.is_reg () ? ref.mode : BLKmode;
>  	use_info *use = find_access (unshared_uses, ref.regno);
> -	gcc_assert (use);
> +	if (!use)
> +	  {
> +	    // For now, we only support inferring uses of mem.
> +	    gcc_assert (regno == MEM_REGNO);
> +
> +	    if (mem_use)
> +	      {
> +		mem_use->record_reference (ref, false);
> +		continue;
> +	      }
> +
> +	    resource_info resource { mode, regno };
> +	    auto def = find_def (resource, pos).prev_def (pos);
> +	    auto set = safe_dyn_cast <set_info *> (def);
> +	    gcc_assert (set);
> +	    mem_use = allocate<use_info> (insn, resource, set);
> +	    mem_use->record_reference (ref, true);
> +	    m_temp_uses.safe_push (mem_use);
> +	    continue;
> +	  }
> +
>  	if (use->m_has_been_superceded)
>  	  {
>  	    // This is the first reference to the resource.
> @@ -656,7 +680,8 @@ function_info::change_insns (array_slice<insn_change *> changes)
>  
>  	  // Finalize the new list of accesses for the change.  Don't install
>  	  // them yet, so that we still have access to the old lists below.
> -	  finalize_new_accesses (change);
> +	  finalize_new_accesses (change,
> +				 placeholder ? placeholder : insn);
>  	}
>        placeholders[i] = placeholder;
>      }
> diff --git a/gcc/rtl-ssa/functions.h b/gcc/rtl-ssa/functions.h
> index d7da9774213..73690a0e63b 100644
> --- a/gcc/rtl-ssa/functions.h
> +++ b/gcc/rtl-ssa/functions.h
> @@ -265,7 +265,7 @@ private:
>  
>    insn_info *add_placeholder_after (insn_info *);
>    void possibly_queue_changes (insn_change &);
> -  void finalize_new_accesses (insn_change &);
> +  void finalize_new_accesses (insn_change &, insn_info *);
>    void apply_changes_to_insn (insn_change &);
>  
>    void init_function_data ();