[gcc r14-8359] rtl-ssa: Support for creating new uses [PR113070]

[Alex Coplan <acoplan@gcc.gnu.org>]

https://gcc.gnu.org/g:fce3994d04fc5d7d1c91f6db5a1f144aa291439a

commit r14-8359-gfce3994d04fc5d7d1c91f6db5a1f144aa291439a
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Fri Jan 12 10:14:33 2024 +0000

    rtl-ssa: Support for creating new uses [PR113070]
    
    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):
            Ensure new uses end up referring to permanent defs.
            * rtl-ssa/functions.h (function_info::create_use): Declare.

Diff:
---
 gcc/rtl-ssa/accesses.cc | 10 ++++++++++
 gcc/rtl-ssa/changes.cc  | 20 ++++++++++++++++----
 gcc/rtl-ssa/functions.h |  7 +++++++
 3 files changed, 33 insertions(+), 4 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..8181e5248c5 100644
--- a/gcc/rtl-ssa/changes.cc
+++ b/gcc/rtl-ssa/changes.cc
@@ -609,15 +609,27 @@ 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..e00a398069a 100644
--- a/gcc/rtl-ssa/functions.h
+++ b/gcc/rtl-ssa/functions.h
@@ -73,6 +73,13 @@ public:
 			insn_info *insn,
 			resource_info resource);
 
+  // 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.
+  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,