rtl-ssa: Run finalize_new_accesses forwards [PR113070]

The next patch in this series exposes an interface for creating new uses
in RTL-SSA.  The intent is that new user-created uses can consume new
user-created defs in the same change group.  This is so that we can
correctly update uses of memory when inserting a new store pair insn in
the aarch64 load/store pair fusion pass (the affected uses need to
consume the new store pair insn).

As it stands, finalize_new_accesses is called as part of the backwards
insn placement loop within change_insns, but if we want new uses to be
able to depend on new defs in the same change group, we need
finalize_new_accesses to be called on earlier insns first.  This is so
that when we process temporary uses and turn them into permanent uses,
we can follow the last_def link on the temporary def to ensure we end up
with a permanent use consuming a permanent def.

gcc/ChangeLog:

	PR target/113070
	* rtl-ssa/changes.cc (function_info::change_insns): Split out the call
	to finalize_new_accesses from the backwards placement loop, run it
	forwards in a separate loop.

1 files changed, 16 insertions, 5 deletions

diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
index 2fac45a..e538b63 100644
--- a/gcc/rtl-ssa/changes.cc
+++ b/gcc/rtl-ssa/changes.cc
@@ -775,15 +775,26 @@ function_info::change_insns (array_slice<insn_change *> changes)
 	      placeholder = add_placeholder_after (after);
 	      following_insn = placeholder;
 	    }
-
-	  // 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,
-				 placeholder ? placeholder : insn);
 	}
       placeholders[i] = placeholder;
     }
 
+  // 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.
+  //
+  // Note that we do this forwards instead of in the backwards loop above so
+  // that any new defs being inserted are processed before new uses of those
+  // defs, so that the (initially) temporary uses referring to temporary defs
+  // can be easily updated to become permanent uses referring to permanent defs.
+  for (unsigned i = 0; i < changes.size (); i++)
+    {
+      insn_change &change = *changes[i];
+      insn_info *placeholder = placeholders[i];
+      if (!change.is_deletion ())
+	finalize_new_accesses (change,
+			       placeholder ? placeholder : change.insn ());
+    }
+
   // Remove all definitions that are no longer needed.  After the above,
   // the only uses of such definitions should be dead phis and now-redundant
   // live-out uses.