rtl-ssa: Add entry point to allow re-parenting uses

This is needed by the upcoming aarch64 load pair pass, as it can
re-order stores (when alias analysis determines this is safe) and thus
change which mem def a given use consumes (in the RTL-SSA view, there is
no alias disambiguation of memory).

gcc/ChangeLog:

	* rtl-ssa/accesses.cc (function_info::reparent_use): New.
	* rtl-ssa/functions.h (function_info): Declare new member
	function reparent_use.

2 files changed, 11 insertions, 0 deletions

diff --git a/gcc/rtl-ssa/accesses.cc b/gcc/rtl-ssa/accesses.cc
index f12b5f4..774ab9d 100644
--- a/gcc/rtl-ssa/accesses.cc
+++ b/gcc/rtl-ssa/accesses.cc
@@ -1239,6 +1239,14 @@ function_info::add_use (use_info *use)
     insert_use_before (use, neighbor->value ());
 }
 
+void
+function_info::reparent_use (use_info *use, set_info *new_def)
+{
+  remove_use (use);
+  use->set_def (new_def);
+  add_use (use);
+}
+
 // If USE has a known definition, remove USE from that definition's list
 // of uses.  Also remove if it from the associated splay tree, if any.
 void
diff --git a/gcc/rtl-ssa/functions.h b/gcc/rtl-ssa/functions.h
index 8b53b26..d7da977 100644
--- a/gcc/rtl-ssa/functions.h
+++ b/gcc/rtl-ssa/functions.h
@@ -159,6 +159,9 @@ public:
   // Like change_insns, but for a single change CHANGE.
   void change_insn (insn_change &change);
 
+  // Given a use USE, re-parent it to get its def from NEW_DEF.
+  void reparent_use (use_info *use, set_info *new_def);
+
   // If the changes that have been made to instructions require updates
   // to the CFG, perform those updates now.  Return true if something changed.
   // If it did: