[gcc r12-5978] regrename: Skip renaming if instruction is noop move.

[gcc r12-5978] regrename: Skip renaming if instruction is noop move.

[Jeff Law]

https://gcc.gnu.org/g:a888259a71fbbb7f14923751251e056829d76342

commit r12-5978-ga888259a71fbbb7f14923751251e056829d76342
Author: JoJo R <rjiejie@linux.alibaba.com>
Date:   Tue Dec 14 16:55:57 2021 -0500

    regrename: Skip renaming if instruction is noop move.
    
    gcc/
            * regrename.c (find_rename_reg): Return satisfied regno
            if instruction is noop move.

Diff:
---
 gcc/regrename.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gcc/regrename.c b/gcc/regrename.c
index b8a9ca36f22..fe72fcc3624 100644
--- a/gcc/regrename.c
+++ b/gcc/regrename.c
@@ -394,6 +394,11 @@ find_rename_reg (du_head_p this_head, enum reg_class super_class,
 			  this_head, *unavailable))
     return this_head->tied_chain->regno;
 
+  /* If this insn is a noop move, then do not rename in this chain as doing so
+     would inhibit removal of the noop move.  */
+  if (noop_move_p (this_head->first->insn))
+    return best_new_reg;
+
   /* If PREFERRED_CLASS is not NO_REGS, we iterate in the first pass
      over registers that belong to PREFERRED_CLASS and try to find the
      best register within the class.  If that failed, we iterate in