IRA combine_and_move_insns fix, PR78669

[Uros Bizjak]

Hello!

> In this PR, we have two registers with "replace" set for them. When processing the first, we
> delete its setter, which happens to be the only use of the other register. In the second iteration we
> then assert that the other register has a use, which would be reasonable if we hadn't deleted it.

--- gcc/testsuite/gcc.target/i386/pr78669.c (nonexistent)
+++ gcc/testsuite/gcc.target/i386/pr78669.c (working copy)
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target lp64 } */

/* { dg-require-effective-target int128 } */

Uros.