PR101260 regcprop: Add mode change check for copy reg

When propagating a multi-word register into an access with a smaller
mode the can_change_mode backend hook is already consulted for the
original register.  This however is also required for the intermediate
copy in copy_regno which might use a different register class.

gcc/ChangeLog:

	PR rtl-optimization/101260
	* regcprop.cc (maybe_mode_change): Invoke mode_change_ok also for
	copy_regno.

gcc/testsuite/ChangeLog:

	PR rtl-optimization/101260
	* gcc.target/s390/pr101260.c: New testcase.

gcc/regcprop.cc

@@ -426,7 +426,8 @@ maybe_mode_change (machine_mode orig_mode, machine_mode copy_mode,
 
   if (orig_mode == new_mode)
     return gen_raw_REG (new_mode, regno);
-  else if (mode_change_ok (orig_mode, new_mode, regno))
+  else if (mode_change_ok (orig_mode, new_mode, regno)
+	   && mode_change_ok (copy_mode, new_mode, copy_regno))
     {
       int copy_nregs = hard_regno_nregs (copy_regno, copy_mode);
       int use_nregs = hard_regno_nregs (copy_regno, new_mode);

gcc/testsuite/gcc.target/s390/pr101260.c

@@ -0,0 +1,63 @@
+/* PR rtl-optimization/101260 */
+/* { dg-do run { target s390_useable_hw } } */
+/* { dg-options "-O1 -march=z14" } */
+
+/* This used to fail with commit: 5dc1390b41d */
+
+struct a
+{
+  unsigned b:7;
+  int c;
+  int d;
+  short e;
+} p, *q = &p;
+int f, g, h, i, r, s;
+static short j[8][1][6] = { };
+
+char k[7];
+short l, m;
+int *n;
+int **o = &n;
+void
+t ()
+{
+  for (; f;)
+    ;
+}
+
+static struct a
+u (int x)
+{
+  struct a a = { 4, 8, 5, 4 };
+  for (; i <= 6; i++)
+    {
+      struct a v = { };
+      for (; l; l++)
+	h = 0;
+      for (; h >= 0; h--)
+	{
+	  j[i];
+	  struct a *w = &p;
+	  s = 0;
+	  for (; s < 3; s++)
+	    {
+	      r ^= x;
+	      m = j[i][g][h] == (k[g] = g);
+	      *w = v;
+	    }
+	  r = 2;
+	  for (; r; r--)
+	    *o = &r;
+	}
+    }
+  t ();
+  return a;
+}
+
+int
+main ()
+{
+  *q = u (636);
+  if (p.b != 4)
+    __builtin_abort ();
+}