Fix PR97497

This works around a limitation of gcse with handling of partially
clobbered registers.  With this patch our GOT pointer register r12 is
not marked as partially clobbered anymore for the -m31 -mzarch -fpic
combination. This is correct since all the bits in r12 we actually
care about are in fact preserved.

gcc/ChangeLog:

	PR rtl-optimization/97497
	* config/s390/s390.c (s390_hard_regno_call_part_clobbered): Do not
	return true for r12 when -fpic is used.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/pr97497.c: New test.

gcc/config/s390/s390.c

@@ -10376,9 +10376,16 @@ static bool
 s390_hard_regno_call_part_clobbered (unsigned int, unsigned int regno,
 				     machine_mode mode)
 {
+  /* For r12 we know that the only bits we actually care about are
+     preserved across function calls.  Since r12 is a fixed reg all
+     accesses to r12 are generated by the backend.
+
+     This workaround is necessary until gcse implements proper
+     tracking of partially clobbered registers.  */
   if (!TARGET_64BIT
       && TARGET_ZARCH
       && GET_MODE_SIZE (mode) > 4
+      && (!flag_pic || regno != PIC_OFFSET_TABLE_REGNUM)
       && ((regno >= 6 && regno <= 15) || regno == 32))
     return true;
 

gcc/testsuite/gcc.target/s390/pr97497.c

@@ -0,0 +1,36 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -march=z900 -mzarch -fpic" } */
+
+char *t;
+
+void __attribute__((noinline,noclone))
+bar(int a, char* b)
+{
+  if (a != 1)
+    __builtin_abort();
+}
+
+void __attribute__((noinline,noclone))
+baz(char* a, int b)
+{
+  if (b != 1)
+    __builtin_abort();
+}
+
+int __attribute__((noinline,noclone))
+foo (int a)
+{
+  bar (1, t);
+  if (a)
+    baz (t, 1);
+
+  bar (1, t);
+}
+
+int
+main ()
+{
+  foo (1);
+
+  return 0;
+}