rs6000: Don't use r12 for CR save on ELFv2 (PR102107)

CR is saved and/or restored on some paths where GPR12 is already live
since it has a meaning in the calling convention in the ELFv2 ABI.

It is not completely clear to me that we can always use r11 here, but
it does seem save, there is checking code (to detect conflicts here),
and it is stage 1.  So here goes.

2021-09-03  Segher Boessenkool <segher@kernel.crashing.org>

	PR target/102107
	* config/rs6000/rs6000-logue.c (rs6000_emit_prologue): On ELFv2 use r11
	instead of r12 for CR save, in all cases.

diff --git a/gcc/config/rs6000/rs6000-logue.c b/gcc/config/rs6000/rs6000-logue.c
index 07337c4..e363d56 100644 (file)
--- a/gcc/config/rs6000/rs6000-logue.c
+++ b/gcc/config/rs6000/rs6000-logue.c
@@ -3293,10 +3293,13 @@ rs6000_emit_prologue (void)
 
   /* If we need to save CR, put it into r12 or r11.  Choose r12 except when
      r12 will be needed by out-of-line gpr save.  */
-  cr_save_regno = ((DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2)
-                  && !(strategy & (SAVE_INLINE_GPRS
-                                   | SAVE_NOINLINE_GPRS_SAVES_LR))
-                  ? 11 : 12);
+  if (DEFAULT_ABI == ABI_AIX
+      && !(strategy & (SAVE_INLINE_GPRS | SAVE_NOINLINE_GPRS_SAVES_LR)))
+    cr_save_regno = 11;
+  else if (DEFAULT_ABI == ABI_ELFv2)
+    cr_save_regno = 11;
+  else
+    cr_save_regno = 12;
   if (!WORLD_SAVE_P (info)
       && info->cr_save_p
       && REGNO (frame_reg_rtx) != cr_save_regno