[Bug target/80080] S390: Isses with emitted cs-instructions for __atomic builtins.

["vogt at linux dot vnet.ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80080

Dominik Vogt <vogt at linux dot vnet.ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vogt at linux dot vnet.ibm.com

--- Comment #3 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
Most of this can be fixed in the backend, but all attempts to get rid of the
additional load ("lr %r3,%31") in "bar" within the backend have failed.  This
is caused by overly complicated code being generated in
expand_compare_and_swap_loop().  I'm currently testing the patch below which
eliminates the superfluous variable cmp_reg (and the register allocated for
it).  Is there any chance to get something like this into Gcc7?  The patch
could possibly also help other targets.  (Will post on gcc-patches when the
tests are complete.)


--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -5798,17 +5798,15 @@ find_cc_set (rtx x, const_rtx pat, void *data)
 static bool
 expand_compare_and_swap_loop (rtx mem, rtx old_reg, rtx new_reg, rtx seq)
 {
-  machine_mode mode = GET_MODE (mem);
   rtx_code_label *label;
-  rtx cmp_reg, success, oldval;
+  rtx success, oldval;

   /* The loop we want to generate looks like

-       cmp_reg = mem;
+       old_reg = mem;
       label:
-        old_reg = cmp_reg;
        seq;
-       (success, cmp_reg) = compare-and-swap(mem, old_reg, new_reg)
+       (success, old_reg) = compare-and-swap(mem, old_reg, new_reg)
        if (success)
          goto label;

@@ -5816,23 +5814,21 @@ expand_compare_and_swap_loop (rtx mem, rtx old_reg, rtx
new_reg, rtx seq)
      iterations use the value loaded by the compare-and-swap pattern.  */

   label = gen_label_rtx ();
-  cmp_reg = gen_reg_rtx (mode);

-  emit_move_insn (cmp_reg, mem);
+  emit_move_insn (old_reg, mem);
   emit_label (label);
-  emit_move_insn (old_reg, cmp_reg);
   if (seq)
     emit_insn (seq);

   success = NULL_RTX;
-  oldval = cmp_reg;
+  oldval = old_reg;
   if (!expand_atomic_compare_and_swap (&success, &oldval, mem, old_reg,
                                       new_reg, false, MEMMODEL_SYNC_SEQ_CST,
                                       MEMMODEL_RELAXED))
     return false;

-  if (oldval != cmp_reg)
-    emit_move_insn (cmp_reg, oldval);
+  if (oldval != old_reg)
+    emit_move_insn (old_reg, oldval);

   /* Mark this jump predicted not taken.  */
   emit_cmp_and_jump_insns (success, const0_rtx, EQ, const0_rtx,