[PATCH] recog.c: Fix RTX unsharing in change groups

[Andreas Krebbel]

Hi,

we currently miss to do RTX unsharing in some cases when mixing
validate_change requests with and without rtx unsharing in the same
change group.

Debugging a setjmp testcase on s390 I've seen the following behaviour:

In an insn like A = B + C B is replaced with D in fold_rtx. Unsharing is
requested for D in this replacement (A = D + C). Later on fold_rtx
invokes canonicalize_change_group which decides to swap D and C
without requesting unsharing again (A = C + D). Since the unsharing
for a change group is delayed until confirm_change_group and is bound
to a location rather then the expression C is unshared instead of D
then.

The attached patch prevents that by doing RTX unsharing for all
subsequent changes after finding a single change where unsharing has
been explicitly requested.

Ok for mainline?

Bye,

-Andreas-


2011-03-04  Andreas Krebbel  <andreas.kreb...@de.ibm.com>

        * recog.c (confirm_change_group): Unshare all RTXs after finding
        one in the group where unsharing has been requested.


Index: gcc/recog.c
===================================================================
*** gcc/recog.c.orig
--- gcc/recog.c
*************** confirm_change_group (void)
*** 454,465 ****
  {
    int i;
    rtx last_object = NULL;
  
    for (i = 0; i < num_changes; i++)
      {
        rtx object = changes[i].object;
  
!       if (changes[i].unshare)
        *changes[i].loc = copy_rtx (*changes[i].loc);
  
        /* Avoid unnecessary rescanning when multiple changes to same 
instruction
--- 454,471 ----
  {
    int i;
    rtx last_object = NULL;
+   bool unshare_p = false;
  
    for (i = 0; i < num_changes; i++)
      {
        rtx object = changes[i].object;
  
!       /* After doing one change which needs unsharing all subsequent
!        changes need unsharing as well.  A subsequent change might
!        move parts of the object which have been requested to get
!        unshared before without requesting unsharing itself.  */
!       unshare_p = unshare_p || changes[i].unshare;
!       if (unshare_p)
        *changes[i].loc = copy_rtx (*changes[i].loc);
  
        /* Avoid unnecessary rescanning when multiple changes to same 
instruction