[Bug middle-end/47790] New: [4.5/4.6 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[Bug middle-end/47790] New: [4.5/4.6 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

           Summary: [4.5/4.6 Regression] optimize_bitfield_assignment_op
                    no longer works in 4.5.x
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: pinskia@gcc.gnu.org


Created attachment 23391
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23391
Patch which needs testing but should fix it

Ever since expand-ssa was added optimize_bitfield_assignment_op no longer
works.  You can see the difference in the code generated in
gcc.c-torture/execute/20040629-1.c.

[Bug middle-end/47790] [4.5/4.6 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
           See Also|                            |http://gcc.gnu.org/bugzilla
                   |                            |/show_bug.cgi?id=18030,
                   |                            |http://gcc.gnu.org/bugzilla
                   |                            |/show_bug.cgi?id=18029
   Target Milestone|---                         |4.5.3

[Bug middle-end/47790] [4.5/4.6 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #23391|0                           |1
        is obsolete|                            |

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-02-18 20:47:55 UTC ---
Created attachment 23401
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23401
New patch which fixes one check dealing with code

[Bug middle-end/47790] [4.5/4.6 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.02.21 23:31:43
                 CC|                            |law at redhat dot com
     Ever Confirmed|0                           |1

[Bug middle-end/47790] [4.5/4.6 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

--- Comment #2 from Jeffrey A. Law <law at redhat dot com> 2011-02-22 17:09:36 UTC ---
A couple early comments.

First, it appears that it's never possible to get into this code via the old
path where SRC is a binary operation of some sort.  This is presumably an
artifact of how we handle expansion.

If I understand your change correctly, you're walking the use-def chain when
SRC is an SSA_NAME in the hopes of finding a suitable binary operation to set
SRC.  After that, you can just let the original code from
optimize_bitfield_assignment_op do its thing.

I found this fragment somewhat odd, what's its purpose?

+  if (TREE_CODE (op0) == SSA_NAME)
+    {
+      gimple op0stmt = get_gimple_for_ssa_name (op0);
+      if (!op0stmt || !is_gimple_assign (op0stmt) || gimple_assign_rhs_code
(op0stmt) != TREE_CODE (to) )
+    return false;
+      op0 = gimple_assign_rhs1 (op0stmt);
+    }


At this point OP0 is the RHS1 of the statement which set SRC via binary
operator.

Second, the original code stripped nops from OP0.  Is there some reason you
don't do that?  It probably doesn't matter, but you might be missing some
optimization opportunities as a result.

>From peeking at the testcase, if we could handle the case where SRC is a
typecast which is fed by a binary operation, we might have many more
opportunities to optimize.  I guess that should be considered extra credit.

[Bug middle-end/47790] [4.5/4.6/4.7 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[law at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

--- Comment #3 from Jeffrey A. Law <law at gcc dot gnu.org> 2011-03-18 14:01:47 UTC ---
Author: law
Date: Fri Mar 18 14:01:41 2011
New Revision: 171139

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=171139
Log:
    PR middle-end/47790
    * expr.c (optimize_bitfield_assignment_op): Revamp to work
    again after expansion changes.



Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/expr.c

[Bug middle-end/47790] [4.5/4.6/4.7 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #4 from Jeffrey A. Law <law at redhat dot com> 2011-03-18 14:03:00 UTC ---
Patch installed after minor formatting and comment tweaks.

[Bug middle-end/47790] [4.5/4.6/4.7 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47790

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.5.3                       |4.7.0