[Bug tree-optimization/65658] New: Jump threading too pessimistic when optimizing for size

[Bug tree-optimization/65658] New: Jump threading too pessimistic when optimizing for size

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65658

            Bug ID: 65658
           Summary: Jump threading too pessimistic when optimizing for
                    size
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: law at redhat dot com

Created attachment 35209
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35209&action=edit
testcase, compile with -O2 -Wall note uninitialized warnings for SRA's
variables and trivially threadable block in setup()

The jump threader will cancel jump threads when optimizing for size and the
block will need to be duplicated.  But that heuristic fails for something a
block like this:

  # _36 = PHI <1(2), 1(4), 0(7)>
  # problem$l3_101 = PHI <problem$l3_8(D)(2), problem$l3_8(D)(4),
problem$l3_35(7)>
  # problem$l4_100 = PHI <problem$l4_124(D)(2), problem$l4_124(D)(4),
problem$l4_34(7)>
  amt ={v} {CLOBBER};
  if (_36 != 0)
    goto <bb 25>;
  else
    goto <bb 9>;


All incoming edges are threadable and the block produces no code.  It's really
just a redirection block that's not recognized as such -- probably due to the
clobber statement.  

The net result is we cancel the jump thread, get worse code and issue false
positive warnings for uninitialized variables.  All around a lose.

[Bug tree-optimization/65658] Jump threading too pessimistic when optimizing for size

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65658

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-04-02
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug tree-optimization/65658] Jump threading too pessimistic when optimizing for size

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65658

--- Comment #2 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Author: law
Date: Mon Apr 20 17:13:52 2015
New Revision: 222242

URL: https://gcc.gnu.org/viewcvs?rev=222242&root=gcc&view=rev
Log:
    PR tree-optimization/65658
    * tree-ssa-threadupdate.c (redirection_block_p): Ignore clobber
    statements too.

    PR tree-optimization/65658
    * gcc.dg/pr65658.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/pr65658.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-threadupdate.c

[Bug tree-optimization/65658] Jump threading too pessimistic when optimizing for size

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65658

--- Comment #3 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Author: law
Date: Mon Apr 20 19:35:50 2015
New Revision: 222247

URL: https://gcc.gnu.org/viewcvs?rev=222247&root=gcc&view=rev
Log:
       PR tree-optimization/65658
        * tree-ssa-threadupdate.c (redirection_block_p): Remove
        redundant test for GIMPLE_ASSIGN in last change.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-ssa-threadupdate.c

[Bug tree-optimization/65658] Jump threading too pessimistic when optimizing for size

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65658

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> ---
Fixed with trunk commits.