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* [Bug tree-optimization/21596] New: [4.0/4.1 Regression] extra temporaries when using global register variables
@ 2005-05-15 23:45 rth at gcc dot gnu dot org
  2005-05-15 23:57 ` [Bug tree-optimization/21596] " pinskia at gcc dot gnu dot org
                   ` (2 more replies)
  0 siblings, 3 replies; 21+ messages in thread
From: rth at gcc dot gnu dot org @ 2005-05-15 23:45 UTC (permalink / raw)
  To: gcc-bugs

register int *reg __asm__("%edi");
int test () { return *--reg <= 0; }

With -O2 -fomit-frame-pointer, 4.0,

        movl    %edi, %eax
        leal    -4(%edi), %edi
        movl    -4(%eax), %eax
        testl   %eax, %eax

With 3.4,

        subl    $4, %edi
        cmpl    $0, (%edi)

The problem appears to begin at the tree level, with extra temporaries:

  reg.0 = reg;
  reg.2 = reg.0 - 4B;
  reg = reg.2;
  return *reg.2 <= 0;

We do consider hard register variables not is_gimple_reg, due to needing
to V_MAY_DEF them at call sites.  It would be nice if we could eliminate
these temporaries during TER, or something.

-- 
           Summary: [4.0/4.1 Regression] extra temporaries when using global
                    register variables
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rth at gcc dot gnu dot org
                CC: amacleod at redhat dot com,gcc-bugs at gcc dot gnu dot
                    org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21596


^ permalink raw reply	[flat|nested] 21+ messages in thread
end of thread, other threads:[~2009-03-30 15:45 UTC | newest]

Thread overview: 21+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
     [not found] <bug-21596-119@http.gcc.gnu.org/bugzilla/>
2005-10-22  4:08 ` [Bug tree-optimization/21596] [4.0/4.1 Regression] extra temporaries when using global register variables pinskia at gcc dot gnu dot org
2005-10-31  3:36 ` mmitchel at gcc dot gnu dot org
2006-02-24  0:31 ` [Bug tree-optimization/21596] [4.0/4.1/4.2 " mmitchel at gcc dot gnu dot org
2006-05-25  2:34 ` mmitchel at gcc dot gnu dot org
2006-07-05  9:27 ` pinskia at gcc dot gnu dot org
2006-07-22 11:08 ` steven at gcc dot gnu dot org
2007-02-14  9:13 ` [Bug tree-optimization/21596] [4.0/4.1/4.2/4.3 " mmitchel at gcc dot gnu dot org
2007-03-05 22:43 ` amacleod at redhat dot com
2007-03-05 22:52 ` amacleod at redhat dot com
2007-03-06 15:02 ` amacleod at redhat dot com
2007-03-07  8:23 ` bonzini at gnu dot org
2007-03-10  1:40 ` mmitchel at gcc dot gnu dot org
2007-08-23 16:15 ` rguenth at gcc dot gnu dot org
2007-11-19  8:56 ` steven at gcc dot gnu dot org
2007-11-19  9:08 ` pinskia at gcc dot gnu dot org
2007-11-19  9:35 ` [Bug tree-optimization/21596] [4.0/4.1/4.2 " pinskia at gcc dot gnu dot org
2008-07-04 16:54 ` [Bug tree-optimization/21596] [4.2 " jsm28 at gcc dot gnu dot org
2009-03-30 15:45 ` jsm28 at gcc dot gnu dot org
2005-05-15 23:45 [Bug tree-optimization/21596] New: [4.0/4.1 " rth at gcc dot gnu dot org
2005-05-15 23:57 ` [Bug tree-optimization/21596] " pinskia at gcc dot gnu dot org
2005-07-08  1:42 ` mmitchel at gcc dot gnu dot org
2005-09-27 16:23 ` mmitchel at gcc dot gnu dot org

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