[Bug tree-optimization/36646] New: [4.4 regression] Unnecessary moves generated on loop boundaries

[Bug tree-optimization/36646] New: [4.4 regression] Unnecessary moves generated on loop boundaries

[astrange at ithinksw dot com]

The attached source is a loop+switch statement, where only some of the switch
cases change the variable 'val'. 4.4 generates moves for it in every case, even
the ones where it's not mentioned, while 4.2 didn't; the difference is visible
in tree dumps.

This part:
            case Op_Inc1: (*tape)++; break;

with 4.2 at -O:

<L3>:;
  *tape = *tape + 1;
  goto <bb 3> (<L0>);

L5:
        incb    (%edx)
        jmp     L13

SVN at -O:
<L3>:;
  *tape.17 = *tape.17 + 1;
  val.16 = val;
  goto <bb 3> (<L10>);

L6:
        incb    (%esi)
        movl    %edx, %eax
        jmp     L10

Suprisingly, -O3 is worse:
L6:
        movl    %edx, %eax
        incb    (%esi)
        movl    %eax, %edx
        jmp     L2

IRA doesn't improve it.
This isn't from real-world code, so it's not really important, but I'd like to
make a code-copying VM out of this.


-- 
           Summary: [4.4 regression] Unnecessary moves generated on loop
                    boundaries
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: astrange at ithinksw dot com
GCC target triplet: i?86-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.4 regression] Unnecessary moves generated on loop boundaries

[astrange at ithinksw dot com]

------- Comment #1 from astrange at ithinksw dot com  2008-06-27 04:57 -------
Created an attachment (id=15818)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15818&action=view)
testcase


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.4 regression] Unnecessary moves generated on loop boundaries

[astrange at ithinksw dot com]

------- Comment #2 from astrange at ithinksw dot com  2008-06-27 05:04 -------
Created an attachment (id=15819)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15819&action=view)
svn 20080625 + -O compile


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.3/4.4 regression] Unnecessary moves generated on loop boundaries

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-06-27 09:23 -------
This is just out-of-SSA not coalescing "properly" because of

  val_16 = val_3 + 8;
  D.2623_17 = val_3->ptr_off;

which has overlapping life-ranges for val_3 and val_16.  Earlier
compilers either didn't eliminate o in favor of val or were able
to fix this during rtl optimization.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
 GCC target triplet|i?86-*-*                    |i?86-*-*, x86_64-*-*
           Keywords|                            |missed-optimization
      Known to work|                            |4.2.4
   Last reconfirmed|0000-00-00 00:00:00         |2008-06-27 09:23:50
               date|                            |
            Summary|[4.4 regression] Unnecessary|[4.3/4.4 regression]
                   |moves generated on loop     |Unnecessary moves generated
                   |boundaries                  |on loop boundaries
   Target Milestone|---                         |4.3.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.3/4.4 Regression] Unnecessary moves generated on loop boundaries

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
            Summary|[4.3/4.4 regression]        |[4.3/4.4 Regression]
                   |Unnecessary moves generated |Unnecessary moves generated
                   |on loop boundaries          |on loop boundaries


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.3/4.4 Regression] Unnecessary moves generated on loop boundaries

[jsm28 at gcc dot gnu dot org]

------- Comment #4 from jsm28 at gcc dot gnu dot org  2008-08-27 22:04 -------
4.3.2 is released, changing milestones to 4.3.3.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.2                       |4.3.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.3/4.4 Regression] Unnecessary moves generated on loop boundaries

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2009-01-24 10:20 -------
GCC 4.3.3 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.3                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.3/4.4/4.5 Regression] Unnecessary moves generated on loop boundaries

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2009-08-04 12:29 -------
GCC 4.3.4 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.4                       |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.3/4.4/4.5 Regression] Unnecessary moves generated on loop boundaries

[astrange at ithinksw dot com]

------- Comment #7 from astrange at ithinksw dot com  2009-10-20 21:10 -------
Tried with SVN today and it's fixed:

L6:
        incb    (%ebx)
        jmp     L12
        .align 4,0x90

Close if you want; I don't think it's worth finding when this happened.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646

[Bug tree-optimization/36646] [4.3/4.4/4.5 Regression] Unnecessary moves generated on loop boundaries

[astrange at ithinksw dot com]

------- Comment #8 from astrange at ithinksw dot com  2009-11-07 09:03 -------
Closing.


-- 

astrange at ithinksw dot com changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36646