[Bug middle-end/33714] New: ivopts miscompiles insn-output.c

[Bug middle-end/33714] New: ivopts miscompiles insn-output.c

[matz at gcc dot gnu dot org]

This was noticed by building a cross compiler from i386 to x86_64.  gcc 4.2.1
will miscompile insn-output.c, the prologue_save_insn emitter.  Can be
extracted to the attached runtime testcase.  The loop exit condition is
miscompiled by ivopts with simply -O2.  Before ivopts we have:

  i_28 = i_48 - 1;
  D.1652_15 = (long long int) i_28;
  D.1654_18 = *D.1653_45;
  D.1655_19 = D.1654_18->u.hwint[0];
  if (D.1652_15 >= D.1655_19) goto <L19>; else goto <L11>;

i.e. it compares with i_48-1, which is the loop iterator.  ivopts transforms
this into:

  i_28 = i_48 - 1;
  D.1858_83 = i_4 - 1;
  D.1859_84 = (long long unsigned int) D.1858_83;
  D.1860_85 = ivtmp.163_71 * 16;
  D.1861_86 = D.1859_84 + D.1860_85;
  D.1652_87 = (long long int) D.1861_86;
  D.1652_15 = D.1652_87;
  D.1654_18 = *D.1653_45;
  D.1655_19 = D.1654_18->u.hwint[0];
  ivtmp.163_72 = ivtmp.163_71 - 16;
  if (D.1652_15 >= D.1655_19) goto <L19>; else goto <L11>;

i_4-1 is the base variable for the loop iterator.  ivopts tries to express
the D.1652_15 in terms of that base and the new ivtmp.163.  Unfortunately
that ivtmp is multiplied by 16, and also has a stepsize of 16 (the
multiplication by 16 actually is wrong even if the stepsize would be 16 as
that then would multiply by 256 for the use in the D.1860_85 expression).


-- 
           Summary: ivopts miscompiles insn-output.c
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: matz at gcc dot gnu dot org
  GCC host triplet: i686-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33714

[Bug middle-end/33714] ivopts miscompiles insn-output.c

[matz at gcc dot gnu dot org]

------- Comment #1 from matz at gcc dot gnu dot org  2007-10-09 15:52 -------
Created an attachment (id=14331)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14331&action=view)
runtime testcase


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33714

[Bug middle-end/33714] [4.2 Regression] ivopts miscompiles insn-output.c

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2007-10-09 16:16 -------
Confirmed.  You need HWI of 32bits to trigger the problem.  Maybe latent on
the trunk (I didn't check if it fails there, too).


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org, rakdver at gcc dot gnu
                   |                            |dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
 GCC target triplet|                            |i?86-*-*
           Keywords|                            |wrong-code
      Known to fail|                            |4.2.2
      Known to work|                            |4.1.1
   Last reconfirmed|0000-00-00 00:00:00         |2007-10-09 16:16:38
               date|                            |
            Summary|ivopts miscompiles insn-    |[4.2 Regression] ivopts
                   |output.c                    |miscompiles insn-output.c


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33714

[Bug middle-end/33714] [4.2 Regression] ivopts miscompiles insn-output.c

[rakdver at gcc dot gnu dot org]

-- 

rakdver at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rakdver at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-10-09 16:16:38         |2007-10-09 16:51:25
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33714

[Bug middle-end/33714] [4.2 Regression] ivopts miscompiles insn-output.c

[rakdver at gcc dot gnu dot org]

------- Comment #3 from rakdver at gcc dot gnu dot org  2007-10-12 03:03 -------
(In reply to comment #2)
> Confirmed.  You need HWI of 32bits to trigger the problem.  Maybe latent on
> the trunk (I didn't check if it fails there, too).

The problem was fixed in mainline in this commit (I somehow did not realize
that this code was present also in 4.2):

2006-12-13  Zdenek Dvorak <dvorakz@suse.cz>

        * tree-ssa-loop-ivopts.c:
        ...
        (constant_multiple_of): Fix order of operators for division.
        ...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33714

[Bug middle-end/33714] [4.2 Regression] ivopts miscompiles insn-output.c

[rakdver at gcc dot gnu dot org]

------- Comment #4 from rakdver at gcc dot gnu dot org  2007-10-12 22:27 -------
Subject: Bug 33714

Author: rakdver
Date: Fri Oct 12 22:26:47 2007
New Revision: 129277

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=129277
Log:
        PR tree-optimization/33714
        * tree-ssa-loop-ivopts.c (constant_multiple_of): Pass the arguments to
        division in the correct order.

        * gcc.dg/tree-ssa/pr33714.c: New test.


Added:
    branches/gcc-4_2-branch/gcc/testsuite/gcc.dg/tree-ssa/pr33714.c
Modified:
    branches/gcc-4_2-branch/gcc/ChangeLog
    branches/gcc-4_2-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_2-branch/gcc/tree-ssa-loop-ivopts.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33714

[Bug middle-end/33714] [4.2 Regression] ivopts miscompiles insn-output.c

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2007-10-22 08:38 -------
Fixed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.2.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33714