[Bug target/56513] New: Wrong code generation with -O3 on ARM

[Bug target/56513] New: Wrong code generation with -O3 on ARM

[tim.kosse@filezilla-project.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56513

             Bug #: 56513
           Summary: Wrong code generation with -O3 on ARM
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: tim.kosse@filezilla-project.org


Created attachment 29571
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29571
Small test program exhibiting the problem

If I'm cross-compiling the attached sample-program using gcc 4.7.2 for ARM on
an x86-64 system, the resulting binary behaves wrongly if -O3 is used.

Output with -O0:

value: -23
best:  -10000
a:     -68
value: -22
best:  -23
a:     -23

Output with -O3:

value: -23
best:  -10000
a:     -68
value: -22
best:  -23
a:     65513
BUG

[Bug target/56513] Wrong code generation with -O3 on ARM

[tim.kosse@filezilla-project.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56513

--- Comment #1 from Tim Kosse <tim.kosse@filezilla-project.org> 2013-03-03 18:47:18 UTC ---
Created attachment 29572
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29572
Preprocessed file

Created using the following command:
arm-unknown-linux-gnueabi-g++ -v -save-temps -O3 bug.cpp

[Bug target/56513] Wrong code generation with -O3 on ARM

[tim.kosse@filezilla-project.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56513

--- Comment #2 from Tim Kosse <tim.kosse@filezilla-project.org> 2013-03-03 18:48:49 UTC ---
Created attachment 29573
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29573
Compiler output

Output of arm-unknown-linux-gnueabi-g++ -v -save-temps -O3 bug.cpp

[Bug target/56513] Wrong code generation with -O3 on ARM

[tim.kosse@filezilla-project.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56513

--- Comment #3 from Tim Kosse <tim.kosse@filezilla-project.org> 2013-03-03 18:55:20 UTC ---
Also happens with GCC 4.7.1 and 4.6.3.

[Bug target/56513] Wrong code generation with -O3 on ARM

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56513

Mikael Pettersson <mikpe at it dot uu.se> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mikpe at it dot uu.se

--- Comment #4 from Mikael Pettersson <mikpe at it dot uu.se> 2013-03-03 20:11:08 UTC ---
I can reproduce the wrong-code on armv5tel-linux-gnueabi with gcc-4.7-20130302
and gcc-4.6-20121109, but not with gcc-4.8-20130224.  I can't reproduce on
x86_64, sparc64, aarch64, or m68k.

[Bug target/56513] Wrong code generation with -O3 on ARM

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56513

--- Comment #5 from Mikael Pettersson <mikpe at it dot uu.se> 2013-03-03 23:26:49 UTC ---
The wrong-code stopped for 4.8 with r188526, the introduction and enabling of
-ftree-coalesce-vars.  At that point the wrong-code reappears with -O3
-fno-tree-coalesce-vars, however with current trunk those options give correct
code.  I'll investigate some more tomorrow.

[Bug target/56513] Wrong code generation with -O3 on ARM

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56513

--- Comment #6 from Mikael Pettersson <mikpe at it dot uu.se> 2013-03-04 13:24:04 UTC ---
The wrong-code with -O3 -fno-tree-coalesce-vars stopped occurring at r190284,
Richard Biener's large "Allow anonymous SSA names" patch.  The patch
description mentions minor code generation differences, but it doesn't appear
to contain actual wrong code fixes so the underlying issue may still be latent
on trunk.