[Bug c/53083] New: gcc bug in moving from the SSE registers back onto the heap.

[da_fox at mad dot scientist.com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53083

             Bug #: 53083
           Summary: gcc bug in moving from the SSE registers back onto the
                    heap.
    Classification: Unclassified
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: da_...@mad.scientist.com


After investigation of a suspected graphics-driver bug, it was found that the
issue lay with gcc. Please see
https://bugs.freedesktop.org/show_bug.cgi?id=47559 .

The problem as I understand is that gcc-4.6.0 miscompiles miarc.c from the
xorg-server package if -ftree-vectorize is enabled. This flag is enabled with
-O3.

The following minimal set of CFLAGS worked:
"-g -O2"

Adding the -ftree-vectorize separately, "-g -O2 -ftree-vectorize", caused the
program to misbehave at runtime.

I am running gentoo, the default CFLAGS for my system are:
CFLAGS="-march=native -O3 -pipe -fomit-frame-pointer -fweb -ffast-math
-mtune=native -mfpmath=sse"
I don't know if these match exactly with what is passed by portage for
compiling GCC.

Software versions (gentoo package versions):
sys-devel/gcc-4.6.0 
x11-base/xorg-server-1.11.2-r2

My hardware is a Dell XPS 15 (L502x) laptop with a 'Intel(R) Core(TM) i7-2630QM
CPU @ 2.00GHz'

I additional information is required please let me know.