[Bug c/29925] New: Wrong code with -ftree-vectorize

["jean-marc dot valin at usherbrooke dot ca" <gcc-bugzilla at gcc dot gnu dot org>]

I just hit what seems to be a wrong code generation bug in gcc. The bug happens
only when compiling the attached file with:
gcc -g -O1 -ffast-math -ftree-vectorize gcc_bug.c -o gcc_bug

Removing any one of -O1 -ffast-math -ftree-vectorize makes the problem go away.
When I run the complete code (which is in the Speex codec BTW), not only do I
get the wrong result, but there is a "read past array" that happens. With the
reduced example, only the read error is visible and valgrind reports:

==9508== Invalid read of size 8
==9508==    at 0x4004E3: interp_pitch (gcc_bug.c:17)
==9508==    by 0x4005D2: main (gcc_bug.c:29)
==9508==  Address 0x4D64224 is 500 bytes inside a block of size 504 alloc'd
==9508==    at 0x4A1FB37: calloc (vg_replace_malloc.c:279)
==9508==    by 0x4005A8: main (gcc_bug.c:25)

This is on an Ubuntu 64-bit Edgy machine with gcc -v:

Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --enable-mpfr --enable-checking=release
x86_64-linux-gnu
Thread model: posix
gcc version 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5)


-- 
           Summary: Wrong code with -ftree-vectorize
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jean-marc dot valin at usherbrooke dot ca


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29925