Soundtouch crashes in sse_gcc.cpp due to unaligned variable

[Jeff Lu <jll544@…>]

calcCrossCorrMulti and calcCrossCorrStereo use movdqa, which requires 16-byte alignment, but variable "out" is declared as dynamic unaligned. This patch redefines "out" as global static aligned(16). Global because gcc versions <4.4 reportedly fail to align dynamic variables properly. Tested on x86_32 with gcc 4.2.4

[danielk]

Jeff, a global is no good. Please create a larger variable on the stack yourself and align a pointer into it and call it out. Something like "int x[16+4]; int *out=((&x+15)&~0xf);" but of course tested. Also a comment should reference the gcc bug report # for the fix, or at least the version it was fixed in.

PS I believe all versions of gcc actually do successfully give you 8 byte alignment; you could use that to make x smaller...

[Jeff Lu <jll544@…>]

GCC bug: ​http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16660 Comment 14 indicates gcc 4.4 revision 138335 fixes dynamic alignment > required alignment. I'll try your suggested workaround.

[Jeff Lu <jll544@…>]

Revised patch

[Jeff Lu <jll544@…>]

Revised the patch using Daniel's workaround. I tried attribute((aligned(8))) to make x smaller, but gcc then incorrectly calculated (int*)out. I believe this is the behavior described in comment 5 of the gcc bugzilla.

[Jeff Lu <jll544@…>]

To clarify my last comment, the revised patch (which doesn't use the aligned attribute) works and was tested against gcc 4.2.4. Debugging showed proper data alignment and pointer calculation.

[danielk]

(In [20599]) Fixes #6535. Hack to avoid segfault with older gcc which failed to enforce 16 byte alignment for stack variable when requested via alignment attribute. Bug fixed in gcc 4.4.0+.