tgsi_exec is simple; llvm is fast; and tgsi_sse2 ends up being neither. So really serves no purpose and is currently broken. Patch is big, so please see it in: http://cgit.freedesktop.org/mesa/mesa/commit/?h=remove-tgsi-sse2&id=aa7a6ec9d2bba743166c93ab15ba2e0872aff0d2