On Wed, 6 Feb 2013 09:02:04 +0000 "Woodhouse, David" <david.woodho...@intel.com> wrote:
> On Tue, 2013-02-05 at 21:04 -0600, Kim Phillips wrote: > > gcc -Os emits calls to __bswapsi2 on those platforms to save space > > because they don't have the single rev byte swap instruction. > > Is that the right thing for GCC to do in that situation? if it saves space, why wouldn't it be? "Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function is emitted." [1] I see "(arm_arch6 || !optimize_size)" in gcc's define_expand "bswapsi2" source, so GCC considers size optimization as a legitimate one of those cases. > If so, perhaps we should be *providing* __bswap[sd]i2 functions for it > to use? either that, or link with libgcc - why does arch/arm64 do this and arch/arm not? It's not obvious from git log. > If not, perhaps there should be a PR filed? > > Or is our use case justifiably different to the general case of '-Os'? > If so, why? shouldn't be - a patch, such as this, that claims to reduce code size, and that only turns on the new built-in when CC_OPTIMIZE_FOR_SIZE is off, is generally not good :) OTOH, the target here is armv6+ performance - not armv4,5 code density - the OPTIMIZE_FOR_SIZE protection prevents armv4,5 build breakage. Kim [1] http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other-Builtins -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
