On 9/22/17, 8:00 AM, "linux-kernel-ow...@vger.kernel.org on behalf of Colin King" <linux-kernel-ow...@vger.kernel.org on behalf of colin.k...@canonical.com> wrote: > From: Colin Ian King <colin.k...@canonical.com> > > Don't populate const array rtbTable on the stack, instead make it > static. Also split overly long line to clean a chechkpach warning. > Makes the object code smaller by nearly 500 bytes: > > Before: > text data bss dec hex filename > 13297 104 0 13401 3459 lib/zstd/fse_compress.o > > After: > text data bss dec hex filename > 12742 160 0 12902 3266 lib/zstd/fse_compress.o > > (gcc 6.3.0, x86-64) > > Signed-off-by: Colin Ian King <colin.k...@canonical.com>
I tested your patch with gcc-7.1 on x86, and benchmarked the speed on upstream zstd. There isn't a noticeable speed difference, since it isn't a particularly hot piece of code. Would you be able to submit the same patch upstream [1], or would you be okay with me porting it back upstream, so it doesn't get lost on an update? I didn't expect gcc to leave constant arrays on the stack, that seems silly. Clang makes it static, but gcc loads it onto the stack, and in 6.3+ it saves the data statically, and then uses vector instructions to load it onto the stack [2]. Tested-by: Nick Terrell <terre...@fb.com> [1] https://github.com/facebook/zstd [2] https://godbolt.org/g/fvTcED
