Re: [PATCH] lib/lz4: make arrays static const, reduces object code size

Arnd Bergmann
2017-09-22T07:48:25Z

On Fri, Sep 22, 2017 at 1:11 AM, Colin Ian King
<colin.king@canonical.com> wrote:
> On 22/09/17 00:09, Christophe JAILLET wrote:
>> Le 22/09/2017 à 00:19, Colin King a écrit :
>>> From: Colin Ian King <colin.king@canonical.com>
>>>
>>> Don't populate the read-only arrays dec32table and dec64table on the
>>> stack, instead make them both static const. Makes the object code
>>> smaller by over 10K bytes:
>> 10k? Wouaouh! This is way much more than what you usually win with such
>> patches.
>
> Yes, I had to triple check it because it was an unbelievable win.
>

I wonder whether this should be reported as a gcc bug. I tried reproducing
it here with gcc-7.1.1 and gcc-8.0.0, but I only see a 4K difference:

text data bss dec hex filename
18220 176 0 18396 47dc build/tmp/lib/lz4/lz4_decompress-after.o
22297 0 0 22297 5719
build/tmp/lib/lz4/lz4_decompress-before.o

I tried x86 defconfig and allmodconfig on a slightly patched mainline kernel.

Arnd