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SubjectRe: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return
On 27/11/2014 13:25, David Laight wrote:
> From: Joe Perches
>> On Wed, 2014-11-26 at 10:34 -0800, Alexei Starovoitov wrote:
>>> On Wed, Nov 26, 2014 at 10:02 AM, Joe Perches <joe@perches.com> wrote:
>>>> On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote:
>>>>> On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches <joe@perches.com> wrote:
>>>>>> Is there any value in reordering these tests for frequency
>>>>>> or maybe using | instead of || to avoid multiple jumps?
>>>>> probably not. It's not a critical path.
>>>>> compiler may fuse conditions depending on values anyway.
>>>>> If it was a critical path, we could have used
>>>>> (1 << reg) & mask trick.
>>>>> I picked explicit 'return true' else 'return false' here,
>>>>> because it felt easier to read. Just a matter of taste.
>>>> There is a size difference though: (allyesconfig)
>>>>
>>>> $ size arch/x86/net/built-in.o*
>>>> text data bss dec hex filename
>>>> 12999 1012 4336 18347 47ab arch/x86/net/built-in.o.new
>>>> 13177 1076 4592 18845 499d arch/x86/net/built-in.o.old
>>> interesting. Compiler obviously thinks that 178 byte increase
>>> with -O2 is the right trade off. Which I agree with :)
>>>
>>> If I think dropping 'inline' and using -Os will give bigger savings...
>> This was allyesconfig which already uses -Os
>>
>> Using -O2, there is no difference using inline
>> or not, but the size delta with the bitmask is
>> much larger
>>
>> $ size arch/x86/net/built-in.o* (allyesconfig, but not -Os)
>> text data bss dec hex filename
>> 13410 820 3624 17854 45be arch/x86/net/built-in.o.new
>> 16130 884 4200 21214 52de arch/x86/net/built-in.o.old
>> 16130 884 4200 21214 52de arch/x86/net/built-in.o.static
> That is quite a big % change in the code size.
> Why the change in data?
>
> David
>
>
>
Do you want me to propose a second version, or should I just
drop it all together ?

I am a new contributor so I have no experience in that sort of thing.

Quentin


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