Re: [PATCH] x86: bpf_jit_comp: Reduce is_ereg() code size

From: Alexei Starovoitov
Date: Thu Dec 04 2014 - 18:31:05 EST

On Thu, Dec 4, 2014 at 3:14 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> On Thu, 2014-12-04 at 15:00 -0800, Joe Perches wrote:
>> Use the (1 << reg) & mask trick to reduce code size.
>> x86-64 size difference -O2 without profiling for various
>> gcc versions:
>> Signed-off-by: Joe Perches <joe@xxxxxxxxxxx>
>> ---
>> compiled, untested by me, but per Alexei Starovoitov this passes
>> the test_bpf suite
> Really, the root cause of this is the 'inline' abuse in non fast paths
> for non trivial functions.

well, it is a trivial function even from compiler point of view.
Dropping inline keyword doesn't help. gcc still inlines them.
Changing all 3 functions to _noinline_ doesn't help either.
So I think this patch is actually quite helpful to reduce code size.
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