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

[Alexei Starovoitov]

On Thu, Dec 4, 2014 at 3:00 PM, Joe Perches <joe@xxxxxxxxxxx> wrote:
> Use the (1 << reg) & mask trick to reduce code size.
>
> x86-64 size difference -O2 without profiling for various
> gcc versions:
>
> $ size arch/x86/net/bpf_jit_comp.o*
>    text    data     bss     dec     hex filename
>    9266       4       0    9270    2436 arch/x86/net/bpf_jit_comp.o.4.4.new
>   10042       4       0   10046    273e arch/x86/net/bpf_jit_comp.o.4.4.old
>    9109       4       0    9113    2399 arch/x86/net/bpf_jit_comp.o.4.6.new
>    9717       4       0    9721    25f9 arch/x86/net/bpf_jit_comp.o.4.6.old
>    8789       4       0    8793    2259 arch/x86/net/bpf_jit_comp.o.4.7.new
>   10245       4       0   10249    2809 arch/x86/net/bpf_jit_comp.o.4.7.old
>    9671       4       0    9675    25cb arch/x86/net/bpf_jit_comp.o.4.9.new
>   10679       4       0   10683    29bb arch/x86/net/bpf_jit_comp.o.4.9.old
>
> Signed-off-by: Joe Perches <joe@xxxxxxxxxxx>

probably it was worth noting in comment that
reg is 4-bit value and AUX_REG==12, so it won't overflow.

Dave, it's for net-next of course.

Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Tested-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
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