Messages in this thread Patch in this message | | | Subject | Re: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return | From | Joe Perches <> | Date | Wed, 26 Nov 2014 10:02:45 -0800 |
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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 --- diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 3f62734..09e2cea 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -135,11 +135,11 @@ static const int reg2hex[] = { */ static inline bool is_ereg(u32 reg) { - if (reg == BPF_REG_5 || reg == AUX_REG || - (reg >= BPF_REG_7 && reg <= BPF_REG_9)) - return true; - else - return false; + return (1 << reg) & (BIT(BPF_REG_5) | + BIT(AUX_REG) | + BIT(BPF_REG_7) | + BIT(BPF_REG_8) | + BIT(BPF_REG_9)); } /* add modifiers if 'reg' maps to x64 registers r8..r15 */
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