From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Perches Subject: Re: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return Date: Wed, 26 Nov 2014 10:02:45 -0800 Message-ID: <1417024965.19695.7.camel@perches.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: Quentin Lambert , "David S. Miller" , Alexey Kuznetsov , James Morris , Hideaki YOSHIFUJI , Patrick McHardy , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: Alexei Starovoitov Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote: > On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches 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 */