Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752960AbaKZRYC (ORCPT ); Wed, 26 Nov 2014 12:24:02 -0500 Received: from mail-qa0-f48.google.com ([209.85.216.48]:51445 "EHLO mail-qa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750927AbaKZRYA (ORCPT ); Wed, 26 Nov 2014 12:24:00 -0500 MIME-Version: 1.0 Date: Wed, 26 Nov 2014 09:23:59 -0800 Message-ID: Subject: Re: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return From: Alexei Starovoitov To: Joe Perches 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" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches wrote: > On Wed, 2014-11-26 at 08:42 -0800, Alexei Starovoitov wrote: >> On Wed, Nov 26, 2014 at 1:18 AM, Quentin Lambert >> wrote: >> > Remove if then else statements preceding >> > boolean return. > [] >> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > [] >> > @@ -135,11 +135,9 @@ 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 (reg == BPF_REG_5 || >> > + reg == AUX_REG || >> > + (reg >= BPF_REG_7 && reg <= BPF_REG_9)); >> >> please remove extra () around the whole expression, and >> align in properly, and >> don't move reg==AUX_REG check to a different line. >> Subject is not warranted. I don't think it's a simplification. > > It's not really a simplification, > gcc should emit the same object code. exactly. >> imo existing code is fine and I don't think the time spent >> reviewing such changes is worth it when there is no >> improvement in readability. > > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/