Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753164AbaKZSCx (ORCPT ); Wed, 26 Nov 2014 13:02:53 -0500 Received: from smtprelay0092.hostedemail.com ([216.40.44.92]:47023 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750828AbaKZSCv (ORCPT ); Wed, 26 Nov 2014 13:02:51 -0500 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2198:2199:2393:2553:2559:2562:2828:3138:3139:3140:3141:3142:3353:3622:3866:3867:3870:3871:3872:4321:5007:6119:6261:6742:7974:8603:10004:10400:10848:11026:11232:11658:11914:12517:12519:12555:12740:13069:13161:13229:13311:13357:13972:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: way33_8cc430988cc4c X-Filterd-Recvd-Size: 2760 Message-ID: <1417024965.19695.7.camel@perches.com> Subject: Re: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return From: Joe Perches To: Alexei Starovoitov 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" Date: Wed, 26 Nov 2014 10:02:45 -0800 In-Reply-To: References: Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.12.7-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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 */ -- 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/