linux-kernel - Re: [PATCH] Input: alps: Drop unlikely before IS_ERR(_OR

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Date:   Wed, 12 Jun 2019 01:35:34 -0700
From:   Joe Perches <joe@...ches.com>
To:     Pali Rohár <pali.rohar@...il.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH] Input: alps: Drop unlikely before IS_ERR(_OR_NULL)

On Wed, 2019-06-12 at 09:14 +0200, Pali Rohár wrote:
> On Tuesday 11 June 2019 17:59:13 Dmitry Torokhov wrote:
> > Hi Joe,
> > 
> > On Wed, Jun 05, 2019 at 07:28:53PM -0700, Joe Perches wrote:
> > > On Thu, 2019-06-06 at 09:08 +0800, Kefeng Wang wrote:
> > > > On 2019/6/5 22:42, Pali Rohár wrote:
> > > > > On Wednesday 05 June 2019 22:24:28 Kefeng Wang wrote:
> > > > > > IS_ERR(_OR_NULL) already contain an 'unlikely' compiler flag,
> > > > > > so no need to do that again from its callers. Drop it.
> > > > > Hi! I already reviewed this patch and rejected it, see:
> > > > > https://patchwork.kernel.org/patch/10817475/
> > > > OK, please ignore it.
> > > 
> > > I think the stated reason of better readability isn't
> > > particularly sensible as the object code produced is
> > > actually slightly larger.
> > > 
> > > x86-64 defconfig (gcc 8.3.0)
> > > 
> > > $ size drivers/input/mouse/alps.o*
> > >    text	   data	    bss	    dec	    hex	filename
> > >   29416	     56	      0	  29472	   7320	drivers/input/mouse/alps.o.new
> > >   29432	     56	      0	  29488	   7330	drivers/input/mouse/alps.o.old
> > 
> > If gcc produces worse code for double unlikely, you should probably
> > report it to gcc folks, no? Or double unlikely turns into likely?
> 
> Is measured size of stripped or unstripped binary? Plus with or without
> debug symbols? Double unlikely version should have more debug symbols
> and therefore also larger size.
> 
> But if unstripped version with double unlikely is larger then it is for
> sure compiler bug.

defconfig so no debug symbols.

It's not necessarily a gcc bug as gcc doesn't
guarantee compiler repeatability.