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Sender: Arvind Sankar <niveditas98@gmail.com>
From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Thu, 29 Oct 2020 13:20:48 -0400
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        David Laight <David.Laight@ACULAB.COM>,
        'Arnd Bergmann' <arnd@kernel.org>,
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Subject: Re: [PATCH] [v2] x86: apic: avoid -Wshadow warning in header
Message-ID: <20201029172048.GA2571425@rani.riverdale.lan>
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On Thu, Oct 29, 2020 at 05:59:54PM +0100, Paolo Bonzini wrote:
> On 29/10/20 17:56, Arvind Sankar wrote:
> >> For those two just add:
> >> 	struct apic *apic = x86_system_apic;
> >> before all the assignments.
> >> Less churn and much better code.
> >>
> > Why would it be better code?
> > 
> 
> I think he means the compiler produces better code, because it won't
> read the global variable repeatedly.  Not sure if that's true,(*) but I
> think I do prefer that version if Arnd wants to do that tweak.
> 
> Paolo
> 
> (*) if it is, it might also be due to Linux using -fno-strict-aliasing
> 

Nope, it doesn't read it multiple times. I guess it still assumes that
apic isn't in the middle of what it points to: it would reload the
address if the first element of *apic was modified, but doesn't for
other elements. Interesting.