linux-kernel - Re: Build failure with v4.9-rc1 and GCC trunk -- compiler weirdness

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Date:   Thu, 2 Feb 2017 10:02:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Markus Trippelsdorf <markus@...ppelsdorf.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>, james.greenhalgh@....com,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: Build failure with v4.9-rc1 and GCC trunk -- compiler weirdness

On Wed, Feb 01, 2017 at 11:04:54AM -0800, Joe Perches wrote:
> > +#define order_base_2(n)                                \
> > +(                                              \
> > +       __builtin_constant_p(n) ? (             \
> > +               ((n) < 2) ? (n) :               \
> > +               ilog2((n) - 1) + 1) :           \
> > +       __order_base_2(n)                       \
> > + )
> 
> Does this work properly when n is a signed negative value?

Do you see it returning a complex number?