linux-kernel - Re: + fls-change-parameter-to-unsigned-int.patch added to -mm tree

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Message-ID: <20181106170149.GA12947@avx2>
Date:   Tue, 6 Nov 2018 20:01:49 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        linux-arch@...r.kernel.org
Subject: Re: + fls-change-parameter-to-unsigned-int.patch added to -mm tree

On Tue, Nov 06, 2018 at 07:44:37AM -0800, Matthew Wilcox wrote:
> On Tue, Nov 06, 2018 at 06:14:44PM +0300, Alexey Dobriyan wrote:
> > On Mon, Nov 05, 2018 at 03:33:01PM -0800, akpm@...ux-foundation.org wrote:
> > 
> > > -static inline int fls(int x)
> > > +static inline int fls(unsigned int x)
> > >  {
> > > -	return fls64((unsigned int) x);
> > > +	return fls64(x);
> > >  }
> > 
> > Should it return "unsigned"? Logically it should.
> > I remember doing this and there was some code size increase :-(
> 
> Yes, it returns a number in the range [0-32], so it can absolutely
> be unsigned.  I'm kind of surprised it made any difference.
> 
> When you say "doing this", what did you try?  unsigned fls(unsigned),
> int fls(unsigned) or unsigned fls(int) ?

I did "unsigned fls()" with and without

	if (rv > 32)
		__builtin_unreachable();

but I didn't send anything because there was something erratic with code
generation.