Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implementadaptive spinning

[H. Peter Anvin]

Andi Kleen wrote:
> On Mon, Jan 12, 2009 at 11:02:17AM -0800, Linus Torvalds wrote:
> > > Something at the back of my mind said "aliasing".
> > >
> > > $ gcc linus.c -O2 -S ; grep subl linus.s
> > >         subl    $1624, %esp
> > > $ gcc linus.c -O2 -S -fno-strict-aliasing; grep subl linus.s
> > >         subl    $824, %esp
> > >
> > > That's with 4.3.2.
> > Interesting. 
> >
> > Nonsensical, but interesting.
>
> What I find nonsensical is that -fno-strict-aliasing generates
> better code here. Normally one would expect the compiler seeing
> more aliases with that option and then be more conservative
> regarding any sharing. But it seems to be the other way round
> here.

For this to be convolved with aliasing *AT ALL* indicates this is done 
incorrectly.

This is about storage allocation, not aliases.  Storage allocation only 
depends on lifetime.

	-hpa

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