Re: [PATCH][2.6.8-rc1-mm1] drivers/scsi/sg.c gcc341 inlining fix

[Jeff Garzik]

Mikael Pettersson wrote:
> On Wed, 14 Jul 2004 23:12:54 -0700, William Lee Irwin III wrote:
>
> > Jeff Garzik <jgarzik@xxxxxxxxx> wrote:
> >
> > > > > Or you could just call it "gcc is dumb" rather than a compiler bug.
> >
> > On Wed, Jul 14 2004, Andrew Morton wrote:
> > [... code snippet ...]
> >
> > > > is pretty dumb too.  I don't see any harm if this compiler feature/problem
> > > > pushes us to fix the above in the obvious way.
> >
> > On Thu, Jul 15, 2004 at 07:56:56AM +0200, Jens Axboe wrote:
> >
> > > Excuse my ignorance, but why on earth would that be dumb? Looks
> > > perfectly legit to me, and I have to agree with Jeff that the compiler
> > > is exceedingly dumb if it fails to inline that case.
> >
> > Enter gcc...
> >
> > Maybe "the obvious way" is sending a someone off to whip gcc into shape,
> > or possibly reporting it as a gcc problem.
>
>
> It shows you guys aren't compiler writers.

Actually, I have written most of a [simple] compiler backend.


> Compilers for top-down (define-before-use) languages like C
> have traditionally also worked in a top-down fashion, processing
> one top-level declaration at a time. Forward references are
> either errors, or are (when a proper declaration is in scope)
> left to the linker to resolve.
>
> Processing an entire compilation-unit (e.g. whole C file)
> as a single unit is typically _only_ done when either the
> language semantics requires it (not C, but e.g. Haskell),
> or when very high optimisation levels are requested.

Or in the case where you parse the entire file, then generate code for 
the entire file in a separate pass.  Which does NOT imply 
unit-at-a-time, for the readers at home.  It just implies generation of 
the AST.


> In the case of gcc-3.4.1 failing to inline, you are asking
> gcc to do something (peeking forward) which it never has
> promised to do. And with the kernel using -fno-unit-at-a-time
> for stack conservation reasons, gcc is actually being _told_
> not to do global compilation.
>
> This is not a gcc bug, nor is it being "exceedingly dumb".

Actually, yes it is.

	Jeff


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