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Re: %destructor feedback

From: Frank Heckenbach
Subject: Re: %destructor feedback
Date: Wed, 7 Dec 2005 04:20:25 +0100
User-agent: semail 20050409

Joel E. Denny wrote:

> On Wed, 7 Dec 2005, Frank Heckenbach wrote:
> > And doesn't it also prevent the compiler from putting e in a
> > register (when applied to a local variable), thus pessimizing the
> > code generated?
> If the variable is unused except for the one reference within YYUSE(), how 
> much of an impact will it have if the compiler is unable to put it in a 
> register?

Maybe a small one, though it does have to allocate space ...

> > And what about the yyunused variable? If it's declared locally, some
> > version of a compiler or lint may find that it's assigned a value
> > that's never used
> It is used at the next YYUSE() execution:

And for the last (or only) one?

> >, and if declared globally, a compiler cannot
> > readily optimize away the spurious assignment.
> Unless YYUSE() appears in a short loop (not in bison, I believe), wouldn't 
> the performance penalty be trivial?

Probably, though if the macro is made available to the user, they
may use it in a short loop ...

> I ask these questions out of ignorance, but if you wouldn't mind 
> entertaining them anyway, I'd appreciate it.

I'm wondering if any kind of performance penalty is justified only
to please lint ...


Frank Heckenbach, address@hidden
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