From:	Nate Eldredge <neldredge AT hmc DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: inefficiency of GCC output code & -O problem
Date:	18 Apr 2000 13:23:14 -0700
Organization:	InterWorld Communications
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dontmailme AT iname DOT com (Steamer) writes:

> Nate Eldredge wrote:
> 
> >GCC can do this.  Look up `regparm' in the Function Attributes section
> >of the gcc manual.
> 
> Unfortunately, regparm is incompatible with profiling (at least in
> GCC 2.8.1, which I'm using) because the -pg option inserts code
> at the beginning of each function which trashes eax and edx (and
> maybe ecx, which I didn't look at) and therefore destroys the passed
> parameters - with inevitably gruesome results.
> 
> Has this been fixed in later versions?

Hmm, so it does.  Still present in 2.95.2.  Maybe you should report
this as a bug.

> Of course, it's possible to work around it with something like
> 
> #if defined __DJGPP__ && !defined PROFILING
> #define REGPARM(n) __attribute__ ((regparm(n)))
> #else
> #define REGPARM(n)
> #endif
> 
> but then it's necessary to remember -DPROFILING in addition to -pg.

And you'll get different profiling results, thus preventing you from
finding whether regparm actually sped up the code any.  Pity.

-- 

Nate Eldredge
neldredge AT hmc DOT edu

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