Date: Mon, 15 Mar 1999 20:31:41 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: "Andrew Reilly" <andrew@lake.com.au> Cc: "Stephen J. Roznowski" <sjr@home.net>, freebsd-hackers@FreeBSD.ORG Subject: Re: Use of "register" in code Message-ID: <199903160431.UAA05835@apollo.backplane.com> References: <199903160333.WAA06493@istari.home.net> <199903160349.TAA05543@apollo.backplane.com> <19990316151744.A39973@reilly.home>
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:> :
:> :Thanks,
:> :--
:> :Stephen J. Roznowski (sjr@home.net)
:>
:> The register declarations are useless historical artifacts.
:
:Why do you say that? "register" in a declaration has a specific
:semantic meaning that isn't (to my knowledge) duplicated by any
:other language mechanism, and that is "this variable does not exist
:in the memory space, and so _cannot_ be de-referenced with "&" or
:modified by an asignment through a pointer." Register pointer
:variables and temporaries are very important for preventing C
:compilers from producing pessimistic inner loop code.
:
:--
:Andrew
Firstly, that is not what register means. Secondly, all modern C
compilers that I know about, including one I wrote years ago, can
trivially detect the stack locality of a variable and put it in a
register as part of standard optimizations. It's one of the *easiest*
optimizations a C compiler can do, in fact.
Some compilers will add a little weight to the potential optimization
if you use the 'register' keyword, but modern compilers tend to do a
better job without the manual weighting.
-Matt
Matthew Dillon
<dillon@backplane.com>
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