Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mailrus!sharkey!atanasoff!hascall
From: hascall@atanasoff.cs.iastate.edu (John Hascall)
Newsgroups: comp.lang.c
Subject: Re: Short code to determine compiler's
Message-ID: <1240@atanasoff.cs.iastate.edu>
Date: 24 Jul 89 14:03:46 GMT
References: <396@uop.uop.EDU> <225800197@uxe.cso.uiuc.edu> <579@targon.UUCP> <171@bms-at.UUCP> <14497@dartvax.Dartmouth.EDU> <1038@cernvax.UUCP> <26470@amdcad.AMD.COM>
Reply-To: hascall@atanasoff.cs.iastate.edu.UUCP (John Hascall)
Organization: Iowa State Univ. Computation Center
Lines: 21

In article <26470@amdcad.AMD.COM> tim@amd.com (Tim Olson) writes:
>In article <1038@cernvax.UUCP> hjm@cernvax.UUCP (Hubert Matthews) writes:
>| I have a question for the authors of smart C compilers: is the
>| register declaration useful at all for such compilers?
>
>Yes, the register keyword does indicate such things, but they can all be
>determined by flow analysis anyway.

    There are times that the programmer has more information than the
    compiler, consider this code fragment for example:

	for(i=0; i<foo; i++) ...
	for(j=0; j<bar; j++) ...

    and suppose the programmer knows `foo' will be large and `bar' will be
    small, then hopefully `register int i' could be a hint to the
    compiler that the first loop will be executed many times more than
    the second--something it has no clue about.

    John Hascall
    ISU Comp Center