Re: Writing fast compilers...

alex@vmars.tuwien.ac.at (Alexander Vrchoticky)
13 Aug 91 17:28:09 GMT

          From comp.compilers

Related articles
Re: Writing fast compilers... pcg@aber.ac.uk (1991-08-11)
Re: Writing fast compilers... preston@helena.rice.edu (1991-08-11)
Re: Writing fast compilers... pardo@gar.cs.washington.edu (1991-08-13)
Re: Writing fast compilers... davidsen@crdos1.crd.ge.com (1991-08-13)
Re: Writing fast compilers... preston@helena.rice.edu (1991-08-13)
Re: Writing fast compilers... alex@vmars.tuwien.ac.at (1991-08-13)
Re: Writing fast compilers... pcg@aber.ac.uk (1991-08-14)
Re: Writing fast compilers... markh@csd4.csd.uwm.edu (1991-08-16)
Re: Writing fast compilers... glew@pdx007.intel.com (1991-08-16)
Re: Writing fast compilers... blenko-tom@CS.YALE.EDU (1991-08-16)
Re: Writing fast compilers... brnstnd@kramden.acf.nyu.edu (1991-08-18)
Re: Writing fast compilers... henry@zoo.toronto.edu (1991-08-20)
[1 later articles]
| List of all articles for this month |

Newsgroups: comp.compilers
From: alex@vmars.tuwien.ac.at (Alexander Vrchoticky)
Keywords: performance, optimize
Organization: Technical University Vienna, Dept. for Realtime Systems, AUSTRIA
References: <1991Aug10.132405.19359@walter.bellcore.com> <20167@helios.TAMU.EDU> <3593@crdos1.crd.ge.COM>
Date: 13 Aug 91 17:28:09 GMT

[From comp.arch -John]


davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) writes:


> An overstatement, I think. Optimizing compilers are not going to
>produce as much improvement on well written code as they will on student
>first attempts, because the common subexpressions have be done in
>source, the invariant stuff is out of loops, the loops are unrolled, the
>register type has been used here and there... all by a one pass code
>generator called a programmer.


The only program i ever generated in one pass did little more than
print out `Hello world!', and even then i cheated by looking
up the hard parts :-).


About doing optimizations at the source level ... yes, but. Not all
common subexpressions are available at the source level, and many of
those that are tend to turn a readable program into a morass of
pointer arithmetic and mysterious extra variables. excessive loop
unrolling is maybe attractive for people who get paid by the line,
hardly for the maintenance programmer. Using the `register' storage
class specifier (in languages where such an anachronism is available)
to achieve speedups is hardly worthwhile with modern compilers. they
tend to ignore it.


The gist is, a reasonable amount of optimization seems worthwhile
even for `well written code'.
--
Alexander Vrchoticky | alex@vmars.tuwien.ac.at
TU Vienna, CS/Real-Time Systems | +43/222/58801-8168
--


Post a followup to this message

Return to the comp.compilers page.
Search the comp.compilers archives again.