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From: usenet@nlm.nih.gov (usenet news poster)
Newsgroups: comp.arch,comp.lang.misc
Subject: Re: Compiler Costs
Message-ID: <1990Jul8.183551.13891@nlm.nih.gov>
Date: 8 Jul 90 18:35:51 GMT
References: <1797@apctrc.UUCP> <1565@uvm-gen.UUCP>
Reply-To: states@tech.NLM.NIH.GOV (David States)
Organization: National Library of Medicine, Bethesda, Md.
Lines: 34

cavrak@uvm-gen.UUCP (Steve Cavrak,113 Waterman,6561483,) writes:
>in response to zrra07@backus (Randall R. Appleton):
>> I have a simple question:  Does anyone know what sort of speed-up
>> on gets by going from a good implementation of some algorithm in a
>> third generation language (C, Fortran) and a good optimizing compiler
>> to hand-coded assembly?
>
>An example with VS-FORTRAN on an IBM-3090 with a vector processor.
>
>a.  plain fortran matrix		1.0
>b.  full optimized fortran		0.3
>c.  IBM's ESSL hand coded library	0.1 or better

It is my understanding that on the RS/6000, ESSL is implemented in Fortran,
and IBM claims that most ports have experienced zero or negative gains
in attempting to hand code assembler on the machine.  There have been a 
number of references to "the ill conceived notions" of higher level 
languages in this thread, but it is not at all clear to me what these are
supposed to be.  C was designed as a higher level alternative to assembler.
On a RISC machine with a good compiler, a C programmer willing to work 
on his code ought to be able to do almost anything hand coded assembler can.
This may involve looking at assembly output, recoding routines a few times
and testing alternative alogorithms, but in the end you still have C (that
will run on another processor even if not as fast).

On a complicated processor (CISC, non-orthogonal registers, segmented
addresses etc.) assembler may do better because the compiler writers made
simplifying assumptions about the processor, making some instructions and
address constructs inaccessible.  Seems like Intel processors will be the
last bastion of assembly language.

>Steve

David States