Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!husc6!seismo!mcnc!unc!rentsch
From: rentsch@unc.UUCP
Newsgroups: comp.arch,comp.sys.nsc.32k
Subject: Dhrystones vs. Optimizing compilers
Message-ID: <104@unc.unc.UUCP>
Date: Wed, 15-Apr-87 21:34:43 EST
Article-I.D.: unc.104
Posted: Wed Apr 15 21:34:43 1987
Date-Received: Sat, 18-Apr-87 01:20:32 EST
References: <4190@nsc.nsc.com> <951@moscom.UUCP> <2577@intelca.UUCP>
Reply-To: rentsch@unc.UUCP (Tim Rentsch)
Organization: CS Dept, U. of N. Carolina, Chapel Hill
Lines: 27
Xref: utgpu comp.arch:895 comp.sys.nsc.32k:74
Summary: Dhrystone is bad for benchmarking

In article <2577@intelca.UUCP> clif@intelca.UUCP (Clif Purkiser) writes:
> While, I agree that using a global optimizing compiler is not exactly
> kosher for the dhrystone benchmark it sometimes neccessary.  For 
> instance: the GreenHills C compiler is a globally optimizing compiler
> which generates good Dhrystone numbers for many architectures including
> the 80386 and 68020.	 Unfortunately, I can not find a compiler
> switch to turn off the global optimizer.  This leaves me with two choices:
> post the numbers with the cavet that this a global optimizing compiler 
> or use the results of a medicore compiler like CC.  I don't really
> think that global optimization is a problem as long as it is clearly
> labeled. 

I see this drawback as saying something not about the suitability of
optimizing compilers but about the suitability of the Dhrystone
program as a benchmark.  

If Dhrystone really is prone to sweeping global optimizations (with
corresponding improvements in running time), then doesn't it seem to
be pretty poor as a benchmark?  I heard a similar about a program
used to benchmark an early FORTRAN H compiler -- the global
optimizer reduced the entire program to just a print statement
(after having removed loop invariants, constant folding, and
removing the now empty loop).  The program took a long time to
compiler, but it ran VERY fast.

So, here is my vote for benchmark programs which are not prone to
huge improvements through global optimization.