Another silly question

[Pete Holsberg]

In article <17635 at mimsy.UUCP> chris at mimsy.UUCP (Chris Torek) writes:
=In article <749 at mccc.UUCP> pjh at mccc.UUCP (Pete Holsberg) writes:
=[in response to article <607 at kl-cs.UUCP> by pc at cs.keele.ac.uk (Phil Cornes)]
=>Can you explain why compilers produce different code for "a[i]" and "*(a+i)"?
=
=I have never observed one to do so.  There is no reason for a compiler
=to generate different code, as the expressions are semantically identical.

Perhaps I've asked the wrong question.  I saw a couple of simple test
programs that assigned 0 to each member of an array.  One used array
subscript notation, and the other, pointer notation.  I compiled these
on a 7300, a 3B2/400, and a 386 running Microport V/386, using a variety
of compilers (cc and gnu-cc on the 7300, fpcc on the 3B2, and cc and
Greenhills on the 386).  I ran each version and timed the execution. 
The subscript versions had different run times from the pointer versions
(some slower, some faster!).  I assumed - perhaps naively - that the
differences were caused by differences in code produced by the different
compilers (and of course the hardware differences).  Was that wrong? 
How does one account for the differences?




-- 
Pete Holsberg, Mercer County Community College, Trenton, NJ 08690  
{backbone}!rutgers!njin!princeton!njsmu!mccc!pjh