short circuit evaluation

[m5d at bobkat.UUCP]

In article <5178 at mimsy.UUCP> chris at mimsy.UUCP (Chris Torek) writes:
>>>>[ he's quoting me here ]
>>>>These are bitwise logical operators.  Short-circuiting these makes
>>>>no more sense than short-circuiting a sequence of multiplies as
>>>>soon as one of the operands evaluates to `1'.
>>>>Mike McNally                                    Digital Lynx Inc.
>
>Not so!
>

I know, I know, I'm sorry, I'm sorry!

> [ 
>   Chris then goes on to accurately describe the possible
>   paths of evaluation for |, &, ||, and &&, although he
>   omits ^, which is OK I think, because you can't say
>   much about ^ given an intermediate result
> ]
>
>In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
>UUCP:  seismo!mimsy!chris  ARPA/CSNet: chris at mimsy.umd.edu

I realize that my first posting(s? I can't remember how many I did)
were a little confused.  I do know what's going on, and would like to
ask a related question.

If the compiler decides to generate code that notices when part of a
sequence of sibling `|' or `&' operations have generated an inevitable
result, do side effects of sub-expressions still have to be performed?
In other words, let's look at this:

    x = f1(something) | f2(something) | f3(something) ...

If I wrote this, I would expect all the functions to be called, even if
one of them returns ~0.  Am I nuts?  Seems to me that an optimization
like that would be naughty.

As I look at that example, I realize that people might still think I'm
confused.  Try this example:

    x = f1(something) * f2(something) * f3(something) ...

Shouldn't I expect all the multiplications to be performed, even if one
function returns zero?

I don't think I've ever used a compiler that does such optimizations
(not that that really means much).  Has anyone else?

If I actually *am* lost, please don't tell my employer.

--
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Mike McNally (feeling sheepish nowadays)        Digital Lynx Inc.
Software (not hardware) Person                  Dallas  TX  75243
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