Re: programmer optimizations?

kerch@albion.camb.inmet.com (Kerchival F. Holt)
Thu, 12 Jan 1995 15:57:46 GMT

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Newsgroups: comp.compilers
From: kerch@albion.camb.inmet.com (Kerchival F. Holt)
Keywords: optimize, C
Organization: Intermetrics, Inc.
References: 94-12-145
Date: Thu, 12 Jan 1995 15:57:46 GMT

I would agree with the other postings that say leave this type of
transformation up to the compiler.


I have a comment on the second transformation:
>
> replacing if ((i < 0) || (j < 0) || (k < 0))
> by if ((i | j | k) < 0)
>
This does not seem quite legal in C/C++ because it doesn't preserve the
semantics of short circuiting in the original code. That is, (j < 0) and
(k < 0) should not be evaluated if (i < 0) is true. If i, j, and k
have no side effects (they are not declared volatile) this type of
transformation would be OK.


--
----
Kerchival Holt
Intermetrics Microsystems Software Inc.
kerch@inmet.camb.inmet.com
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