Re: optimization and register allocation

sethml@puree.ugcs.caltech.edu (Seth LaForge)
Sat, 4 Mar 1995 12:32:31 GMT

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Newsgroups: comp.compilers
From: sethml@puree.ugcs.caltech.edu (Seth LaForge)
Keywords: optimize, registers, comment
Organization: California Institute of Technology, Pasadena, CA
References: 95-02-182 95-03-009
Date: Sat, 4 Mar 1995 12:32:31 GMT

David Moore <davidm@Rational.COM> wrote:
>Note that f2-a is not quite the same as (-a)+f2 because the
>latter may overflow while the former does not. In C you


How is this? Suppose a == -200 and f2 == 100, and you are evaluating
in an 8-bit context... It seems to me that both would overflow...


Seth
[-a can overflow on a two's complement machine if it's the largest negative
number, while in that case f2-a would not overflow if f2 is any negative
number. -John]
--


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