Re: Compiler optimization and floating point operations

christian.bau@cbau.wanadoo.co.uk
Mon, 28 Oct 2013 15:54:46 -0700 (PDT)

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Related articles
[3 earlier articles]
Re: Compiler optimization and floating point operations gneuner2@comcast.net (George Neuner) (2013-10-24)
Re: Compiler optimization and floating point operations jm@bourguet.org (Jean-Marc Bourguet) (2013-10-24)
Re: Compiler optimization and floating point operations sgk@troutmask.apl.washington.edu (Steven G. Kargl) (2013-10-24)
Re: Compiler optimization and floating point operations gneuner2@comcast.net (George Neuner) (2013-10-24)
Re: Compiler optimization and floating point operations gah@ugcs.caltech.edu (glen herrmannsfeldt) (2013-10-24)
Re: Compiler optimization and floating point operations christian.bau@cbau.wanadoo.co.uk (2013-10-28)
Re: Compiler optimization and floating point operations christian.bau@cbau.wanadoo.co.uk (2013-10-28)
Re: Compiler optimization and floating point operations cameron.mcinally@nyu.edu (Cameron McInally) (2013-10-28)
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From: christian.bau@cbau.wanadoo.co.uk
Newsgroups: comp.compilers
Date: Mon, 28 Oct 2013 15:54:46 -0700 (PDT)
Organization: Compilers Central
References: 13-10-026 13-10-029 <13-10-030 @comp.compilers> 13-10-032
Keywords: optimize
Posted-Date: 28 Oct 2013 22:46:52 EDT

On Thursday, October 24, 2013 5:38:13 PM UTC+1, Steven G. Kargl wrote:
> #include <stdio.h>
> int
> main(void)
> {
> float a, b;
> a = 0.;
> b = a / a;
> if (a + b != b + a) printf("fubar\n");
> return (0);
> }
>
> Can an optimizing compiler eliminate the if-statement?


It can eliminate the test because it will always be true (on IEEE
implementations where 0.0 / 0.0 is NaN). It cannot eliminate the
if-statement because printf () should be called.


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