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Re: c/8395: gcc 2.95.4 and 3.2 generate wrong code for double onintel
- From: Bruce Allen <ballen at gravity dot phys dot uwm dot edu>
- To: Marco Bernardo <bernardo at sti dot uniurb dot it>
- Cc: Bruce Allen <ballen at aei dot mpg dot de>, gcc-gnats at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, gcc-bugs at gcc dot gnu dot org, nobody at gcc dot gnu dot org
- Date: Mon, 4 Nov 2002 04:58:02 -0600 (CST)
- Subject: Re: c/8395: gcc 2.95.4 and 3.2 generate wrong code for double onintel
> 2. I hope we all agree on the fact that the output produced by
> a (sequential) C program is the same for a given input,
> regardless of the compilation options that are used.
Absolutely false!
C does not specify the order in which mathematical expressions are
evaluated, unless the programmer makes these completely explicity.
And indeed compiling with optimizations turned on can eliminate many
subexpressions, cause compile-time evaluatiosn, register sorage etc, which
can also change results.
Bruce Allen