Re: [eigen] Clang issue on MacOS when the set variable is used in the given data

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 19.04.2013 13:14, Gael Guennebaud wrote:
> On Fri, Apr 19, 2013 at 12:53 PM, Christoph Hertzberg
> <chtz@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> > I always assumed that
> >    foo << A, B, C;
> > is basically the same as
> >    foo.segment<dim_A>(0          ) = A;
> >    foo.segment<dim_B>(dim_A      ) = B;
> >    foo.segment<dim_C>(dim_A+dim_B) = C;
>
> yes, in theory it's what happen in that order. but in that case
> Arnaud's 1st example should fail regardless on the compiler. So there
> might a c++ subtlety I'm missing.

I assume the compiler does some over-optimization here, i.e., loads 
values of foo and starts evaluating the product before beginning to 
write to foo. I don't know if that kind of optimization is allowed by 
the C++ standard (it would not surprise me if it was).

Christoph



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Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
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Universität Bremen
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