small improvement for fill and fill_n

[Paolo Carlini]

Hi Dan,

> Note that the memory location pointed to by __value is accessed in
> each loop iteration, the compiler cannot prove that __first and
> __value do not alias. One solution would be to use a temporary like
> so:

First, thanks for the analysis: in order to seriously pursue performance
improvements we really need this kind of work.

Coming to the point, however, I wonder whether there are hopes that the
alias analysis will be improved in a not-to-far future... It would be
so sad to add those temporaries: I suspect *many* would be needed in
the whole libraries... .-(

Is an optimization PR in order?

Thanks again,
Paolo.