Re: status of Ada STL?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Vinzent Hoefler <JeLlyFish.software@gmx.net> writes:

> 18k11tm001@sneakemail.com (Russ) wrote:
> >Every good C++ programmer knows that "+=" is much more efficient than
> >"+" for vector/matrix addition because it eliminates the need for
> >constructing a temporary matrix to hold the sum.
> 
> Every good compiler should see in its data flow analysis that both
> statements simply are the same. It *should* not be a matter of how it
> is *expressed*. So, what am I missing?

I think Russ is right here.

X := F(X, Y);

is *not* equivalent to the code that overwrites X in place,
in the general case.  In the usual case, where the called function
is not inlined, and the compiler doesn't look at its body,
the compiler has no hope of doing this optimization.
Even if it's inlined, the proof is not trivial.

(Whether you call it "+" or F or Add_Vector is irrelevant to the
optimization issue.)

- Bob