Re: std::pow implementation

[Martin Reinecke <martin at MPA-Garching dot MPG dot DE>]

Gabriel Dos Reis wrote:

> It is tempting to make the analogy with "register", but you have to
> acknowledge the fact that inlining strategy is not at the same level
> of sophistication as register allocation.  Therefore, any answer you
> get for the question above is irrelevant to whether you should decide
> whether your programmed inliner always knows better than the
> programmer.   Until then, please listen to the programmer.  Don't
> transmute "inline".

Yes, you should listen to the programmer. But unless the programmer
has a chance to express his intent _exactly_, there is no way to find
out what he really meant. And he cannot do so in the discussed situation.

When writing a member function, the programmer has to adress the question
"Should this function be inlined?", and you agreed that there are three
valid answers: "yes", "no", and "it depends; let the compiler decide".

But current g++ only allows two ansers:
 "yes" (i.e. make the function inline), and
 "no"  (i.e. define the function in some .cc file)

If the programmer can only choose two of three alternatives, it is not
possible to determine whether he didn't actually want to say "it depends".
If he says "no", he most certainly means "no", because then g++ has not much
chance of inlining the function if it's not defined in the current translation
unit.
But if he says "yes", how can you be sure he really meant "yes" and not
"it depends"? The language practically forces him to lie, and therefore
you can't trust him blindly.

My opinion is that if the programmer says "yes", the only thing you can be sure
about is that he didn't mean "no", but that's not enough to determine whether
g++ should unconditionally inline or not.

Of course, this argument breaks down if there is some way to say "it depends".
I don't know of any. If there is, please show me!

Martin