Re: Is global optimization worth it?

Nick Maclaren wrote:


> safely. In C, you cannot, because of the aliasing problems - hence
> the need for global optimisation to detect such aliasing.
>
> Even larger gains on modern systems come from things like operand
> preloading, but let's consider just register use. It isn't unusual
> for a C code not to be able to make use of more than a few registers
> because everything has to be in memory over every function call.
> Global optimisation can remove most of that constraint, and allow the
> use of (say) 20 registers where only 4 could be used before.


Again, I think this is mostly theoretical. If you use local variables and
parameters instead of ugly globals this is not much of a problem. Register
allocation etc provide much gain in loops that are in most real programs
quite simple and don't use 16 globals, or 20 registers at all.


Regards,
        Rinie Kervel

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