Compiler Optimisation?

[Iain Bate <iain.bate@cs.york.ac.uk>]

I am looking for some specific information on compiler optimisation
and I was wondering if anyone could help. Basically, I would like to
get some idea how much faster code executes due to optimisation. I am
looking for the information at two levels:

1. How much faster code executes due to the overall optimisation
process?
2. How much faster code executes due to specific optimisation stages,
e.g. the speed-up due to the peephole stage?

I realise there are some quite large variations in the type of
optimisation algorithms that are used, but I am simply looking for
some typical figures - if these exist.

I would be very grateful for any help that people can provide in terms
of actual information or guidance of where to look (I'm sure there
must be loads of data on this subject). Also, is there any chance any
replies can be copied directly to me at iain.bate@cs.york.ac.uk since
I will read it faster that way

Thanks in Advance

Iain
[The answer to both questions is "somewhat, usually, depending on the
application and the compiler" but perhaps some people can offer some rules
of thumb. -John]