Re: Is interprocedural optimization worth it?

Dmitry,


It's a difficult question to answer without knowing what architecture
you're generating code for, and what interproc optimizations you're
considering. Not having access to the entire code generator can
definitely be a significant drawback.


The latest revision of the Microsoft Visual C++ compiler does
whole-program optimization at link-time. See:
http://www.codeproject.com/tips/gloption.asp for more information.


My experience from having worked on this definitely showed that
inlining across the entire program can often be a big win, but it can
be relatively hard to tune this inlining without profile information
being available. It can also be a big loss if not tuned properly (in
particular inlining very agressively, on all but the smallest
programs, tends to blow the I-cache out so badly that it's an overall
loss).


Improved memory disambiguation can have a large effect on
architectures where you have a lot of registers (like IA-64) but less
of an effect on architectures where you have very few registers (like
IA-32).


You may want to consider referencing one of the recent compiler texts
and the papers referenced in those texts before embarking on a
detailed design or implementation. Muchnick's book (Advanced Compiler
Design and Implementation) has a chapter on interprocedural
optimizations and if it's like the rest of the book (sorry, don't have
it handy) it should have a lot of references.


--
Mark Lacey
mlacey at microsoft dot com
Microsoft Visual C++ Program Management


"Dmitry Shaporenkov" <dsha@tercom.ru> wrote in message
> My question is, does anybody know the successful examples of
> interprocedural optimizers in modern C compilers, commercial or free?
> Or, aliasing problems and procedure boundaries are too hard obstacles
> to make such optimizations really useful (on the other hand, is it
> better to inline as much code as possible)? It would also be
> interesting which interprocedural optimizations are performed in
> compilers, and which of them produce best results?

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