[LLVMdev] PassManager Error

[David Greene]

On Friday 27 July 2007 15:15, Devang Patel wrote:

> Now, if pass sequence is - ModuleLevelPass A, FunctionLevelPass B,
> ModuleLevelPass D, FunctionLevelPass C then
>
> For each Module
> 	run ModuleLevelPass A
> 	for each function in this module
> 		run FunctionLevelPass B
> 	run ModuleLevelPass D
> 	for each function in this module
> 		run FunctionLevelPass C
>
>
> In this situation, while processing 'foo' FunctionLevelPass C can not
> use analysis info generated by FunctionLevelPass B for 'foo'.

Why?  I expect the answer is something like, "because B doesn't exist 
anymore,"  or, "because you processed function 'bar' with B after 'foo.'"
But why?  B doesn't _have_ to exist and it shouldn't necessarily matter
in what order PassManager processes functions.  Only the information
that pass B generates for foo need exist.

If you're running module-level passes anyway, you're probably burning a bit
of memory to hold state, so maybe keeping around information for all functions
is feasible.  I don't know.

Yes, I understand that these questions imply rethinking how PassManager
works.  That's why I'm asking them.  I reordered my code and got things to
work but it's always good to take a step back from time-to-time and ask
fundamental questions.  Even if no changes are immediately forthcoming,
it at least helps to identify areas of potential future work.

                                               -Dave