[LLVMdev] PassManager

[Vikram Adve]

Chris and Devang,

Before you implement the LoopPassManager class, I'd like to discuss  
this a little bit.  I have a suggestion and a question; we can  
discuss this now or later, as you wish:

1. The LoopPassManager might become much simpler if the more complex  
loop passes are given control over how they iterate over the loops,  
rather always rely on the manager to enumerate the loops in some  
fixed order.  Then the pass could be responsible for making sure that  
it handles issues like loops that are deleted during the pass.  For  
example, some algorithms make internal decisions about which loops to  
handle together and also what order to visit them.  For example, the  
LoopFusion class may need to inspect loop headers to decide which  
subsets of loops to fuse and then fuse them as it goes.

I think you could do this just by adding an iterator method somewhere  
that enumerates sets of loops (i.e,. returns a vector of Loop  
objects).  The bottom-up iterator could just be a default choice.

2. The question is how you plan to handle unimodular  
transformations.  I think it's a very nice abstraction and a number  
of loop transforms should be implemented using that rather than more  
ad hoc code, e.g., interchange, reversal, skewing.  But that requires  
implementing support for unimodular transforms before those passes  
are implemented.

--Vikram
http://www.cs.uiuc.edu/~vadve
http://llvm.cs.uiuc.edu/


On Nov 7, 2006, at 11:32 AM, Devang Patel wrote:

> Hi All,
>
> I am planning to re-implement PassManager in llvm 2.0. The goal is to
> address
>
>    http://nondot.org/sabre/LLVMNotes/Inliner-PassManager.txt   and
>    http://nondot.org/sabre/LLVMNotes/LoopOptimizerNotes.txt
>
> and other crazy ideas Chris has. Current implementation of PassManager
> is very complex. Initially I attempted to update it to  address above
> notes but realized that redoing PassManager in simple way makes more
> sense, and Chris agreed. Instead of replacing current PassManager with
> new PassManager in one big scoop I'm going to follow these steps:
>
> 1) Rename existing Managers using _X suffix.
> 2) Introduce new PassManager skeleton
> 3) Add functionality in new Pass Manager
> 4) Start Using new Pass Manager
> 5) Remove existing Pass Manager
> 6) Implement LoopPassManager
> 7) Update existing Loop transformations to conform LoopPassManager
>
> -
> Devang
>
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