Hoopl advice: How to extend the graph?

[Jan Stolarek]

> What function I should reach for when I want to look at each block (or
> each Last node) in an CmmGraph, possibly modifying it and possibly
> adding auxillary nodes on the way?
Take a look at Compiler.Hoopl.Block in hoopl library - it has some useful functions for working on 
blocks. blockSplitTail might be what you're looking for if you want to look at the last block. If 
you want to look at each block in a graph you most likely need postorderDfs from CmmUtils. I 
suggest studying one of existing Cmm passes to see how to traverse a Cmm graph and operate on it. 
CmmContFlowOpt seems to be a good candidate - good comments, fairly short, uses many functions 
that you should learn if you want to work with Cmm.

> It seems that one could use dataflowPassFwd for it, but
>  * I could not find any use of it, and
>  * I do not need to run an analysis along, I just want to rewrite
>    the blocks,
> so I am not sure if this is the right thing.
You most likely don't want to use Hoopl's machinery for doing analyses and optimisation passes. 
From what I know Hoopl is very slow compared to hand-written graph traversals and 
transformations - Edward's CmmRewriteAssignments is a good example here [1].

Does that help?

Janek

[1] https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/Hoopl/Examples

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Politechnika Łódzka
Lodz University of Technology

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