[cfe-dev] Transforming the AST

Olaf Krzikalla Olaf.Krzikalla at tu-dresden.de
Fri Jul 9 06:34:22 PDT 2010

Hi @clang,

Douglas Gregor schrieb:
> Whenever you manipulate the AST, you could make the same (textual) transformation via the Rewriter. Then the Rewriter becomes responsible for storing all of the changes.
This doesnt work if you change a part of an AST that was already changed 
before (and thus rewritten) because you have no correct source loc info 
anymore. Suppose you inline a function via an AST transformation and 
later on perform some loop unrolling on that inlined function 
statements. To rewrite that properly you need the source loc infos of 
the original AST.

> If you find a better solution, we'd love to hear about it!
Well, as I said in my mail before, it's not a solution yet:
Before I start the AST processing I store the tree structure of the 
original AST.
Then the first idea was to compare the completely transformed AST with 
that stored structure and rewrite the changes on the tree level they 
appear (IMHO this is still the correct approach).
But the function dealing with the level comparision grew bigger and 
bigger as more special cases popped up and eventually became 
unmanageable. Hence I decided to simply propagate changes one level up 
to the appropriate parent and thus rewrite the parent statement. However 
this means that just one introduced local variable at function scope 
leads to a completely rewritten function body. Thus for the moment I've 
canceled all efforts in this direction and just rewrite the function 
body (I don't even use parent propagation). It works for my puposes but 
it is a flawed solution.

Best regards
Olaf Krzikalla

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