Design multiple approaches to attach information to CFG or Values

[michkot]

Design several possible ways how to attach information to instructions or values.
Present motivation for this is dead/live variable analysis - results of such an analysis could be precomputed and assigned either to CfgNodes (instructions) or to FrontendIds (values / SSA registers).

Info sources:
https://github.com/kdudka/predator/blob/master/cl/killer.cc
http://llvm.org/docs/doxygen/html/LiveVariables_8h_source.html
http://llvm.org/docs/doxygen/html/classllvm_1_1LiveVariables.html

[michkot]

From meeting 14.03.2017:
It is some kind of "information bag" attached to CFG nodes.
Annotation should be both framework provided/predefined and analysis specific

@michkot suggests something like Type->instance of Type info dictionary.

// sample code for non-sharing annotations 
info.Get<MySpecialCfgAttribute>();
info.Set<MySpecialCfgAttribute>(uptr<MySpecialCfgAttribute>&& element); //ptr constructor
info.Set<MySpecialCfgAttribute>(args&&..); //emplace constructor
info.Set<MySpecialCfgAttribute>(MySpecialCfgAttribute&&) //move constructor
// sample for sharing annotations
info.SetShared<MySpecialCfgAttribute>(const MySpecialCfgAttribute&) //store ref/ptr 
// both could be mixed if needed (there is an endless amount of ways how to implement this) 

@peringer suggests mapping custom keys to 0-based indexes, and then using those indexes under the hood. Annotation storage could be small_vector<uptr>
my comment: registration of annotation types could

1. be done manually in some Init function
2. happen at start-up time (linking-safe, static instance of class, constructor magic)
3. ... other ideas?

@tfiedor also suggested something similar to those ideas, but i forgot what it was...

Notes:

• Base class is needed, because it provides interface with virtual destructor and/or deleter
• uptr<> stands for std::unique_ptr<>

I believe this is a critical feature of Angie framework and I would like to make it right and call for a wider discussion here or at slack.

[peringer]

maybe we can use the access method: AttrBasePtr p = node.annotation(indexEnum4myAppendix);

[michkot]

@peringer I am not sure if understand the access method. Could you give a longer example?

[peringer]

I created proof of concept code - see sarka:/home/local/0-angie/angie-test2.cc

[michkot]

I've created a gist (github snippet) with the code:
https://gist.github.com/michkot/971ddd5e5c53d7113660d8c0d4dc94f4