[cfe-dev] Attach state from clang to LLVM

[Alejandro Jimenez Martinez]

I'd like to evaluate a couple of extensions to a C-like language, and I was
hoping to use Clang and LLVM to do that.

I ran into a couple of issues, and I'd appreciate if you could advise on the
best practices to address them.

 

-1- I modified Clang parser to accept the extension syntax (say a property
for a function, statement, parameter, or variable), 

but how do I propagate the state from Clang to LLVM IR?

I need the state to be "persistent"; i.e., IR assembly or bitcode should
contain it, and IR reader should get it into memory when deserializing.

How do I do this without changing LLVM IR, IR readers and writers? Is there
any way to attach "custom" state to IR classes?

I noticed that there are annotations and metadata mechanisms. Should I use
one of these, which one, or there are better ways?

 

-2- I need to keep this custom state (per functions, instruction, operand,
variable) in LLVM IR for my optimization passes.

In addition, I'd like to leverage a few existing optimizations: the extra
state will not interfere with these, but I do not want to "educate" the
existing optimizations to ignore it (I still need it preserved though).

What is the best way to do this? Should I subclass existing IR classes, use
metadata, use annotations, or do it somehow else?

I'll need to query and modify extra state frequently, so the mechanism
should be performant.

Some of the state should also make it to the persistent IR forms.

 

Thanks in advance,

Alex

 

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