Making the Clang AST Leaner and Faster | Hacker News Reader

Making the Clang AST Leaner and Faster

cppalliance.org

50 pointsvitaut9 comments

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Impressive work! Also waiting for fine-grained caching:

https://discourse.llvm.org/t/rfc-add-an-llvm-cas-library-and...

That is dated Feb 2022. Do you know if anything came of it?

Quite a few patches have landed. A couple features using this have already shipped in Apple’s downstream clang.

Great stuff!

But, I’m afraid it will actually lead to even more heavily templated C++ in a rebound effect!

>Modern C++ codebases — from browsers to GPU frameworks — rely heavily on templates, and that often means massive abstract syntax trees.

Symptom of a symptom. Templates are abhorrent abominations. However, there’s no way to do generics without them. It just becomes a hairball mess at compile time… kudos for alleviating some of the pain in waiting.

The C++ implementation, sure. But there is plenty of other implementation space without giving up like Java.

With a trait-first implementation that mostly defers monomorphization and prefers "static if" over C++-style specialized implementations, the only hard choice is whether to optimize codegen for size or speed.

Trying to retrofit this onto standard C++ is ... not actually as difficult as you might think. The real problem is the implementation of builtins that rely heavily on "this really must be a constant during X phase of compilation".

Im not sure what the originating symptom is in your comment. I read your comment as saying:

‘requiring generics’ -> C++ Templates -> massive ASTs

Is that correct? If so I’d then wonder if the applies from strictly within the bounds of C++ the language. Is there an alternate meaning? I think there are quite a few viable ways to present what are usually called ‘generics’ at several levels of abstraction and in several programming paradigms, so any reading outside of C++ seems strange.

That's awesome improvement!

Optimizations that require changes to data flow are some of the trickiest to get through. Even when the benefits are great, it will feel like a loss to some to take something away to make everything faster. Is this really worth it?

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