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Note that this refers to ML as in machine learning and not the ML language family, as I hoped.
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My mind still unabbreviates "ML" into "Machine Language" before anything else, only because it was the first of these three for me.
There are so many flavors of machine learning that we should probably just refer to whole field as XML.
At some point we might need to cross-reference (X-ref) language models. This may involve using a dedicated data interchange format - perhaps an extensible markup language for language model cross-referencing. Or, in short, LMX-XML.
I know it is irrational - as compilers already perform optimizations that are non intuitive - but my lizard brain really doesn’t like the idea of ML possibly changing semantics at a layer that is unobservable.
Yeah, funny enough I was reading the “coding machines” short story yesterday after someone linked it and I had a bit of a giggle imagining the sentient compiler here.
This sort of work isn't going "i dunno, emit some new instructions based on a model and hope it is correct." ML techniques fall into one of two categories:

1. Decisions that have no semantic change in the program but affect performance. This is things like code layout or register allocation that will be more cache friendly. This is what I expect to show up in industrial optimizing compilers more and more over the next bunch of years.

2. Decisions where you can prove that the new code sequence is semantically identical to the original code sequence via some formal technique. This is basically the same as various superoptimization techniques but with a new search strategy and therefore no new concerns about correctness. I'd expect this to remain niche and only used offline to generate particularly optimized sequences in extremely hot and small code paths.

> Decisions that have no semantic change

Yeah the problem is that there are not a whole lot of those in PL.

There are a huge number of these things in compilers. I listed two: code layout and register allocation. And you've got plenty of other things like inlining, outlining, and unrolling decisions.
I think some functions with exhaustively enumerable could be good candidates as well (I guess somewhat rare though?). For example an Int->(...) or Float->(...) function (Doubles are not exhaustively enumerable though, I guess, since 2^64 ~= 10^19, 10,000-Peta items). If the programmer can give an error threshold, e.g. in bits of precision (maximum relative error), that should work quite well too.
WE "just" need to get the models outputting machine checkable proofs that semantics are preserved. I wonder what like this are going on in the math scene.
You forgot valid machine checkable proofs.

That's quite a tall order. Godel and all that.

There is a mathematical description of programming compilers I read once (think it was a survey paper) that I found very clear but I've never been able to find since. Basically defined a compiler as a type of function. Any good suggestions?
Perhaps this one from Graham Hutton?

“A parser for things

Is a function from strings

To lists of pairs

Of things and strings”

Thanks for sharing this. I became a bit of a fan of Dr Hutton after I followed his Functional Programming in Haskell classes on Youtube.
My research (ML for binary function recognition) uses obfuscation and diverse compilation for data augmentation.

Intuitively, obfuscation is a form of anti-optimization. My hope is that it's differentiable, so perhaps given enough knowledge of obfuscation, an ML model can make corresponding optimizations to "undo" them, then for more performance, apply those same un-obfuscations to code that hasn't already been obfuscated.

I think this is a great line of research as it may solve the reasoning portion of AGI. The difficulty is that you would want to prove equivalence. LLMs can output stuff but for programs to execute you need to output correct stuff.
It's interesting to add the work about Deepmind AlphaDev to this list.