WIP: Add @code_llvm macro

[quinnj]

This allows you to do:

In  [74]: @code_llvm 1 + 1

define i64 @"julia_+672"(i64, i64) {
top:
  %2 = add i64 %1, %0, !dbg !2075
  ret i64 %2, !dbg !2075
}

Reference issue: #5674

I based this entirely after the implementation of @which, but it seems like it could be a bit cleaner. If we get some more thorough review here I can accordingly add the other code_ macros.

[StefanKarpinski]

In general, I think it would be good to make all the function versions of these kinds of things take fun, types arguments and then have corresponding macro versions that operate on expressions applied to actual values. We're pretty close to this now – I think the main exception is that the which function takes a tuple of values instead of a tuple of types.

[StefanKarpinski]

Also, this is lovely.

[JeffBezanson]

I do like the idea of this, but this should clearly share code with which.
It may not be obvious that this shows the code only of the outermost called function; @code_llvm sin(cos(x)) looks like it will show the code for calling cos then sin. This problem is less serious for which since it's clear that which is only telling you about one method.

[quinnj]

Yeah, I had a drive tonight and realized we need a _fun_arg_split internal function that does the expression splitting for @which and @code_ macros.

In terms of just showing the outermost function only, I guess my natural expectation was that it would indeed only show the outermost.

In  [79]: macroexpand(:(@code_llvm sin(cos(1))))

Out [79]: :(code_llvm(sin,(typeof(cos(1)),)))

AKA what's the llvm for calling sin with the argument I pass it, in this case it's the result of cos(1), though I see what you're saying. In any case, we can add a doc snippet about the behavior of outermost. Unless there's a way we can allow showing everything? Recursive code_llvm calls with the results appended?

[StefanKarpinski]

One option would be to show code for all of the function calls in the expression in some order, but that would probably be a lot of code.

[mbauman]

I didn't mean to supersede this, but I happened to stumble upon a solution that completely shares code with @which that works for @edit and @less (as I intended) as well as all these @code_* flavors. Of course, my solution still has the @code_llvm sin(cos(x)) problem that @JeffBezanson talks about. #5832

[ivarne]

I would love to be proven wrong, but I do not think it is possible to present the information Jeff wants in a way that would be intuitive in a terminal interface. I think it would be a job for Julia Studio, iJulia and Julietta to rewrite these macros to be more useful in their rich environments. The documentation @mbauman wrote, says very clear that only the outer function is considered.

[quinnj]

Subsumed by #5832.