Use slot names to get names of variables for metadata

[phipsgabler]

The question is how to get them out of the IR objects, and where to put them.

julia> f2(x) = (y = x + 1; 2y)
f2 (generic function with 1 method)        

julia> code_lowered(f2, (Int,))[1]
CodeInfo(
1 ─      y = x + 1
│   %2 = 2 * y
└──      return %2

julia> code_lowered(f2, (Int,))[1].slotnames
3-element Array{Symbol,1}:
 Symbol("#self#")
 :x              
 :y      

julia> c = code_lowered(f3, (Int,))[1]
CodeInfo(
1 ─      y = x + 1
│   %2 = 2 * y
│   %3 = Main.sin(%2)
└──      return %3
)

julia> c.code[2]
:(2 * _3)

julia> c.code[2].args[3]
:(_3)

julia> c.code[2].args[3].id
3

julia> c.slotnames[c.code[2].args[3].id]
:y

[phipsgabler]

For IRTools, to circumvent FluxML/IRTools.jl#31:

julia> ir = IRTools.IR(typeof(f3), Int; slots = true)
1: (%1, %2)
  %3 = %2 + 1
  %4 = @_3 = %3
  %5 = 2 * @_3
  %6 = Main.sin(%5)
  return %6


julia> ir.meta.code.slotnames[1:ir.meta.nargs]
2-element Array{Symbol,1}:
 Symbol("#self#")
 :x  

[phipsgabler]

The simplese approach would probably be to implement an IR transformation working on "slotted" IR to produce something equivalent to its "unslotted" version, but with the relevant Vars replaced by a new NamedVar type containing the name as well, and apply it right after or before explicitbranch!.