is_type_unstable for unoptimized code

[aviatesk]

As discussed in #193, the current implementation of is_type_unstable may not work well for unoptimized code.

Especially, it doesn't handle lhs = rhs statements where rhs is type unstable:

julia> const globalvar = Ref(42)
Base.RefValue{Int64}(42)

julia> descend(; optimize=false) do
           a = sin(globalvar[])
           b = sin(undefvar)
           return (a, b)
       end
│ ─ %-1  = invoke #3()::Tuple{Float64, Any}
    @ REPL[4]:2 within `#3`
1 ─ %1 = Base.getindex(Main.globalvar)::Int64
│        (a = Main.sin(%1))::Float64
│   @ REPL[4]:3 within `#3`
│        (b = Main.sin(Main.undefvar))::Any
│   @ REPL[4]:4 within `#3`
│   %4 = Core.tuple(a, b)::Tuple{Float64, Any}
└──      return %4
Select a call to descend into or ↩ to ascend. [q]uit. [b]ookmark.
Toggles: [o]ptimize, [w]arn, [h]ide type-stable statements, [d]ebuginfo, [i]nlining costs, [s]yntax highlight for Source/LLVM/Native.
Show: [S]ource code, [A]ST, [L]LVM IR, [N]ative code
Actions: [E]dit source code, [R]evise and redisplay
Advanced: dump [P]arams cache.
 • %1  = getindex(::Base.RefValue{Int64})::Int64
   %2  = sin(::Int64)::Float64
   ↩

# toggle `h` option

│ ─ %-1  = invoke #3()::Tuple{Float64, Any}
│   @ REPL[4]:4 within `#3`
│   %4 = Core.tuple(a, b)::Tuple{Float64, Any}
Select a call to descend into or ↩ to ascend. [q]uit. [b]ookmark.
Toggles: [o]ptimize, [w]arn, [h]ide type-stable statements, [d]ebuginfo, [i]nlining costs, [s]yntax highlight for Source/LLVM/Native.
Show: [S]ource code, [A]ST, [L]LVM IR, [N]ative code
Actions: [E]dit source code, [R]evise and redisplay
Advanced: dump [P]arams cache.
 • %1  = getindex(::Base.RefValue{Int64})::Int64
   %2  = sin(::Int64)::Float64
   ↩

, where we still want (b = Main.sin(Main.undefvar))::Any to be shown even on h mode.

As additional information, I found it idx in used returns false for that case:

Cthulhu.jl/src/codeview.jl

Line 76 in 93743cb

return (idx in used) && type isa Type && (!Base.isdispatchelem(type) || type == Core.Box)