inference: refactoring to allow irinterp to perform :call inference

This commit implements a significant refactoring of the inference routines,
which is necessary to enable `:call` inference in irinterp. While this
commit does not yet enable `:call` inference, a subsequent small commit
will do so. This is because external `AbstractInterpreter`s first need
to adjust their code for this refactoring, and in the event of a
regression detected by the recursive `:call` inference, we will be able
to simply revert the small commit.

Additionally, this commit improves the robustness of irinterp by
allowing it to handle invoke calls, which currently result in a crash.

TODOs:
- [x] implement a simple recursion detection mechanism for `IRInterpretationState`
- [x] add proper invalidation support
- [x] allow constant inference from semi-concrete interpretation
- [x] propagate callinfo and allow double inlining

base/compiler/compiler.jl

@@ -152,7 +152,6 @@ include("compiler/ssair/domtree.jl")
 include("compiler/ssair/ir.jl")
 
 include("compiler/abstractlattice.jl")
-
 include("compiler/inferenceresult.jl")
 include("compiler/inferencestate.jl")
 

base/compiler/inferenceresult.jl

@@ -86,7 +86,7 @@ function va_process_argtypes(@nospecialize(va_handler!), 𝕃::AbstractLattice,
     nargs = Int(def.nargs)
     if isva || isvarargtype(given_argtypes[end])
         isva_given_argtypes = Vector{Any}(undef, nargs)
-        for i = 1:(nargs - isva)
+        for i = 1:(nargs-isva)
             isva_given_argtypes[i] = argtype_by_index(given_argtypes, i)
         end
         if isva
@@ -110,10 +110,8 @@ function most_general_argtypes(method::Union{Method, Nothing}, @nospecialize(spe
     isva = !toplevel && method.isva
     linfo_argtypes = Any[(unwrap_unionall(specTypes)::DataType).parameters...]
     nargs::Int = toplevel ? 0 : method.nargs
-    if !withfirst
-        # For opaque closure, the closure environment is processed elsewhere
-        nargs -= 1
-    end
+    # For opaque closure, the closure environment is processed elsewhere
+    withfirst || (nargs -= 1)
     cache_argtypes = Vector{Any}(undef, nargs)
     # First, if we're dealing with a varargs method, then we set the last element of `args`
     # to the appropriate `Tuple` type or `PartialStruct` instance.