compiler: remove dead code (JuliaLang#42460)

- inferenceresult.jl: just dead allocations
- inlining.jl: `UnionSplitSignature` (and its `SimpleCartesian` helper)
  is no longer used
- abstractinterpretation.jl: the use of `precise_container_type` seems
  to be introduced in JuliaLang#26826, but `getfield_tfunc` at this
  moment is precise enough to propagate elements of constant tuples.

base/compiler/abstractinterpretation.jl

@@ -1086,16 +1086,7 @@ function abstract_call_builtin(interp::AbstractInterpreter, f::Builtin, fargs::U
         end
     end
     rt = builtin_tfunction(interp, f, argtypes[2:end], sv)
-    if f === getfield && isa(fargs, Vector{Any}) && la == 3 &&
-       (a3 = argtypes[3]; isa(a3, Const)) && (idx = a3.val; isa(idx, Int)) &&
-       (a2 = argtypes[2]; a2 ⊑ Tuple)
-        # TODO: why doesn't this use the getfield_tfunc?
-        cti_info = precise_container_type(interp, iterate, a2, sv)
-        cti = cti_info[1]::Vector{Any}
-        if 1 <= idx <= length(cti)
-            rt = unwrapva(cti[idx])
-        end
-    elseif (rt === Bool || (isa(rt, Const) && isa(rt.val, Bool))) && isa(fargs, Vector{Any})
+    if (rt === Bool || (isa(rt, Const) && isa(rt.val, Bool))) && isa(fargs, Vector{Any})
         # perform very limited back-propagation of type information for `is` and `isa`
         if f === isa
             a = ssa_def_slot(fargs[2], sv)

base/compiler/inferenceresult.jl

@@ -71,10 +71,8 @@ function most_general_argtypes(method::Union{Method, Nothing}, @nospecialize(spe
                 va = linfo_argtypes[linfo_argtypes_length]
                 if isvarargtype(va)
                     new_va = rewrap_unionall(unconstrain_vararg_length(va), specTypes)
-                    vargtype_elements = Any[new_va]
                     vargtype = Tuple{new_va}
                 else
-                    vargtype_elements = Any[]
                     vargtype = Tuple{}
                 end
             else

base/compiler/ssair/inlining.jl

@@ -842,51 +842,6 @@ function InliningTodo(mi::MethodInstance, src::Union{CodeInfo, Array{UInt8, 1}})
     end
 end
 
-# Neither the product iterator not CartesianIndices are available
-# here, so use this poor man's version
-struct SimpleCartesian
-    ranges::Vector{UnitRange{Int}}
-end
-function iterate(s::SimpleCartesian, state::Vector{Int}=Int[1 for _ in 1:length(s.ranges)])
-    state[end] > last(s.ranges[end]) && return nothing
-    vals = copy(state)
-    any = false
-    for i = 1:length(s.ranges)
-        if state[i] < last(s.ranges[i])
-            for j = 1:(i-1)
-                state[j] = first(s.ranges[j])
-            end
-            state[i] += 1
-            any = true
-            break
-        end
-    end
-    if !any
-        state[end] += 1
-    end
-    (vals, state)
-end
-
-# Given a signure, iterate over the signatures to union split over
-struct UnionSplitSignature
-    it::SimpleCartesian
-    typs::Vector{Any}
-end
-
-function UnionSplitSignature(atypes::Vector{Any})
-    typs = Any[uniontypes(widenconst(atypes[i])) for i = 1:length(atypes)]
-    ranges = UnitRange{Int}[1:length(typs[i]) for i = 1:length(typs)]
-    return UnionSplitSignature(SimpleCartesian(ranges), typs)
-end
-
-function iterate(split::UnionSplitSignature, state::Vector{Int}...)
-    y = iterate(split.it, state...)
-    y === nothing && return nothing
-    idxs, state = y
-    sig = Any[split.typs[i][j] for (i, j) in enumerate(idxs)]
-    return (sig, state)
-end
-
 function handle_single_case!(ir::IRCode, stmt::Expr, idx::Int, @nospecialize(case), isinvoke::Bool, todo::Vector{Pair{Int, Any}})
     if isa(case, ConstantCase)
         ir[SSAValue(idx)] = case.val