Optimize abstract_iteration a little bit

Avoid recomputation of a `widenconst` and initialize `valtype` and
`statetype` to `Bottom` before second loop to simplify a `⊑`to a `<:`
there.

Author: martinholters

base/compiler/abstractinterpretation.jl

@@ -840,9 +840,11 @@ function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @n
             return ret, AbstractIterationInfo(calls)
         end
         if Nothing <: stateordonet_widened || length(ret) >= InferenceParams(interp).MAX_TUPLE_SPLAT
+            stateordonet = stateordonet_widened
             break
         end
         if !isa(stateordonet_widened, DataType) || !(stateordonet_widened <: Tuple) || isvatuple(stateordonet_widened) || length(stateordonet_widened.parameters) != 2
+            stateordonet = stateordonet_widened
             break
         end
         nstatetype = getfield_tfunc(stateordonet, Const(2))
@@ -860,15 +862,17 @@ function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @n
     end
     # From here on, we start asking for results on the widened types, rather than
     # the precise (potentially const) state type
-    valtype = widenconst(valtype)
+    # statetype and valtype are reinitialized in the first iteration below from the
+    # (widened) stateordonet, which has not yet been fully analyzed in the loop above
+    statetype = Bottom
+    valtype = Bottom
     while valtype !== Any
-        stateordonet = widenconst(stateordonet)
         nounion = typesubtract(stateordonet, Nothing, 0)
         if !isa(nounion, DataType) || !(nounion <: Tuple) || isvatuple(nounion) || length(nounion.parameters) != 2
             valtype = Any
             break
         end
-        if nounion.parameters[1] <: valtype && nounion.parameters[2] ⊑ statetype
+        if nounion.parameters[1] <: valtype && nounion.parameters[2] <: statetype
             if typeintersect(stateordonet, Nothing) === Union{}
                 # Reached a fixpoint, but Nothing is not possible => iterator is infinite or failing
                 return Any[Bottom], nothing
@@ -878,6 +882,7 @@ function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @n
         valtype = tmerge(valtype, nounion.parameters[1])
         statetype = tmerge(statetype, nounion.parameters[2])
         stateordonet = abstract_call_known(interp, iteratef, nothing, Any[Const(iteratef), itertype, statetype], sv).rt
+        stateordonet = widenconst(stateordonet)
     end
     push!(ret, Vararg{valtype})
     return ret, nothing