Fix a precision issue in abstract_iteration

If the first loop exits in the first iteration, the `statetype` is still
`Bottom`. In that case, the new `stateordonet` needs to be determined
with the two-arg version of `iterate` again.

Fixes #41022.

Author: martinholters

base/compiler/abstractinterpretation.jl

@@ -862,8 +862,12 @@ function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @n
     # the precise (potentially const) state type
     statetype = widenconst(statetype)
     valtype = widenconst(valtype)
-    while valtype !== Any
+    if statetype === Bottom
+        stateordonet = abstract_call_known(interp, iteratef, nothing, Any[Const(iteratef), itertype], sv).rt
+    else
         stateordonet = abstract_call_known(interp, iteratef, nothing, Any[Const(iteratef), itertype, statetype], sv).rt
+    end
+    while valtype !== Any
         stateordonet = widenconst(stateordonet)
         nounion = typesubtract(stateordonet, Nothing, 0)
         if !isa(nounion, DataType) || !(nounion <: Tuple) || isvatuple(nounion) || length(nounion.parameters) != 2
@@ -879,6 +883,7 @@ function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @n
         end
         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
     end
     push!(ret, Vararg{valtype})
     return ret, nothing

test/compiler/inference.jl

@@ -2875,6 +2875,7 @@ partial_return_2(x) = Val{partial_return_1(x)[2]}
 # Precision of abstract_iteration
 f_splat(x) = (x...,)
 @test Base.return_types(f_splat, (Pair{Int,Int},)) == Any[Tuple{Int, Int}]
+@test Base.return_types(f_splat, (UnitRange{Int},)) == Any[Tuple{Vararg{Int}}]
 
 # issue #32699
 f32699(a) = (id = a[1],).id