inference: handle Vararg in abstract_call_unionall for argtypes…

… computed by `abstract_apply` (#51393)

This commit adds special handling for `Vararg` types that may appear at
the end of `argtypes`, as computed by `abstract_apply`. Even though PR
#42583 has ensured that `Vararg` and `TypeVar` should never appear
within the abstract state, they can still be part of `argtypes`. As a
result, this kind of special handling is still necessary. It remains an
open question whether we can refactor `abstract_apply` to prevent
`Vararg`s from appearing in `argtypes` in the first place.

base/compiler/abstractinterpretation.jl

@@ -1858,7 +1858,12 @@ function abstract_call_unionall(interp::AbstractInterpreter, argtypes::Vector{An
         a2 = argtypes[2]
         a3 = argtypes[3]
         ⊑ᵢ = ⊑(typeinf_lattice(interp))
-        nothrow = a2 ⊑ᵢ TypeVar && (a3 ⊑ᵢ Type || a3 ⊑ᵢ TypeVar)
+        if isvarargtype(a3)
+            a3 = unwrapva(a3)
+            nothrow = false
+        else
+            nothrow = a2 ⊑ᵢ TypeVar && (a3 ⊑ᵢ Type || a3 ⊑ᵢ TypeVar)
+        end
         if isa(a3, Const)
             body = a3.val
         elseif isType(a3)
@@ -2253,7 +2258,6 @@ function abstract_eval_value_expr(interp::AbstractInterpreter, e::Expr, vtypes::
     return Any
 end
 
-
 function abstract_eval_value(interp::AbstractInterpreter, @nospecialize(e), vtypes::Union{VarTable,Nothing}, sv::AbsIntState)
     if isa(e, Expr)
         return abstract_eval_value_expr(interp, e, vtypes, sv)

test/compiler/inference.jl

@@ -5,7 +5,7 @@ import Core.Compiler: Const, Conditional, ⊑, ReturnNode, GotoIfNot
 isdispatchelem(@nospecialize x) = !isa(x, Type) || Core.Compiler.isdispatchelem(x)
 
 using Random, Core.IR
-using InteractiveUtils: code_llvm
+using InteractiveUtils
 
 include("irutils.jl")
 
@@ -5230,3 +5230,8 @@ end |> only == Val{false}
 @test Base.return_types((Bool,)) do b
     Val(Core.Intrinsics.or_int(true, b))
 end |> only == Val{true}
+
+# https://github.com/JuliaLang/julia/issues/51310
+@test code_typed() do
+    b{c} = d...
+end |> only |> first isa Core.CodeInfo