fix Base.return_types for direct builtin calls (#46443)

This commit also changed this fragile test case
```
@test Base.return_types(Expr) == Any[Expr]
```
to
```
@test only(Base.return_types(Core._expr)) === Expr
```
since `Expr` is just a generic function and can be overloaded
in the future (e.g. the JuliaSyntax.jl integration PR).

base/reflection.jl

@@ -1402,14 +1402,19 @@ function return_types(@nospecialize(f), @nospecialize(types=default_tt(f));
         return Any[rt]
     end
     types = to_tuple_type(types)
-    rt = []
+    if isa(f, Core.Builtin)
+        argtypes = Any[types.parameters...]
+        rt = Core.Compiler.builtin_tfunction(interp, f, argtypes, nothing)
+        return Any[rt]
+    end
+    rts = []
     for match in _methods(f, types, -1, world)::Vector
         match = match::Core.MethodMatch
         meth = func_for_method_checked(match.method, types, match.sparams)
         ty = Core.Compiler.typeinf_type(interp, meth, match.spec_types, match.sparams)
-        push!(rt, something(ty, Any))
+        push!(rts, something(ty, Any))
     end
-    return rt
+    return rts
 end
 
 function infer_effects(@nospecialize(f), @nospecialize(types=default_tt(f));
@@ -1421,22 +1426,21 @@ function infer_effects(@nospecialize(f), @nospecialize(types=default_tt(f));
         argtypes = Any[types.parameters...]
         rt = Core.Compiler.builtin_tfunction(interp, f, argtypes, nothing)
         return Core.Compiler.builtin_effects(f, argtypes, rt)
-    else
-        effects = Core.Compiler.EFFECTS_TOTAL
-        matches = _methods(f, types, -1, world)::Vector
-        if isempty(matches)
-            # this call is known to throw MethodError
-            return Core.Compiler.Effects(effects; nothrow=false)
-        end
-        for match in matches
-            match = match::Core.MethodMatch
-            frame = Core.Compiler.typeinf_frame(interp,
-                match.method, match.spec_types, match.sparams, #=run_optimizer=#false)
-            frame === nothing && return Core.Compiler.Effects()
-            effects = Core.Compiler.merge_effects(effects, frame.ipo_effects)
-        end
-        return effects
     end
+    effects = Core.Compiler.EFFECTS_TOTAL
+    matches = _methods(f, types, -1, world)::Vector
+    if isempty(matches)
+        # this call is known to throw MethodError
+        return Core.Compiler.Effects(effects; nothrow=false)
+    end
+    for match in matches
+        match = match::Core.MethodMatch
+        frame = Core.Compiler.typeinf_frame(interp,
+            match.method, match.spec_types, match.sparams, #=run_optimizer=#false)
+        frame === nothing && return Core.Compiler.Effects()
+        effects = Core.Compiler.merge_effects(effects, frame.ipo_effects)
+    end
+    return effects
 end
 
 """

test/compiler/inference.jl

@@ -3324,7 +3324,8 @@ f_generator_splat(t::Tuple) = tuple((identity(l) for l in t)...)
 @test Core.Compiler.sizeof_tfunc(UnionAll) === Int
 @test !Core.Compiler.sizeof_nothrow(UnionAll)
 
-@test Base.return_types(Expr) == Any[Expr]
+@test only(Base.return_types(Core._expr)) === Expr
+@test only(Base.return_types(Core.svec, (Any,))) === Core.SimpleVector
 
 # Use a global constant to rely less on unrelated constant propagation
 const const_int32_typename = Int32.name

test/reflection.jl

@@ -202,7 +202,7 @@ end
 
 @test which(===, Tuple{Int, Int}) isa Method
 @test length(code_typed(===, Tuple{Int, Int})) === 1
-@test only(Base.return_types(===, Tuple{Int, Int})) === Any
+@test only(Base.return_types(===, Tuple{Int, Int})) === Bool
 
 module TestingExported
 using Test