make emit_isa change more minimal

Author: jrevels

src/cgutils.cpp

@@ -1060,33 +1060,22 @@ static void emit_type_error(jl_codectx_t &ctx, const jl_cgval_t &x, Value *type,
 
 static std::pair<Value*, bool> emit_isa(jl_codectx_t &ctx, const jl_cgval_t &x, jl_value_t *type, const std::string *msg)
 {
-    jl_value_t *intersected_type = type;
-
+    // TODO: The subtype check below suffers from incorrectness issues due to broken
+    // subtyping for kind types (see https://github.com/JuliaLang/julia/issues/27078). For
+    // actual `isa` calls, this optimization should already have been performed upstream
+    // anyway, but having this optimization in codegen might still be beneficial for
+    // `typeassert`s if we can make it correct.
     Optional<bool> known_isa;
-    if (x.constant) {
+    jl_value_t *intersected_type = type;
+    if (x.constant)
         known_isa = jl_isa(x.constant, type);
+    else if (jl_subtype(x.typ, type)) {
+        // known_isa = true;
     } else {
         intersected_type = jl_type_intersection(x.typ, type);
         if (intersected_type == (jl_value_t*)jl_bottom_type)
             known_isa = false;
     }
-
-    // TODO: This commented-out version of the above check suffers from incorrectness
-    // issues due to broken subtyping for kind types (see
-    // https://github.com/JuliaLang/julia/issues/27078). For actual `isa` calls, this
-    // optimization should already have been performed upstream anyway, but having this
-    // optimization in codegen might still be beneficial for `typeassert`s if we can make it
-    // correct.
-    // if (x.constant) {
-    //     known_isa = jl_isa(x.constant, type);
-    // else if (jl_subtype(x.typ, type))
-    //     known_isa = true;
-    // else {
-    //     intersected_type = jl_type_intersection(x.typ, type);
-    //     if (intersected_type == (jl_value_t*)jl_bottom_type)
-    //         known_isa = false;
-    // }
-
     if (known_isa) {
         if (!*known_isa && msg) {
             emit_type_error(ctx, x, literal_pointer_val(ctx, type), *msg);