@cpp class | null tested for truth with a boolean (h && cond): no instanceof

tslang/lib/TypeScript/MLIRGenCast.cpp

@@ -3177,6 +3177,36 @@ namespace mlirgen
 
                 auto toBoolean = isa<mlir_ts::BooleanType>(type) || isa<mlir_ts::TypePredicateType>(type);
 
+                // The tag says "class"; `instanceof` tells the classes apart. A @cpp class's objects
+                // are C++ objects with no type information, so `instanceof` refuses them: when the
+                // class need not be told - the only class of the union, or tested for truth, as
+                // `h && n == 3` with h a `Handle | null` is - `typeof` has already narrowed t enough.
+                // Otherwise only the other classes are tested.
+                auto writeClassTests = [&]() {
+                    auto hasCppClass = llvm::any_of(classInstances, [&](mlir::Type classType) { return isCppVTableClass(classType); });
+                    if (hasCppClass && (toBoolean || classInstances.size() == 1))
+                    {
+                        ss << S("return t;\n");
+                        return;
+                    }
+
+                    ss << S("{ \n");
+
+                    for (auto [index, classType] : enumerate(classInstances))
+                    {
+                        if (isCppVTableClass(classType))
+                        {
+                            continue;
+                        }
+
+                        ss << S("if (t instanceof TYPE_INST_ALIAS");
+                        ss << index;
+                        ss << S(") return t;\n");
+                    }
+
+                    ss << S(" }\n");
+                };
+
                 // A union whose actual type has no null member but whose members all hold null in
                 // their own pointer (`A | B | null`) is null when that pointer is null, whatever its
                 // tag: asked first, so that no member's test - `instanceof` reads the vtable - meets a
@@ -3216,16 +3246,7 @@ namespace mlirgen
                         ss << S("') ");
                         if (pair.getKey() == "class")
                         {
-                            ss << S("{ \n");
-
-                            for (auto [index, _] : enumerate(classInstances))
-                            {
-                                ss << S("if (t instanceof TYPE_INST_ALIAS");
-                                ss << index;
-                                ss << S(") return t;\n");
-                            }
-
-                            ss << S(" }\n");
+                            writeClassTests();
                         }
                         else
                         {
@@ -3261,16 +3282,7 @@ namespace mlirgen
                         }
                         else if (pair.getKey() == "class")
                         {
-                            ss << S("{ \n");
-
-                            for (auto [index, _] : enumerate(classInstances))
-                            {
-                                ss << S("if (t instanceof TYPE_INST_ALIAS");
-                                ss << index;
-                                ss << S(") return t;\n");
-                            }
-
-                            ss << S(" }\n");
+                            writeClassTests();
                         }
                         else
                         {

tslang/test/tester/CMakeLists.txt

@@ -487,6 +487,8 @@ tslang_add_test(NAME test-compile-own-00-cpp-slot COMMAND test-runner -mm=own "$
 tslang_add_test(NAME test-compile-own-00-cpp-overloads COMMAND test-runner -mm=own "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_overloads.ts")
 tslang_add_test(NAME test-compile-00-cpp-slot COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_slot.ts")
 tslang_add_test(NAME test-compile-00-cpp-overloads COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_overloads.ts")
+tslang_add_test(NAME test-compile-00-cpp-union-truth COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_union_truth.ts")
+tslang_add_test(NAME test-compile-own-00-cpp-union-truth COMMAND test-runner -mm=own "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_union_truth.ts")
 tslang_add_test(NAME test-compile-00-union-value-equality COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00union_value_equality.ts")
 tslang_add_test(NAME test-compile-00-strict-equals-mismatched-types COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00strict_equals_mismatched_types.ts")
 tslang_add_test(NAME test-compile-00-any-number-compare COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00any_number_compare.ts")
@@ -1139,6 +1141,8 @@ tslang_add_test(NAME test-jit-00-cpp-overloads COMMAND test-runner -jit "${PROJE
 tslang_add_test(NAME test-jit-own-00-cppvtable-class COMMAND test-runner -jit -mm=own "${PROJECT_SOURCE_DIR}/test/tester/tests/00cppvtable_class.ts")
 tslang_add_test(NAME test-jit-own-00-cpp-slot COMMAND test-runner -jit -mm=own "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_slot.ts")
 tslang_add_test(NAME test-jit-own-00-cpp-overloads COMMAND test-runner -jit -mm=own "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_overloads.ts")
+tslang_add_test(NAME test-jit-00-cpp-union-truth COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_union_truth.ts")
+tslang_add_test(NAME test-jit-own-00-cpp-union-truth COMMAND test-runner -jit -mm=own "${PROJECT_SOURCE_DIR}/test/tester/tests/00cpp_union_truth.ts")
 tslang_add_test(NAME test-jit-00-union-value-equality COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00union_value_equality.ts")
 tslang_add_test(NAME test-jit-00-strict-equals-mismatched-types COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00strict_equals_mismatched_types.ts")
 tslang_add_test(NAME test-jit-00-any-number-compare COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00any_number_compare.ts")
@@ -2747,6 +2751,7 @@ set(TSLANG_CORPUS
     00cppvtable_class.ts
     00cpp_slot.ts
     00cpp_overloads.ts
+    00cpp_union_truth.ts
     )
 
 # the default model runs these ahead of time only, so the other models do too

tslang/test/tester/tests/00cpp_union_truth.ts

@@ -0,0 +1,59 @@
+// A @cpp class that may be null in a union with a boolean (`h && n == 3`) is tested for truth by
+// its pointer alone: its objects are C++ objects, and `instanceof` can't ask them what they are.
+// The "C++ object" is made by hand, as in tests/00cppvtable_class.ts.
+
+@cpp
+class Handle {
+    value: s32;
+    @slot(0) first(): s32;
+}
+
+@cpp
+class Other {
+    @slot(0) first(): s32;
+}
+
+type ObjectData = [vtable: Opaque, value: s32];
+
+function slot0(self: Opaque): s32 {
+    return 10;
+}
+
+function both(h: Handle | null, n: number): boolean {
+    if (h && n == 3) {
+        return true;
+    }
+
+    return false;
+}
+
+function either(enabled: boolean, h: Handle | null): boolean {
+    return enabled && h ? true : false;
+}
+
+function main() {
+    let vtable: Opaque[] = [<Opaque>slot0];
+    let data: ObjectData = [<Opaque>Ref(vtable[0]), 32];
+    const object = <Opaque>Ref(data);
+
+    const handle = <Handle>object;
+    const none: Handle | null = null;
+
+    assert(both(handle, 3), "a handle and true");
+    assert(!both(handle, 4), "a handle and false");
+    assert(!both(none, 3), "null and true");
+
+    assert(either(true, handle), "true and a handle");
+    assert(!either(false, handle), "false and a handle");
+    assert(!either(true, none), "true and null");
+
+    // two @cpp classes and a boolean: neither class needs telling apart to be tested for truth
+    const other = <Other>object;
+    const flag = true;
+    let a: Handle | Other | boolean | null = flag && other;
+    assert(a ? true : false, "a @cpp object of either class");
+    a = null;
+    assert(!(a ? true : false), "null");
+
+    print("done.");
+}