[mypyc] Raise AttributeError also for non-refcounted types (python#11940

)

Previously we only raised it for refcounted types, potentially resulting in
errors like this:

```
SystemError: initialization of m failed without raising an exception
```

Unfortunately, this slows down the richards benchmark by about 15%. We
can get the lost performance back once we have support for always
defined attributes, at the latest.

mypyc/codegen/emitfunc.py

@@ -292,17 +292,17 @@ def visit_get_attr(self, op: GetAttr) -> None:
             # Otherwise, use direct or offset struct access.
             attr_expr = self.get_attr_expr(obj, op, decl_cl)
             self.emitter.emit_line('{} = {};'.format(dest, attr_expr))
+            self.emitter.emit_undefined_attr_check(
+                attr_rtype, attr_expr, '==', unlikely=True
+            )
+            exc_class = 'PyExc_AttributeError'
+            self.emitter.emit_line(
+                'PyErr_SetString({}, "attribute {} of {} undefined");'.format(
+                    exc_class, repr(op.attr), repr(cl.name)))
             if attr_rtype.is_refcounted:
-                self.emitter.emit_undefined_attr_check(
-                    attr_rtype, attr_expr, '==', unlikely=True
-                )
-                exc_class = 'PyExc_AttributeError'
-                self.emitter.emit_lines(
-                    'PyErr_SetString({}, "attribute {} of {} undefined");'.format(
-                        exc_class, repr(op.attr), repr(cl.name)),
-                    '} else {')
+                self.emitter.emit_line('} else {')
                 self.emitter.emit_inc_ref(attr_expr, attr_rtype)
-                self.emitter.emit_line('}')
+            self.emitter.emit_line('}')
 
     def visit_set_attr(self, op: SetAttr) -> None:
         dest = self.reg(op)

mypyc/test-data/run-classes.test

@@ -336,6 +336,7 @@ class C:
     b: bool
     c: C
     d: object
+    e: int
 
 def setattrs(o: C, a: List[int], b: bool, c: C) -> None:
     o.a = a
@@ -346,6 +347,8 @@ def getattrs(o: C) -> Tuple[List[int], bool, C]:
     return o.a, o.b, o.c
 [file driver.py]
 from native import C, setattrs, getattrs
+from testutil import assertRaises
+
 c1 = C()
 c2 = C()
 aa = [2]
@@ -359,6 +362,18 @@ o = object()
 c1.d = o
 assert c1.d is o
 
+c3 = C()
+with assertRaises(AttributeError, "attribute 'a' of 'C' undefined"):
+    c3.a
+with assertRaises(AttributeError, "attribute 'b' of 'C' undefined"):
+    c3.b
+with assertRaises(AttributeError, "attribute 'c' of 'C' undefined"):
+    c3.c
+with assertRaises(AttributeError, "attribute 'd' of 'C' undefined"):
+    c3.d
+with assertRaises(AttributeError, "attribute 'e' of 'C' undefined"):
+    c3.e
+
 [case testInitMethodWithMissingNoneReturnAnnotation]
 class C:
     def __init__(self):

mypyc/test/test_emitfunc.py

@@ -288,6 +288,15 @@ def test_get_attr(self) -> None:
                }
             """)
 
+    def test_get_attr_non_refcounted(self) -> None:
+        self.assert_emit(
+            GetAttr(self.r, 'x', 1),
+            """cpy_r_r0 = ((mod___AObject *)cpy_r_r)->_x;
+               if (unlikely(((mod___AObject *)cpy_r_r)->_x == 2)) {
+                   PyErr_SetString(PyExc_AttributeError, "attribute 'x' of 'A' undefined");
+               }
+            """)
+
     def test_set_attr(self) -> None:
         self.assert_emit(
             SetAttr(self.r, 'y', self.m, 1),