merge default

9 files changed, 80 insertions, 15 deletions

diff --git a/pypy/doc/whatsnew-head.rst b/pypy/doc/whatsnew-head.rst
index f932c3b2d8..d195d41f61 100644
--- a/pypy/doc/whatsnew-head.rst
+++ b/pypy/doc/whatsnew-head.rst
@@ -55,6 +55,11 @@ Backport fixes to winreg adding reflection and fix for passing None (bpo
 Change parameter type of ``PyModule_New`` to ``const char*``, add
 ``PyModule_Check`` and ``PyModule_CheckExact``
 
+.. branch: rpython-never-allocate
+
+Introduce a ``@never_allocate`` class decorator, which ensure that a certain
+RPython class is never actually instantiated at runtime. Useful to ensure that
+e.g. it's always constant-folded away
 
 .. branch: map-improvements
 
diff --git a/rpython/memory/gctransform/transform.py b/rpython/memory/gctransform/transform.py
index d793f91ef2..d3dd64702f 100644
--- a/rpython/memory/gctransform/transform.py
+++ b/rpython/memory/gctransform/transform.py
@@ -19,6 +19,8 @@ from rpython.rtyper.lltypesystem.lloperation import llop
 from rpython.translator.simplify import cleanup_graph
 from rpython.memory.gctransform.log import log
 
+class GCTransformError(Exception):
+    pass
 
 class GcHighLevelOp(object):
     def __init__(self, gct, op, index, llops):
@@ -236,8 +238,12 @@ class BaseGCTransformer(object):
             inserted_empty_startblock = True
         is_borrowed = self.compute_borrowed_vars(graph)
 
-        for block in graph.iterblocks():
-            self.transform_block(block, is_borrowed)
+        try:
+            for block in graph.iterblocks():
+                self.transform_block(block, is_borrowed)
+        except GCTransformError as e:
+            e.args = ('[function %s]: %s' % (graph.name, e.message),)
+            raise
 
         for link, livecounts in self.links_to_split.iteritems():
             llops = LowLevelOpList()
@@ -519,6 +525,12 @@ class GCTransformer(BaseGCTransformer):
 
     def gct_malloc(self, hop, add_flags=None):
         TYPE = hop.spaceop.result.concretetype.TO
+        if TYPE._hints.get('never_allocate'):
+            raise GCTransformError(
+                "struct %s was marked as @never_allocate but a call to malloc() "
+                "was found. This probably means that the corresponding class is "
+                "supposed to be constant-folded away, but for some reason it was not."
+                % TYPE._name)
         assert not TYPE._is_varsize()
         flags = hop.spaceop.args[1].value
         flavor = flags['flavor']
diff --git a/rpython/rlib/objectmodel.py b/rpython/rlib/objectmodel.py
index 5faa6850fd..37ccdf9cb1 100644
--- a/rpython/rlib/objectmodel.py
+++ b/rpython/rlib/objectmodel.py
@@ -1067,3 +1067,13 @@ def import_from_mixin(M, special_methods=['__init__', '__del__']):
         target[key] = value
     if immutable_fields:
         target['_immutable_fields_'] = target.get('_immutable_fields_', []) + immutable_fields
+
+def never_allocate(cls):
+    """
+    Class decorator to ensure that a class is NEVER instantiated at runtime.
+
+    Useful e.g for context manager which are expected to be constant-folded
+    away.
+    """
+    cls._rpython_never_allocate_ = True
+    return cls
diff --git a/rpython/rlib/test/test_objectmodel.py b/rpython/rlib/test/test_objectmodel.py
index 6bcb9d60c6..5f14528556 100644
--- a/rpython/rlib/test/test_objectmodel.py
+++ b/rpython/rlib/test/test_objectmodel.py
@@ -7,7 +7,8 @@ from rpython.rlib.objectmodel import (
     resizelist_hint, is_annotation_constant, always_inline, NOT_CONSTANT,
     iterkeys_with_hash, iteritems_with_hash, contains_with_hash,
     setitem_with_hash, getitem_with_hash, delitem_with_hash, import_from_mixin,
-    fetch_translated_config, try_inline, delitem_if_value_is, move_to_end)
+    fetch_translated_config, try_inline, delitem_if_value_is, move_to_end,
+    never_allocate, dont_inline)
 from rpython.translator.translator import TranslationContext, graphof
 from rpython.rtyper.test.tool import BaseRtypingTest
 from rpython.rtyper.test.test_llinterp import interpret
@@ -851,3 +852,37 @@ def test_import_from_mixin_immutable_fields():
         import_from_mixin(C)
 
     assert BA._immutable_fields_ == ['c', 'a']
+
+
+def test_never_allocate():
+    from rpython.translator.c.test.test_genc import compile as c_compile
+    from rpython.memory.gctransform.transform import GCTransformError
+
+    @never_allocate
+    class MyClass(object):
+        def __init__(self, x):
+            self.x = x + 1
+
+    @dont_inline
+    def allocate_MyClass(x):
+        return MyClass(x)
+
+    def f(x):
+        # this fails because the allocation of MyClass can't be
+        # constant-folded (because it's inside a @dont_inline function)
+        return allocate_MyClass(x).x
+
+    def g(x):
+        # this works because MyClass is constant folded, so the GC transformer
+        # never sees a malloc(MyClass)
+        return MyClass(x).x
+
+    # test what happens if MyClass escapes
+    with py.test.raises(GCTransformError) as exc:
+        c_compile(f, [int])
+    assert '[function allocate_MyClass]' in str(exc)
+    assert 'was marked as @never_allocate' in str(exc)
+
+    # test that it works in the "normal" case
+    compiled_g = c_compile(g, [int])
+    assert compiled_g(41) == 42
diff --git a/rpython/rtyper/lltypesystem/ll2ctypes.py b/rpython/rtyper/lltypesystem/ll2ctypes.py
index d9fdd322d7..efa6f11a2f 100644
--- a/rpython/rtyper/lltypesystem/ll2ctypes.py
+++ b/rpython/rtyper/lltypesystem/ll2ctypes.py
@@ -374,9 +374,9 @@ def build_new_ctypes_type(T, delayed_builders):
     elif isinstance(T, lltype.OpaqueType):
         if T is lltype.RuntimeTypeInfo:
             return ctypes.c_char * 2
-        if T.hints.get('external', None) != 'C':
+        if T._hints.get('external', None) != 'C':
             raise TypeError("%s is not external" % T)
-        return ctypes.c_char * T.hints['getsize']()
+        return ctypes.c_char * T._hints['getsize']()
     else:
         _setup_ctypes_cache()
         if T in _ctypes_cache:
@@ -934,7 +934,7 @@ def lltype2ctypes(llobj, normalize=True):
                     convert_array(container)
                 elif isinstance(T.TO, lltype.OpaqueType):
                     if T.TO != lltype.RuntimeTypeInfo:
-                        cbuf = ctypes.create_string_buffer(T.TO.hints['getsize']())
+                        cbuf = ctypes.create_string_buffer(T.TO._hints['getsize']())
                     else:
                         cbuf = ctypes.create_string_buffer("\x00")
                     cbuf = ctypes.cast(cbuf, ctypes.c_void_p)
diff --git a/rpython/rtyper/lltypesystem/lltype.py b/rpython/rtyper/lltypesystem/lltype.py
index eaa51f1edc..c75fd90e7a 100644
--- a/rpython/rtyper/lltypesystem/lltype.py
+++ b/rpython/rtyper/lltypesystem/lltype.py
@@ -584,7 +584,7 @@ class OpaqueType(ContainerType):
         """
         self.tag = tag
         self.__name__ = tag
-        self.hints = frozendict(hints)
+        self._hints = frozendict(hints)
 
     def __str__(self):
         return "%s (opaque)" % self.tag
diff --git a/rpython/rtyper/rclass.py b/rpython/rtyper/rclass.py
index 0d09123617..a98a04649b 100644
--- a/rpython/rtyper/rclass.py
+++ b/rpython/rtyper/rclass.py
@@ -527,6 +527,9 @@ class InstanceRepr(Repr):
             if hints is None:
                 hints = {}
             hints = self._check_for_immutable_hints(hints)
+            if self.classdef.classdesc.get_param('_rpython_never_allocate_'):
+                hints['never_allocate'] = True
+
             kwds = {}
             if self.gcflavor == 'gc':
                 kwds['rtti'] = True
diff --git a/rpython/translator/c/database.py b/rpython/translator/c/database.py
index f21f661ba3..bf0ced6418 100644
--- a/rpython/translator/c/database.py
+++ b/rpython/translator/c/database.py
@@ -84,7 +84,7 @@ class LowLevelDatabase(object):
                     node = BareBoneArrayDefNode(self, T, varlength)
                 else:
                     node = ArrayDefNode(self, T, varlength)
-            elif isinstance(T, OpaqueType) and T.hints.get("render_structure", False):
+            elif isinstance(T, OpaqueType) and T._hints.get("render_structure", False):
                 node = ExtTypeOpaqueDefNode(self, T)
             elif T == WeakRef:
                 REALT = self.gcpolicy.get_real_weakref_type()
@@ -102,8 +102,8 @@ class LowLevelDatabase(object):
             return '%s @' % T.c_name
         elif isinstance(T, Ptr):
             if (isinstance(T.TO, OpaqueType) and
-                T.TO.hints.get('c_pointer_typedef') is not None):
-                return '%s @' % T.TO.hints['c_pointer_typedef']
+                T.TO._hints.get('c_pointer_typedef') is not None):
+                return '%s @' % T.TO._hints['c_pointer_typedef']
             try:
                 node = self.gettypedefnode(T.TO)
             except NoCorrespondingNode:
@@ -134,13 +134,13 @@ class LowLevelDatabase(object):
         elif isinstance(T, OpaqueType):
             if T == RuntimeTypeInfo:
                 return  self.gcpolicy.rtti_type()
-            elif T.hints.get("render_structure", False):
+            elif T._hints.get("render_structure", False):
                 node = self.gettypedefnode(T, varlength=varlength)
                 if who_asks is not None:
                     who_asks.dependencies.add(node)
                 return 'struct %s @' % node.name
-            elif T.hints.get('external', None) == 'C':
-                return '%s @' % T.hints['c_name']
+            elif T._hints.get('external', None) == 'C':
+                return '%s @' % T._hints['c_name']
             else:
                 #raise Exception("don't know about opaque type %r" % (T,))
                 return 'struct %s @' % (
@@ -182,7 +182,7 @@ class LowLevelDatabase(object):
             return PrimitiveName[T](obj, self)
         elif isinstance(T, Ptr):
             if (isinstance(T.TO, OpaqueType) and
-                T.TO.hints.get('c_pointer_typedef') is not None):
+                T.TO._hints.get('c_pointer_typedef') is not None):
                 if obj._obj is not None:
                     value = rffi.cast(rffi.SSIZE_T, obj)
                     return '((%s) %s)' % (cdecl(self.gettype(T), ''),
diff --git a/rpython/translator/c/node.py b/rpython/translator/c/node.py
index 91458b643c..7898be2bdb 100644
--- a/rpython/translator/c/node.py
+++ b/rpython/translator/c/node.py
@@ -947,7 +947,7 @@ class ExtType_OpaqueNode(ContainerNode):
 def opaquenode_factory(db, T, obj):
     if T == RuntimeTypeInfo:
         return db.gcpolicy.rtti_node_factory()(db, T, obj)
-    if T.hints.get("render_structure", False):
+    if T._hints.get("render_structure", False):
         return ExtType_OpaqueNode(db, T, obj)
     raise Exception("don't know about %r" % (T,))