Add support for self referential metadata

llvmlite/ir/module.py

@@ -42,22 +42,32 @@ def _fix_di_operands(self, operands):
             fixed_ops.append((name, op))
         return fixed_ops
 
-    def add_metadata(self, operands):
+    def add_metadata(self, operands, *, self_ref=False):
         """
         Add an unnamed metadata to the module with the given *operands*
         (a sequence of values) or return a previous equivalent metadata.
         A MDValue instance is returned, it can then be associated to
         e.g. an instruction.
+
+        A self referential metadata entry has itself as the first
+        operand to ensure uniquencess. These references are never
+        cached.
         """
         if not isinstance(operands, (list, tuple)):
             raise TypeError("expected a list or tuple of metadata values, "
                             "got %r" % (operands,))
         operands = self._fix_metadata_operands(operands)
         key = tuple(operands)
-        if key not in self._metadatacache:
+        if self_ref or key not in self._metadatacache:
             n = len(self.metadata)
-            md = values.MDValue(self, operands, name=str(n))
-            self._metadatacache[key] = md
+            md = values.MDValue(
+                self,
+                operands,
+                name=str(n),
+                self_ref=self_ref,
+            )
+            if not self_ref:
+                self._metadatacache[key] = md
         else:
             md = self._metadatacache[key]
         return md

llvmlite/ir/values.py

@@ -662,11 +662,14 @@ class MDValue(NamedValue):
     """
     name_prefix = '!'
 
-    def __init__(self, parent, values, name):
+    def __init__(self, parent, values, name, *, self_ref=False):
         super(MDValue, self).__init__(parent,
                                       types.MetaDataType(),
                                       name=name)
-        self.operands = tuple(values)
+        # Store only the non-self params to avoid
+        # ref counting cycles
+        self._operands = tuple(values)
+        self._is_self_ref = self_ref
         parent.metadata.append(self)
 
     def descr(self, buf):
@@ -687,6 +690,8 @@ def _get_reference(self):
 
     def __eq__(self, other):
         if isinstance(other, MDValue):
+            if self._is_self_ref:
+                return self is other
             return self.operands == other.operands
         else:
             return False
@@ -695,7 +700,13 @@ def __ne__(self, other):
         return not self.__eq__(other)
 
     def __hash__(self):
-        return hash(self.operands)
+        return hash(self._operands)
+
+    @property
+    def operands(self):
+        if self._is_self_ref:
+            return (self,) + self._operands
+        return self._operands
 
 
 class DIToken:

llvmlite/tests/test_ir.py

@@ -323,6 +323,17 @@ def test_unnamed_metadata_3(self):
         self.assert_ir_line('!1 = !{ i32 789 }', mod)
         self.assert_ir_line('!2 = !{ i32 123, !0, !1, !0 }', mod)
 
+    def test_self_relf_metadata(self):
+        mod = self.module()
+        value = mod.add_metadata((), self_ref=True)
+        self.assert_ir_line('!0 = !{ !0 }', mod)
+        value2 = mod.add_metadata((value,))
+        assert value is not value2
+        self.assert_ir_line('!1 = !{ !0 }', mod)
+        value3 = mod.add_metadata((), self_ref=True)
+        self.assert_ir_line('!2 = !{ !2 }', mod)
+        assert value is not value3
+
     def test_metadata_string(self):
         # Escaping contents of a metadata string
         mod = self.module()