[PatternLang] Add ConstantPattern (apache#5689)

* Add ConstantPattern

* update doc

docs/langref/relay_pattern.rst

@@ -37,6 +37,11 @@ for more use cases.
 
 .. _tests/python/relay/test_dataflow_pattern.py: https://github.com/apache/incubator-tvm/blob/master/tests/python/relay/test_dataflow_pattern.py
 
+.. note::
+
+    If you cannot find the corresponding pattern node to match the Relay node you want,
+    you are welcome to raise an issue or submit a PR to add it.
+
 Matching One of Two Ops
 ***********************
 
@@ -131,6 +136,44 @@ The next example is matching a pattern of batch_norm -> get(0) -> relu:
         out = relay.nn.relu(tuple_get_item_node)
         pat.match(out)
 
+The next example is matching a constant node regarding its values. This is useful to check
+if a specific parameter in a subgraph has been bind or not.
+
+.. code-block:: python
+
+    def test_match_constant():
+        conv2d = is_op('nn.conv2d')(wildcard(), ConstantPattern())
+        pattern = is_op('nn.bias_add')(conv2d, wildcard())
+
+        x = relay.var('x', shape=(1, 3, 224, 224))
+        w = relay.var('w', shape=(3, 3, 3, 3))
+        b = relay.var('b', shape=(3, ))
+        conv2d = relay.op.nn.conv2d(x, w)
+        out = relay.op.nn.bias_add(conv2d, b)
+        func = relay.Function([x, w, b], out)
+        mod = tvm.IRModule.from_expr(func)
+
+        # Two inputs of the conv2d in the graph are VarNode by default, so no match.
+        assert not pattern.match(mod['main'].body)
+
+        # The second input (weight) has been bind with constant values so it is now a constant node.
+        mod["main"] = bind_params_by_name(mod["main"],
+                                        {'w': tvm.nd.array(np.ones(shape=(3, 3, 3, 3)))})
+        assert pattern.match(mod['main'].body)
+
+On the other hand, if you need to match the constant with a specific value, you can directly
+use ``ExprPattern``. This could be useful for algebraic simplify.
+
+.. code-block:: python
+
+    def test_match_plus_zero():
+        zero = (ExprPattern(relay.const(0)) | ExprPattern(relay.const(0.0)))
+        pattern = wildcard() + zero
+        
+        x = relay.Var('x')
+        y = x + relay.const(0)
+        assert pattern.match(y)
+
 The next example is matching function nodes with a specific attribute:
 
 .. code-block:: python

include/tvm/relay/dataflow_pattern.h

@@ -111,6 +111,24 @@ class VarPattern : public DFPattern {
   TVM_DEFINE_OBJECT_REF_METHODS(VarPattern, DFPattern, VarPatternNode);
 };
 
+/*!
+ * \brief A Pattern to Match a Relay Constant
+ */
+class ConstantPattern;
+/*! \brief Container for Constant */
+class ConstantPatternNode : public DFPatternNode {
+ public:
+  void VisitAttrs(tvm::AttrVisitor* v) {}
+
+  static constexpr const char* _type_key = "relay.dataflow_pattern.ConstantPattern";
+  TVM_DECLARE_FINAL_OBJECT_INFO(ConstantPatternNode, DFPatternNode);
+};
+
+class ConstantPattern : public DFPattern {
+ public:
+  TVM_DEFINE_OBJECT_REF_METHODS(ConstantPattern, DFPattern, ConstantPatternNode);
+};
+
 /*!
  * \brief Call corresponds to operator invocation.
  *  Corresponds to the operator in computational graph terminology.

include/tvm/relay/dataflow_pattern_functor.h

@@ -91,6 +91,7 @@ class DFPatternFunctor<R(const DFPattern& n, Args...)> {
   virtual R VisitDFPattern_(const TuplePatternNode* op, Args... args) DFPATTERN_FUNCTOR_DEFAULT;
   virtual R VisitDFPattern_(const TypePatternNode* op, Args... args) DFPATTERN_FUNCTOR_DEFAULT;
   virtual R VisitDFPattern_(const VarPatternNode* op, Args... args) DFPATTERN_FUNCTOR_DEFAULT;
+  virtual R VisitDFPattern_(const ConstantPatternNode* op, Args... args) DFPATTERN_FUNCTOR_DEFAULT;
   virtual R VisitDFPattern_(const WildcardPatternNode* op, Args... args) DFPATTERN_FUNCTOR_DEFAULT;
   virtual R VisitDFPatternDefault_(const Object* op, Args...) {
     LOG(FATAL) << "Do not have a default for " << op->GetTypeKey();
@@ -111,6 +112,7 @@ class DFPatternFunctor<R(const DFPattern& n, Args...)> {
     RELAY_DFPATTERN_FUNCTOR_DISPATCH(TuplePatternNode);
     RELAY_DFPATTERN_FUNCTOR_DISPATCH(TypePatternNode);
     RELAY_DFPATTERN_FUNCTOR_DISPATCH(VarPatternNode);
+    RELAY_DFPATTERN_FUNCTOR_DISPATCH(ConstantPatternNode);
     RELAY_DFPATTERN_FUNCTOR_DISPATCH(WildcardPatternNode);
     return vtable;
   }
@@ -134,6 +136,7 @@ class DFPatternVisitor : public DFPatternFunctor<void(const DFPattern&)> {
   void VisitDFPattern_(const TuplePatternNode* op) override;
   void VisitDFPattern_(const TypePatternNode* op) override;
   void VisitDFPattern_(const VarPatternNode* op) override;
+  void VisitDFPattern_(const ConstantPatternNode* op) override;
   void VisitDFPattern_(const WildcardPatternNode* op) override;
 
  protected:

python/tvm/relay/dataflow_pattern/__init__.py

@@ -331,6 +331,14 @@ def __init__(self, name_hint: str, type_annotation=None):
             ffi.VarPattern, name_hint, type_annotation)
 
 
+@register_df_node
+class ConstantPattern(DFPattern):
+    """A pattern matching a Relay Constant.
+    """
+    def __init__(self):
+        self.__init_handle_by_constructor__(ffi.ConstantPattern)
+
+
 @register_df_node
 class CallPattern(DFPattern):
     """A pattern matching a function call node in Relay.

src/relay/ir/dataflow_matcher.cc

@@ -56,6 +56,7 @@ class DFPatternMatcher : public DFPatternFunctor<bool(const DFPattern&, const Ex
   bool VisitDFPattern_(const TuplePatternNode* op, const Expr& expr) override;
   bool VisitDFPattern_(const TypePatternNode* op, const Expr& expr) override;
   bool VisitDFPattern_(const VarPatternNode* op, const Expr& expr) override;
+  bool VisitDFPattern_(const ConstantPatternNode* op, const Expr& expr) override;
   bool VisitDFPattern_(const WildcardPatternNode* op, const Expr& expr) override;
 
   void ClearMap(size_t watermark);
@@ -394,6 +395,10 @@ bool DFPatternMatcher::VisitDFPattern_(const VarPatternNode* op, const Expr& exp
   return matches;
 }
 
+bool DFPatternMatcher::VisitDFPattern_(const ConstantPatternNode* op, const Expr& expr) {
+  return expr.as<ConstantNode>() != nullptr;
+}
+
 bool DFPatternMatcher::VisitDFPattern_(const WildcardPatternNode* op, const Expr& expr) {
   return true;
 }

src/relay/ir/dataflow_pattern.cc

@@ -69,6 +69,18 @@ TVM_STATIC_IR_FUNCTOR(ReprPrinter, vtable)
       p->stream << ")";
     });
 
+TVM_REGISTER_NODE_TYPE(ConstantPatternNode);
+
+TVM_REGISTER_GLOBAL("relay.dataflow_pattern.ConstantPattern").set_body_typed([]() {
+  auto c = ConstantPattern(make_object<ConstantPatternNode>());
+  return c;
+});
+
+TVM_STATIC_IR_FUNCTOR(ReprPrinter, vtable)
+    .set_dispatch<ConstantPatternNode>([](const ObjectRef& ref, ReprPrinter* p) {
+      p->stream << "ConstantPattern()";
+    });
+
 CallPattern::CallPattern(DFPattern op, Array<DFPattern> args, Attrs attrs, Array<Type> type_args) {
   ObjectPtr<CallPatternNode> n = make_object<CallPatternNode>();
   n->op = std::move(op);

src/relay/ir/dataflow_pattern_functor.cc

@@ -71,6 +71,8 @@ void DFPatternVisitor::VisitDFPattern_(const TypePatternNode* op) { VisitDFPatte
 
 void DFPatternVisitor::VisitDFPattern_(const VarPatternNode* op) {}
 
+void DFPatternVisitor::VisitDFPattern_(const ConstantPatternNode* op) {}
+
 void DFPatternVisitor::VisitDFPattern_(const WildcardPatternNode* op) {}
 
 }  // namespace relay

src/relay/ir/indexed_graph.cc

@@ -270,6 +270,8 @@ IndexedGraph<DFPattern> CreateIndexedGraph(const DFPattern& pattern) {
 
     void VisitDFPattern_(const VarPatternNode* op, NodePtr parent) override {}
 
+    void VisitDFPattern_(const ConstantPatternNode* op, NodePtr parent) override {}
+
     void VisitDFPattern_(const WildcardPatternNode* op, NodePtr parent) override {}
   };
   return Annotator(Creator().CreateGraph(pattern)).Annotate();