[RELAY][PASS] FoldScaleAxis Backward (apache#2024)

include/tvm/relay/expr_functor.h

@@ -135,9 +135,9 @@ class ExprVisitor
   void VisitExpr_(const TupleGetItemNode* op) override;
   virtual void VisitType(const Type& t);
 
- private:
-  // internal visited flag.
-  std::unordered_set<const Node*> visited_;
+ protected:
+  // Internal visiting counter
+  std::unordered_map<const Node*, size_t> visit_counter_;
 };
 
 /*!

python/tvm/relay/ir_pass.py

@@ -31,6 +31,29 @@ def infer_type(expr, env=None):
     return _ir_pass.infer_type(expr, env)
 
 
+def backward_fold_scale_axis(expr):
+    """Backward fold axis scaling into weights of conv2d/dense.
+
+    Parameters
+    ----------
+    expr : tvm.relay.Expr
+        The input expression, we expect that expr's types
+        should be fully inferred by infer_type.
+
+    Returns
+    -------
+    folded_expr : tvm.relay.Expr
+        The folded expression after transformation.
+
+    Note
+    ----
+    It is recommended to call backward_fold_scale_axis
+    before using forward_fold_scale_axis.
+    As backward folding targets common conv-bn pattern.
+    """
+    return _ir_pass.backward_fold_scale_axis(expr)
+
+
 def forward_fold_scale_axis(expr):
     """Fold the scaling of axis into weights of conv2d/dense.
 
@@ -44,6 +67,12 @@ def forward_fold_scale_axis(expr):
     -------
     folded_expr : tvm.relay.Expr
         The folded expression after transformation.
+
+    Note
+    ----
+    It is recommended to call backward_fold_scale_axis
+    before using forward_fold_scale_axis.
+    As backward folding targets common conv-bn pattern.
     """
     return _ir_pass.forward_fold_scale_axis(expr)
 

src/relay/ir/expr_functor.cc

@@ -160,10 +160,14 @@ Expr ExprMutator::VisitExpr_(const TupleGetItemNode* g) {
 Type ExprMutator::VisitType(const Type& t) { return t; }
 
 void ExprVisitor::VisitExpr(const Expr& expr) {
-  if (visited_.count(expr.get())) return;
-  using TParent = ExprFunctor<void(const Expr&)>;
-  TParent::VisitExpr(expr);
-  visited_.insert(expr.get());
+  auto it = visit_counter_.find(expr.get());
+  if (it != visit_counter_.end()) {
+    ++it->second;
+  } else {
+    using TParent = ExprFunctor<void(const Expr&)>;
+    TParent::VisitExpr(expr);
+    visit_counter_.insert({expr.get(), 1});
+  }
 }
 
 void ExprVisitor::ExprVisitor::VisitExpr_(const VarNode* op) {