[RELAY][PASS] FuseOps, fix input fusion rule for conv2d (#2110)

src/relay/pass/fuse_ops.cc

@@ -464,14 +464,15 @@ class GraphPartitioner {
     return true;
   }
   /*!
-   * \brief Check all the node between src and sink satisfies fcond.
+   * \brief Check all the node and edge pattern
+   *  between src and sink satisfies fcond.
    *
-   * src and sink are not checked.
+   * src is not checked.
    *
    * \param src The source node.
    * \param sink The termination node.
    * \param fcond The condition to be checked.
-   * \tparam F the condition function.
+   * \tparam F the condition function, with signature
    * \note sink must be a post-dominator of src.
    */
   template<typename F>
@@ -596,7 +597,12 @@ class GraphPartitioner {
           }
         }
       } else if (group_node->pattern <= kBroadcast) {
-        // The fuse can be executed if all the intermediate ops are still broadcast.
+        // Pre-condition: can only be fused to parent which is injective or reduction.
+        if (dom_node->parent != nullptr &&
+            (dom_node->pattern <= kInjective ||
+             dom_node->pattern == kCommReduce)) {
+          // Check if all the intermediate ops are still broadcast.
+          // The final terminal node can already be fused to a OutEWiseFusable group.
           auto fcond = [](OpPatternKind kind, bool is_sink) {
             if (!is_sink) {
               return kind <= kBroadcast;
@@ -609,6 +615,7 @@ class GraphPartitioner {
           if (CheckPath(graph_node, dom_node->parent->gnode, fcond)) {
             CommitFuse(graph_node, dom_node->parent->gnode);
           }
+        }
       } else if (group_node->pattern == kInjective) {
         // defer injective fusion to second phase.
         // so conv2d always finishes fusing.

tests/python/relay/test_pass_fuse_ops.py

@@ -29,10 +29,12 @@ def test_fuse_simple():
 
 
 
+
 def test_conv2d_fuse():
     """Test fusion case of conv2d"""
     def before(dshape):
         x = relay.var("x", shape=dshape)
+        x = relay.add(x, relay.const(1, "float32"))
         y = relay.nn.conv2d(x, relay.var("w1"),
                             kernel_size=(3, 3),
                             padding=(1, 1),
@@ -54,6 +56,10 @@ def test_conv2d_fuse():
         return relay.Function(relay.ir_pass.free_vars(z), z)
 
     def expected(dshape):
+        # segment 0
+        x = relay.var("p0", shape=dshape)
+        y = relay.add(x, relay.const(1, "float32"))
+        f0 = relay.Function([x], y)
         # segment 1
         x = relay.var("p0", shape=dshape)
         w = relay.var("p1")
@@ -84,7 +90,8 @@ def test_conv2d_fuse():
         f3 = relay.Function([x, w, offset], z3)
         # compose
         x = relay.var("x", shape=dshape)
-        y = relay.Call(f1, [x, relay.var("w1")])
+        y = relay.Call(f0, [x])
+        y = relay.Call(f1, [y, relay.var("w1")])
         z2 = relay.Call(f2, [y, relay.var("w3")])
         z3 = relay.Call(f3, [y, relay.var("w2"), z2])
         z = z3