[GitHub] [incubator-mxnet] junrushao1994 commented on a change in pull request #14192: [MXNET-1324] Add NaiveRunGraph to imperative utils

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junrushao1994 commented on a change in pull request #14192: [MXNET-1324] Add NaiveRunGraph to imperative utils
URL: https://github.com/apache/incubator-mxnet/pull/14192#discussion_r293638551
 
 

 ##########
 File path: src/imperative/cached_op.cc
 ##########
 @@ -262,6 +262,35 @@ std::vector<nnvm::NodeEntry> CachedOp::Gradient(
   return ret;
 }
 
+bool CachedOp::CheckDynamicShapeExists(const Context& default_ctx,
+                                       const std::vector<NDArray*>& inputs,
+                                       bool erase_result) {
+  using namespace nnvm;
+  using namespace imperative;
+  CHECK_EQ(inputs.size(), num_inputs());
+
+  auto state_ptr = GetCachedOpState(default_ctx);
+  auto& state = state_ptr.get_state<CachedOpState>();
+
+  nnvm::Graph& g = state.info.fwd_graph;
+  ShapeVector shape_inputs;
+  shape_inputs.reserve(inputs.size());
+  for (auto input : inputs) {
+    shape_inputs.emplace_back(input->shape());
+  }
+  // We leverage the shape inference pass to detect whether dynamic shape exists.
+  // If so, the pass will fail with `contain_dynamic_shape = true`,
+  // This method is only called once, so the overhead is negligible.
 
 Review comment:
   If infer shape fails, it means there is probably an op of dynamic shape (np.unique, boolean mask).
   
   MXNet didn't support this kind of op before, because of the limitation of our system. Because of these lines, we now can support it in Gluon blocks.
   
   I would suggest to clearly mention the behavior in our docs that if infer shape fails, the code will go to the slow path (naive run graph, etc).

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