[PASS] Enhance scale fold axis (#424)

nnvm/src/compiler/fold_scale_axis.cc

@@ -18,12 +18,10 @@ namespace compiler {
 enum FoldScaleKind {
   // No folding is applied
   kNone,
-  // The folding decision is pending
+  // The folding decision is pending, we can fold on a state.
   kPending,
   // The original operator that contains the scale.
   kProvider,
-  // Pass through the scale to parent/child to the first axis.
-  kPassTroughFirst,
   // The final conumer of axis scale using multiply
   // Likely be a conv or dense operator.
   kMulConsumer,
@@ -31,21 +29,23 @@ enum FoldScaleKind {
   kDivConsumer
 };
 
-// Input fold information
-struct FoldScaleInput {
-  uint32_t index;
-  int axis;
-};
-
-// The entry of folding chains on which
-// we should perform folding on
-struct FoldChainEntry {
+struct FoldChainInfo {
   // Entry kind
   FoldScaleKind kind{kNone};
   // The output axis to be folded
   int axis{0};
   // Source node in the fold chain
   int source{0};
+};
+
+// The entry of folding chains on which
+// we should perform folding on
+struct FoldChainEntry {
+  // Fold information
+  FoldChainInfo info;
+  // Number of outgoing fork count
+  // in forward propagation.
+  int fork_count{0};
   // Following field only used by provider.
   // The input index
   int fold_input_index{1};
@@ -55,12 +55,26 @@ struct FoldChainEntry {
 
 // Try to pass axis scaling to backward,
 // Given that we we know the status of current fold axis.
+// return whether the forward signal is consumed.
 using FScaleAxisBackward = std::function<
-  FoldScaleKind(const NodeAttrs& attrs,
-                int axis,
+  bool(const NodeAttrs& attrs,
+       const std::vector<TShape>& in_shape,
+       const std::vector<TShape>& out_shape,
+       const FoldChainInfo& out_info,
+       std::vector<FoldChainInfo>* in_info)>;
+
+
+// Try to pass axis scaling to forward,
+// Given that we we know the status of one of its input to be pending
+// also update other input info
+// return whether the forward signal is consumed.
+using FScaleAxisForward = std::function<
+  bool(const NodeAttrs& attrs,
        const std::vector<TShape>& in_shape,
        const std::vector<TShape>& out_shape,
-                std::vector<std::pair<uint32_t, int> >* in_axis)>;
+       std::vector<FoldChainInfo>* in_info,
+       FoldChainInfo* out_info)>;
+
 
 // Detect if there is a scaling axis happening
 bool DetectScaleAxis(const IndexedGraph& idx,
@@ -99,15 +113,19 @@ bool DetectScaleAxis(const IndexedGraph& idx,
       } else {
         return false;
       }
-      e.axis = axis.first;
-      e.kind = kPending;
-      e.source = nid;
+      e.info.axis = axis.first;
+      e.info.kind = kPending;
+      e.info.source = nid;
+      e.fork_count = 1;
+      // In the backward message passing
+      // We need to eagerly pass it to the input
+      // In the forward message passing
+      // we will "pull" the message from input.
       if (!is_forward) {
-        // pass message to another input
         FoldChainEntry& enext = (*chain)[b.node_id];
-        enext.axis = e.axis;
-        enext.kind = kPending;
-        enext.source = nid;
+        enext.info.axis = e.info.axis;
+        enext.info.kind = kPending;
+        enext.info.source = nid;
       }
       return true;
     }
@@ -119,12 +137,16 @@ Graph FoldScaleAxis(Graph src) {
   // Operator pattern
   static auto& fbackward =
       nnvm::Op::GetAttr<FScaleAxisBackward>("FScaleAxisBackward");
+  static auto& fforward =
+      nnvm::Op::GetAttr<FScaleAxisForward>("FScaleAxisForward");
   const IndexedGraph& idx = src.indexed_graph();
   const ShapeVector& shape_vec = src.GetAttr<ShapeVector>("shape");
   std::vector<uint32_t> ref_count = GetNodeRefCounts(idx);
   std::vector<FoldChainEntry> bwd_chain(idx.num_nodes());
+  std::vector<FoldChainEntry> fwd_chain(idx.num_nodes());
   // shape hint for the inference.
   std::vector<TShape> in_shape, out_shape;
+
   // perform backward folding.
   for (uint32_t i = idx.num_nodes(); i != 0; --i) {
     uint32_t nid = i - 1;
@@ -132,9 +154,10 @@ Graph FoldScaleAxis(Graph src) {
     if (inode.source->is_variable()) continue;
     if (DetectScaleAxis(idx, nid, shape_vec,
                         ref_count, false, &bwd_chain)) continue;
-    if (bwd_chain[nid].kind != kPending) continue;
+    if (bwd_chain[nid].info.kind != kPending) continue;
+    // if referred by multiple node, cannot do propagation
     if (ref_count[nid] != 1 || !fbackward.count(inode.source->op())) {
-      bwd_chain[nid].kind = kNone; continue;
+      bwd_chain[nid].info.kind = kNone; continue;
     }
     // get input shape and output shape.
     in_shape.clear(); out_shape.clear();
@@ -144,58 +167,151 @@ Graph FoldScaleAxis(Graph src) {
     for (uint32_t i = 0; i < inode.source->num_outputs(); ++i) {
       out_shape.push_back(shape_vec[idx.entry_id(nid, i)]);
     }
-    std::vector<std::pair<uint32_t, int> > in_axis;
-    FoldScaleKind kind =
-        fbackward[inode.source->op()](
-            inode.source->attrs, bwd_chain[nid].axis,
-            in_shape, out_shape, &in_axis);
-    bwd_chain[nid].kind = kind;
-    if (kind == kNone) continue;
-    CHECK_GE(in_axis.size(), 1U);
-    CHECK(kind == kPassTroughFirst || kind == kMulConsumer);
+    std::vector<FoldChainInfo> in_info(in_shape.size(), FoldChainInfo());
+    bool consumed = fbackward[inode.source->op()](
+        inode.source->attrs,
+        in_shape,
+        out_shape,
+        bwd_chain[nid].info,
+        &in_info);
+    CHECK_EQ(in_info.size(), in_shape.size());
     // propagate back.
     bool can_prop = true;
-    for (size_t i = 0; i < in_axis.size(); ++i) {
-      const IndexedGraph::NodeEntry& e = inode.inputs[in_axis[0].first];
+    for (size_t i = 0; i < in_info.size(); ++i) {
+      const IndexedGraph::NodeEntry& e = inode.inputs[i];
       if (ref_count[e.node_id] != 1 ||
           idx[e.node_id].source->num_outputs() != 1) {
         can_prop = false; break;
       }
     }
     if (!can_prop) continue;
-    for (size_t i = 0; i < in_axis.size(); ++i) {
-      const IndexedGraph::NodeEntry& e = inode.inputs[in_axis[i].first];
-      if (kind == kPassTroughFirst && i == 0) {
-        bwd_chain[e.node_id].kind = kPending;
+    for (size_t i = 0; i < in_info.size(); ++i) {
+      const IndexedGraph::NodeEntry& e = inode.inputs[i];
+      bwd_chain[e.node_id].info = in_info[i];
+    }
+    // mark consumed by making the source as provider.
+    if (consumed) {
+      bwd_chain[bwd_chain[nid].info.source].info.kind = kProvider;
+    }
+  }
+
+
+  // perform forward folding.
+  for (uint32_t nid = 0; nid < idx.num_nodes(); ++nid) {
+    const auto& inode = idx[nid];
+    if (inode.source->is_variable()) continue;
+    // skip scales that are already folded in backward.
+    if (bwd_chain[nid].info.kind == kProvider) continue;
+    if (DetectScaleAxis(idx, nid, shape_vec,
+                        ref_count, true, &fwd_chain)) continue;
+    if (inode.source->num_outputs() != 1) continue;
+    // Do state update
+    // get input shape and output shape.
+    std::vector<FoldChainInfo> in_info;
+    FoldChainInfo out_info;
+    int num_inpending = 0;
+    in_shape.clear(); out_shape.clear();
+    for (const IndexedGraph::NodeEntry& e : inode.inputs) {
+      in_shape.push_back(shape_vec[idx.entry_id(e)]);
+      // input information
+      in_info.push_back(fwd_chain[e.node_id].info);
+      if (fwd_chain[e.node_id].info.kind == kPending) {
+        ++num_inpending;
+      }
+    }
+    for (uint32_t i = 0; i < inode.source->num_outputs(); ++i) {
+      out_shape.push_back(shape_vec[idx.entry_id(nid, i)]);
+    }
+    if (num_inpending != 1 ||
+        !fforward.count(inode.source->op())) continue;
+    bool consumed = fforward[inode.source->op()](
+        inode.source->attrs,
+        in_shape,
+        out_shape,
+        &in_info,
+        &out_info);
+    // update input info
+    for (size_t i = 0; i < in_info.size(); ++i) {
+      fwd_chain[inode.inputs[i].node_id].info = in_info[i];
+    }
+    if (consumed) {
+      fwd_chain[nid].info = out_info;
+      for (size_t i = 0; i < in_info.size(); ++i) {
+        if (in_info[i].kind == kPending) {
+          if (--fwd_chain[in_info[i].source].fork_count == 0) {
+            fwd_chain[in_info[i].source].info.kind = kProvider;
+          }
+        }
+      }
     } else {
-        bwd_chain[nid].kind = kNone;
-        bwd_chain[e.node_id].kind = kMulConsumer;
+      // can propagate condition
+      if (inode.source->num_outputs() == 1) {
+        fwd_chain[nid].info = out_info;
+        if (out_info.kind == kPending) {
+          // When there is multiple reference to input
+          // every path have to be consumed
+          fwd_chain[out_info.source].fork_count += ref_count[nid] - 1;
         }
-      bwd_chain[e.node_id].axis = in_axis[i].second;
-      bwd_chain[e.node_id].source = bwd_chain[nid].source;
       }
-    if (kind == kMulConsumer) {
-      bwd_chain[bwd_chain[nid].source].kind = kProvider;
     }
   }
+
   auto transform = [&](uint32_t nid, const NodePtr& n, std::vector<NodeEntry>* ret) {
+    NodeEntry rvalue = NodeEntry{n, 0, 0};
+    {
+      // Backward chain
       const FoldChainEntry& e = bwd_chain[nid];
-    if (e.kind == kMulConsumer && bwd_chain[e.source].kind == kProvider) {
-      const FoldChainEntry& se = bwd_chain[e.source];
+      if (e.info.kind == kMulConsumer &&
+          bwd_chain[e.info.source].info.kind == kProvider) {
+        const FoldChainEntry& se = bwd_chain[e.info.source];
         CHECK_EQ(n->num_outputs(), 1);
         NodeEntry scale = ExpandBiasToMatchAxis(
             se.scale_entry,
             shape_vec[idx.entry_id(nid, 0)].ndim(),
             shape_vec[idx.entry_id(se.scale_entry)].ndim(),
-          e.axis);
-      *ret = {MakeNode("broadcast_mul", n->attrs.name + "_sc",
-                       {NodeEntry{n, 0, 0}, scale})};
-      return true;
-    } else if (e.kind == kProvider) {
-      *ret = {n->inputs[e.fold_input_index]};
-      return true;
-    } else {
+            e.info.axis);
+        rvalue = MakeNode("broadcast_mul", n->attrs.name + "_sc",
+                          {rvalue, scale});
+      } else if (e.info.kind == kProvider) {
+        rvalue = n->inputs[e.fold_input_index];
+      }
+    }
+    // Note that the value might get transformed twice if it
+    // folds value from both fwd and backward chain.
+    {
+      // forward chain
+      const FoldChainEntry& e = fwd_chain[nid];
+      if (e.info.kind == kMulConsumer &&
+          fwd_chain[e.info.source].info.kind == kProvider) {
+        const FoldChainEntry& se = fwd_chain[e.info.source];
+        CHECK_EQ(n->num_outputs(), 1);
+        NodeEntry scale = ExpandBiasToMatchAxis(
+            se.scale_entry,
+            shape_vec[idx.entry_id(nid, 0)].ndim(),
+            shape_vec[idx.entry_id(se.scale_entry)].ndim(),
+            e.info.axis);
+        rvalue = MakeNode("broadcast_mul", n->attrs.name + "_sc",
+                          {rvalue, scale});
+      } else if (e.info.kind == kDivConsumer &&
+                 fwd_chain[e.info.source].info.kind == kProvider) {
+        const FoldChainEntry& se = fwd_chain[e.info.source];
+        CHECK_EQ(n->num_outputs(), 1);
+        NodeEntry scale = ExpandBiasToMatchAxis(
+            se.scale_entry,
+            shape_vec[idx.entry_id(nid, 0)].ndim(),
+            shape_vec[idx.entry_id(se.scale_entry)].ndim(),
+            e.info.axis);
+        rvalue = MakeNode("broadcast_div", n->attrs.name + "_sc",
+                          {rvalue, scale});
+      } else if (e.info.kind == kProvider) {
+        rvalue = n->inputs[e.fold_input_index];
+      }
+    }
+    if (rvalue.node == n) {
       return false;
+    } else {
+      *ret = {rvalue};
+      return true;
     }
   };
   return GraphTransform(src, transform);
@@ -205,14 +321,24 @@ NNVM_REGISTER_PASS(FoldScaleAxis)
 .set_body(FoldScaleAxis);
 
 // property registration.
-FoldScaleKind ReluScaleAxisBackward(
+bool ReluScaleAxisBackward(
+    const NodeAttrs& attrs,
+    const std::vector<TShape>& in_shape,
+    const std::vector<TShape>& out_shape,
+    const FoldChainInfo& out_info,
+    std::vector<FoldChainInfo>* in_axis) {
+  (*in_axis)[0] = out_info;
+  return false;
+}
+
+bool ReluScaleAxisForward(
     const NodeAttrs& attrs,
-    int axis,
     const std::vector<TShape>& in_shape,
     const std::vector<TShape>& out_shape,
-    std::vector<std::pair<uint32_t, int> >* in_axis) {
-  in_axis->emplace_back(0, axis);
-  return kPassTroughFirst;
+    std::vector<FoldChainInfo>* in_info,
+    FoldChainInfo* out_info) {
+  *out_info = (*in_info)[0];
+  return false;
 }
 
 NNVM_REGISTER_OP(relu)
@@ -221,21 +347,102 @@ NNVM_REGISTER_OP(relu)
 NNVM_REGISTER_OP(leaky_relu)
 .set_attr<FScaleAxisBackward>("FScaleAxisBackward", ReluScaleAxisBackward);
 
-FoldScaleKind BroadcastAddSubScaleAxisBackward(
+NNVM_REGISTER_OP(relu)
+.set_attr<FScaleAxisForward>("FScaleAxisForward", ReluScaleAxisForward);
+
+NNVM_REGISTER_OP(leaky_relu)
+.set_attr<FScaleAxisForward>("FScaleAxisForward", ReluScaleAxisForward);
+
+// property registration.
+bool Pool2DBackward(
+    const NodeAttrs& attrs,
+    const std::vector<TShape>& in_shape,
+    const std::vector<TShape>& out_shape,
+    const FoldChainInfo& out_info,
+    std::vector<FoldChainInfo>* in_axis) {
+  using top::Pool2DParam;
+  const Pool2DParam& param = nnvm::get<Pool2DParam>(attrs.parsed);
+  if (out_info.axis == 1 && param.layout == top::kNCHW) {
+    (*in_axis)[0] = out_info;
+  }
+  return false;
+}
+
+bool Pool2DForward(
     const NodeAttrs& attrs,
-    int axis,
     const std::vector<TShape>& in_shape,
     const std::vector<TShape>& out_shape,
-    std::vector<std::pair<uint32_t, int> >* in_axis) {
+    std::vector<FoldChainInfo>* in_info,
+    FoldChainInfo* out_info) {
+  using top::Pool2DParam;
+  const Pool2DParam& param = nnvm::get<Pool2DParam>(attrs.parsed);
+  if ((*in_info)[0].axis == 1 && param.layout == top::kNCHW) {
+    *out_info = (*in_info)[0];
+  }
+  return false;
+}
+
+NNVM_REGISTER_OP(max_pool2d)
+.set_attr<FScaleAxisBackward>("FScaleAxisBackward", Pool2DBackward);
+
+NNVM_REGISTER_OP(avg_pool2d)
+.set_attr<FScaleAxisBackward>("FScaleAxisBackward", Pool2DBackward);
+
+NNVM_REGISTER_OP(max_pool2d)
+.set_attr<FScaleAxisForward>("FScaleAxisForward", Pool2DForward);
+
+NNVM_REGISTER_OP(avg_pool2d)
+.set_attr<FScaleAxisForward>("FScaleAxisForward", Pool2DForward);
+
+
+
+bool BroadcastAddSubScaleAxisBackward(
+    const NodeAttrs& attrs,
+    const std::vector<TShape>& in_shape,
+    const std::vector<TShape>& out_shape,
+    const FoldChainInfo& out_info,
+    std::vector<FoldChainInfo>* in_axis) {
+  if (out_info.kind != kPending) return false;
   for (int i = 0; i < 2; ++i) {
-    std::pair<int, int> m = MatchBroadcast1DAxis(out_shape[0], in_shape[i]);
-    if (m.second != -1 && in_shape[1 - i] == out_shape[0]) {
-      in_axis->emplace_back(i, axis);
-      in_axis->emplace_back(1 - i, m.second);
-      return kPassTroughFirst;
+    std::pair<int, int> m = MatchBroadcast1DAxis(out_shape[0], in_shape[1 - i]);
+    if (m.second != -1 &&
+        in_shape[i] == out_shape[0] &&
+        m.first == out_info.axis) {
+      (*in_axis)[i].kind = kPending;
+      (*in_axis)[i].axis = out_info.axis;
+      (*in_axis)[i].source = out_info.source;
+      (*in_axis)[1 - i].kind = kMulConsumer;
+      (*in_axis)[1 - i].axis = m.second;
+      (*in_axis)[1 - i].source = out_info.source;
+      return false;
     }
   }
-  return kNone;
+  return false;
+}
+
+bool BroadcastAddSubScaleAxisForward(
+    const NodeAttrs& attrs,
+    const std::vector<TShape>& in_shape,
+    const std::vector<TShape>& out_shape,
+    std::vector<FoldChainInfo>* in_info,
+    FoldChainInfo* out_info) {
+  for (int i = 0; i < 2; ++i) {
+    if ((*in_info)[i].kind == kPending) {
+      std::pair<int, int> m = MatchBroadcast1DAxis(out_shape[0], in_shape[1 - i]);
+      if (m.second != -1 &&
+          in_shape[i] == out_shape[0] &&
+          m.first == (*in_info)[i].axis) {
+        out_info->kind = kPending;
+        out_info->axis = m.first;
+        out_info->source = (*in_info)[i].source;
+        (*in_info)[1 - i].kind = kDivConsumer;
+        (*in_info)[1 - i].axis = m.second;
+        (*in_info)[1 - i].source = (*in_info)[i].source;
+        return false;
+      }
+    }
+  }
+  return false;
 }
 
 NNVM_REGISTER_OP(broadcast_add)
@@ -244,28 +451,62 @@ NNVM_REGISTER_OP(broadcast_add)
 NNVM_REGISTER_OP(broadcast_sub)
 .set_attr<FScaleAxisBackward>("FScaleAxisBackward", BroadcastAddSubScaleAxisBackward);
 
-FoldScaleKind Conv2DScaleAxisBackward(
+NNVM_REGISTER_OP(broadcast_add)
+.set_attr<FScaleAxisForward>("FScaleAxisForward", BroadcastAddSubScaleAxisForward);
+
+NNVM_REGISTER_OP(broadcast_sub)
+.set_attr<FScaleAxisForward>("FScaleAxisForward", BroadcastAddSubScaleAxisForward);
+
+bool Conv2DScaleAxisBackward(
     const NodeAttrs& attrs,
-    int axis,
     const std::vector<TShape>& in_shape,
     const std::vector<TShape>& out_shape,
-    std::vector<std::pair<uint32_t, int> >* in_axis) {
+    const FoldChainInfo& out_info,
+    std::vector<FoldChainInfo>* in_axis) {
   using top::Conv2DParam;
   const Conv2DParam& param = nnvm::get<Conv2DParam>(attrs.parsed);
+  if (out_info.kind != kPending) return false;
   // only optimize for nchw for now
-  if (param.layout == top::kNCHW) {
-    in_axis->emplace_back(1, 0);
+  if (param.layout == top::kNCHW && out_info.axis == 1) {
+    (*in_axis)[1].kind = kMulConsumer;
+    (*in_axis)[1].axis = 0;
+    (*in_axis)[1].source = out_info.source;
     if (param.use_bias) {
-      in_axis->emplace_back(2, 0);
+      (*in_axis)[2].kind = kMulConsumer;
+      (*in_axis)[2].axis = 0;
+      (*in_axis)[2].source = out_info.source;
+    }
+    return true;
+  } else {
+    return false;
   }
-    return kMulConsumer;
+}
+
+bool Conv2DScaleAxisForward(
+    const NodeAttrs& attrs,
+    const std::vector<TShape>& in_shape,
+    const std::vector<TShape>& out_shape,
+    std::vector<FoldChainInfo>* in_info,
+    FoldChainInfo* out_info) {
+  using top::Conv2DParam;
+  const Conv2DParam& param = nnvm::get<Conv2DParam>(attrs.parsed);
+  if ((*in_info)[0].kind != kPending) return false;
+  // only optimize for nchw for now
+  if (param.layout == top::kNCHW && (*in_info)[0].axis == 1) {
+    (*in_info)[1].kind = kMulConsumer;
+    (*in_info)[1].axis = 1;
+    (*in_info)[1].source = (*in_info)[0].source;
+    return true;
   } else {
-    return kNone;
+    return false;
   }
 }
 
 NNVM_REGISTER_OP(conv2d)
 .set_attr<FScaleAxisBackward>("FScaleAxisBackward", Conv2DScaleAxisBackward);
 
+NNVM_REGISTER_OP(conv2d)
+.set_attr<FScaleAxisForward>("FScaleAxisForward", Conv2DScaleAxisForward);
+
 }  // namespace compiler
 }  // namespace nnvm

nnvm/src/pass/plan_memory.cc

@@ -196,7 +196,7 @@ size_t AllocMemory(const Graph& ret, const IndexedGraph& idx,
         if (taken[kv.first] == false &&
             sid_out == GraphAllocator::kBadStorageID &&
             sid_in >= 0 &&
-            (storage_ref_count[sid_in] == 1 && !ignore_all_inputs || identity[ipair]) &&
+            ((storage_ref_count[sid_in] == 1 && !ignore_all_inputs) || identity[ipair]) &&
             entry_ref_count[eid_out] > 0 &&
             shape_vec[eid_out].Size() == shape_vec[eid_in].Size() &&
             dtype_vec[eid_out] == dtype_vec[eid_in]) {

nnvm/tests/python/compiler/test_fold_axis.py

 """Unittest cases for fold_axis"""
 import nnvm
+import nnvm.testing.resnet
+import numpy as np
 from nnvm import symbol as sym
 from nnvm.compiler import graph_util, graph_attr
 
 def test_fold_axis_conv():
-    def before(x, conv_weight, conv_bias, scale, channels):
+    def before(x, conv_weight, conv_bias, in_scale, out_scale, channels):
+        x = x * sym.expand_dims(in_scale, axis=1, num_newaxis=2)
         y = sym.conv2d(x, conv_weight, conv_bias,
                        channels=channels,
                        kernel_size=(3, 3),
                        padding=(1, 1),
                        name="conv")
         y = sym.relu(y)
-        y = y * sym.expand_dims(scale, axis=1, num_newaxis=2)
+        y = y * sym.expand_dims(out_scale, axis=1, num_newaxis=2)
         return y
 
-    def expected(x, conv_weight, conv_bias, scale, channels):
-        conv_weight = conv_weight * sym.expand_dims(scale, axis=1, num_newaxis=3)
-        conv_bias = conv_bias * scale
+    def expected(x, conv_weight, conv_bias, in_scale, out_scale, channels):
+        conv_weight = conv_weight * sym.expand_dims(out_scale, axis=1, num_newaxis=3)
+        conv_weight = conv_weight * sym.expand_dims(in_scale, axis=1, num_newaxis=2)
+        conv_bias = conv_bias * out_scale
         y = sym.conv2d(x,
                        conv_weight,
                        conv_bias,
@@ -32,10 +36,11 @@ def test_fold_axis_conv():
         x = sym.Variable("x") + 1
         weight = sym.Variable("weight")
         bias = sym.Variable("bias")
-        scale = sym.Variable("scale")
-        y1 = before(x, weight, bias, scale, channels)
-        y2 = expected(x, weight, bias, scale, channels)
-        ishape = {"x": shape, "scale": (channels,)}
+        in_scale = sym.Variable("in_scale")
+        out_scale = sym.Variable("out_scale")
+        y1 = before(x, weight, bias, in_scale, out_scale, channels)
+        y2 = expected(x, weight, bias, in_scale, out_scale, channels)
+        ishape = {"x": shape, "out_scale": (channels,), "in_scale": (shape[1],)}
         g1 = nnvm.graph.create(y1)
         g2 = nnvm.graph.create(y2)
         graph_attr.set_shape_inputs(g1, ishape)
@@ -45,5 +50,61 @@ def test_fold_axis_conv():
 
     check((2, 4, 10, 10), 2)
 
+
+def test_fold_fail():
+    def before(x, scale, channels):
+        y = sym.conv2d(x,
+                       channels=channels,
+                       kernel_size=(3, 3),
+                       padding=(1, 1),
+                       name="conv")
+        y = y * sym.expand_dims(scale, axis=1, num_newaxis=1)
+        return y
+
+    # Before simplify
+    def check(shape, channels):
+        x = sym.Variable("x")
+        bias = sym.Variable("bias")
+        scale = sym.Variable("scale")
+        y1 = before(x, scale, channels)
+        ishape = {"x": shape, "scale": (channels,), "bias": (channels,)}
+        g1 = nnvm.graph.create(y1)
+        graph_attr.set_shape_inputs(g1, ishape)
+        g2 = g1.apply("InferShape").apply("FoldScaleAxis")
+        # assert graph equals as expected
+        graph_util.check_graph_equal(g1, g2)
+
+    check((2, 10, 10, 10), 10)
+
+
+def test_fold_resnet():
+    batch_size = 1
+    num_classes = 1000
+    image_shape = (3, 224, 224)
+    data_shape = (batch_size,) +image_shape
+    net, params = nnvm.testing.resnet.get_workload(
+        batch_size=1, image_shape=image_shape)
+    ishape = {"data" : data_shape}
+    graph = nnvm.graph.create(net)
+    data = np.random.uniform(size=data_shape).astype("float32")
+    # Initial pass do shape type inference
+    shape, _ = graph_util.infer_shape(graph, **ishape)
+    ishape.update(zip(graph.index.input_names, shape))
+
+    def run_prune(graph, params, opt_level):
+        # Apply optimization
+        with nnvm.compiler.build_config(opt_level=0):
+            graph = nnvm.compiler.optimize(graph, ishape)
+        graph, params = nnvm.compiler.build_module.precompute_prune(graph, params)
+        params["data"] = data
+        return nnvm.compiler.build_module._run_graph(graph, params)
+
+    x = run_prune(graph, params, 0)
+    y = run_prune(graph, params, 3)
+    np.testing.assert_allclose(y[0].asnumpy(), x[0].asnumpy())
+
+
 if __name__ == "__main__":
+    test_fold_resnet()
     test_fold_axis_conv()
+    test_fold_fail()