apeforest commented on a change in pull request #14836: Refactor AGInfo and
Imperative
URL: https://github.com/apache/incubator-mxnet/pull/14836#discussion_r305027116
##########
File path: src/imperative/imperative.cc
##########
@@ -316,181 +312,223 @@ std::vector<NDArray*> Imperative::Backward(
info.outputs.back() = static_cast<real_t>(1.0);
}
}
+ return ograd_entries;
+}
- // Get gradient graph
- Symbol sym;
- sym.outputs = graph.outputs;
- std::vector<NodeEntry> xs;
- std::vector<NDArray*> x_grads;
- std::vector<OpReqType> x_reqs;
- if (variables.size()) {
- xs.reserve(variables.size());
- x_grads.reserve(variables.size());
- x_reqs.reserve(variables.size());
+struct Imperative::GradientVariableNodes {
+ std::vector<nnvm::NodeEntry> variable_nodes;
+ std::vector<NDArray*> gradients;
+ std::vector<OpReqType> op_req_types;
+};
+
+Imperative::GradientVariableNodes Imperative::CreateGradientVariableNodes(
+ const std::vector<NDArray *> &variables,
+ const std::vector<nnvm::NodeEntry> &outputs) {
+ GradientVariableNodes var_nodes;
+ if (!variables.empty()) {
+ var_nodes.variable_nodes.reserve(variables.size());
+ var_nodes.gradients.reserve(variables.size());
+ var_nodes.op_req_types.reserve(variables.size());
for (size_t i = 0; i < variables.size(); ++i) {
CHECK(!AGInfo::IsNone(*variables[i]) &&
AGInfo::IsVariable(variables[i]->entry_.node))
<< "Cannot differentiate with respect to the " << i+1 << "-th
variable"
<< " because it does not require gradient.";
- xs.emplace_back(variables[i]->entry_);
- x_grads.push_back(new NDArray());
- x_reqs.push_back(kWriteTo);
+ var_nodes.variable_nodes.emplace_back(variables[i]->entry_);
+ var_nodes.gradients.push_back(new NDArray());
+ var_nodes.op_req_types.push_back(kWriteTo);
}
} else {
- std::vector<NodePtr> args = sym.ListInputs(Symbol::kReadOnlyArgs);
- xs.reserve(args.size());
- x_grads.reserve(args.size());
- x_reqs.reserve(args.size());
- for (const auto& i : args) {
- AGInfo& info = AGInfo::Get(i);
- if (info.grad_req == kNullOp) continue;
- xs.emplace_back(NodeEntry{i, 0, 0});
- x_grads.push_back(&info.out_grads[0]);
- x_reqs.push_back(info.grad_req);
- info.fresh_out_grad = true;
+ nnvm::Symbol s;
+ s.outputs = outputs;
+ std::vector<nnvm::NodePtr> input_ro_nodes =
s.ListInputs(Symbol::kReadOnlyArgs);
+ var_nodes.variable_nodes.reserve(input_ro_nodes.size());
+ var_nodes.gradients.reserve(input_ro_nodes.size());
+ var_nodes.op_req_types.reserve(input_ro_nodes.size());
+ for (const auto& node : input_ro_nodes) {
+ AGInfo& info = AGInfo::Get(node);
+ if (info.grad_req != kNullOp) {
+ var_nodes.variable_nodes.emplace_back(node);
+ var_nodes.gradients.push_back(&info.out_grads[0]);
+ var_nodes.op_req_types.push_back(info.grad_req);
+ info.fresh_out_grad = true;
+ }
}
- CHECK_GT(xs.size(), 0)
+ CHECK_GT(var_nodes.variable_nodes.size(), 0)
<< "There are no inputs in computation graph that require gradients.";
}
+ return var_nodes;
+}
+
+
- Graph g_graph = pass::MXGradient(
- graph, graph.outputs, xs, ograd_entries,
+std::vector<NDArray*> Imperative::Backward(
+ const std::vector<NDArray*>& outputs,
+ const std::vector<NDArray*>& ograds,
+ const std::vector<NDArray*>& variables,
+ bool is_train, bool retain_graph,
+ bool create_graph) {
+ using namespace nnvm;
+ using namespace imperative;
+ static const std::vector<const Op*> zero_ops{Op::Get("zeros_like"),
Op::Get("_zeros")};
+ static const Op* copy_op = Op::Get("_copy");
+
+ Graph graph;
+ graph.outputs = CreateForwardGraph(outputs);
+
+
+ // Prepare head gradient nodes
+ std::vector<NodeEntry> ograd_entries = CreateHeadGradientNodes(outputs,
ograds);
+
+ // Get variable nodes
+ GradientVariableNodes gvars = CreateGradientVariableNodes(variables,
graph.outputs);
+
+ // Run backward on the graph
+ Graph gradient_graph = pass::MXGradient(
+ graph, graph.outputs, gvars.variable_nodes, ograd_entries,
exec::AggregateGradient, nullptr, nullptr,
zero_ops, "_copy");
- CHECK_EQ(g_graph.outputs.size(), xs.size());
- for (const auto& e : g_graph.outputs) {
- if (e.node->op() == nullptr) {
+
+ CHECK_EQ(gradient_graph.outputs.size(), gvars.variable_nodes.size());
+ std::vector<nnvm::NodeEntry> forward_outputs = graph.outputs;
+ const size_t num_forward_outputs = graph.outputs.size();
+
+ // TODO(larroy): move inside pass::MXGradient
+ for (const auto& backward_node : gradient_graph.outputs) {
+ if (backward_node.node->is_variable()) {
auto node = Node::Create();
node->attrs.op = copy_op;
- node->inputs.push_back(e);
+ node->inputs.push_back(backward_node);
graph.outputs.emplace_back(std::move(node));
} else {
- graph.outputs.push_back(e);
+ graph.outputs.push_back(backward_node);
}
}
- const auto& idx = graph.indexed_graph();
+
+ const auto& indexed_graph = graph.indexed_graph();
// get number of nodes used in forward pass
size_t num_forward_nodes = 0;
size_t num_forward_entries = 0;
for (size_t i = 0; i < num_forward_outputs; ++i) {
num_forward_nodes = std::max(
- num_forward_nodes, static_cast<size_t>(idx.outputs()[i].node_id + 1));
+ num_forward_nodes,
static_cast<size_t>(indexed_graph.outputs()[i].node_id + 1));
num_forward_entries = std::max(
- num_forward_entries,
static_cast<size_t>(idx.entry_id(idx.outputs()[i])) + 1);
+ num_forward_entries, static_cast<size_t>(indexed_graph.entry_id(
+ indexed_graph.outputs()[i])) + 1);
}
// Allocate buffer
- std::vector<NDArray> buff(idx.num_node_entries());
+ std::vector<NDArray> buff(indexed_graph.num_node_entries());
std::vector<uint32_t> ref_count(buff.size(), 0);
std::vector<OpStatePtr> states;
std::vector<NDArray*> arrays;
arrays.reserve(buff.size());
- for (auto& buffered_array : buff) {
+ for (auto& buffered_array : buff)
arrays.push_back(&buffered_array);
- }
+
if (create_graph) {
states.resize(num_forward_nodes);
- nnvm::DFSVisit(sym.outputs, [&](const nnvm::NodePtr& n) {
+ nnvm::DFSVisit(forward_outputs, [&](const nnvm::NodePtr& n) {
AGInfo& info = AGInfo::Get(n);
- states[idx.node_id(n.get())] = info.state;
+ states.at(indexed_graph.node_id(n.get())) = info.state;
for (uint32_t i = 0; i < info.outputs.size(); ++i) {
Review comment:
change i to `size_t` to be consistent in your refactoring?
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