[C API]: Bugfix for TF_AddGradients.

TF_AddGradients could create nodes in the graph with names that conflicted with
other nodes in the graph. This would most clearly happen if TF_AddGradients()
was called twice on the same graph, and could also happen if there were other
nodes in the graph that happened to have "gradients" as a prefix of their name.

Fix that.

The added test in c_api_test.cc would fail in the call to TF_SessionRun() with
  Node 'gradients/OnesLike' is not unique
without the changes to c_api.cc and c_api_internal.h

While at it, also fixed a possible name collision bug when using the C++ API
to constructor graphs (using Scope).

Thanks @karllessard for pointing this out.

PiperOrigin-RevId: 202087996

7 files changed, 116 insertions, 15 deletions

diff --git a/tensorflow/c/c_api.cc b/tensorflow/c/c_api.cc
index 09a03639d6..37c8302e08 100644
--- a/tensorflow/c/c_api.cc
+++ b/tensorflow/c/c_api.cc
@@ -2414,7 +2414,18 @@ void TF_AddGradients(TF_Graph* g, TF_Output* y, int ny, TF_Output* x, int nx,
     for (int i = first_new_node_id; i < g->graph.num_node_ids(); ++i) {
       Node* n = g->graph.FindNodeId(i);
       if (n == nullptr) continue;
-      g->name_map[n->name()] = n;
+      // We have a convoluted scheme here: Using the C++ graph construction API
+      // to add potentially many nodes to the graph without running the checks
+      // (such as uniqueness of the names of nodes) we run with other functions
+      // that add a node to the graph (like TF_FinishOperation).
+      if (!g->name_map.insert(std::make_pair(n->name(), n)).second) {
+        status->status = tensorflow::errors::Internal(
+            "BUG: The API allowed construction of a graph with duplicate node "
+            "names (",
+            n->name(),
+            "). This is a bug. Please file an issue at "
+            "https://github.com/tensorflow/tensorflow/issues.");
+      }
     }
   }
 
diff --git a/tensorflow/c/c_api_test.cc b/tensorflow/c/c_api_test.cc
index 577f10c5e6..bc04b53fbb 100644
--- a/tensorflow/c/c_api_test.cc
+++ b/tensorflow/c/c_api_test.cc
@@ -1160,7 +1160,7 @@ TEST(CAPI, GetOpDef) {
 }
 
 void StringVectorToArrays(const std::vector<string>& v,
-                          std::unique_ptr<const void* []>* ptrs,
+                          std::unique_ptr<const void*[]>* ptrs,
                           std::unique_ptr<size_t[]>* lens) {
   ptrs->reset(new const void*[v.size()]);
   lens->reset(new size_t[v.size()]);
@@ -1196,7 +1196,7 @@ class CApiColocationTest : public ::testing::Test {
 
   void SetViaStringList(TF_OperationDescription* desc,
                         const std::vector<string>& list) {
-    std::unique_ptr<const void* []> list_ptrs;
+    std::unique_ptr<const void*[]> list_ptrs;
     std::unique_ptr<size_t[]> list_lens;
     StringVectorToArrays(list, &list_ptrs, &list_lens);
     TF_SetAttrStringList(desc, tensorflow::kColocationAttrName, list_ptrs.get(),
@@ -1700,6 +1700,61 @@ TEST_F(CApiGradientsTest, OpWithNoGradientRegistered_NoGradInputs) {
   TestGradientsError(false);
 }
 
+void ScalarFloatFromTensor(const TF_Tensor* t, float* f) {
+  ASSERT_TRUE(t != nullptr);
+  ASSERT_EQ(TF_FLOAT, TF_TensorType(t));
+  ASSERT_EQ(0, TF_NumDims(t));
+  ASSERT_EQ(4, TF_TensorByteSize(t));
+  float* p = static_cast<float*>(TF_TensorData(t));
+  *f = *p;
+}
+
+TEST_F(CApiGradientsTest, MultipleCallsToAddGradients) {
+  const float X = 3.0f, Y = 7.0f;
+  TF_Operation* x = Placeholder(graph_, s_, "x", TF_FLOAT);
+  TF_Operation* y = Placeholder(graph_, s_, "y", TF_FLOAT);
+  TF_Operation* xy = Mul(x, y, graph_, s_, "xy");
+  TF_Output dxy_dx, dxy_dy;
+
+  TF_Output outputs[1] = {{xy, 0}};
+  TF_Output inputs[1] = {{x, 0}};
+  TF_AddGradients(graph_, outputs, 1, inputs, 1, nullptr, s_, &dxy_dx);
+  ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
+
+  inputs[0] = {y, 0};
+  TF_AddGradients(graph_, outputs, 1, inputs, 1, nullptr, s_, &dxy_dy);
+  ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
+
+  TF_SessionOptions* opts = TF_NewSessionOptions();
+  TF_Session* sess = TF_NewSession(graph_, opts, s_);
+  TF_DeleteSessionOptions(opts);
+  ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
+
+  TF_Output feeds[] = {{x, 0}, {y, 0}};
+  TF_Tensor* feedValues[] = {FloatTensor(X), FloatTensor(Y)};
+  TF_Output fetches[] = {dxy_dx, dxy_dy};
+  TF_Tensor* fetchValues[] = {nullptr, nullptr};
+
+  TF_SessionRun(sess, nullptr /* run_options */, feeds, feedValues, 2, fetches,
+                fetchValues, 2, nullptr /* target_opers */, 0,
+                nullptr /* run_metadata */, s_);
+  TF_DeleteTensor(feedValues[0]);
+  TF_DeleteTensor(feedValues[1]);
+  ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
+  TF_DeleteSession(sess, s_);
+  ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
+
+  float dxy_dxValue = 0.0f, dxy_dyValue = 0.0f;
+  ScalarFloatFromTensor(fetchValues[0], &dxy_dxValue);
+  EXPECT_EQ(Y, dxy_dxValue);
+
+  ScalarFloatFromTensor(fetchValues[1], &dxy_dyValue);
+  EXPECT_EQ(X, dxy_dyValue);
+
+  TF_DeleteTensor(fetchValues[0]);
+  TF_DeleteTensor(fetchValues[1]);
+}
+
 // REGISTER_OP for CApiAttributesTest test cases.
 // Registers two ops, each with a single attribute called 'v'.
 // The attribute in one op will have a type 'type', the other
@@ -1784,7 +1839,7 @@ TEST_F(CApiAttributesTest, String) {
 
 TEST_F(CApiAttributesTest, StringList) {
   std::vector<string> list = {"bugs", "bunny", "duck"};
-  std::unique_ptr<const void* []> list_ptrs;
+  std::unique_ptr<const void*[]> list_ptrs;
   std::unique_ptr<size_t[]> list_lens;
   StringVectorToArrays(list, &list_ptrs, &list_lens);
   int list_total_size = 0;
@@ -1800,7 +1855,7 @@ TEST_F(CApiAttributesTest, StringList) {
   ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
 
   EXPECT_TF_META("v", list.size(), TF_ATTR_STRING, list_total_size);
-  std::unique_ptr<void* []> values(new void*[list.size()]);
+  std::unique_ptr<void*[]> values(new void*[list.size()]);
   std::unique_ptr<size_t[]> lens(new size_t[list.size()]);
   std::unique_ptr<char[]> storage(new char[list_total_size]);
   TF_OperationGetAttrStringList(oper, "v", values.get(), lens.get(),
@@ -2025,7 +2080,7 @@ TEST_F(CApiAttributesTest, TensorShapeProtoList) {
   tensorflow::PartialTensorShape(pts2).AsProto(&proto);
   proto.SerializeToString(&bytes2);
 
-  std::unique_ptr<const void* []> list_ptrs;
+  std::unique_ptr<const void*[]> list_ptrs;
   std::unique_ptr<size_t[]> list_lens;
   const std::vector<string> list = {bytes1, bytes2};
   StringVectorToArrays(list, &list_ptrs, &list_lens);
diff --git a/tensorflow/c/c_test_util.cc b/tensorflow/c/c_test_util.cc
index f3b28c1708..24eb6c069b 100644
--- a/tensorflow/c/c_test_util.cc
+++ b/tensorflow/c/c_test_util.cc
@@ -216,6 +216,13 @@ TF_Operation* Min(TF_Operation* l, TF_Operation* r, TF_Graph* graph,
   return MinWithDevice(l, r, graph, /*op_device=*/"", s, name);
 }
 
+TF_Operation* Mul(TF_Operation* l, TF_Operation* r, TF_Graph* graph,
+                  TF_Status* s, const char* name) {
+  TF_Operation* op;
+  BinaryOpHelper("Mul", l, r, graph, s, name, &op, "", true);
+  return op;
+}
+
 TF_Operation* Add(TF_Output l, TF_Output r, TF_Graph* graph, TF_Status* s,
                   const char* name) {
   TF_OperationDescription* desc = TF_NewOperation(graph, "AddN", name);
diff --git a/tensorflow/c/c_test_util.h b/tensorflow/c/c_test_util.h
index c16aba666e..38313d647c 100644
--- a/tensorflow/c/c_test_util.h
+++ b/tensorflow/c/c_test_util.h
@@ -80,6 +80,9 @@ TF_Operation* Add(TF_Output l, TF_Output r, TF_Graph* graph, TF_Status* s,
 TF_Operation* Min(TF_Operation* l, TF_Operation* r, TF_Graph* graph,
                   TF_Status* s, const char* name = "min");
 
+TF_Operation* Mul(TF_Operation* l, TF_Operation* r, TF_Graph* graph,
+                  TF_Status* s, const char* name = "mul");
+
 // If `op_device` is non-empty, set the created op on that device.
 TF_Operation* MinWithDevice(TF_Operation* l, TF_Operation* r, TF_Graph* graph,
                             const string& op_device, TF_Status* s,
diff --git a/tensorflow/cc/framework/scope.cc b/tensorflow/cc/framework/scope.cc
index 62a889181e..8c886f3171 100644
--- a/tensorflow/cc/framework/scope.cc
+++ b/tensorflow/cc/framework/scope.cc
@@ -37,6 +37,11 @@ Scope& Scope::operator=(const Scope& other) {
   return *this;
 }
 
+namespace {
+const char kScopeSeparator[] = "/";
+const char kSuffixSeparator[] = "_";
+}  // namespace
+
 Scope::Impl::Impl(Graph* graph, Status* status, NameMap* name_map,
                   ShapeRefiner* refiner, bool disable_shape_inference)
     : graph_(graph),
@@ -308,19 +313,23 @@ string Scope::Impl::GetUniqueName(const string& prefix,
     return prefix;
   }
   auto entry = name_map_->find(prefix);
-  string unique_name = prefix;
   if (entry == name_map_->end()) {
     name_map_->insert({prefix, 0});
-  } else {
-    unique_name = strings::StrCat(unique_name, "_", ++entry->second);
+    return prefix;
   }
+  string unique_name;
+  do {
+    unique_name = strings::StrCat(prefix, kSuffixSeparator, ++entry->second);
+  } while (name_map_->find(unique_name) != name_map_->end());
+  name_map_->insert({unique_name, 0});
   return unique_name;
 }
 
 string Scope::Impl::GetNameForOp(const string& default_name) const {
   const string unique_name =
       GetUniqueName(default_name, true /* check_single_use */);
-  const string sep = name_.empty() || unique_name.empty() ? "" : "/";
+  const string sep =
+      name_.empty() || unique_name.empty() ? "" : kScopeSeparator;
   return strings::StrCat(name_, sep, unique_name);
 }
 
@@ -345,7 +354,8 @@ Scope Scope::NewSubScope(const string& child_scope_name) const {
   }
   const string unique_name =
       impl()->GetUniqueName(child_scope_name, false /* check_single_use */);
-  const string sep = impl()->name_.empty() || unique_name.empty() ? "" : "/";
+  const string sep =
+      impl()->name_.empty() || unique_name.empty() ? "" : kScopeSeparator;
   return Scope(new Impl(*this, Impl::Tags::ScopeName(),
                         strings::StrCat(impl()->name_, sep, unique_name),
                         false /* copy_names */));
@@ -412,7 +422,7 @@ CompositeOpScopes Scope::GetCompositeOpScopes(
   if (!impl()->single_use_scope()) {
     Scope child = NewSubScope(impl()->op_name_.empty() ? composite_op_name
                                                        : impl()->op_name_);
-    const string child_op_sep = impl()->name_.empty() ? "" : "_";
+    const string child_op_sep = impl()->name_.empty() ? "" : kSuffixSeparator;
     const string child_name =
         strings::StrCat(impl()->name_, child_op_sep, child.impl()->name_);
     return {child,
@@ -435,7 +445,13 @@ class InternalScope {
   static Scope NewScope(Graph* graph, Status* status, ShapeRefiner* refiner) {
     Scope::Impl::NameMap* name_map = new Scope::Impl::NameMap;
     for (const Node* node : graph->nodes()) {
-      (*name_map)[node->name()] = 0;
+      const string& name = node->name();
+      (*name_map)[name] = 0;
+      // Add all name prefixes ('/' separated).
+      size_t idx = -1;
+      while ((idx = name.find(kScopeSeparator, idx + 1)) != string::npos) {
+        (*name_map)[name.substr(0, idx)] = 0;
+      }
     }
     // We provide null destructors for these shared ptrs (except for name_map)
     // since the caller owns them and doesn't want the scope to destroy them.
diff --git a/tensorflow/cc/framework/scope_internal.h b/tensorflow/cc/framework/scope_internal.h
index 8efcfed20d..58adaef2e9 100644
--- a/tensorflow/cc/framework/scope_internal.h
+++ b/tensorflow/cc/framework/scope_internal.h
@@ -34,8 +34,7 @@ class Scope::Impl {
   // name that has not been used so far in a scope will get no suffix. Later
   // uses of the same name will get suffixes _1, _2, _3, etc. Multiple scopes
   // can share the same NameMap. For instance, a new scope created using
-  // WithControlDependencies() should would share the same NameMap with the
-  // parent.
+  // WithControlDependencies() would share the same NameMap with the parent.
   typedef std::unordered_map<string, int> NameMap;
 
   Impl(const std::shared_ptr<Graph>& graph,
diff --git a/tensorflow/cc/framework/scope_test.cc b/tensorflow/cc/framework/scope_test.cc
index 9eca9d3fac..b40b345eb8 100644
--- a/tensorflow/cc/framework/scope_test.cc
+++ b/tensorflow/cc/framework/scope_test.cc
@@ -26,6 +26,16 @@ TEST(ScopeTest, BasicNames) {
   EXPECT_EQ(root.GetUniqueNameForOp("mul"), "mul");
 }
 
+TEST(ScopeTest, OpAndScopeNameCollision) {
+  Scope root = Scope::NewRootScope();
+  EXPECT_EQ(root.GetUniqueNameForOp("foo"), "foo");
+  EXPECT_EQ(root.GetUniqueNameForOp("foo"), "foo_1");
+  EXPECT_EQ(root.GetUniqueNameForOp("foo_1"), "foo_1_1");
+  EXPECT_EQ(root.GetUniqueNameForOp("foo_2"), "foo_2");
+  EXPECT_EQ(root.GetUniqueNameForOp("foo"), "foo_3");
+  EXPECT_EQ(root.GetUniqueNameForOp("foo_2"), "foo_2_1");
+}
+
 TEST(ScopeTest, HierarchicalNames) {
   Scope root = Scope::NewRootScope();
   Scope child = root.NewSubScope("child");