Update LegalizeNodeName to mutate inplace (NFC).

*NameMappers already return copies of strings for GetName. As the legalization of names is via substituting characters with `.`, this can be done inplace instead.
tensorflow name space is removed in preparation of name utils being used for converting locations to strings for XLA OpMetadata tracking.

PiperOrigin-RevId: 328762081
Change-Id: I4d460d2fe6ea1cccd0165b4bb02e5cc0d0994167

tensorflow/compiler/mlir/op_or_arg_name_mapper.cc

@@ -106,14 +106,14 @@ bool OpOrArgNameMapper::IsUnique(llvm::StringRef name) { return true; }
 
 std::string OpOrArgLocNameMapper::GetName(OpOrVal op_or_val) {
   if (auto* op = op_or_val.dyn_cast<mlir::Operation*>()) {
-    auto name_from_loc = mlir::tensorflow::GetNameFromLoc(op->getLoc());
+    auto name_from_loc = mlir::GetNameFromLoc(op->getLoc());
     if (!name_from_loc.empty()) return name_from_loc;
     // If the location is none of the expected types, then simply use name
     // generated using the op type.
     return std::string(op->getName().getStringRef());
   }
   auto val = op_or_val.dyn_cast<mlir::Value>();
-  auto name_from_loc = mlir::tensorflow::GetNameFromLoc(val.getLoc());
+  auto name_from_loc = mlir::GetNameFromLoc(val.getLoc());
   if (!name_from_loc.empty()) return name_from_loc;
   // If the location is none of the expected types, then simply use name
   // generated using the op type. Follow TF convention and append the result

tensorflow/compiler/mlir/tensorflow/translate/export_graphdef.cc

@@ -85,8 +85,10 @@ constexpr char kResourceArgUniqueIdAttr[] = "tf._resource_arg_unique_id";
 class LegalizedOpOrValLocNameMapper : public OpOrArgLocNameMapper {
  private:
   std::string GetName(OpOrVal op_or_val) override {
-    return mlir::tensorflow::LegalizeNodeName(
-        OpOrArgLocNameMapper::GetName(op_or_val));
+    std::string name = OpOrArgLocNameMapper::GetName(op_or_val);
+    assert(!name.empty() && "expected non-empty name");
+    mlir::LegalizeNodeName(name);
+    return name;
   }
 };
 
@@ -490,13 +492,14 @@ StatusOr<std::unique_ptr<Graph>> Exporter::Convert(
       if (index >= num_data_results) break;
       // TODO(jpienaar): If there is a result index specified, ensure only one
       // and that it matches the result index of the op.
-      std::string orig_name(output_names[index]);
-      auto tensor_id = ParseTensorName(orig_name);
-      auto name = mlir::tensorflow::LegalizeNodeName(
-          llvm::StringRef(tensor_id.node().data(), tensor_id.node().size()));
+      std::string name(output_names[index]);
+      auto tensor_id = ParseTensorName(name);
+      std::string tensor_id_node(tensor_id.node());
+      assert(!tensor_id_node.empty() && "expected non-empty name");
+      mlir::LegalizeNodeName(tensor_id_node);
 
       // Ensure name does not get reused.
-      (void)exporter.op_to_name_.GetUniqueName(name);
+      (void)exporter.op_to_name_.GetUniqueName(tensor_id_node);
     }
   }
 
@@ -504,8 +507,9 @@ StatusOr<std::unique_ptr<Graph>> Exporter::Convert(
     TF_RET_CHECK(input_names.size() == block.getNumArguments());
     for (const auto& it : llvm::enumerate(function.getArguments())) {
       // TODO(lyandy): Update when changing feed/fetch import.
-      std::string orig_name(input_names[it.index()]);
-      std::string name = mlir::tensorflow::LegalizeNodeName(orig_name);
+      std::string name(input_names[it.index()]);
+      assert(!name.empty() && "expected non-empty name");
+      mlir::LegalizeNodeName(name);
       auto tensor_id = ParseTensorName(name);
       TF_RET_CHECK(tensor_id.index() == 0)
           << "input port designation not supported";

tensorflow/compiler/mlir/utils/name_utils.cc

@@ -23,7 +23,6 @@ limitations under the License.
 #include "mlir/IR/Identifier.h"  // from @llvm-project
 
 namespace mlir {
-namespace tensorflow {
 
 namespace {
 // Checks if a character is legal for a TensorFlow node name, with special
@@ -45,21 +44,13 @@ bool IsLegalChar(char c, bool first_char) {
 }
 }  // anonymous namespace
 
-std::string LegalizeNodeName(llvm::StringRef name) {
-  assert(!name.empty() && "expected non-empty name");
+void LegalizeNodeName(std::string& name) {
+  if (name.empty()) return;
 
-  std::string legalized_name;
-  bool first = true;
-  for (auto c : name) {
-    if (IsLegalChar(c, first)) {
-      legalized_name += c;
-    } else {
-      legalized_name += '.';
-    }
-    first = false;
-  }
+  if (!IsLegalChar(name[0], /*first_char=*/true)) name[0] = '.';
 
-  return legalized_name;
+  for (char& c : llvm::drop_begin(name, 1))
+    if (!IsLegalChar(c, /*first_char=*/false)) c = '.';
 }
 
 std::string GetNameFromLoc(Location loc) {
@@ -105,5 +96,4 @@ std::string GetNameFromLoc(Location loc) {
   return "";
 }
 
-}  // namespace tensorflow
 }  // namespace mlir

tensorflow/compiler/mlir/utils/name_utils.h

@@ -22,16 +22,14 @@ limitations under the License.
 #include "mlir/IR/Location.h"  // from @llvm-project
 
 namespace mlir {
-namespace tensorflow {
 
 // Converts characters in name that are considered illegal in TensorFlow Node
 // name to '.'.
-std::string LegalizeNodeName(llvm::StringRef name);
+void LegalizeNodeName(std::string& name);
 
 // Creates a TensorFlow node name from a location.
 std::string GetNameFromLoc(Location loc);
 
-}  // namespace tensorflow
 }  // namespace mlir
 
 #endif  // TENSORFLOW_COMPILER_MLIR_UTILS_NAME_UTILS_H_