Enable move warnings for torch targets (#149923)

This PR enables more move warnings for torch targets and fixes some code.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/149923
Approved by: https://github.com/malfet

CMakeLists.txt

@@ -1084,7 +1084,6 @@ if(NOT MSVC)
   if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 13)
     append_cxx_flag_if_supported("-Wno-dangling-reference" CMAKE_CXX_FLAGS)
     append_cxx_flag_if_supported("-Wno-error=dangling-reference" CMAKE_CXX_FLAGS)
-    append_cxx_flag_if_supported("-Wno-error=redundant-move" CMAKE_CXX_FLAGS)
   endif()
 else()
   # Define export functions for AOTI.

c10/macros/Macros.h

@@ -508,4 +508,14 @@ __host__ __device__
 
 #endif
 
+// This macro is used to find older C++ compilers
+// that don't support move optimization for return values.
+
+#if (defined(__GNUC__) && __GNUC__ < 13) || \
+    (defined(__clang_major__) && __clang_major__ < 13)
+#define C10_RETURN_MOVE_IF_OLD_COMPILER 1
+#else
+#define C10_RETURN_MOVE_IF_OLD_COMPILER 0
+#endif
+
 #endif // C10_MACROS_MACROS_H_

cmake/public/utils.cmake

@@ -393,10 +393,10 @@ function(torch_compile_options libname)
     list(APPEND private_compile_options -Wunused-function)
     list(APPEND private_compile_options -Wunused-variable)
     if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-      list(APPEND private_compile_options -Wunused-but-set-variable)
+      list(APPEND private_compile_options -Wunused-but-set-variable -Wredundant-move)
     endif()
     if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-      list(APPEND private_compile_options -Wunused-private-field -Wextra-semi -Wno-error=extra-semi)
+      list(APPEND private_compile_options -Wunused-private-field -Wextra-semi -Wno-error=extra-semi -Wmove)
     else()
       list(APPEND private_compile_options
         # Considered to be flaky.  See the discussion at

torch/csrc/jit/python/pybind_utils.cpp

@@ -641,7 +641,11 @@ py::object toPyObject(IValue ivalue) {
     for (const auto i : c10::irange(list.size())) {
       t[i] = toPyObject(IValue{list.get(i)});
     }
+#if C10_RETURN_MOVE_IF_OLD_COMPILER
     return std::move(t);
+#else
+    return t;
+#endif
   } else if (ivalue.isTuple()) {
     auto tuple = std::move(ivalue).toTuple();
     const auto& elements = tuple->elements();
@@ -676,7 +680,11 @@ py::object toPyObject(IValue ivalue) {
           .attr("_create_named_tuple")(
               t, unqualName, fieldNames, py::make_tuple(defaults));
     } else {
+#if C10_RETURN_MOVE_IF_OLD_COMPILER
       return std::move(t);
+#else
+      return t;
+#endif
     }
   } else if (ivalue.isDevice()) {
     return py::cast(std::move(ivalue).toDevice());
@@ -689,7 +697,11 @@ py::object toPyObject(IValue ivalue) {
       py_dict[toPyObject(IValue{pair.key()})] =
           toPyObject(IValue{pair.value()});
     }
+#if C10_RETURN_MOVE_IF_OLD_COMPILER
     return std::move(py_dict);
+#else
+    return py_dict;
+#endif
   } else if (ivalue.isRRef()) {
 #ifdef USE_RPC
     auto RRefPtr =

torch/csrc/jit/python/python_arg_flatten.cpp

@@ -117,7 +117,11 @@ py::object cast_sequence(std::vector<py::object> objs) {
   for (const auto i : c10::irange(num_objs)) {
     sequence[i] = std::move(objs[i]);
   }
+#if C10_RETURN_MOVE_IF_OLD_COMPILER
   return std::move(sequence);
+#else
+  return sequence;
+#endif
 }
 
 py::object cast_dict(std::vector<py::object> objs) {
@@ -127,7 +131,11 @@ py::object cast_dict(std::vector<py::object> objs) {
     py::tuple obj = py::reinterpret_borrow<py::tuple>(objs[i]);
     sequence[obj[0]] = obj[1];
   }
+#if C10_RETURN_MOVE_IF_OLD_COMPILER
   return std::move(sequence);
+#else
+  return sequence;
+#endif
 }
 
 py::object unflatten_rec(

torch/csrc/jit/tensorexpr/kernel.cpp

@@ -483,7 +483,11 @@ ExprHandle TensorExprKernel::getVarForShape(const c10::ShapeSymbol& ss) {
   if (it == shapeSymbolToVar_.end()) {
     VarHandle var("ss" + std::to_string(-value), kLong);
     shapeSymbolToVar_.emplace(value, var);
+#if C10_RETURN_MOVE_IF_OLD_COMPILER
     return std::move(var);
+#else
+    return var;
+#endif
   }
   return it->second;
 }
@@ -1020,7 +1024,11 @@ ExprHandle TensorExprKernel::getStrideArg(
         kLong);
     strideArgToVar_[std::pair<size_t, size_t>(
         tensor_input_index, stride_index)] = var;
+#if C10_RETURN_MOVE_IF_OLD_COMPILER
     return std::move(var);
+#else
+    return var;
+#endif
   }
   return it->second;
 }