make TensorImpl::data_ptr_impl() non-const and have mutable in the name (#97744)

See D44409928.

Differential Revision: [D44450468](https://our.internmc.facebook.com/intern/diff/D44450468/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97744
Approved by: https://github.com/ezyang

aten/src/ATen/templates/TensorMethods.cpp

@@ -14,7 +14,7 @@ namespace at {
          #name                                                       \
          " but found ",                                              \
          scalar_type());                                             \
-     return this->unsafeGetTensorImpl()->data_ptr_impl<T>();         \
+     return this->unsafeGetTensorImpl()->mutable_data_ptr_impl<T>(); \
    }
 
  AT_FORALL_SCALAR_TYPES_WITH_COMPLEX(DEFINE_CAST)

c10/core/TensorImpl.h

@@ -1503,7 +1503,7 @@ struct C10_API TensorImpl : public c10::intrusive_ptr_target {
         ", while tensor contains ",
         data_type_.name(),
         ". ");
-    return data_ptr_impl<T>();
+    return legacy_mutable_data_ptr_impl<T>();
   }
 
   /**
@@ -1512,7 +1512,18 @@ struct C10_API TensorImpl : public c10::intrusive_ptr_target {
    * check has_storage() and storage_initialized().
    */
   template <typename T>
-  inline T* data_ptr_impl() const {
+  inline T* mutable_data_ptr_impl() {
+    return legacy_mutable_data_ptr_impl<T>();
+  }
+
+ private:
+  // The real implementation of mutable_data_ptr_impl, but in a
+  // non-const method.
+  //
+  // TODO: move the implementation into mutable_data_ptr_impl() and
+  // delete this when data<T>() is no longer const.
+  template <typename T>
+  inline T* legacy_mutable_data_ptr_impl() const {
     TORCH_CHECK(
         has_storage(),
         "Cannot access data pointer of Tensor that doesn't have storage");
@@ -1525,6 +1536,7 @@ struct C10_API TensorImpl : public c10::intrusive_ptr_target {
     return static_cast<T*>(storage_.mutable_data()) + storage_offset_;
   }
 
+ public:
   /**
    * Return a void* data pointer to the actual data which this tensor refers to.
    *

test/cpp/jit/test_backend_compiler_lib.cpp

@@ -59,7 +59,7 @@ std::vector<std::tuple<std::string, int64_t>> parseMethodHandle(
 }
 
 float* float_data_ptr(const at::Tensor& t) {
-  return t.unsafeGetTensorImpl()->data_ptr_impl<float>();
+  return t.data_ptr<float>();
 }
 } // namespace