Optimize memory when exporting. (#2341)

Summary:
CoreML delegate when converting the `mlpackage` to an in-memory representation reads the directory contents in the `mlpackage` directory and writes it to a memory buffer this is expensive and the copying is not required.

The change in the PR addresses by memory mapping the file contents to fixed addresses in the allocated memory, no memory is dirtied and the OS will bring the pages only when the bytes are read.

Pull Request resolved: #2341

Reviewed By: digantdesai

Differential Revision: D54997652

Pulled By: shoumikhin

fbshipit-source-id: 2f479be5241f6d2c60005a2f6410514ee967a46e

Author: cymbalrush

backends/apple/coreml/runtime/delegate/ETCoreMLModelManager.mm

@@ -457,7 +457,7 @@ - (nullable NSURL *)compiledModelURLWithIdentifier:(NSString *)identifier
     using namespace inmemoryfs;
 
     auto buffer = MemoryBuffer::make_unowned(const_cast<void *>(data.bytes), data.length);
-    std::unique_ptr<InMemoryFileSystem> inMemoryFS = inmemoryfs::make(buffer);
+    std::unique_ptr<InMemoryFileSystem> inMemoryFS = inmemoryfs::make_from_buffer(std::move(buffer));
     if (!inMemoryFS) {
         ETCoreMLLogErrorAndSetNSError(error,
                                       ETCoreMLErrorCorruptedModel,

backends/apple/coreml/runtime/delegate/backend_delegate.mm

@@ -63,7 +63,7 @@ MLMultiArrayDataType get_data_type(MultiArray::DataType dataType) {
             return MLMultiArrayDataTypeFloat32;
         }
         case MultiArray::DataType::Double: {
-            return MLMultiArrayDataTypeFloat64;
+            return MLMultiArrayDataTypeDouble;
         }
         case MultiArray::DataType::Int: {
             return MLMultiArrayDataTypeInt32;

backends/apple/coreml/runtime/delegate/coreml_backend_delegate.mm

@@ -149,7 +149,7 @@ ModelLoggingOptions get_logging_options(BackendExecutionContext& context) {
     ET_CHECK_OR_RETURN_ERROR(handle != nullptr,
                              InvalidProgram,
                              "%s: Failed to init the model.", ETCoreMLStrings.delegateIdentifier.UTF8String);
-    
+    processed->Free();
     return handle;
 }