[xnnpack-ep] NEW EP API in objc (#13941)

### Description
<!-- Describe your changes. -->



### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

Co-authored-by: Edward Chen <18449977+edgchen1@users.noreply.github.com>

objectivec/include/onnxruntime.h

@@ -5,6 +5,7 @@
 // the headers below can also be imported individually
 
 #import "ort_coreml_execution_provider.h"
+#import "ort_xnnpack_execution_provider.h"
 #import "ort_enums.h"
 #import "ort_env.h"
 #import "ort_session.h"

objectivec/include/ort_session.h

@@ -105,6 +105,18 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (nullable instancetype)initWithError:(NSError**)error NS_SWIFT_NAME(init());
 
+/**
+ * Available since 1.14.
+ * Appends an execution provider to the session configuration options.
+ * The execution provider list is ordered by decreasing priority
+ * @param providerName Provider name. For example, "xnnpack".
+ * @param providerOptions Provider-specific options. For example, for provider "xnnpack", {"intra_op_num_threads": "2"}.
+ * @param error Optional error information set if an error occurs.
+ * @return Whether the execution provider was appended successfully
+ */
+- (BOOL)appendExecutionProvider:(NSString*)providerName
+                providerOptions:(NSDictionary<NSString*, NSString*>*)providerOptions
+                          error:(NSError**)error;
 /**
  * Sets the number of threads used to parallelize the execution within nodes.
  * A value of 0 means ORT will pick a default value.

objectivec/include/ort_xnnpack_execution_provider.h

@@ -0,0 +1,39 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+#import <Foundation/Foundation.h>
+
+#import "ort_session.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * Options for configuring the Xnnpack execution provider.
+ */
+@interface ORTXnnpackExecutionProviderOptions : NSObject
+
+/**
+ * How many threads used for the Xnnpack execution provider.
+ */
+@property int intra_op_num_threads;
+
+@end
+
+@interface ORTSessionOptions (ORTSessionOptionsXnnpackEP)
+
+/**
+ * Available since 1.14.
+ * Enables the Xnnpack execution provider in the session configuration options.
+ * It is appended to the execution provider list which is ordered by
+ * decreasing priority.
+ *
+ * @param options The Xnnpack execution provider configuration options.
+ * @param error Optional error information set if an error occurs.
+ * @return Whether the provider was enabled successfully.
+ */
+- (BOOL)appendXnnpackExecutionProviderWithOptions:(ORTXnnpackExecutionProviderOptions*)options
+                                            error:(NSError**)error;
+
+@end
+
+NS_ASSUME_NONNULL_END

objectivec/src/ort_session.mm

@@ -213,6 +213,24 @@ NS_ASSUME_NONNULL_BEGIN
   ORT_OBJC_API_IMPL_CATCH_RETURNING_NULLABLE(error)
 }
 
+- (BOOL)appendExecutionProvider:(NSString*)providerName
+                providerOptions:(NSDictionary<NSString*, NSString*>*)providerOptions
+                          error:(NSError**)error {
+  try {
+    std::unordered_map<std::string, std::string> options;
+    NSArray* keys = [providerOptions allKeys];
+  
+    for (NSString* key in keys) {
+      NSString* value = [providerOptions objectForKey:key];
+      options.emplace(key.UTF8String, value.UTF8String);
+    }
+  
+    _sessionOptions->AppendExecutionProvider(providerName.UTF8String, options);
+    return YES;
+  }
+  ORT_OBJC_API_IMPL_CATCH_RETURNING_BOOL(error);
+}
+
 - (BOOL)setIntraOpNumThreads:(int)intraOpNumThreads
                        error:(NSError**)error {
   try {

objectivec/src/ort_xnnpack_execution_provider.mm

@@ -0,0 +1,31 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+#import "ort_xnnpack_execution_provider.h"
+
+#import "src/cxx_api.h"
+#import "src/error_utils.h"
+#import "src/ort_session_internal.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@implementation ORTXnnpackExecutionProviderOptions
+
+@end
+
+@implementation ORTSessionOptions (ORTSessionOptionsXnnpackEP)
+
+- (BOOL)appendXnnpackExecutionProviderWithOptions:(ORTXnnpackExecutionProviderOptions*)options
+                                            error:(NSError**)error {
+  try {
+    NSDictionary* provider_options = @{
+      @"intra_op_num_threads" : [NSString stringWithFormat:@"%d", options.intra_op_num_threads]
+    };
+    return [self appendExecutionProvider:@"XNNPACK" providerOptions:provider_options error:error];
+  }
+  ORT_OBJC_API_IMPL_CATCH_RETURNING_BOOL(error);
+}
+
+@end
+
+NS_ASSUME_NONNULL_END

objectivec/test/ort_session_test.mm

@@ -4,6 +4,7 @@
 #import <XCTest/XCTest.h>
 
 #import "ort_coreml_execution_provider.h"
+#import "ort_xnnpack_execution_provider.h"
 #import "ort_env.h"
 #import "ort_session.h"
 #import "ort_value.h"
@@ -215,6 +216,28 @@ NS_ASSUME_NONNULL_BEGIN
   ORTAssertNullableResultSuccessful(session, err);
 }
 
+- (void)testAppendXnnpackEP {
+  NSError* err = nil;
+  ORTSessionOptions* sessionOptions = [ORTSessionTest makeSessionOptions];
+  ORTXnnpackExecutionProviderOptions* XnnpackOptions = [[ORTXnnpackExecutionProviderOptions alloc] init];
+  XnnpackOptions.intra_op_num_threads = 2;
+
+  BOOL appendResult = [sessionOptions appendXnnpackExecutionProviderWithOptions:XnnpackOptions
+                                                                          error:&err];
+  // Without xnnpack EP in building also can pass the test
+  NSString* err_msg = [err localizedDescription];
+  if (!appendResult && [err_msg containsString:@"XNNPACK execution provider is not supported in this build. "]) {
+    return;
+  }
+
+  ORTAssertBoolResultSuccessful(appendResult, err);
+
+  ORTSession* session = [[ORTSession alloc] initWithEnv:self.ortEnv
+                                              modelPath:[ORTSessionTest getAddModelPath]
+                                         sessionOptions:sessionOptions
+                                                  error:&err];
+  ORTAssertNullableResultSuccessful(session, err);
+}
 @end
 
 NS_ASSUME_NONNULL_END