Fix coreml rank0 (#10534)

coremltools wraps rank 0 tensors as rank1 tensors in the AOT flow when
producing a PTE file. This PR:

* Applies the same change on the coreml runtime
* Changes CoreML model tests to use the partitioner

Fixes #10451

Author: metascroy

.ci/scripts/test_model.sh

@@ -222,7 +222,7 @@ test_model_with_coreml() {
 
   DTYPE=float16
 
-  "${PYTHON_EXECUTABLE}" -m examples.apple.coreml.scripts.export --model_name="${MODEL_NAME}" --compute_precision "${DTYPE}"
+  "${PYTHON_EXECUTABLE}" -m examples.apple.coreml.scripts.export --model_name="${MODEL_NAME}" --compute_precision "${DTYPE}" --use_partitioner
   EXPORTED_MODEL=$(find "." -type f -name "${MODEL_NAME}*.pte" -print -quit)
 
   if [ -n "$EXPORTED_MODEL" ]; then

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

@@ -88,9 +88,17 @@
         ET_LOG(Error, "%s: DataType=%d is not supported", ETCoreMLStrings.delegateIdentifier.UTF8String, (int)tensor.scalar_type());
         return std::nullopt;
     }
-
+    
     std::vector<ssize_t> strides(tensor.strides().begin(), tensor.strides().end());
     std::vector<size_t> shape(tensor.sizes().begin(), tensor.sizes().end());
+    
+    // If tensor is rank 0, wrap in rank 1
+    // See https://github.com/apple/coremltools/blob/8.2/coremltools/converters/mil/frontend/torch/exir_utils.py#L73
+    if (shape.size() == 0) {
+        shape.push_back(1);
+        strides.push_back(1);
+    }
+    
     MultiArray::MemoryLayout layout(dataType.value(), std::move(shape), std::move(strides));
     switch (argType) {
         case ArgType::Input: {
@@ -233,6 +241,12 @@ ModelLoggingOptions get_logging_options(BackendExecutionContext& context) {
     std::array<SizesType, kTensorDimensionLimit> new_shape;
     for (size_t i = nInputs; i < nInputs + nOutputs; i++) {
         Tensor& t = args[i]->toTensor();
+        // If t has rank 0, do not resize.  delegate_args[i] will have rank 1
+        // because we resized it in get_multi_array
+        if (t.dim() == 0) {
+            continue;
+        }
+
         int rank = delegate_args[i].layout().rank();
         assert (rank <= new_shape.size());
         for (int d = 0; d < rank; d++) {

backends/apple/coreml/runtime/test/ETCoreMLModelManagerTests.mm

@@ -113,7 +113,7 @@ - (void)testAddModelExecution {
     XCTAssertNotNil(inputs);
     MLMultiArray *output = [ETCoreMLTestUtils filledMultiArrayWithShape:inputs[0].shape dataType:inputs[0].dataType repeatedValue:@(0) error:&localError];
     NSArray<MLMultiArray *> *args = [inputs arrayByAddingObject:output];
-    XCTAssertTrue([self.modelManager executeModelWithHandle:handle 
+    XCTAssertTrue([self.modelManager executeModelWithHandle:handle
                                                        args:args
                                              loggingOptions:executorchcoreml::ModelLoggingOptions()
                                                 eventLogger:nullptr