[FPGADataflow] Add InferGlobalAccPoolLayer transform to support the...

[FPGADataflow] Add InferGlobalAccPoolLayer transform to support the implementation of GlobalAveragePool

src/finn/transformation/fpgadataflow/convert_to_hls_layers.py

@@ -600,3 +600,88 @@ class InferChannelwiseLinearLayer(Transformation):
             model = model.transform(InferShapes())
             model = model.transform(InferDataTypes())
         return (model, graph_modified)
+
+
+class InferGlobalAccPoolLayer(Transformation):
+    """Convert any GlobalAveragePool into a GlobalAccPool HLS layer and a scalar Mul."""
+
+    def apply(self, model):
+        graph = model.graph
+        node_ind = 0
+        graph_modified = False
+        for node in graph.node:
+            node_ind += 1
+            if node.op_type == "GlobalAveragePool":
+                in0 = node.input[0]
+                result = node.output[0]
+                in0_shape = model.get_tensor_shape(in0)
+
+                idt = model.get_tensor_datatype(in0)
+
+                # skip conversion for layers with float input
+                if not idt.is_integer():
+                    continue
+
+                # check layout and convert if necessary
+                in0_layout = model.get_tensor_layout(in0)
+                result_layout = model.get_tensor_layout(result)
+
+                if in0_layout == DataLayout.NCHW:
+                    in0 = nchw_to_nhwc(in0, model, node_ind)
+                    node_ind += 1
+                    in0_shape = model.get_tensor_shape(in0)
+
+                # keep track of where we need to insert the HLS Op
+                # it has to be ahead of the output transform
+                insert_point = node_ind
+
+                if result_layout == DataLayout.NCHW:
+                    result = nchw_to_nhwc(result, model, node_ind, reverse=True)
+                    node_ind += 1
+
+                num_ch = int(in0_shape[-1])
+                vecs = in0_shape[:-1]
+                # create node with no parallelization first
+                pe = 1
+                assert (
+                    num_ch % pe == 0
+                ), "Requirement Labels divisable by PE is violated."
+
+                # create an additional tensor of the same shape and layout as result
+                out_shape = model.get_tensor_shape(result)
+                pool_out = helper.make_tensor_value_info(
+                    model.make_new_valueinfo_name(), TensorProto.FLOAT, out_shape
+                )
+                model.graph.value_info.append(pool_out)
+                pool_out = pool_out.name
+                model.set_tensor_layout(pool_out, model.get_tensor_layout(result))
+
+                new_pool = helper.make_node(
+                    "GlobalAccPool_Batch",
+                    [in0],
+                    [pool_out],
+                    domain="finn",
+                    backend="fpgadataflow",
+                    NumChannels=num_ch,
+                    PE=pe,
+                    inputDataType=idt.name,
+                    numInputVectors=vecs,
+                )
+
+                mul_value = helper.make_tensor_value_info(
+                    model.make_new_valueinfo_name(), TensorProto.FLOAT, [1]
+                )
+                model.graph.value_info.append(mul_value)
+                model.set_initializer(mul_value.name, np.array(1 / (vecs[1] * vecs[2])))
+                new_mul = helper.make_node("Mul", [pool_out, mul_value.name], [result],)
+                graph.node.insert(insert_point, new_pool)
+                graph.node.insert(insert_point + 1, new_mul)
+                node_ind += 1
+                # remove old node
+                graph.node.remove(node)
+                graph_modified = True
+
+        if graph_modified:
+            model = model.transform(InferShapes())
+            model = model.transform(InferDataTypes())
+        return (model, graph_modified)