Add clamp operator to Arm backend

* Add support for aten.clamp
* Amend QuantizeFullArgument pass to include quantization of clamp arguments

Signed-off-by: Tom Allsop <[email protected]>

Change-Id: I432f4ec60facc50fe45ca05c98308924d6e18109

Author: tom-arm

backends/arm/_passes/arm_pass_manager.py

@@ -37,7 +37,7 @@
 from executorch.backends.arm._passes.decompose_var_pass import DecomposeVarPass
 from executorch.backends.arm._passes.fold_qdq_with_annotated_qparams_pass import (
     FoldAndAnnotateQParamsPass,
-    QuantizeFullArgument,
+    QuantizeOperatorArguments,
     RetraceFoldedDtypesPass,
 )
 from executorch.backends.arm._passes.fuse_quantized_activation_pass import (
@@ -88,7 +88,7 @@ def _tosa_080_BI_pipeline(self, exported_program: ExportedProgram) -> GraphModul
         self.add_pass(ConvertMeanDimToAveragePoolPass())
 
         self.add_pass(AnnotateDecomposedMatmulPass())
-        self.add_pass(QuantizeFullArgument())
+        self.add_pass(QuantizeOperatorArguments())
         self.add_pass(FoldAndAnnotateQParamsPass())
         self.add_pass(RetraceFoldedDtypesPass())
         self.add_pass(InsertTableOpsPass(exported_program))
@@ -124,7 +124,7 @@ def _tosa_080_MI_pipeline(self, exported_program: ExportedProgram) -> GraphModul
         self.add_pass(DecomposeSoftmaxesPass())
 
         self.add_pass(AnnotateDecomposedMatmulPass())
-        self.add_pass(QuantizeFullArgument())
+        self.add_pass(QuantizeOperatorArguments())
         self.add_pass(FoldAndAnnotateQParamsPass())
         self.add_pass(RetraceFoldedDtypesPass())
         self.add_pass(InsertTableOpsPass(exported_program))

backends/arm/_passes/fold_qdq_with_annotated_qparams_pass.py

@@ -182,19 +182,25 @@ def call(self, graph_module: GraphModule) -> PassResult:
         return PassResult(graph_module, True)
 
 
-class QuantizeFullArgument(ExportPass):
+class QuantizeOperatorArguments(ExportPass):
     """
-    Make sure the fill_value for full.default is quantized. This pass needs to be run before
-    the folding pass above to make sure that the retraced output of the full.default op is
-    the right dtype.
+    This pass makes sure that the arguments to full.default and clamp.default are quantized correctly.
+    More specifically, this pass:
+        - Makes sure the fill_value for full.default is quantized. This pass needs to be run before
+        the folding pass above to make sure that the retraced output of the full.default op is
+        the right dtype.
+        - Makes sure the min and max values to clamp.default are quantized, if it's a quantized operator.
     """
 
     def call(self, graph_module: GraphModule) -> PassResult:
         modified = False
         # Loop over the graph nodes and find full.default nodes.
         for n in graph_module.graph.nodes:
             n = cast(Node, n)
-            if n.target != exir_ops.edge.aten.full.default:
+            if n.target not in {
+                exir_ops.edge.aten.clamp.default,
+                exir_ops.edge.aten.full.default,
+            }:
                 continue
 
             # Make sure we have a quantized operator
@@ -203,13 +209,29 @@ def call(self, graph_module: GraphModule) -> PassResult:
                 continue
 
             qargs = QuantArgs.from_operator(user.target, user.args)
-            if "dtype" not in n.kwargs.keys() or n.kwargs["dtype"] != qargs.dtype:
-                # replace the node arg with a quantized dito and also set dtype
-                # to get the right output according to the Edge IR specification:
-                # exir/dialects/edge/edge.yaml:3596
-                quantized_full_value = qargs.quantize_value(n.args[1]).item()
-                n.update_arg(1, quantized_full_value)
-                n.update_kwarg("dtype", qargs.dtype)
+
+            if n.target == exir_ops.edge.aten.full.default:
+                if "dtype" not in n.kwargs.keys() or n.kwargs["dtype"] != qargs.dtype:
+                    # replace the node arg with a quantized dito and also set dtype
+                    # to get the right output according to the Edge IR specification:
+                    # exir/dialects/edge/edge.yaml:3596
+                    quantized_full_value = qargs.quantize_value(n.args[1]).item()
+                    n.update_arg(1, quantized_full_value)
+                    n.update_kwarg("dtype", qargs.dtype)
+                    modified = True
+            elif n.target == exir_ops.edge.aten.clamp.default:
+                # Quantize the min and max arguments of clamp, if they are not None
+                min_val = n.args[1]
+                max_val = None if len(n.args) <= 2 else n.args[2]
+
+                if min_val is not None:
+                    quantized_min_val = qargs.quantize_value(min_val).item()
+                    n.update_arg(1, quantized_min_val)
+
+                if max_val is not None:
+                    quantized_max_val = qargs.quantize_value(max_val).item()
+                    n.update_arg(2, quantized_max_val)
+
                 modified = True
 
         return PassResult(graph_module, modified)

backends/arm/operator_support/tosa_supported_operators.py

@@ -76,6 +76,7 @@ def is_node_supported(self, submodules, node: fx.Node) -> bool:
             exir_ops.edge.aten.add.Tensor,
             exir_ops.edge.aten.expand_copy.default,
             exir_ops.edge.aten.cat.default,
+            exir_ops.edge.aten.clamp.default,
             exir_ops.edge.aten.bmm.default,
             exir_ops.edge.aten.permute_copy.default,
             exir_ops.edge.aten.hardtanh.default,

backends/arm/operators/__init__.py

@@ -12,6 +12,7 @@
     op_batch_norm,
     op_bmm,
     op_cat,
+    op_clamp,
     op_conv2d,
     op_eq,
     op_exp,

backends/arm/operators/op_clamp.py

@@ -0,0 +1,140 @@
+# Copyright 2025 Arm Limited and/or its affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree
+
+from numbers import Number
+from typing import List, Tuple
+
+import serializer.tosa_serializer as ts
+
+import torch
+from executorch.backends.arm.operators.node_visitor import (
+    NodeVisitor,
+    register_node_visitor,
+)
+
+from executorch.backends.arm.tosa_mapping import TosaArg
+from executorch.backends.arm.tosa_specification import TosaSpecification
+from serializer.tosa_serializer import TosaOp
+from torch.fx import Node
+
+
+@register_node_visitor
+class ClampVisitor_080_BI(NodeVisitor):
+    target = "aten.clamp.default"
+
+    tosa_specs = [
+        TosaSpecification.create_from_string("TOSA-0.80+BI"),
+    ]
+
+    def __init__(self, *args):
+        super().__init__(*args)
+
+    def _create_clamp_node(
+        self,
+        tosa_graph: ts.TosaSerializer,
+        input_name: str,
+        output_name: str,
+        min_int: int,
+        max_int: int,
+        min_fp32: float,
+        max_fp32: float,
+    ):
+        attr = ts.TosaSerializerAttribute()
+        attr.ClampAttribute(
+            tosa_graph.builder,
+            min_int,
+            max_int,
+            min_fp32,
+            max_fp32,
+        )
+        tosa_graph.addOperator(TosaOp.Op().CLAMP, [input_name], [output_name], attr)
+
+    def _get_min_max_arguments(
+        self,
+        node: Node,
+        dtype_min: Number,
+        dtype_max: Number,
+    ) -> Tuple[Number, Number]:
+        assert 2 <= len(node.args) <= 3
+
+        min_arg = dtype_min
+        max_arg = dtype_max
+
+        if node.args[1] is not None:
+            min_arg = node.args[1]
+
+        if len(node.args) > 2:
+            if node.args[2] is not None:
+                max_arg = node.args[2]
+
+        return min_arg, max_arg
+
+    def define_node(
+        self,
+        node: Node,
+        tosa_graph: ts.TosaSerializer,
+        inputs: List[TosaArg],
+        output: TosaArg,
+    ) -> None:
+        assert len(node.all_input_nodes) == 1
+
+        min_int8, max_int8 = self._get_min_max_arguments(
+            node,
+            torch.iinfo(torch.int8).min,
+            torch.iinfo(torch.int8).max,
+        )
+
+        # NOTE: Quantization of the min/max arguments is handled by QuantizeOperatorArguments
+        self._create_clamp_node(
+            tosa_graph,
+            inputs[0].name,
+            output.name,
+            min_int8,
+            max_int8,
+            0,
+            0,
+        )
+
+
+@register_node_visitor
+class ClampVisitor_080_MI(ClampVisitor_080_BI):
+    # inheriting 'target' from BI class
+
+    tosa_specs = [
+        TosaSpecification.create_from_string("TOSA-0.80+MI"),
+    ]
+
+    def __init__(self, *args):
+        super().__init__(*args)
+
+    def define_node(
+        self,
+        node: Node,
+        tosa_graph: ts.TosaSerializer,
+        inputs: List[TosaArg],
+        output: TosaArg,
+    ) -> None:
+        assert len(node.all_input_nodes) == 1
+
+        if inputs[0].dtype == ts.DType.INT8:
+            # Call the inherited define_node for handling integers
+            super().define_node(node, tosa_graph, inputs, output)
+        else:
+            min_fp32, max_fp32 = self._get_min_max_arguments(
+                node,
+                torch.finfo(torch.float32).min,
+                torch.finfo(torch.float32).max,
+            )
+
+            self._create_clamp_node(
+                tosa_graph,
+                inputs[0].name,
+                output.name,
+                0,
+                0,
+                min_fp32,
+                max_fp32,
+            )

backends/arm/quantizer/quantization_annotator.py

@@ -186,6 +186,8 @@ def _match_pattern(
     torch.ops.aten.full.default,
     torch.ops.aten.flatten.using_ints,
     torch.ops.aten.dropout.default,
+    torch.ops.aten.clamp.default,
+    torch.ops.aten.clamp.Tensor,
     operator.getitem,
 ]