Arm backend: Fix quantization issue in meandim decomposition (#15558)

In certain cases, avg_pool2d becomes a mean after lowering to edge. When
this happens, the meandim decomposition pass is not triggered until the
backend preprocess pipeline. To work properly, the pass needs to insert
q-dq pairs manually when this happens.

Signed-off-by: Erik Lundell <[email protected]>

Author: Erik-Lundell

backends/arm/_passes/decompose_meandim_pass.py

@@ -13,6 +13,7 @@
 from executorch.backends.arm._passes.decompose_sum_pass import DecomposeSumPass
 from executorch.backends.arm._passes.fuse_constant_ops_pass import ComputeConstantOpsAOT
 from executorch.backends.arm._passes.size_adjust_input_pass import SizeAdjustInputPass
+from executorch.backends.arm.constants import DQ_OPS, Q_OPS
 from executorch.exir.backend.utils import WhyNoPartitionReporter
 from executorch.exir.dialects._ops import ops as exir_ops
 from executorch.exir.pass_base import ExportPass
@@ -50,6 +51,15 @@ def get_view(op):
     raise RuntimeError(f"Can't get meandim decomposition for op {op}")
 
 
+def get_quantization(op):
+    """Returns quant and dequant op of same type (per_channel/ tensor) as op if op is a dequant node, None otherwise."""
+    if op in DQ_OPS:
+        # Input of op can be placeholder, can't use that to get quant node directly.
+        quant_type_index = DQ_OPS.index(op)
+        return Q_OPS[quant_type_index], op
+    return None
+
+
 class DecomposeMeanDimPass(ArmPass):
     """
     Decomposes a meandim into avg_pool and/or sum + mul (1/N) depending on which dims the mean is taken for:
@@ -121,6 +131,7 @@ def call_operator(self, op, args, kwargs, meta):
                 dims_to_reduce = [dim - 1 for dim in dims_to_reduce]
 
             x = super().call_operator(view_op, (x, new_shape), {}, meta, True)
+            x = self._maybe_insert_q_dq_after(x, meta)
 
         # Reduce (h,w) dims by avg pool if possible
         x, dims_to_reduce = self._reduce_by_average_pool(op, x, dims_to_reduce, meta)
@@ -133,7 +144,7 @@ def call_operator(self, op, args, kwargs, meta):
             dims_to_reduce = [dim + len(original_dims) - 1 for dim in dims_to_reduce]
 
             x = super().call_operator(view_op, (x, temp_shape), {}, meta, True)
-
+            x = self._maybe_insert_q_dq_after(x, meta)
         # Reduce remaining dims by sum
         x = self._reduce_by_sum(op, x, dims_to_reduce, meta, dtype)
 
@@ -156,6 +167,45 @@ def _reduce_by_sum(self, op, input_node, dims, meta, dtype):
         full = super().call_operator(
             full_op, ([1] * len(output_shape), 1 / N), {"dtype": dtype}, meta, True
         )
+        if (quant_ops := get_quantization(input_node.node.target)) is not None:
+            # Insert Q and DQ nodes after full op.
+            # Since the value of full is known, we can compute quant params such that dq(q_max_value)
+            q_op, dq_op = quant_ops
+            qmax = input_node.node.args[4]
+            full_quant_args = (
+                1 / (N * qmax),  # Scale to map qmax to 1/N
+                0,  # Zero point
+                *input_node.node.args[3:],
+            )
+            q_args = (full, *full_quant_args)
+            full = super().call_operator(
+                q_op,
+                q_args,
+                kwargs={},
+                meta=meta,
+                updated=True,
+            )
+            dq_args = (full, *full_quant_args)
+            full = super().call_operator(
+                dq_op, dq_args, kwargs={}, meta=meta, updated=True
+            )
+
+            # Insert Q and DQ nodes after sum op.
+            # Scale needs to be adjusted with N, since it was computed on data after the division with N.
+            sum_quant_args = (input_node.node.args[1] * N, *input_node.node.args[2:])
+            q_args = (sum, *sum_quant_args)
+            sum = super().call_operator(
+                q_op,
+                q_args,
+                kwargs={},
+                meta=meta,
+                updated=True,
+            )
+            dq_args = (sum, *sum_quant_args)
+            sum = super().call_operator(
+                dq_op, dq_args, kwargs={}, meta=meta, updated=True
+            )
+
         return super().call_operator(mul_op, (sum, full), {}, meta, True)
 
     def _reduce_by_average_pool(self, op, input_node, dims, meta):
@@ -190,10 +240,38 @@ def _reduce_by_average_pool(self, op, input_node, dims, meta):
         )
 
         if is_supported:
+            out = super().call_operator(avgpool_op, args, {}, meta, True)
+            out = self._maybe_insert_q_dq_after(out, meta)
             return (
-                super().call_operator(avgpool_op, args, {}, meta, True),
+                out,
                 dims_to_reduce_by_sum,
             )
 
         else:
             return input_node, dims
+
+    def _maybe_insert_q_dq_after(self, op, meta):
+        """If the input node of op is a dequant node, insert a q-dq pair after op with identical quantization parameters."""
+
+        if len(op.node.all_input_nodes) > 1:
+            raise ValueError(
+                f"Expected one input to {op.node}, got inputs {op.node.all_input_nodes}"
+            )
+        input_node = op.node.all_input_nodes[0]
+        if (quant_ops := get_quantization(input_node.target)) is not None:
+            q_op, dq_op = quant_ops
+            quant_args = list(input_node.args[1:])
+            q_args = (op, *quant_args)
+            out = super().call_operator(
+                q_op,
+                q_args,
+                kwargs={},
+                meta=meta,
+                updated=True,
+            )
+            dq_args = (out, *quant_args)
+            return super().call_operator(
+                dq_op, dq_args, kwargs={}, meta=meta, updated=True
+            )
+        else:
+            return op

backends/arm/test/ops/test_avg_pool2d.py

@@ -23,7 +23,7 @@
     VgfPipeline,
 )
 
-aten_op = "torch.ops.aten.avg_pool2d.default"
+aten_op = "avg_pool2d.default"
 exir_op = "executorch_exir_dialects_edge__ops_aten_avg_pool2d_default"
 
 input_t = Tuple[torch.Tensor]
@@ -34,6 +34,15 @@ def forward(self, *args, **kwargs):
         return super().forward(*args, **kwargs)
 
 
+class BecomesMeanInToEdge(torch.nn.Module):
+    """This averagepool will be converted to mean when lowering to edge. This causes the decompose_meandim  pass to not
+    trigger until the backend pipeline, which requires extra care.
+    """
+
+    def forward(self, x: torch.Tensor):
+        return torch.nn.functional.adaptive_avg_pool2d(x, (1, 1))
+
+
 test_modules = {
     "zeros": lambda: (AvgPool2d(4, 2, 0, False), (torch.zeros(1, 16, 50, 32),)),
     "ones": lambda: (AvgPool2d(4, 2, 0, False, True), (torch.ones(1, 16, 50, 32),)),
@@ -110,6 +119,9 @@ def forward(self, *args, **kwargs):
         AvgPool2d(3, (1, 3), 1, count_include_pad=False),
         (torch.rand(1, 16, 54, 54),),
     ),
+    "becomes_mean_rank3": lambda: (BecomesMeanInToEdge(), (torch.rand(2, 8, 8),)),
+    "becomes_mean_rank4": lambda: (BecomesMeanInToEdge(), (torch.rand(2, 2, 8, 8),)),
+    "becomes_mean_rank5": lambda: (BecomesMeanInToEdge(), (torch.rand(2, 2, 8, 8),)),
 }