Arm backend: Add correction for floor mode (#14776)

Correct implementation of div.tensor_mode for 'floor' case to make it
numerically stable.


Signed-off-by: Elena Zhelezina <[email protected]>

Author: wwwind

backends/arm/_passes/decompose_div_tensor_mode.py

@@ -22,6 +22,8 @@
     "full": exir_ops.edge.aten.full.default,
     "lt": exir_ops.edge.aten.lt.Tensor,
     "where": exir_ops.edge.aten.where.self,
+    "mul": exir_ops.edge.aten.mul.Tensor,
+    "sub": exir_ops.edge.aten.sub.Tensor,
 }
 
 aten_unary = {
@@ -31,6 +33,8 @@
     "full": torch.ops.aten.full.default,
     "lt": torch.ops.aten.lt.Tensor,
     "where": torch.ops.aten.where.self,
+    "mul": torch.ops.aten.mul.Tensor,
+    "sub": torch.ops.aten.sub.Tensor,
 }
 
 
@@ -70,13 +74,57 @@ def call_operator(self, op, args, kwargs, meta):
             return q
 
         if rounding_mode == "floor":
-            return super().call_operator(opset["floor"], (q,), {}, meta)
+            q_raw = q
+
+            # trunc(q_raw) = where(q_raw < 0, ceil(q_raw), floor(q_raw))
+            q_floor = super().call_operator(opset["floor"], (q_raw,), {}, meta)
+            q_ceil = super().call_operator(opset["ceil"], (q_raw,), {}, meta)
+
+            # a zero tensor with the right shape
+            out_shape = (1,) * len(meta["val"].size())
+            zero = super().call_operator(
+                opset["full"],
+                args=(out_shape, 0.0),
+                kwargs={},
+                meta=meta,
+            )
+
+            is_neg = super().call_operator(opset["lt"], (q_raw, zero), {}, meta)
+            q_trunc = super().call_operator(
+                opset["where"], (is_neg, q_ceil, q_floor), {}, meta
+            )
+
+            # r = a - q_trunc * b (true remainder under truncation)
+            q_times_b = super().call_operator(opset["mul"], (q_trunc, b), {}, meta)
+            r = super().call_operator(opset["sub"], (a, q_times_b), {}, meta)
+
+            # Decide if we need to subtract 1:
+            # for b > 0, adjust if r < 0; for b < 0, adjust if r > 0.
+            b_pos = super().call_operator(opset["lt"], (zero, b), {}, meta)  # b > 0
+            r_lt0 = super().call_operator(opset["lt"], (r, zero), {}, meta)  # r < 0
+            r_gt0 = super().call_operator(opset["lt"], (zero, r), {}, meta)  # r > 0
+
+            adjust_if = super().call_operator(
+                opset["where"], (b_pos, r_lt0, r_gt0), {}, meta
+            )
+
+            one = super().call_operator(
+                opset["full"],
+                args=(out_shape, 1.0),
+                kwargs={},
+                meta=meta,
+            )
+            q_minus_1 = super().call_operator(opset["sub"], (q_trunc, one), {}, meta)
+
+            return super().call_operator(
+                opset["where"], (adjust_if, q_minus_1, q_trunc), {}, meta
+            )
 
         if rounding_mode == "trunc":
             zero = super().call_operator(
                 opset["full"],
                 args=((1,) * len(meta["val"].size()), 0.0),
-                kwargs={"dtype": torch.float32},
+                kwargs={},
                 meta=meta,
             )
             lt0 = self.call_operator(opset["lt"], (q, zero), {}, meta)

backends/arm/test/ops/test_div_tensor_mode.py

@@ -36,6 +36,14 @@ def forward(self, x: torch.Tensor, y: torch.Tensor) -> torch.Tensor:
         return torch.div(x, y, rounding_mode=self.mode)
 
 
+def _rank4_large_randn_case():
+    torch.manual_seed(0)
+    x = 200 * torch.randn(5, 10, 25, 20) + 1
+    torch.manual_seed(1)
+    y = torch.rand(5, 10, 25, 20) + 1
+    return x, y
+
+
 test_data = {
     "mode_none": lambda: (None, (torch.randn(4, 8), torch.randn(4, 8).abs() + 1e-3)),
     "mode_floor": lambda: (
@@ -47,6 +55,13 @@ def forward(self, x: torch.Tensor, y: torch.Tensor) -> torch.Tensor:
         (torch.randn(4, 8), torch.randn(4, 8).abs() + 1e-3),
     ),
     "int_denominator": lambda: (None, (torch.randn(4, 8), 2)),
+    "op_floor_div_rank4_large_randn": lambda: (
+        "floor",
+        (
+            200 * torch.randn(5, 10, 25, 20) + 1,
+            torch.rand(5, 10, 25, 20) + 1,
+        ),
+    ),
 }
 
 
@@ -84,7 +99,13 @@ def test_div_tensor_mode_tosa_INT(data):
 
 @common.XfailIfNoCorstone300
 @common.parametrize(
-    "data", test_data, xfails={"mode_trunc": "CPU op missing in unittests"}
+    "data",
+    test_data,
+    xfails={
+        "mode_trunc": "CPU op missing in unittests",
+        "mode_floor": "Not supported",
+        "op_floor_div_rank4_large_randn": "Not supported",
+    },
 )
 def test_div_tensor_mode_u55_INT(data):
     mode, inputs = data()
@@ -94,9 +115,10 @@ def test_div_tensor_mode_u55_INT(data):
         model,
         inputs,
         aten_ops=model.aten_ops_int,
-        exir_ops=[],
         use_to_edge_transform_and_lower=True,
     )
+    pipeline.pop_stage("check_not.exir")
+    pipeline.pop_stage("check_count.exir")
     pipeline.run()