Add a16w8 MHA softmax FVP coverage for Ethos-U85 (#19493)

backends/arm/test/ops/test_softmax.py

@@ -7,6 +7,8 @@
 
 from typing import Tuple
 
+import pytest
+
 import torch
 from executorch.backends.arm.test import common
 from executorch.backends.arm.test.tester.test_pipeline import (
@@ -120,3 +122,118 @@ def test_softmax_vgf_quant(test_data):
     # TODO: MLETORCH-1136 Change args of run_method_and_compare_outputs of the vgf tests
     # pipeline.change_args("run_method_and_compare_outputs", qtol=1)
     pipeline.run()
+
+
+# ---------------------------------------------------------------------------
+# a16w8 (int16 IO + int8 weights) softmax FVP coverage.
+#
+# Sweeps a multi-head-attention-shaped softmax over a wide range of
+# pre-softmax input magnitudes to surface int16 numerics issues in the
+# lowered graph (e.g. the Ethos-U85 ReduceSum int16 silent-zero issue in the
+# softmax decomposition, fixed by the follow-up Vela patch in this stack).
+# ---------------------------------------------------------------------------
+
+
+class MultiHeadAttentionSoftmax(torch.nn.Module):
+    """Generic multi-head-attention softmax: reshape -> softmax(dim=-1) -> flatten.
+
+    H heads, M query tokens, W K/V window. Output shape: (N, T, H*M*W).
+    """
+
+    H = 4
+    M = 1
+    W = 16
+    IN_FEATURES = H * M * W  # 64
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        n, t, _ = x.shape
+        x = x.reshape(n, t, self.H, self.M, self.W)
+        x = torch.softmax(x, dim=-1)
+        x = x.reshape(n, t, self.IN_FEATURES)
+        return x
+
+
+# (input_low, input_high) per case. Keys are the parametrize ids.
+# Range coverage spans realistic post-1/sqrt(d) attention logits (typically
+# in [-10, +10]) plus a couple of wider buffer cases. atol below is sized
+# at ~1.5x the observed FVP max-abs softmax error across the sweep at
+# qtol=0, measured against the quantized reference.
+mha_softmax_sweep = {
+    "range_neg0p01_to_0p01": (-0.01, 0.01),
+    "range_neg0p1_to_0p1": (-0.1, 0.1),
+    "range_neg1_to_1": (-1.0, 1.0),
+    "range_neg3_to_3": (-3.0, 3.0),
+    "range_neg5_to_5": (-5.0, 5.0),
+    "range_neg10_to_10": (-10.0, 10.0),
+    "range_neg30_to_30": (-30.0, 30.0),
+}
+
+_MHA_ATOL = 0.003
+
+
+def _make_mha_softmax_inputs(
+    input_low: float, input_high: float, num_test: int = 8, seed: int = 42
+) -> Tuple[torch.Tensor]:
+    # Local Generator so this helper does not mutate the global RNG state
+    # and the test suite stays order-independent.
+    gen = torch.Generator().manual_seed(seed)
+    span = input_high - input_low
+    return (
+        torch.rand(
+            num_test,
+            1,
+            MultiHeadAttentionSoftmax.IN_FEATURES,
+            generator=gen,
+        )
+        * span
+        + input_low,
+    )
+
+
+@common.parametrize("sweep_case", mha_softmax_sweep)
+@common.XfailIfNoCorstone300
+def test_mha_softmax_a16w8_u55_INT(sweep_case: Tuple[float, float]) -> None:
+    input_low, input_high = sweep_case
+    pipeline = EthosU55PipelineINT[input_t1](
+        MultiHeadAttentionSoftmax(),
+        _make_mha_softmax_inputs(input_low, input_high),
+        [],
+        exir_ops=[],
+        a16w8_quantization=True,
+        symmetric_io_quantization=True,
+        epsilon=2**-16,
+        atol=_MHA_ATOL,
+    )
+    pipeline.add_stage_after("quantize", pipeline.tester.check_not, [aten_op])
+    pipeline.run()
+
+
+# All cases hit the Ethos-U85 int16 ReduceSum silent-zero issue inside the
+# softmax decomposition. strict=False so the test target stays green both
+# on stock Vela 5.0 (cases XFAIL) and once the upstream Vela fix lands
+# (cases XPASS).
+# Upstream report:
+#   https://gitlab.arm.com/artificial-intelligence/ethos-u/ethos-u-vela/-/issues/23
+@common.parametrize("sweep_case", mha_softmax_sweep)
+@common.XfailIfNoCorstone320
+@pytest.mark.xfail(
+    reason=(
+        "Ethos-U85 int16 ReduceSum silent-zero in softmax decomposition: "
+        "https://gitlab.arm.com/artificial-intelligence/ethos-u/ethos-u-vela/-/issues/23"
+    ),
+    strict=False,
+)
+def test_mha_softmax_a16w8_u85_INT(sweep_case: Tuple[float, float]) -> None:
+    input_low, input_high = sweep_case
+    pipeline = EthosU85PipelineINT[input_t1](
+        MultiHeadAttentionSoftmax(),
+        _make_mha_softmax_inputs(input_low, input_high),
+        [],
+        exir_ops=[],
+        a16w8_quantization=True,
+        symmetric_io_quantization=True,
+        epsilon=2**-16,
+        atol=_MHA_ATOL,
+    )
+    pipeline.add_stage_after("quantize", pipeline.tester.check_not, [aten_op])
+    pipeline.run()

backends/arm/test/targets.bzl

@@ -29,6 +29,7 @@ def define_arm_tests():
         "ops/test_rsqrt.py",
         "ops/test_slice.py",
         "ops/test_sigmoid.py",
+        "ops/test_softmax.py",
         "ops/test_sub.py",
         "ops/test_sum.py",
         "ops/test_tanh.py",