ekalda commented on a change in pull request #9547:
URL: https://github.com/apache/tvm/pull/9547#discussion_r757438005
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File path: python/tvm/relay/backend/contrib/ethosu/legalize.py
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@@ -123,6 +124,80 @@ def __call__(self, *args, **kwargs):
pass
+def round_away_zero(f):
+ r = -0.5 if (f < 0) else 0.5
+ return np.trunc(f + r)
+
+
+def find_tanh_values(ifm_scale, ifm_zp, ofm_scale, ofm_zp):
+ """Method to calculate the values of the tanh lookup table"""
+ lut_values = list()
+ # Only int8 is currently supported
+ dtype = np.int8
+ qmin, qmax = np.iinfo(dtype).min, np.iinfo(dtype).max
+ for x in range(qmin, qmax + 1):
+ x_real = ifm_scale * (x - ifm_zp)
+ out_real = math.tanh(x_real)
+ lut_result = int(round_away_zero(ofm_zp + out_real / ofm_scale))
+ lut_result = min(qmax, max(qmin, lut_result))
+ lut_values.append(lut_result)
+
+ return lut_values
+
+
+class TanhRewriter(DFPatternCallback):
+ """This pass adds tanh as a LUT to the identity operator"""
+
+ def __init__(self):
+ super().__init__(require_type=True, rewrite_once=True)
+ self.pattern = (
+ wildcard().has_attr({"Composite":
ethosu_patterns.TanhParams.composite_name})
+ )(wildcard())
+
+ def callback(self, pre, post, node_map):
+ id_input = post.args[0]
+
+ quantize_args = post.op.body.args
+ output_scale = float(quantize_args[1].data.asnumpy())
+ output_zp = int(quantize_args[2].data.asnumpy())
+
+ dequantize_args = quantize_args[0].args[0].args
+ input_scale = float(dequantize_args[1].data.asnumpy())
+ input_zp = int(dequantize_args[2].data.asnumpy())
+
+ lut_values = find_tanh_values(input_scale, input_zp, output_scale,
output_zp)
+ lut = relay.const(lut_values, dtype="uint8")
Review comment:
Currently, the values are calculated for an `int8` activation and then
cast into `uint8` due to that can of worms dtype problem in the
`tir_to_cs_translator.py`
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