MLBEDSW-6909: Use int32 acc for the Mean op

Changed acc type from int16 to int32. This will solve
saturation problems and the constraint added in
commit "MLBEDSW-5029: Output diff for Mean op"
can be removed.

Signed-off-by: Johan Alfven <johan.alfven@arm.com>
Change-Id: I05ec8835b43313b1a264d61a2b147fa62da123fe

1 files changed, 6 insertions, 40 deletions

diff --git a/ethosu/vela/tflite_supported_operators.py b/ethosu/vela/tflite_supported_operators.py
index f01a6690..24cc26e0 100644
--- a/ethosu/vela/tflite_supported_operators.py
+++ b/ethosu/vela/tflite_supported_operators.py
@@ -796,9 +796,10 @@ class TFLiteSupportedOperators:
         max_prod = cls.mean_kernel_product
         return h * w <= max_prod, f"Product of height and width is {h * w}"
 
-    @staticmethod
-    def constraint_mean_height_width_product_int8(op):
-        """Number of IFM height and width elements might cause accumulator saturation when;
+    @classmethod
+    @docstring_format_args([mean_kernel_product_int8])
+    def constraint_mean_height_width_product_int8(cls, op):
+        """Product of IFM height and width must be no greater than {} when:
         The IFM shape has 4 dimensions; and
         The axis indices specify reduction across 2 dimensions; and
         The axis indices correspond to the width and height dimensions of the IFM; and
@@ -817,43 +818,8 @@ class TFLiteSupportedOperators:
             return True, ""
         h = shape[-3]
         w = shape[-2]
-
-        ifmq, ofmq = op.ifm.quantization, op.ofm.quantization
-
-        # Scale factor
-        real_scale = ifmq.scale_f32 / ofmq.scale_f32
-
-        # Min and max value
-        ifm_min_val = np.iinfo(np.int8).min - ifmq.zero_point
-        ifm_max_val = np.iinfo(np.int8).max - ifmq.zero_point
-
-        # Accumulator limits
-        min_acc_limit = np.iinfo(np.int16).min
-        max_acc_limit = np.iinfo(np.int16).max
-
-        # Theoretical max/min value that accumulator need to store
-        min_acc_sum = h * w * ifm_min_val * real_scale + ofmq.zero_point
-        max_acc_sum = h * w * ifm_max_val * real_scale + ofmq.zero_point
-
-        # Max product of heigth and width that will not saturate the accumulator
-        ifm_min_val = 1 if ifm_min_val == 0 else ifm_min_val
-        ifm_max_val = 1 if ifm_max_val == 0 else ifm_max_val
-        if max_acc_sum > abs(min_acc_sum):
-            max_hw = int((max_acc_limit - ofmq.zero_point) / real_scale / ifm_max_val)
-        else:
-            max_hw = int((min_acc_limit - ofmq.zero_point) / real_scale / ifm_min_val)
-
-        extra = []
-
-        extra.append(f"   Possible accumulator range is ({min_acc_sum} - {max_acc_sum})\n")
-        extra.append(f"   Maximum  accumulator range is ({min_acc_limit} - {max_acc_limit})\n")
-        extra.append(
-            f"   Based on the IFM and OFM quantization the IFM height and width must be no greater than {max_hw}"
-        )
-
-        extra = "".join(extra)
-
-        return (min_acc_sum >= min_acc_limit and max_acc_sum <= max_acc_limit, f"\n{extra}")
+        max_prod = cls.mean_kernel_product_int8
+        return h * w <= max_prod, f"Product of height and width is {h * w}"
 
     @classmethod
     @docstring_format_args([filter_height_range[1], dilated_height_range[1]])