FixedQParamsFakeQuantize: adjust default quant_min and quant_max (#47423)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47423
Since the dtype of this fake_quant is `quint8`, the output range should be
from 0 to 255. Fixing. This should address the numerical inaccuracies with
sigmoid and hardsigmoid with `FixedQParamsFakeQuantize` attached compared
to their quantized counterparts.
In a future PR, might be safer to also make the activation functions
using `FixedQParamsFakeQuantize` to explicitly specify their expected
output range and zero_point. Leaving that for later, as this bugfix
should be landed urgently.
Test Plan:
Manual script which gives low SQNR before this PR and high SQNR after
this PR: https://gist.github.com/vkuzo/9906bae29223da72b10d6b6aafadba42
https://github.com/pytorch/pytorch/pull/47376, which can be landed after
this, adds a proper test.
Imported from OSS
Reviewed By: ayush29feb, jerryzh168
Differential Revision: D24751497
fbshipit-source-id: 4c32e22a30116caaceeedb4cd47146d066054a89
