[quant] Use PlaceholderObserver instead of Fp16Observer and NoopObserver (#42348)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42348
Use the dtype info in placeholderObserver to decide what ops to insert in the graph
In the next PR we can delete NoopObserver
Test Plan:
python test/test_quantization.py
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D22859457
fbshipit-source-id: a5c618f22315534ebd9a2df77b14a0aece196989
