Fix filtering function fallback mechanism (#2953)

Summary:
lfilter, overdrive have faster implementation written in C++. If they are not available, torchaudio is supposed to fall back on Python-based implementation.

The original fallback mechanism relied on error type and messages from PyTorch core, which has been changed.

This commit updates it for more proper fallback mechanism.

Pull Request resolved: https://github.com/pytorch/audio/pull/2953

Reviewed By: hwangjeff

Differential Revision: D42344893

Pulled By: mthrok

fbshipit-source-id: 18ce5c1aa1c69d0d2ab469b0b0c36c0221f5ccfd

torchaudio/functional/filtering.py

@@ -5,6 +5,8 @@ from typing import Optional
 import torch
 from torch import Tensor
 
+from torchaudio._extension import _IS_TORCHAUDIO_EXT_AVAILABLE
+
 
 def _dB2Linear(x: float) -> float:
     return math.exp(x * math.log(10) / 20.0)
@@ -929,11 +931,9 @@ def _lfilter_core_generic_loop(input_signal_windows: Tensor, a_coeffs_flipped: T
         padded_output_waveform[:, :, i_sample + n_order - 1] = o0
 
 
-try:
+if _IS_TORCHAUDIO_EXT_AVAILABLE:
     _lfilter_core_cpu_loop = torch.ops.torchaudio._lfilter_core_loop
-except RuntimeError as err:
-    if str(err) != "No such operator torchaudio::_lfilter_core_loop":
-        raise
+else:
     _lfilter_core_cpu_loop = _lfilter_core_generic_loop
 
 
@@ -991,11 +991,9 @@ def _lfilter_core(
     return output
 
 
-try:
+if _IS_TORCHAUDIO_EXT_AVAILABLE:
     _lfilter = torch.ops.torchaudio._lfilter
-except RuntimeError as err:
-    if str(err) != "No such operator torchaudio::_lfilter":
-        raise
+else:
     _lfilter = _lfilter_core
 
 
@@ -1109,11 +1107,9 @@ def _overdrive_core_loop_generic(
         output_waveform[:, i] = waveform[:, i] * 0.5 + last_out * 0.75
 
 
-try:
+if _IS_TORCHAUDIO_EXT_AVAILABLE:
     _overdrive_core_loop_cpu = torch.ops.torchaudio._overdrive_core_loop
-except RuntimeError as err:
-    if str(err) != "No such operator torchaudio::_overdrive_core_loop":
-        raise
+else:
     _overdrive_core_loop_cpu = _overdrive_core_loop_generic