[quant] Fix per channel weight observer (pytorch#85883)

Summary: `per_channel_weight_observer_range_neg_127_to_127` now correctly uses `PerChannelMinMaxObserver` instead of `MinMaxObserver`

Test Plan:
Adds a new test `quantization.core.test_top_level_apis
` to instansiate and run `forward()` on all `default` observers

Differential Revision: D39916482

Pull Request resolved: pytorch#85883
Approved by: https://github.com/salilsdesai

test/quantization/core/test_top_level_apis.py

@@ -0,0 +1,61 @@
+# Owner(s): ["oncall: quantization"]
+
+import torch
+import torch.ao.quantization
+from torch.testing._internal.common_utils import TestCase
+
+
+class TestDefaultObservers(TestCase):
+    observers = [
+        "default_affine_fixed_qparams_observer",
+        "default_debug_observer",
+        "default_dynamic_quant_observer",
+        "default_placeholder_observer",
+        "default_fixed_qparams_range_0to1_observer",
+        "default_fixed_qparams_range_neg1to1_observer",
+        "default_float_qparams_observer",
+        "default_float_qparams_observer_4bit",
+        "default_histogram_observer",
+        "default_observer",
+        "default_per_channel_weight_observer",
+        "default_reuse_input_observer",
+        "default_symmetric_fixed_qparams_observer",
+        "default_weight_observer",
+        "per_channel_weight_observer_range_neg_127_to_127",
+        "weight_observer_range_neg_127_to_127",
+    ]
+
+    fake_quants = [
+        "default_affine_fixed_qparams_fake_quant",
+        "default_dynamic_fake_quant",
+        "default_embedding_fake_quant",
+        "default_embedding_fake_quant_4bit",
+        "default_fake_quant",
+        "default_fixed_qparams_range_0to1_fake_quant",
+        "default_fixed_qparams_range_neg1to1_fake_quant",
+        "default_fused_act_fake_quant",
+        "default_fused_per_channel_wt_fake_quant",
+        "default_fused_wt_fake_quant",
+        "default_histogram_fake_quant",
+        "default_per_channel_weight_fake_quant",
+        "default_symmetric_fixed_qparams_fake_quant",
+        "default_weight_fake_quant",
+        "fused_per_channel_wt_fake_quant_range_neg_127_to_127",
+        "fused_wt_fake_quant_range_neg_127_to_127",
+    ]
+
+    def _get_observer_ins(self, observer):
+        obs_func = getattr(torch.ao.quantization, observer)
+        return obs_func()
+
+    def test_observers(self) -> None:
+        t = torch.rand(1, 2, 3, 4)
+        for observer in self.observers:
+            obs = self._get_observer_ins(observer)
+            obs.forward(t)
+
+    def test_fake_quants(self) -> None:
+        t = torch.rand(1, 2, 3, 4)
+        for observer in self.fake_quants:
+            obs = self._get_observer_ins(observer)
+            obs.forward(t)

torch/ao/quantization/fake_quantize.py

@@ -428,12 +428,14 @@ def forward(self, X: torch.Tensor) -> torch.Tensor:
 Fused version of `default_weight_fake_quant`, with the 8-bit values restricted to [-127, +127], excluding -128.
 """
 
-fused_per_channel_wt_fake_quant_range_neg_127_to_127 = FusedMovingAvgObsFakeQuantize.with_args(observer=MovingAverageMinMaxObserver,
-                                                                                               quant_min=-127,
-                                                                                               quant_max=127,
-                                                                                               dtype=torch.qint8,
-                                                                                               qscheme=torch.per_channel_symmetric,
-                                                                                               eps=2 ** -12)
+fused_per_channel_wt_fake_quant_range_neg_127_to_127 = \
+    FusedMovingAvgObsFakeQuantize.with_args(observer=MovingAveragePerChannelMinMaxObserver,
+                                            quant_min=-127,
+                                            quant_max=127,
+                                            dtype=torch.qint8,
+                                            qscheme=torch.per_channel_symmetric,
+                                            eps=2 ** -12)
+
 """
 Fused version of `default_per_channel_weight_fake_quant`, with the 8-bit values restricted to [-127, +127], excluding -128.
 """

torch/ao/quantization/observer.py

@@ -1543,7 +1543,7 @@ def load_observer_state_dict(mod, obs_dict):
 weight quantization is supported, such as `fbgemm`.
 """
 
-per_channel_weight_observer_range_neg_127_to_127 = MinMaxObserver.with_args(
+per_channel_weight_observer_range_neg_127_to_127 = PerChannelMinMaxObserver.with_args(
     dtype=torch.qint8, qscheme=torch.per_channel_symmetric,
     quant_min=-127, quant_max=127, eps=2 ** -12)
 """