Avoid in-place ops during logging result updates

CHANGELOG.md

@@ -407,6 +407,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed wrong typehint for `Trainer.lightning_optimizers` ([#11155](https://github.com/PyTorchLightning/pytorch-lightning/pull/11155))
 
 
+- Fixed type promotion when tensors of higher category than float are logged ([#11401](https://github.com/PyTorchLightning/pytorch-lightning/pull/11401))
+
+
 - Fixed the lr-scheduler state not being dumped to checkpoint when using the deepspeed strategy ([#11307](https://github.com/PyTorchLightning/pytorch-lightning/pull/11307))
 
 

pytorch_lightning/trainer/connectors/logger_connector/result.py

@@ -216,6 +216,7 @@ def __init__(self, metadata: _Metadata, is_tensor: bool) -> None:
             # do not set a dtype in case the default dtype was changed
             self.add_state("value", torch.tensor(default), dist_reduce_fx=torch.sum)
             if self.meta.is_mean_reduction:
+                self.cumulated_batch_size: torch.Tensor
                 self.add_state("cumulated_batch_size", torch.tensor(0), dist_reduce_fx=torch.sum)
         # this is defined here only because upstream is missing the type annotation
         self._forward_cache: Optional[Any] = None
@@ -241,14 +242,13 @@ def update(self, value: _IN_METRIC, batch_size: int) -> None:  # type: ignore[ov
 
             # perform accumulation with reduction
             if self.meta.is_mean_reduction:
-                self.value += value.mean() * batch_size
-                # `Metric.add_state` does not work well with mypy, mypy doesn't know this is a `Tensor`
-                # we could add an assertion, but this is a hot code path
-                self.cumulated_batch_size += batch_size  # type: ignore[operator]
+                # do not use `+=` as it doesn't do type promotion
+                self.value = self.value + value.mean() * batch_size
+                self.cumulated_batch_size = self.cumulated_batch_size + batch_size
             elif self.meta.is_max_reduction or self.meta.is_min_reduction:
                 self.value = self.meta.reduce_fx(self.value, value.mean())
             elif self.meta.is_sum_reduction:
-                self.value += value.mean()
+                self.value = self.value + value.mean()
         else:
             value = cast(Metric, value)
             self.value = value

tests/core/test_metric_result_integration.py

@@ -590,6 +590,26 @@ def test_metric_result_respects_dtype(floating_dtype):
     torch.set_default_dtype(torch.float)
 
 
+@pytest.mark.parametrize("reduce_fx", ("mean", sum))
+def test_metric_result_dtype_promotion(reduce_fx):
+    metadata = _Metadata("foo", "bar", reduce_fx=reduce_fx)
+    metadata.sync = _Sync()
+    rm = _ResultMetric(metadata, is_tensor=True)
+    assert rm.value.dtype == torch.float
+
+    # log a double
+    rm.update(torch.tensor(0, dtype=torch.double), 1)
+    # `rm.value.dtype` is promoted
+    assert rm.value.dtype == torch.double
+    # log a float
+    rm.update(torch.tensor(0, dtype=torch.float), 1)
+    # the previous dtype stays
+    assert rm.value.dtype == torch.double
+
+    total = rm.compute()
+    assert total.dtype == torch.double
+
+
 @pytest.mark.parametrize(["reduce_fx", "expected"], [(max, -2), (min, 2)])
 def test_result_metric_max_min(reduce_fx, expected):
     metadata = _Metadata("foo", "bar", reduce_fx=reduce_fx)