fix(loss): drop dead None stores flagged by CodeQL

The inv/_nf/_nloc locals are only read inside if maskf is not None
guards, so the = None fallbacks in the else branch were dead stores
(their None value is never read). CodeQL flagged all three per file as
unused. Remove them and note why the names can stay unset when maskf is
None. Pure no-op: no runtime behavior change.

Author: Han Wang

deepmd/dpmodel/loss/ener.py

@@ -232,10 +232,9 @@ def call(
             _nf = maskf.shape[0]
             _nloc = maskf.shape[1]
         else:
+            # inv, _nf, _nloc are only read inside ``if maskf is not None`` guards,
+            # so leaving them unset here is safe (and avoids dead-store warnings).
             maskf = None
-            inv = None
-            _nf = None
-            _nloc = None
 
         if self.enable_atom_ener_coeff:
             # when ener_coeff (\nu) is defined, the energy is defined as

deepmd/dpmodel/loss/ener_spin.py

@@ -141,10 +141,9 @@ def call(
             _nf = maskf.shape[0]
             _nloc = maskf.shape[1]
         else:
+            # inv, _nf, _nloc are only read inside ``if maskf is not None`` guards,
+            # so leaving them unset here is safe (and avoids dead-store warnings).
             maskf = None
-            inv = None
-            _nf = None
-            _nloc = None
 
         if self.has_e:
             energy_pred = model_dict["energy"]

deepmd/pt/loss/ener.py

@@ -248,10 +248,9 @@ def forward(
             _nf = maskf.shape[0]
             _nloc = maskf.shape[1]
         else:
+            # inv, _nf, _nloc are only read inside ``if maskf is not None`` guards,
+            # so leaving them unset here is safe (and avoids dead-store warnings).
             maskf = None
-            inv = None
-            _nf = None
-            _nloc = None
         # Normalization exponent controls loss scaling with system size:
         # - norm_exp=2 (intensive_ener_virial=True): loss uses 1/N² scaling, making it independent of system size
         # - norm_exp=1 (intensive_ener_virial=False, legacy): loss uses 1/N scaling, which varies with system size

deepmd/pt/loss/ener_spin.py

@@ -169,10 +169,9 @@ def forward(
             _nf = maskf.shape[0]
             _nloc = maskf.shape[1]
         else:
+            # inv, _nf, _nloc are only read inside ``if maskf is not None`` guards,
+            # so leaving them unset here is safe (and avoids dead-store warnings).
             maskf = None
-            inv = None
-            _nf = None
-            _nloc = None
 
         if self.has_e and "energy" in model_pred and "energy" in label:
             energy_pred = model_pred["energy"]