fix(mge/optimizer): fix optimizer update step inplace add grad

GitOrigin-RevId: d677d1ca6b

imperative/python/megengine/optimizer/adadelta.py

@@ -84,7 +84,7 @@ class Adadelta(Optimizer):
             step += c1
             grad = param.grad
             if weight_decay != 0.0:
-                grad += param * _weight_decay
+                grad = grad + param * _weight_decay
 
             square_avg = states["square_avg"]
             acc_delta = states["acc_delta"]

imperative/python/megengine/optimizer/adagrad.py

@@ -82,7 +82,7 @@ class Adagrad(Optimizer):
             step += c1
             grad = param.grad
             if weight_decay != 0.0:
-                grad += param * _weight_decay
+                grad = grad + param * _weight_decay
 
             square_avg = states["square_avg"]
             square_avg += grad ** c2

imperative/python/megengine/optimizer/adam.py

@@ -85,7 +85,7 @@ class Adam(Optimizer):
 
             grad = param.grad
             if weight_decay != 0.0:
-                grad += param * _weight_decay
+                grad = grad + param * _weight_decay
 
             states = self._state[param]
 

imperative/python/megengine/optimizer/sgd.py

@@ -72,7 +72,7 @@ class SGD(Optimizer):
 
             grad = param.grad
             if weight_decay != 0.0:
-                grad += param * _weight_decay
+                grad = grad + param * _weight_decay
 
             if inplace_mode:
                 if momentum: