functionalization: remove some unnecessary view_copies in inplace views

Pull Request resolved: pytorch#77713

Approved by: https://github.com/ezyang

aten/src/ATen/FunctionalTensorWrapper.cpp

@@ -146,9 +146,7 @@ void FunctionalTensorWrapper::mutate_view_meta(at::functionalization::ViewMeta m
   // So, these ops are special - they're mutation AND view ops. They get special codegen.
   // An example is transpose_, e.g. `a.transpose_()`
   // Calling transpose_() should ensure that a gets an alias, and append the new ViewMeta to a's current list of ViewMetas.
-  // We also need to force a sync (even if a is already up to date), because a's underlying tensor hasn't actually
-  // been updated to reflect the new view yet.
-  regenerate_from_base();
+  value_ = meta.forward_fn(value_, meta.out_index);
 }
 
 // Note [Functionalization: Mutation Removal]

test/test_functionalization.py

@@ -376,36 +376,29 @@ def f(x):
 $2 = torch._ops.aten.view_copy.default($1, [8])
 $3 = torch._ops.aten._reshape_alias_copy.default($2, [2, 4], [4, 1])
 $4 = torch._ops.aten.transpose_copy.int($3, 1, 0)
-$5 = torch._ops.aten.view_copy.default($1, [8])
-$6 = torch._ops.aten._reshape_alias_copy.default($5, [2, 4], [4, 1])
-$7 = torch._ops.aten.transpose_copy.int($6, 1, 0)
-$8 = torch._ops.aten.unsqueeze_copy.default($7, 0)
-$9 = torch._ops.aten.view_copy.default($1, [8])
-$10 = torch._ops.aten._reshape_alias_copy.default($9, [2, 4], [4, 1])
-$11 = torch._ops.aten.transpose_copy.int($10, 1, 0)
-$12 = torch._ops.aten.unsqueeze_copy.default($11, 0)
-$13 = torch._ops.aten.squeeze_copy.default($12)
-$14, $15 = torch._ops.aten.split_copy.Tensor($13, 2)
-$16 = torch._ops.aten.add.Tensor($14, tensor([[1., 1.],
+$5 = torch._ops.aten.unsqueeze_copy.default($4, 0)
+$6 = torch._ops.aten.squeeze_copy.default($5)
+$7, $8 = torch._ops.aten.split_copy.Tensor($6, 2)
+$9 = torch._ops.aten.add.Tensor($7, tensor([[1., 1.],
         [1., 1.]]))
-$17 = torch._ops.aten.select_copy.int($3, 0, 0)
-$18 = torch._ops.aten.clone.default($16, memory_format=torch.contiguous_format)
-$19 = torch._ops.aten._unsafe_view.default($18, [4])
-$20 = torch._ops.aten.view_copy.default($1, [8])
-$21 = torch._ops.aten._reshape_alias_copy.default($20, [2, 4], [4, 1])
-$22 = torch._ops.aten.transpose_copy.int($21, 1, 0)
-$23 = torch._ops.aten.unsqueeze_copy.default($22, 0)
-$24 = torch._ops.aten.squeeze_copy.default($23)
-$25 = torch._ops.aten.slice_scatter.default($24, $16, 0, 0, 2)
-$26 = torch._ops.aten.unsqueeze_copy.default($25, 0)
-$27 = torch._ops.aten.squeeze_copy.dim($26, 0)
-$28 = torch._ops.aten.transpose_copy.int($27, 1, 0)
-$29 = torch._ops.aten._reshape_alias_copy.default($28, [8], [1])
-$30 = torch._ops.aten.view_copy.default($29, [4, 2])
-$31 = torch._ops.aten.view_copy.default($30, [8])
-$32 = torch._ops.aten._reshape_alias_copy.default($31, [2, 4], [4, 1])
-$33 = torch._ops.aten.select_copy.int($32, 0, 0)
-$34 = torch._ops.aten.add.Tensor($33, $19)""")
+$10 = torch._ops.aten.select_copy.int($3, 0, 0)
+$11 = torch._ops.aten.clone.default($9, memory_format=torch.contiguous_format)
+$12 = torch._ops.aten._unsafe_view.default($11, [4])
+$13 = torch._ops.aten.view_copy.default($1, [8])
+$14 = torch._ops.aten._reshape_alias_copy.default($13, [2, 4], [4, 1])
+$15 = torch._ops.aten.transpose_copy.int($14, 1, 0)
+$16 = torch._ops.aten.unsqueeze_copy.default($15, 0)
+$17 = torch._ops.aten.squeeze_copy.default($16)
+$18 = torch._ops.aten.slice_scatter.default($17, $9, 0, 0, 2)
+$19 = torch._ops.aten.unsqueeze_copy.default($18, 0)
+$20 = torch._ops.aten.squeeze_copy.dim($19, 0)
+$21 = torch._ops.aten.transpose_copy.int($20, 1, 0)
+$22 = torch._ops.aten._reshape_alias_copy.default($21, [8], [1])
+$23 = torch._ops.aten.view_copy.default($22, [4, 2])
+$24 = torch._ops.aten.view_copy.default($23, [8])
+$25 = torch._ops.aten._reshape_alias_copy.default($24, [2, 4], [4, 1])
+$26 = torch._ops.aten.select_copy.int($25, 0, 0)
+$27 = torch._ops.aten.add.Tensor($26, $12)""")
 
     def test_reapply_views_simple(self):
         def f(x):