From: @bairongz
Reviewed-by: 
Signed-off-by:

From: @liangzhibo
Reviewed-by: @zh_qh,@chenfei52
Signed-off-by: @zh_qh

From: @liangzhibo
Reviewed-by: @zh_qh,@chenfei52
Signed-off-by: @zh_qh

From: @liangzhibo
Reviewed-by: @chenfei52
Signed-off-by:

Merge pull request !7838 from LiangZhibo/master

Merge pull request !6032 from vlne-v1/change_ops_import

Merge pull request !5172 from riemann_penn/remove_name_args_from_gradoperation

Merge pull request !3071 from zhangbuxue/change_ValueError_to_TypeError_for_enumerate_start

Merge pull request !2875 from wangqiuliang/add-grad-all-in-pynative

add comment for control_depend

pynative.

To handle 'break' and 'continue' statement, a loop context is pushed
to a stack before we parse the loop body, and pop it after body parsed.
When a 'break', 'continue' statement is encountered, we retrieve current
loop contex from the stack, and let the current block jump to the end
block or header block;

For 'break' statement, we added an extra 'end_block' follow the 'after_block',
because 'after_block' is called from a ContionalJump in 'header_block', it can
not be set as jump target from other place. to support 'break', we let loop
body jump to the 'end_block' at the 'break' point. and 'after_block'
maybe a good place to handle loop 'else' clause in the future.

Handle 'pass' is simple, just bypass it when doing parse.