Issue 33387: Simplify bytecodes for try-finally, try-except and with blocks.

The six complex bytecodes currently used for implementing 'with' and 'try' statements can be replaced with just two simpler bytecodes.
The six bytecodes are WITH_CLEANUP_START, WITH_CLEANUP_FINISH,
BEGIN_FINALLY, END_FINALLY, CALL_FINALLY and POP_FINALLY.
They can be replaced with RERAISE and WITH_EXCEPT_FINISH.

See https://bugs.python.org/issue32949 for more details of the new bytecodes and how they are used in the 'with' statement.

The try-finally statement can be implemented broadly as 
   SETUP_FINALLY except
   try-body
   POP_BLOCK
   finally-body
   JUMP exit
except:
   finally-body
exit:

What would be the best way to resolve the discussion between this and issue 32949?  Would it be good to try to get one of them into 3.8?

Mark merged his PR 6641 but forgot to mention bpo-33387:

commit fee552669f21ca294f57fe0df826945edc779090
Author: Mark Shannon <mark@hotpy.org>
Date:   Thu Nov 21 09:11:43 2019 +0000

    Produce cleaner bytecode for 'with' and 'async with' by generating separate code for normal and exceptional paths. (#6641)
    
    Remove BEGIN_FINALLY, END_FINALLY, CALL_FINALLY and POP_FINALLY bytecodes. Implement finally blocks by code duplication.
    Reimplement frame.lineno setter using line numbers rather than bytecode offsets.

The new doc seems to use Python version 3.8, but the change was merged into master which is the future Python 3.9, no?

 .. opcode:: RERAISE 

     Re-raises the exception currently on top of the stack. 

     .. versionadded:: 3.8

Thanks for noticing.
https://github.com/python/cpython/pull/17318

New changeset 82f897bf8f72d09f537054d64a94e645ad23d8d6 by Mark Shannon in branch 'master':
Correct release version to 3.9 for RERAISE and WITH_EXCEPT_START bytecodes. (#17318)
https://github.com/python/cpython/commit/82f897bf8f72d09f537054d64a94e645ad23d8d6

sweet! =)

Can this issue be closed now?

New changeset 629023c05be24fa2f01c914c739aaa5a61a0304c by Victor Stinner in branch 'master':
bpo-33387: Fix compiler warning in frame_block_unwind() (GH-18099)
https://github.com/python/cpython/commit/629023c05be24fa2f01c914c739aaa5a61a0304c

The 3.9 changelog mentions WITH_EXCEPT_FINISH but that seems to have ultimately been called WITH_EXCEPT_START, maybe it shoudl be updated also?

Yes, thanks for pointing that out.

I'm reopening this to delete an obsolete comment left behind.

There's another place that needs to be updated: https://docs.python.org/3/library/dis.html#opcode-SETUP_WITH

need to replace WITH_CLEANUP_START by WITH_EXCEPT_START

New changeset dea5bf9d15999bfcc58095b157c0678d45b00bdd by Irit Katriel in branch 'master':
bpo-33387: update documentation for exception handling opcode changes (GH-24334)
https://github.com/python/cpython/commit/dea5bf9d15999bfcc58095b157c0678d45b00bdd

pull_requests: + pull_request21729