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Produce cleaner bytecode for 'with' and 'async with' by generating separate code for normal and exceptional paths. (python#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.
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Lines changed: 4779 additions & 4744 deletions

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‎Doc/library/dis.rst‎

Lines changed: 9 additions & 76 deletions
Original file line numberDiff line numberDiff line change
@@ -706,50 +706,21 @@ iterations of the loop.
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popped values are used to restore the exception state.
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.. opcode:: POP_FINALLY (preserve_tos)
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.. opcode:: RERAISE
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Cleans up the value stack and the block stack. If *preserve_tos* is not
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``0`` TOS first is popped from the stack and pushed on the stack after
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performing other stack operations:
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Re-raises the exception currently on top of the stack.
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* If TOS is ``NULL`` or an integer (pushed by :opcode:`BEGIN_FINALLY`
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or :opcode:`CALL_FINALLY`) it is popped from the stack.
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* If TOS is an exception type (pushed when an exception has been raised)
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6 values are popped from the stack, the last three popped values are
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used to restore the exception state. An exception handler block is
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removed from the block stack.
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.. versionadded:: 3.8
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It is similar to :opcode:`END_FINALLY`, but doesn't change the bytecode
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counter nor raise an exception. Used for implementing :keyword:`break`,
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:keyword:`continue` and :keyword:`return` in the :keyword:`finally` block.
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.. versionadded:: 3.8
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.. opcode:: BEGIN_FINALLY
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Pushes ``NULL`` onto the stack for using it in :opcode:`END_FINALLY`,
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:opcode:`POP_FINALLY`, :opcode:`WITH_CLEANUP_START` and
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:opcode:`WITH_CLEANUP_FINISH`. Starts the :keyword:`finally` block.
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.. versionadded:: 3.8
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.. opcode:: WITH_EXCEPT_START
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Calls the function in position 7 on the stack with the top three
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items on the stack as arguments.
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Used to implement the call ``context_manager.__exit__(*exc_info())`` when an exception
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has occurred in a :keyword:`with` statement.
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.. opcode:: END_FINALLY
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Terminates a :keyword:`finally` clause. The interpreter recalls whether the
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exception has to be re-raised or execution has to be continued depending on
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the value of TOS.
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* If TOS is ``NULL`` (pushed by :opcode:`BEGIN_FINALLY`) continue from
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the next instruction. TOS is popped.
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* If TOS is an integer (pushed by :opcode:`CALL_FINALLY`), sets the
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bytecode counter to TOS. TOS is popped.
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* If TOS is an exception type (pushed when an exception has been raised)
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6 values are popped from the stack, the first three popped values are
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used to re-raise the exception and the last three popped values are used
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to restore the exception state. An exception handler block is removed
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from the block stack.
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.. versionadded:: 3.8
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.. opcode:: LOAD_ASSERTION_ERROR
@@ -780,35 +751,6 @@ iterations of the loop.
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.. versionadded:: 3.2
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.. opcode:: WITH_CLEANUP_START
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Starts cleaning up the stack when a :keyword:`with` statement block exits.
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At the top of the stack are either ``NULL`` (pushed by
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:opcode:`BEGIN_FINALLY`) or 6 values pushed if an exception has been
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raised in the with block. Below is the context manager's
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:meth:`~object.__exit__` or :meth:`~object.__aexit__` bound method.
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If TOS is ``NULL``, calls ``SECOND(None, None, None)``,
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removes the function from the stack, leaving TOS, and pushes ``None``
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to the stack. Otherwise calls ``SEVENTH(TOP, SECOND, THIRD)``,
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shifts the bottom 3 values of the stack down, replaces the empty spot
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with ``NULL`` and pushes TOS. Finally pushes the result of the call.
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.. opcode:: WITH_CLEANUP_FINISH
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Finishes cleaning up the stack when a :keyword:`with` statement block exits.
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TOS is result of ``__exit__()`` or ``__aexit__()`` function call pushed
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by :opcode:`WITH_CLEANUP_START`. SECOND is ``None`` or an exception type
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(pushed when an exception has been raised).
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Pops two values from the stack. If SECOND is not None and TOS is true
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unwinds the EXCEPT_HANDLER block which was created when the exception
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was caught and pushes ``NULL`` to the stack.
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All of the following opcodes use their arguments.
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.. opcode:: STORE_NAME (namei)
@@ -1060,15 +1002,6 @@ All of the following opcodes use their arguments.
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stack. *delta* points to the finally block or the first except block.
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.. opcode:: CALL_FINALLY (delta)
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Pushes the address of the next instruction onto the stack and increments
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bytecode counter by *delta*. Used for calling the finally block as a
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"subroutine".
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.. versionadded:: 3.8
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.. opcode:: LOAD_FAST (var_num)
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Pushes a reference to the local ``co_varnames[var_num]`` onto the stack.

‎Include/opcode.h‎

Lines changed: 2 additions & 6 deletions
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‎Lib/importlib/_bootstrap_external.py‎

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Original file line numberDiff line numberDiff line change
@@ -272,6 +272,8 @@ def _write_atomic(path, data, mode=0o666):
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# only args in ast.arguments #37593)
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# Python 3.8b4 3413 (Fix "break" and "continue" in "finally" #37830)
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# Python 3.9a0 3420 (add LOAD_ASSERTION_ERROR #34880)
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# Python 3.9a0 3421 (simplified bytecode for with blocks #32949)
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# Python 3.9a0 3422 (remove BEGIN_FINALLY, END_FINALLY, CALL_FINALLY, POP_FINALLY bytecodes #33387)
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#
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# MAGIC must change whenever the bytecode emitted by the compiler may no
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# longer be understood by older implementations of the eval loop (usually
@@ -280,7 +282,7 @@ def _write_atomic(path, data, mode=0o666):
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# Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
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# in PC/launcher.c must also be updated.
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MAGIC_NUMBER = (3420).to_bytes(2, 'little') + b'\r\n'
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MAGIC_NUMBER = (3422).to_bytes(2, 'little') + b'\r\n'
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_RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little') # For import.c
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_PYCACHE = '__pycache__'

‎Lib/opcode.py‎

Lines changed: 5 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -84,10 +84,12 @@ def jabs_op(name, op):
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def_op('INPLACE_FLOOR_DIVIDE', 28)
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def_op('INPLACE_TRUE_DIVIDE', 29)
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def_op('RERAISE', 48)
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def_op('WITH_EXCEPT_START', 49)
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def_op('GET_AITER', 50)
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def_op('GET_ANEXT', 51)
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def_op('BEFORE_ASYNC_WITH', 52)
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def_op('BEGIN_FINALLY', 53)
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def_op('END_ASYNC_FOR', 54)
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def_op('INPLACE_ADD', 55)
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def_op('INPLACE_SUBTRACT', 56)
@@ -115,14 +117,13 @@ def jabs_op(name, op):
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def_op('INPLACE_AND', 77)
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def_op('INPLACE_XOR', 78)
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def_op('INPLACE_OR', 79)
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def_op('WITH_CLEANUP_START', 81)
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def_op('WITH_CLEANUP_FINISH', 82)
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def_op('RETURN_VALUE', 83)
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def_op('IMPORT_STAR', 84)
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def_op('SETUP_ANNOTATIONS', 85)
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def_op('YIELD_VALUE', 86)
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def_op('POP_BLOCK', 87)
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def_op('END_FINALLY', 88)
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def_op('POP_EXCEPT', 89)
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HAVE_ARGUMENT = 90 # Opcodes from here have an argument:
@@ -210,7 +211,5 @@ def jabs_op(name, op):
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name_op('LOAD_METHOD', 160)
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def_op('CALL_METHOD', 161)
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jrel_op('CALL_FINALLY', 162)
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def_op('POP_FINALLY', 163)
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del def_op, name_op, jrel_op, jabs_op

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