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bpo-17611. Move unwinding of stack for "pseudo exceptions" from interpreter to compiler. (GH-5006)

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Co-authored-by: Mark Shannon <mark@hotpy.org>
Co-authored-by: Antoine Pitrou <antoine@python.org>
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Serhiy Storchaka 2018-02-22 23:33:30 +02:00 • committed by GitHub
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@ -335,6 +335,14 @@ The Python compiler currently generates the following bytecode instructions.
three.
.. opcode:: ROT_FOUR
Lifts second, third and forth stack items one position up, moves top down
to position four.
.. versionadded:: 3.8
.. opcode:: DUP_TOP
Duplicates the reference on top of the stack.
@ -605,17 +613,6 @@ the original TOS1.
is terminated with :opcode:`POP_TOP`.
.. opcode:: BREAK_LOOP
Terminates a loop due to a :keyword:`break` statement.
.. opcode:: CONTINUE_LOOP (target)
Continues a loop due to a :keyword:`continue` statement. *target* is the
address to jump to (which should be a :opcode:`FOR_ITER` instruction).
.. opcode:: SET_ADD (i)
Calls ``set.add(TOS1[-i], TOS)``. Used to implement set comprehensions.
@ -676,7 +673,7 @@ iterations of the loop.
.. opcode:: POP_BLOCK
Removes one block from the block stack. Per frame, there is a stack of
blocks, denoting nested loops, try statements, and such.
blocks, denoting :keyword:`try` statements, and such.
.. opcode:: POP_EXCEPT
@ -687,11 +684,50 @@ iterations of the loop.
popped values are used to restore the exception state.
.. opcode:: POP_FINALLY (preserve_tos)
Cleans up the value stack and the block stack. If *preserve_tos* is not
``0`` TOS first is popped from the stack and pushed on the stack after
perfoming other stack operations:
* If TOS is ``NULL`` or an integer (pushed by :opcode:`BEGIN_FINALLY`
or :opcode:`CALL_FINALLY`) it is popped from the stack.
* If TOS is an exception type (pushed when an exception has been raised)
6 values are popped from the stack, the last three popped values are
used to restore the exception state. An exception handler block is
removed from the block stack.
It is similar to :opcode:`END_FINALLY`, but doesn't change the bytecode
counter nor raise an exception. Used for implementing :keyword:`break`
and :keyword:`return` in the :keyword:`finally` block.
.. versionadded:: 3.8
.. opcode:: BEGIN_FINALLY
Pushes ``NULL`` onto the stack for using it in :opcode:`END_FINALLY`,
:opcode:`POP_FINALLY`, :opcode:`WITH_CLEANUP_START` and
:opcode:`WITH_CLEANUP_FINISH`. Starts the :keyword:`finally` block.
.. versionadded:: 3.8
.. opcode:: END_FINALLY
Terminates a :keyword:`finally` clause. The interpreter recalls whether the
exception has to be re-raised, or whether the function returns, and continues
with the outer-next block.
exception has to be re-raised or execution has to be continued depending on
the value of TOS.
* If TOS is ``NULL`` (pushed by :opcode:`BEGIN_FINALLY`) continue from
the next instruction. TOS is popped.
* If TOS is an integer (pushed by :opcode:`CALL_FINALLY`), sets the
bytecode counter to TOS. TOS is popped.
* If TOS is an exception type (pushed when an exception has been raised)
6 values are popped from the stack, the first three popped values are
used to re-raise the exception and the last three popped values are used
to restore the exception state. An exception handler block is removed
from the block stack.
.. opcode:: LOAD_BUILD_CLASS
@ -704,9 +740,9 @@ iterations of the loop.
This opcode performs several operations before a with block starts. First,
it loads :meth:`~object.__exit__` from the context manager and pushes it onto
the stack for later use by :opcode:`WITH_CLEANUP`. Then,
the stack for later use by :opcode:`WITH_CLEANUP_START`. Then,
:meth:`~object.__enter__` is called, and a finally block pointing to *delta*
is pushed. Finally, the result of calling the enter method is pushed onto
is pushed. Finally, the result of calling the ``__enter__()`` method is pushed onto
the stack. The next opcode will either ignore it (:opcode:`POP_TOP`), or
store it in (a) variable(s) (:opcode:`STORE_FAST`, :opcode:`STORE_NAME`, or
:opcode:`UNPACK_SEQUENCE`).
@ -716,30 +752,31 @@ iterations of the loop.
.. opcode:: WITH_CLEANUP_START
Cleans up the stack when a :keyword:`with` statement block exits. TOS is the
context manager's :meth:`__exit__` bound method. Below TOS are 1--3 values
indicating how/why the finally clause was entered:
Starts cleaning up the stack when a :keyword:`with` statement block exits.
* SECOND = ``None``
* (SECOND, THIRD) = (``WHY_{RETURN,CONTINUE}``), retval
* SECOND = ``WHY_*``; no retval below it
* (SECOND, THIRD, FOURTH) = exc_info()
At the top of the stack are either ``NULL`` (pushed by
:opcode:`BEGIN_FINALLY`) or 6 values pushed if an exception has been
raised in the with block. Below is the context manager's
:meth:`~object.__exit__` or :meth:`~object.__aexit__` bound method.
In the last case, ``TOS(SECOND, THIRD, FOURTH)`` is called, otherwise
``TOS(None, None, None)``. Pushes SECOND and result of the call
to the stack.
If TOS is ``NULL``, calls ``SECOND(None, None, None)``,
removes the function from the stack, leaving TOS, and pushes ``None``
to the stack. Otherwise calls ``SEVENTH(TOP, SECOND, THIRD)``,
shifts the bottom 3 values of the stack down, replaces the empty spot
with ``NULL`` and pushes TOS. Finally pushes the result of the call.
.. opcode:: WITH_CLEANUP_FINISH
Pops exception type and result of 'exit' function call from the stack.
Finishes cleaning up the stack when a :keyword:`with` statement block exits.
If the stack represents an exception, *and* the function call returns a
'true' value, this information is "zapped" and replaced with a single
``WHY_SILENCED`` to prevent :opcode:`END_FINALLY` from re-raising the
exception. (But non-local gotos will still be resumed.)
TOS is result of ``__exit__()`` or ``__aexit__()`` function call pushed
by :opcode:`WITH_CLEANUP_START`. SECOND is ``None`` or an exception type
(pushed when an exception has been raised).
.. XXX explain the WHY stuff!
Pops two values from the stack. If SECOND is not None and TOS is true
unwinds the EXCEPT_HANDLER block which was created when the exception
was caught and pushes ``NULL`` to the stack.
All of the following opcodes use their arguments.
@ -987,22 +1024,19 @@ All of the following opcodes use their arguments.
Loads the global named ``co_names[namei]`` onto the stack.
.. opcode:: SETUP_LOOP (delta)
Pushes a block for a loop onto the block stack. The block spans from the
current instruction with a size of *delta* bytes.
.. opcode:: SETUP_EXCEPT (delta)
Pushes a try block from a try-except clause onto the block stack. *delta*
points to the first except block.
.. opcode:: SETUP_FINALLY (delta)
Pushes a try block from a try-except clause onto the block stack. *delta*
points to the finally block.
Pushes a try block from a try-finally or try-except clause onto the block
stack. *delta* points to the finally block or the first except block.
.. opcode:: CALL_FINALLY (delta)
Pushes the address of the next instruction onto the stack and increments
bytecode counter by *delta*. Used for calling the finally block as a
"subroutine".
.. versionadded:: 3.8
.. opcode:: LOAD_FAST (var_num)