Commit Graph

296 Commits

Author SHA1 Message Date
Jim Mussared
b326edf68c all: Remove MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE.
This commit removes all parts of code associated with the existing
MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE optimisation option, including the
-mcache-lookup-bc option to mpy-cross.

This feature originally provided a significant performance boost for Unix,
but wasn't able to be enabled for MCU targets (due to frozen bytecode), and
added significant extra complexity to generating and distributing .mpy
files.

The equivalent performance gain is now provided by the combination of
MICROPY_OPT_LOAD_ATTR_FAST_PATH and MICROPY_OPT_MAP_LOOKUP_CACHE (which has
been enabled on the unix port in the previous commit).

It's hard to provide precise performance numbers, but tests have been run
on a wide variety of architectures (x86-64, ARM Cortex, Aarch64, RISC-V,
xtensa) and they all generally agree on the qualitative improvements seen
by the combination of MICROPY_OPT_LOAD_ATTR_FAST_PATH and
MICROPY_OPT_MAP_LOOKUP_CACHE.

For example, on a "quiet" Linux x64 environment (i3-5010U @ 2.10GHz) the
change from CACHE_MAP_LOOKUP_IN_BYTECODE, to LOAD_ATTR_FAST_PATH combined
with MAP_LOOKUP_CACHE is:

diff of scores (higher is better)
N=2000 M=2000       bccache -> attrmapcache      diff      diff% (error%)
bm_chaos.py        13742.56 ->   13905.67 :   +163.11 =  +1.187% (+/-3.75%)
bm_fannkuch.py        60.13 ->      61.34 :     +1.21 =  +2.012% (+/-2.11%)
bm_fft.py         113083.20 ->  114793.68 :  +1710.48 =  +1.513% (+/-1.57%)
bm_float.py       256552.80 ->  243908.29 : -12644.51 =  -4.929% (+/-1.90%)
bm_hexiom.py         521.93 ->     625.41 :   +103.48 = +19.826% (+/-0.40%)
bm_nqueens.py     197544.25 ->  217713.12 : +20168.87 = +10.210% (+/-3.01%)
bm_pidigits.py      8072.98 ->    8198.75 :   +125.77 =  +1.558% (+/-3.22%)
misc_aes.py        17283.45 ->   16480.52 :   -802.93 =  -4.646% (+/-0.82%)
misc_mandel.py     99083.99 ->  128939.84 : +29855.85 = +30.132% (+/-5.88%)
misc_pystone.py    83860.10 ->   82592.56 :  -1267.54 =  -1.511% (+/-2.27%)
misc_raytrace.py   21490.40 ->   22227.23 :   +736.83 =  +3.429% (+/-1.88%)

This shows that the new optimisations are at least as good as the existing
inline-bytecode-caching, and are sometimes much better (because the new
ones apply caching to a wider variety of map lookups).

The new optimisations can also benefit code generated by the native
emitter, because they apply to the runtime rather than the generated code.
The improvement for the native emitter when LOAD_ATTR_FAST_PATH and
MAP_LOOKUP_CACHE are enabled is (same Linux environment as above):

diff of scores (higher is better)
N=2000 M=2000        native -> nat-attrmapcache  diff      diff% (error%)
bm_chaos.py        14130.62 ->   15464.68 :  +1334.06 =  +9.441% (+/-7.11%)
bm_fannkuch.py        74.96 ->      76.16 :     +1.20 =  +1.601% (+/-1.80%)
bm_fft.py         166682.99 ->  168221.86 :  +1538.87 =  +0.923% (+/-4.20%)
bm_float.py       233415.23 ->  265524.90 : +32109.67 = +13.756% (+/-2.57%)
bm_hexiom.py         628.59 ->     734.17 :   +105.58 = +16.796% (+/-1.39%)
bm_nqueens.py     225418.44 ->  232926.45 :  +7508.01 =  +3.331% (+/-3.10%)
bm_pidigits.py      6322.00 ->    6379.52 :    +57.52 =  +0.910% (+/-5.62%)
misc_aes.py        20670.10 ->   27223.18 :  +6553.08 = +31.703% (+/-1.56%)
misc_mandel.py    138221.11 ->  152014.01 : +13792.90 =  +9.979% (+/-2.46%)
misc_pystone.py    85032.14 ->  105681.44 : +20649.30 = +24.284% (+/-2.25%)
misc_raytrace.py   19800.01 ->   23350.73 :  +3550.72 = +17.933% (+/-2.79%)

In summary, compared to MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE, the new
MICROPY_OPT_LOAD_ATTR_FAST_PATH and MICROPY_OPT_MAP_LOOKUP_CACHE options:
- are simpler;
- take less code size;
- are faster (generally);
- work with code generated by the native emitter;
- can be used on embedded targets with a small and constant RAM overhead;
- allow the same .mpy bytecode to run on all targets.

See #7680 for further discussion.  And see also #7653 for a discussion
about simplifying mpy-cross options.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
2021-09-16 16:04:03 +10:00
Jim Mussared
7b89ad8dbf py/vm: Add a fast path for LOAD_ATTR on instance types.
When the LOAD_ATTR opcode is executed there are quite a few different cases
that have to be handled, but the common case is accessing a member on an
instance type.  Typically, built-in types provide methods which is why this
is common.

Fortunately, for this specific case, if the member is found in the member
map then there's no further processing.

This optimisation does a relatively cheap check (type is instance) and then
forwards directly to the member map lookup, falling back to the regular
path if necessary.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
2021-09-16 16:02:15 +10:00
Damien George
b8255dd2e0 py/vm: Simplify handling of MP_OBJ_STOP_ITERATION in yield-from opcode.
Signed-off-by: Damien George <damien@micropython.org>
2021-07-15 00:12:41 +10:00
Jeff Epler
413f34cd8f all: Fix signed shifts and NULL access errors from -fsanitize=undefined.
Fixes the following (the line numbers match commit 0e87459e2b):

../../extmod/crypto-algorithms/sha256.c:49:19: runtime error: left shif...
../../extmod/moduasyncio.c:106:35: runtime error: member access within ...
../../py/binary.c:210:13: runtime error: left shift of negative value -...
../../py/mpz.c:744:16: runtime error: negation of -9223372036854775808 ...
../../py/objint.c:109:22: runtime error: left shift of 1 by 31 places c...
../../py/objint_mpz.c:374:9: runtime error: left shift of 4611686018427...
../../py/objint_mpz.c:374:9: runtime error: left shift of negative valu...
../../py/parsenum.c:106:14: runtime error: left shift of 46116860184273...
../../py/runtime.c:395:33: runtime error: left shift of negative value ...
../../py/showbc.c:177:28: runtime error: left shift of negative value -...
../../py/vm.c:321:36: runtime error: left shift of negative value -1```

Testing was done on an amd64 Debian Buster system using gcc-8.3 and these
settings:

    CFLAGS += -g3 -Og -fsanitize=undefined
    LDFLAGS += -fsanitize=undefined

The introduced TASK_PAIRHEAP macro's conditional (x ? &x->i : NULL)
assembles (under amd64 gcc 8.3 -Os) to the same as &x->i, since i is the
initial field of the struct.  However, for the purposes of undefined
behavior analysis the conditional is needed.

Signed-off-by: Jeff Epler <jepler@gmail.com>
2021-06-24 23:01:04 +10:00
David Lechner
ca920f7218 py/mpstate: Make exceptions thread-local.
This moves mp_pending_exception from mp_state_vm_t to mp_state_thread_t.
This allows exceptions to be scheduled on a specific thread.

Signed-off-by: David Lechner <david@pybricks.com>
2021-06-19 09:43:44 +10:00
Damien George
42cf77f48b py/vm: For tracing use mp_printf, and print state when thread enabled.
mp_printf should be used to print the prefix because it's also used in
mp_bytecode_print2 (otherwise, depending on the system, different output
streams may be used).

Also print the current thread state when threading is enabled to easily see
which thread executes what opcode.

Signed-off-by: Damien George <damien@micropython.org>
2021-03-17 12:13:53 +11:00
Damien George
85f2b239d8 py/showbc: Pass in an mp_print_t struct to all bytecode-print functions.
So the output can be redirected if needed.

Signed-off-by: Damien George <damien@micropython.org>
2020-09-11 17:22:28 +10:00
Jim Mussared
243805d776 py/scheduler: Fix race in checking scheduler pending state.
Because the atomic section starts after checking whether the scheduler
state is pending, it's possible it can become a different state by the time
the atomic section starts.

This is especially likely on ports where MICROPY_BEGIN_ATOMIC_SECTION is
implemented with a mutex (i.e. it might block), but the race exists
regardless, i.e. if a context switch occurs between those two lines.
2020-04-13 21:55:47 +10:00
Jim Mussared
def76fe4d9 all: Use MP_ERROR_TEXT for all error messages. 2020-04-05 15:02:06 +10:00
Damien George
3f39d18c2b all: Add *FORMAT-OFF* in various places.
This string is recognised by uncrustify, to disable formatting in the
region marked by these comments.  This is necessary in the qstrdef*.h files
to prevent modification of the strings within the Q(...).  In other places
it is used to prevent excessive reformatting that would make the code less
readable.
2020-02-28 10:31:07 +11:00
Damien George
95473980ef py/vm: Fix comment to refer to MP_BC_RAISE_OBJ instead of RAISE_VARARGS. 2019-12-20 14:57:06 +11:00
Damien George
809d89c794 py/runtime: Fix PEP479 behaviour throwing StopIteration into yield from.
Commit 3f6ffe059f implemented PEP479 but did
not catch the case fixed in this commit.  Found by coverage analysis, that
the VM had uncovered code.
2019-10-04 23:27:00 +10:00
Damien George
82c494a97e py/vm: Fix handling of unwind jump out of active finally.
Prior to this commit, when unwinding through an active finally the stack
was not being correctly popped/folded, which resulting in the VM crashing
for complicated unwinding of nested finallys.

This should be fixed with this commit, and more tests for return/break/
continue within a finally have been added to exercise this.
2019-10-04 23:01:29 +10:00
Damien George
c8c0fd4ca3 py: Rework and compress second part of bytecode prelude.
This patch compresses the second part of the bytecode prelude which
contains the source file name, function name, source-line-number mapping
and cell closure information.  This part of the prelude now begins with a
single varible length unsigned integer which encodes 2 numbers, being the
byte-size of the following 2 sections in the header: the "source info
section" and the "closure section".  After decoding this variable unsigned
integer it's possible to skip over one or both of these sections very
easily.

This scheme saves about 2 bytes for most functions compared to the original
format: one in the case that there are no closure cells, and one because
padding was eliminated.
2019-10-01 12:26:22 +10:00
Damien George
b5ebfadbd6 py: Compress first part of bytecode prelude.
The start of the bytecode prelude contains 6 numbers telling the amount of
stack needed for the Python values and exceptions, and the signature of the
function.  Prior to this patch these numbers were all encoded one after the
other (2x variable unsigned integers, then 4x bytes), but using so many
bytes is unnecessary.

An entropy analysis of around 150,000 bytecode functions from the CPython
standard library showed that the optimal Shannon coding would need about
7.1 bits on average to encode these 6 numbers, compared to the existing 48
bits.

This patch attempts to get close to this optimal value by packing the 6
numbers into a single, varible-length unsigned integer via bit-wise
interleaving.  The interleaving scheme is chosen to minimise the average
number of bytes needed, and at the same time keep the scheme simple enough
so it can be implemented without too much overhead in code size or speed.
The scheme requires about 10.5 bits on average to store the 6 numbers.

As a result most functions which originally took 6 bytes to encode these 6
numbers now need only 1 byte (in 80% of cases).
2019-10-01 12:26:22 +10:00
Damien George
81d04a0200 py: Add n_state to mp_code_state_t struct.
This value is used often enough that it is better to cache it instead of
decode it each time.
2019-10-01 12:26:22 +10:00
Damien George
4c5e1a0368 py/bc: Change mp_code_state_t.exc_sp to exc_sp_idx.
Change from a pointer to an index, to make space in mp_code_state_t.
2019-10-01 12:26:22 +10:00
Damien George
02db91a7a3 py: Split RAISE_VARARGS opcode into 3 separate ones.
From the beginning of this project the RAISE_VARARGS opcode was named and
implemented following CPython, where it has an argument (to the opcode)
counting how many args the raise takes:

    raise # 0 args (re-raise previous exception)
    raise exc # 1 arg
    raise exc from exc2 # 2 args (chained raise)

In the bytecode this operation therefore takes 2 bytes, one for
RAISE_VARARGS and one for the number of args.

This patch splits this opcode into 3, where each is now a single byte.
This reduces bytecode size by 1 byte for each use of raise.  Every byte
counts!  It also has the benefit of reducing code size (on all ports except
nanbox).
2019-09-26 15:39:50 +10:00
Damien George
870e900d02 py: Introduce and use constants for multi-opcode sizes. 2019-09-26 15:27:11 +10:00
Damien George
ea060a42e9 py/vm: Factor cached map lookup code to inline function.
To reduce code duplication and allow to more easily modify this function.
2019-09-10 11:23:52 +10:00
Milan Rossa
310b3d1b81 py: Integrate sys.settrace feature into the VM and runtime.
This commit adds support for sys.settrace, allowing to install Python
handlers to trace execution of Python code.  The interface follows CPython
as closely as possible.  The feature is disabled by default and can be
enabled via MICROPY_PY_SYS_SETTRACE.
2019-08-30 16:44:12 +10:00
Damien George
dbf35d3da3 py/bc: Factor out code to get bytecode line number info into new func. 2019-08-30 16:43:46 +10:00
Damien George
08c1fe5569 py/vm: Don't add traceback info for exceptions that are re-raised.
With this patch exceptions that are re-raised have improved tracebacks
(less confusing, match CPython), and it makes re-raise slightly more
efficient (in time and RAM) because they no longer need to add a traceback.
Also general VM performance is not measurably affected.

Partially fixes issue #2928.
2019-08-28 12:31:53 +10:00
Damien George
16f6169c88 py/vm: Don't add traceback info for exc's propagated through a finally.
With this patch exception tracebacks that go through a finally are improved
(less confusing, match CPython), and it makes finally's slightly more
efficient (in time and RAM) because they no longer need to add a traceback.

Partially fixes issue #2928.
2019-08-28 12:31:49 +10:00
Damien George
2fca0d7f18 py/vm: Shorten error message for not-implemented opcode.
It's really an opcode that's not implemented, so use "opcode" instead of
"byte code".  And remove the redundant "not implemented" text because that
is already implied by the exception type.  There's no need to have a long
error message for an exception that is almost never encountered.  Saves
about 20 bytes of code size on most ports.
2019-08-22 16:13:05 +10:00
Damien George
ab26553759 py/vm: Remove obsolete comments about matching of exception opcodes.
These are incorrect since 5a2599d962
2019-05-27 11:58:32 +10:00
Damien George
5a2599d962 py: Replace POP_BLOCK and POP_EXCEPT opcodes with POP_EXCEPT_JUMP.
POP_BLOCK and POP_EXCEPT are now the same, and are always followed by a
JUMP.  So this optimisation reduces code size, and RAM usage of bytecode by
two bytes for each try-except handler.
2019-03-05 16:09:58 +11:00
Damien George
6f9e3ff719 py/vm: Remove currently_in_except_block variable.
After the previous commit it is no longer needed.
2019-03-05 16:09:41 +11:00
Damien George
e1fb03f3e2 py: Fix VM crash with unwinding jump out of a finally block.
This patch fixes a bug in the VM when breaking within a try-finally.  The
bug has to do with executing a break within the finally block of a
try-finally statement.  For example:

    def f():
        for x in (1,):
            print('a', x)
            try:
                raise Exception
            finally:
                print(1)
                break
            print('b', x)
    f()

Currently in uPy the above code will print:

    a 1
    1
    1
    segmentation fault (core dumped)  micropython

Not only is there a seg fault, but the "1" in the finally block is printed
twice.  This is because when the VM executes a finally block it doesn't
really know if that block was executed due to a fall-through of the try (no
exception raised), or because an exception is active.  In particular, for
nested finallys the VM has no idea which of the nested ones have active
exceptions and which are just fall-throughs.  So when a break (or continue)
is executed it tries to unwind all of the finallys, when in fact only some
may be active.

It's questionable whether break (or return or continue) should be allowed
within a finally block, because they implicitly swallow any active
exception, but nevertheless it's allowed by CPython (although almost never
used in the standard library).  And uPy should at least not crash in such a
case.

The solution here relies on the fact that exception and finally handlers
always appear in the bytecode after the try body.

Note: there was a similar bug with a return in a finally block, but that
was previously fixed in b735208403
2019-03-05 16:05:05 +11:00
Damien George
eee1e8841a py: Downcase all MP_OBJ_IS_xxx macros to make a more consistent C API.
These macros could in principle be (inline) functions so it makes sense to
have them lower case, to match the other C API functions.

The remaining macros that are upper case are:
- MP_OBJ_TO_PTR, MP_OBJ_FROM_PTR
- MP_OBJ_NEW_SMALL_INT, MP_OBJ_SMALL_INT_VALUE
- MP_OBJ_NEW_QSTR, MP_OBJ_QSTR_VALUE
- MP_OBJ_FUN_MAKE_SIG
- MP_DECLARE_CONST_xxx
- MP_DEFINE_CONST_xxx

These must remain macros because they are used when defining const data (at
least, MP_OBJ_NEW_SMALL_INT is so it makes sense to have
MP_OBJ_SMALL_INT_VALUE also a macro).

For those macros that have been made lower case, compatibility macros are
provided for the old names so that users do not need to change their code
immediately.
2019-02-12 14:54:51 +11:00
Paul Sokolovsky
8fea833e3f py: Update my copyright info on some files.
Based on git history.
2019-02-06 00:19:00 +11:00
Paul Sokolovsky
2f5d113fad py/warning: Support categories for warnings.
Python defines warnings as belonging to categories, where category is a
warning type (descending from exception type). This is useful, as e.g.
allows to disable warnings selectively and provide user-defined warning
types.  So, implement this in MicroPython, except that categories are
represented just with strings.  However, enough hooks are left to implement
categories differently per-port (e.g. as types), without need to patch each
and every usage.
2019-01-31 16:48:30 +11:00
Damien George
afecc124e6 py: Fix location of VM returned exception in invalid opcode and comments
The location for a returned exception was changed to state[0] in
d95947b48a
2019-01-04 17:22:40 +11:00
Damien George
d95947b48a py/vm: When VM raises exception put exc obj at beginning of func state.
Instead of at end of state, n_state - 1.  It was originally (way back in
v1.0) put at the end of the state because the VM didn't have a pointer to
the start.  But now that the VM takes a mp_code_state_t pointer it does
have a pointer to the start of the state so can put the exception object
there.

This commit saves about 30 bytes of code on all architectures, and, more
importantly, reduces C-stack usage by a couple of words (8 bytes on Thumb2
and 16 bytes on x86-64) for every (non-generator) call of a bytecode
function because fun_bc_call no longer needs to remember the n_state
variable.
2018-09-29 23:25:08 +10:00
Damien George
0c9d452370 py/vm: Fix case of throwing GeneratorExit type into yield-from.
mp_make_raise_obj must be used to convert a possible exception type to an
instance object, otherwise the VM may raise a non-exception object.

An existing test is adjusted to test this case, with the original test
already moved to generator_throw.py.
2018-09-28 11:39:35 +10:00
Damien George
6d20be31ae py/vm: Reword TODO about invalid ip/sp after an exception to a note. 2018-09-27 15:17:37 +10:00
Damien George
76355c8863 py/vm: Make small optimisation of BUILD_SLICE opcode.
No need to call DECODE_UINT since the value will always be either 2 or 3.
2018-09-27 11:22:33 +10:00
Damien George
b735208403 py/vm: Fix handling of finally-return with complex nested finallys.
Back in 8047340d75 basic support was added in
the VM to handle return statements within a finally block.  But it didn't
cover all cases, in particular when some finally's were active and others
inactive when the "return" was executed.

This patch adds further support for return-within-finally by correctly
managing the currently_in_except_block flag, and should fix all cases.  The
main point is that finally handlers remain on the exception stack even if
they are active (currently being executed), and the unwind return code
should only execute those finally's which are inactive.

New tests are added for the cases which now pass.
2018-09-03 13:08:16 +10:00
Damien George
bace1a16d0 py/objtype: Don't expose mp_obj_instance_attr().
mp_obj_is_instance_type() can be used instead to check for instance types.
2018-06-08 11:48:25 +10:00
Damien George
869024dd6e py/vm: Improve performance of opcode dispatch when using switch stmt.
Before this patch, when using the switch statement for dispatch in the VM
(not computed goto) a pending exception check was done after each opcode.
This is not necessary and this patch makes the pending exception check only
happen when explicitly requested by certain opcodes, like jump.  This
improves performance of the VM by about 2.5% when using the switch.
2018-05-18 11:47:03 +10:00
Damien George
46ce395130 py/vm: Use enum names instead of magic numbers in multi-opcode dispatch. 2018-05-18 11:44:26 +10:00
Damien George
1b7487e519 py/vm: Adjust #if logic for gil_divisor so braces are balanced.
Having balanced braces { and } makes it easier to navigate the function.
2018-05-16 12:33:39 +10:00
Damien George
bc36521386 py/vm: Optimise handling of stackless mode when pystack is enabled.
When pystack is enabled mp_obj_fun_bc_prepare_codestate() will always
return a valid pointer, and if there is no more pystack available then it
will raise an exception (a RuntimeError).  So having pystack enabled with
stackless enabled automatically gives strict stackless mode.  There is
therefore no need to have code for strict stackless mode when pystack is
enabled, and this patch optimises the VM for such a case.
2018-04-04 00:51:10 +10:00
Damien George
c7f880eda3 py/vm: Don't do unnecessary updates of ip and sp variables.
Neither the ip nor sp variables are used again after the execution of the
RAISE_VARARGS opcode, so they don't need to be updated.
2018-04-04 00:46:31 +10:00
Damien George
a9f6d49218 py/vm: Simplify handling of special-case STOP_ITERATION in yield from.
There's no need to have MP_OBJ_NULL a special case, the code can re-use
the MP_OBJ_STOP_ITERATION value to signal the special case and the VM can
detect this with only one check (for MP_OBJ_STOP_ITERATION).
2018-02-27 15:48:09 +11:00
Damien George
22ade2f5c4 py/vm: Fix case of handling raised StopIteration within yield from.
This patch concerns the handling of an NLR-raised StopIteration, raised
during a call to mp_resume() which is handling the yield from opcode.

Previously, commit 6738c1dded introduced code
to handle this case, along with a test.  It seems that it was lucky that
the test worked because the code did not correctly handle the stack pointer
(sp).

Furthermore, commit 79d996a57b improved the
way mp_resume() propagated certain exceptions: it changed raising an NLR
value to returning MP_VM_RETURN_EXCEPTION.  This change meant that the
test introduced in gen_yield_from_ducktype.py was no longer hitting the
code introduced in 6738c1dded.

The patch here does two things:

1. Fixes the handling of sp in the VM for the case that yield from is
   interrupted by a StopIteration raised via NLR.

2. Introduces a new test to check this handling of sp and re-covers the
   code in the VM.
2018-02-27 15:39:31 +11:00
Damien George
73d1d20b46 py/objexcept: Remove long-obsolete mp_const_MemoryError_obj.
This constant exception instance was once used by m_malloc_fail() to raise
a MemoryError without allocating memory, but it was made obsolete long ago
by 3556e45711.  The functionality is now
replaced by the use of mp_emergency_exception_obj which lives in the global
uPy state, and which can handle any exception type, not just MemoryError.
2018-02-15 16:50:02 +11:00
Damien George
0c650d4276 py/vm: Simplify stack sentinel values for unwind return and jump.
This patch simplifies how sentinel values are stored on the stack when
doing an unwind return or jump.  Instead of storing two values on the stack
for an unwind jump it now stores only one: a negative small integer means
unwind-return and a non-negative small integer means unwind-jump with the
value being the number of exceptions to unwind.  The savings in code size
are:

   bare-arm:   -56
minimal x86:   -68
   unix x64:   -80
unix nanbox:    -4
      stm32:   -56
     cc3200:   -64
    esp8266:   -76
      esp32:  -156
2018-02-08 13:30:33 +11:00
Damien George
30fd8484eb py/runtime: Use the Python stack when building *arg and **kwarg state.
With MICROPY_ENABLE_PYSTACK enabled the following language constructs no
longer allocate on the heap: f(*arg), f(**kwarg).
2017-12-11 13:49:09 +11:00
Damien George
1e5a33df41 py: Convert all uses of alloca() to use new scoped allocation API. 2017-12-11 13:49:09 +11:00