Hi Damien,
BTW I just saw (and backed!) your new Kickstarter campaign
to port MicroPython to ESP8266, good stuff!
On 2016-01-29 7:38 AM, Damien George wrote:
Hi Yury,
[..]
Do you use opcode dictionary caching only for LOAD_GLOBAL-like
opcodes? Do you have an equivalent of LOAD_FAST, or you use
dicts to store local variables?
The opcodes that have dict caching are:
LOAD_NAME
LOAD_GLOBAL
LOAD_ATTR
STORE_ATTR
LOAD_METHOD (not implemented yet in mainline repo)
For local variables we use LOAD_FAST and STORE_FAST (and DELETE_FAST).
Actually, there are 16 dedicated opcodes for loading from positions
0-15, and 16 for storing to these positions. Eg:
LOAD_FAST_0
LOAD_FAST_1
...
Mostly this is done to save RAM, since LOAD_FAST_0 is 1 byte.
Interesting. This might actually make CPython slightly faster
too. Worth trying.
If we change the opcode size, it will probably affect libraries
that compose or modify code objects. Modules like "dis" will
also need to be updated. And that's probably just a tip of the
iceberg.
We can still implement your approach if we add a separate
private 'unsigned char' array to each code object, so that
LOAD_GLOBAL can store the key offsets. It should be a bit
faster than my current patch, since it has one less level
of indirection. But this way we loose the ability to
optimize LOAD_METHOD, simply because it requires more memory
for its cache. In any case, I'll experiment!
Problem with that approach (having a separate array for offset_guess)
is that how do you know where to look into that array for a given
LOAD_GLOBAL opcode? The second LOAD_GLOBAL in your bytecode should
look into the second entry in the array, but how does it know?
I've changed my approach a little bit. Now I have a simple
function [1] to initialize the cache for code objects that
are called frequently enough.
It walks through the code object's opcodes and creates the
appropriate offset/cache tables.
Then, in ceval loop I have a couple of convenient macros
to work with the cache [2]. They use INSTR_OFFSET() macro
to locate the cache entry via the offset table initialized
by [1].
Thanks,
Yury
[1] https://github.com/1st1/cpython/blob/opcache4/Objects/codeobject.c#L167
[2] https://github.com/1st1/cpython/blob/opcache4/Python/ceval.c#L1164
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