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py: Rework and compress second part of bytecode prelude.

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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.
This commit is contained in:
Damien George
2019-09-25 15:45:47 +10:00
parent b5ebfadbd6
commit c8c0fd4ca3
14 changed files with 162 additions and 119 deletions
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14
py/bc.c
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@@ -269,19 +269,25 @@ continue2:;
}
}
// get the ip and skip argument names
// read the size part of the prelude
const byte *ip = code_state->ip;
MP_BC_PRELUDE_SIZE_DECODE(ip);
// jump over code info (source file and line-number mapping)
ip += mp_decode_uint_value(ip);
ip += n_info;
// bytecode prelude: initialise closed over variables
size_t local_num;
while ((local_num = *ip++) != 255) {
for (; n_cell; --n_cell) {
size_t local_num = *ip++;
code_state->state[n_state - 1 - local_num] =
mp_obj_new_cell(code_state->state[n_state - 1 - local_num]);
}
#if !MICROPY_PERSISTENT_CODE
// so bytecode is aligned
ip = MP_ALIGN(ip, sizeof(mp_uint_t));
#endif
// now that we skipped over the prelude, set the ip for the VM
code_state->ip = ip;