[Python-Dev] Bytecode analysis (original) (raw)

Damien Morton damien.morton@acm.org
Tue, 25 Feb 2003 17:19:30 -0500

Ive done a static analysis of the bytecodes from compiling the python standard library:

Python 2.2 (#28, Dec 21 2001, 12:21:22) [MSC 32 bit (Intel)] on win32

Some stats about JUMP_IF_FALSE opcodes

Of the 2768 JUMP_IF_FALSE opcodes encountered, 2429 have a POP_TOP on both branches.

Id like to propose that JUMP_IF_FALSE consume the top-of-stack.

Some stats about constants

50% of constant accesses are to a fixed set of 5 constants http://www.bitfurnace.com/python/stats-consts.txt rank, freq, cum%, const 1, 1277, 18.7, None 2, 929, 32.3, 1 3, 741, 43.1, 0 4, 254, 46.8, '' 5, 228, 50.1, 2

Id like to propose the following opcodes be added LOAD_CONST(NONE) LOAD_CONST(1) LOAD_CONST(0) LOAD_CONST(EMPTY_STR)

Some stats about the number of constants and locals used in functions

97% of functions use 16 or less constants 83% of functions use 8 or less constants http://www.bitfurnace.com/python/stats-func-consts.txt

98% of functions use 16 or less locals 85% of functions use 8 or less locals http://www.bitfurnace.com/python/stats-func-locals.txt

Id like to propose the following opcodes be added (I suggest n=15)

LOAD_CONST_[0..n] LOAD_FAST_[0..n] STORE_FAST_[0..n] DELETE_FAST_[0..n]

Some stats about instruction traces Please see the following links for detailed stats http://www.bitfurnace.com/python/stats-traces-original.txt http://www.bitfurnace.com/python/stats-traces-modified.txt The second file contains stats on instruction traces incorporating the proposed changes The score column, in both files, is computed by multiplying the frequency by the length of the trace

Id like to propose the following opcodes, which should reduce number of bytecode instructions used by 20%:

RETURN_FAST == LOAD_FAST, RETURN_VALUE RETURN_CONST == LOAD_CONST, RETURN_VALUE LOAD_FAST+1 == LOAD_FAST, LOAD_FAST STORE_FAST+1 == STORE_FAST, STORE_FAST POP_TOP+1 == POP_TOP, POP_TOP POP_TOP+2 == POP_TOP, POP_TOP, POP_TOP BRANCH_IF == COMPARE_OP, JUMP_IF_FALSE, POP_TOP

Notes:

LOAD_FAST+1 and STORE_FAST+1 could be implemented as a 1 byte instruction code followed by two nibbles encoding the local index numbers. See above for a discussion of local variable index numbers.

BRANCH_IF could be implimented as a set of opcodes, one for each of the possible compare_ops