Hi,
> Maciej Fijalkowski did an opcode analysis for PyPy,
> it also shows the relative frequency of opcodes following a
> specifc one:
>
> http://codespeak.net/svn/user/fijal/opcodes.txt
Nice, but we have to be careful here: what is the tested workload?
For example, I find it hard to believe that CALL_FUNCTION_VAR_KW would
always (99%) be followed by STORE_FAST.
I'm not even sure we're talking about the same VM/compiler. What are
CALL_LIKELY_BUILTIN and LOOKUP_METHOD? :-)
> Might it make sense to add more PREDICT()ions based
> on this, e.g. for BUILD_SLICE -> BINARY_SUBSCR?
This particular one sounds fine, yes.
Another approach is to create opcodes which better reflect actual usage.
For example part of the following patch (*) was to create opcodes fusing
JUMP_IF_{TRUE,FALSE} and POP_TOP. This is because in most cases, you want
to pop the comparison result regardless of its value (true or false), which
nowadays produces the following kind of code:
JUMP_IF_FALSE <branch_for_false>
POP_TOP
[... do stuff and then ...]
JUMP_FORWARD <branch_for_false_after_pop_top>
branch_for_false:
POP_TOP
branch_for_false_after_pop_top:
[etc.]
With a JUMP_IF_FALSE which also pops the pop of the stack, this gives:
JUMP_IF_FALSE <branch_for_false>
[... do stuff and then ...]
branch_for_false:
[etc.]
Prediction doesn't help you in this case.
(*) http://bugs.python.org/issue2459
Regards
Antoine.
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