Opcodes that always go together

[sweeneyde]

Using stats like python/cpython#31957 , I found that on a complete run of python -m test, we have:

• ASYNC_GEN_WRAP always goes to YIELD_VALUE
• BEFORE_ASYNC_WITH always goes to GET_AWAITABLE
• BINARY_OP_INPLACE_ADD_UNICODE always goes to STORE_FAST
• CALL always comes from PRECALL
• DICT_MERGE almost always (but not always) goes to CALL_FUNCTION_EX
• GET_AWAITABLE almost always (but not always) goes to LOAD_CONST
• GET_LEN always goes to LOAD_CONST
• GET_YIELD_FROM_ITER always goes to LOAD_CONST
• IMPORT_NAME always comes from LOAD_CONST
• IMPORT_STAR always comes from IMPORT_NAME
• JUMP_NO_INTERRUPT always goes to SEND
• LIST_TO_TUPLE almost always (but not always) goes to LIST_EXTEND
• LOAD_BUILD_CLASS always comes from PUSH_NULL
• MATCH_CLASS always comes from LOAD_CONST
• MATCH_MAPPING always goes to POP_JUMP_IF_FALSE
• MATCH_SEQUENCE always goes to POP_JUMP_IF_FALSE
• PRECALL always goes to CALL
• PRECALL_NO_KW_LIST_APPEND almost always (but not always) goes to POP_TOP
• PREP_RERAISE_STAR always comes from LIST_APPEND
• PREP_REREAISE_STAR always goes to COPY
• UNPACK_SEQUENCE_LIST almost always (but not always) goes to STORE_FAST_STORE_FAST
• WITH_EXCEPT_START always comes from PUSH_EXC_INFO

Maybe some of these can use JUMP_TO_INSTRUCTION to eliminate a dispatch, and maybe some instructions can be combined, whether that's at compile time or specialization time.

[markshannon]

There are fives cases for pair A B:

• A always precedes B: Probably nothing we can do with this.
• A mostly precedes B: Ditto.
• B always follows A: Use JUMP_TO_INSTRUCTION to skip dispatch.
• B usually follows A: Use PREDICT macros to reduce DISPATCH overhead (on Windows).
• A always precedes B and B always follows A: Merge them into a single instruction. Does this happen at all except for calls?

And one more case, that we already handle:

• A B is common: Make it a superinstruction.

CALL and PRECALL exist because we want two step specialization for some calls. So that's a special case.

[markshannon]

One other thing. If instructions are rare, like PREP_REREAISE_STAR, then we don't want to make them larger or replicate them.