[Python-Dev] Why is Bytecode the way it is?

Sat Jul 10 06:55:50 CEST 2004

While recently goofing around with the bytecode, I thought of doing 
something like this:
 case LOAD_CONST:
 x = GETITEM(consts, oparg);
 Py_INCREF(x);
+ if (*next_instr == RETURN_VAL) {
+ retval = x;
+ why = WHY_RETURN;
+ goto fast_block_end;
+ }
 PUSH(x);
 goto fast_next_opcode;
This would skip the stack and a trip through the loop without changing 
the parser or the bytecode, and with a minimal amount of added code or 
overhead. This could (of course) be applied to other opcodes, too.
Perhaps instead of littering the function with that block, a macro 
"PUSH_MAYBE_RET" could be added that would replace the final PUSH in the 
opcode's case block:
#define PUSH_MAYBE_RET { if (*next_instr == RETURN_VAL) { \
 retval = x; \
 why = WHY_RETURN; \
 goto fast_block_end; } \
 PUSH(x); }
Not sure how much this would help speed, if any.