Issue 9225: Replace DUP_TOPX with DUP_TOP_TWO (original) (raw)

DUP_TOPX(3) is never used, nor is ROT_FOUR. This patch removes the opcodes, replacing DUP_TOPX with DUP_TOP_TWO

Oddly, at least with pybench, use of PREDICT(BINARY_SUBSCR) in DUP_TOP_TWO seems to show an always right PREDICT as slower than FAST_DISPATCH

Oddly, at least with pybench, use of PREDICT(BINARY_SUBSCR) in DUP_TOP_TWO seems to show an always right PREDICT as slower than FAST_DISPATCH

The main point of computed gotos is to allow the CPU's branch predictor to predict opcode pairs by itself. So, yes, adding a manual PREDICT() might actually slow down the code (probably depending on the CPU model).

By the way, when you modify the bytecode, you have to change the magic number in Python/import.c.