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Micro-optimize the LOAD_FAST opcode#92763

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sweeneyde wants to merge 16 commits intopython:mainfrom
sweeneyde:microopt
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Micro-optimize the LOAD_FAST opcode#92763
sweeneyde wants to merge 16 commits intopython:mainfrom
sweeneyde:microopt

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@sweeneyde sweeneyde commented May 13, 2022

The most common opcode before:

TARGET_LOAD_FAST:
    frame->prev_instr = next_instr++;
    PyObject *value = frame->localsplus[oparg]
    if (value == NULL) { goto unbound_local_error; }
    value->ob_refcnt++;
    *stack_pointer++ = value;
    _Py_CODEUNIT word = *next_instr;
    opcode = word & 255;
    oparg = word >> 8;
    opcode |= cframe.use_tracing;
    goto *opcode_targets[opcode];

The most common opcode after:

TARGET_LOAD_FAST_KNOWN_QUICK:
    next_instr++;
    PyObject *value = frame->localsplus[oparg]
    value->ob_refcnt++;
    *stack_pointer++ = value;
    _Py_CODEUNIT word = *next_instr;
    opcode = word & 255;
    oparg = word >> 8;
    goto *opcode_targets[opcode];

In particular:

  • The write to frame->prev_instr is removed.
  • The NULL-check and branch are removed.
  • The memory read and |= are removed.

None of these were particularly significant in isolation, but together, they accounted for an approximately 1% speedup in pyperformance.

@sweeneyde sweeneyde closed this Jun 3, 2022
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