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GeezerVison is showing github.com — gh-91432: Replace JUMP+FOR_ITER with FOR_END by sweeneyde · Pull Request #70016 · python/cpython Conversation
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Below are some benchmarks. My machine is not the most stable, but I believe there is some consistent measurable speedup. PyPerformance:DetailsSlower (9):
Faster (20):
Benchmark hidden because not significant (29): 2to3, chameleon, crypto_pyaes, dulwich_log, fannkuch, go, hexiom, json_dumps, json_loads, logging_format, mako, meteor_contest, pidigits, pyflate, python_startup, python_startup_no_site, richards, scimark_fft, sqlalchemy_declarative, sqlite_synth, sympy_expand, sympy_integrate, sympy_str, tornado_http, unpack_sequence, unpickle, xml_etree_parse, xml_etree_generate, xml_etree_process Geometric mean: 1.01x faster Microbenchmarks:Detailsbenchmark code: from itertools import repeat from pyperf import Runner, perf_counter runner = Runner() def time_this(func): runner.bench_time_func(func.__name__, func) return func ############################### @time_this def range_sum(loops): s = 0 r = iter(range(loops)) t0 = perf_counter() for x in r: s += x return perf_counter() - t0 @time_this def list_sum(loops): s = 0.0 r = iter([1.0] * loops) t0 = perf_counter() for x in r: s += x return perf_counter() - t0 @time_this def repeat_sum(loops): s = 0.0 r = repeat(1.0, loops) t0 = perf_counter() for x in r: s += x return perf_counter() - t0 ############################### @time_this def range_all(loops): r = iter(range(1, loops + 1)) t0 = perf_counter() for x in r: if not x: break return perf_counter() - t0 @time_this def list_all(loops): r = iter([True] * loops) t0 = perf_counter() for x in r: if not x: break return perf_counter() - t0 @time_this def repeat_all(loops): r = repeat(True, loops) t0 = perf_counter() for x in r: if not x: break return perf_counter() - t0 Faster (6):
Geometric mean: 1.03x faster These don't make too much sense (some macro-benchmarks speeding up more than the tightest micro-benchmarks?), so if someone with a stable machine is willing to re-measure, that would be appreciated. |
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| int prev_op = _PyOpcode_Deopt[_Py_OPCODE(code[instr_prev])]; | ||
| int next_op = _PyOpcode_Deopt[_Py_OPCODE(*frame->prev_instr)]; | ||
| // Trace before FOR_END, not after, even though a backwards | ||
| // jump happens after. However, don't trace on the first FOR_END | ||
| // of the for loop, since we're staying on the same line. | ||
| // Also don't trace JUMP_NO_INTERRUPT --> SEND. | ||
| bool line_number_changed = (line != lastline); | ||
| bool first_iteration = (next_op == FOR_END && | ||
| prev_op == JUMP_FORWARD && | ||
| !line_number_changed); | ||
| bool for_loop_end = (next_op == FOR_END && !first_iteration); | ||
| bool back_jump = (_PyInterpreterFrame_LASTI(frame) < instr_prev && | ||
| next_op != SEND && prev_op != FOR_END); | ||
| if (line_number_changed || for_loop_end || back_jump) { |
sweeneyde
Apr 11, 2022
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I'm not yet totally convinced of the robustness of the first_iteration check. It works on the whole test suite, and I couldn't come up with any failing cases, but it feels fragile.
Something like this correctly traces the backwards jumps because the POP_TOP has line number -1:
def for_loop_same_line_with_jump(): # line 0 for x in (0, 1, 2): +x if x >= 0 else -x # line 1
I don't know of any way to get JUMP_FORWARD targeted at FOR_END on the same line, unless it's the first loop iteration.
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I could add something like this if preferred:
#ifdef Py_DEBUG if (first_iteration) { int prevprev_op = _PyOpcode_Deopt[_Py_OPCODE(code[instr_prev-1])]; assert(prevprev_op == GET_ITER || prevprev_op == LOAD_FAST); if (prevprev_op == LOAD_FAST) { assert(_Py_OPARG(code[instr_prev-1]) == 0); PyObject *names = frame->f_code->co_localsplusnames; PyObject *name = PyTuple_GET_ITEM(names, 0); assert(_PyUnicode_EqualToASCIIString(name, ".0")); } } #endif
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@sweeneyde thanks for trying this, but it looks like we want to make all branches go forward (except |
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Is this an older version of the same idea? #46711 |
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