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gh-146073: Add fitness/exit quality mechanism for JIT trace frontend (GH-148089)

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* Replaces ad-hoc logic for ending traces with a simple inequality: `fitness < exit_quality`
* Fitness starts high and is reduced for branches, backward edges, calls and trace length
* Exit quality reflect how good a spot that instruction is to end a trace. Closing a loop is very, specializable instructions are very low and the others in between.
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Hai Zhu 2026-04-24 17:37:01 +08:00 • committed by GitHub
parent 448d7b96c1
commit 618b726d68
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10 changed files with 205 additions and 45 deletions
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5
Python/pystate.c
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@ -630,6 +630,11 @@ init_interpreter(PyInterpreterState *interp,
"PYTHON_JIT_SIDE_EXIT_INITIAL_BACKOFF",
SIDE_EXIT_INITIAL_BACKOFF, 0, MAX_BACKOFF);
// Trace fitness configuration
init_policy(&interp->opt_config.fitness_initial,
"PYTHON_JIT_FITNESS_INITIAL",
FITNESS_INITIAL, EXIT_QUALITY_CLOSE_LOOP, UOP_MAX_TRACE_LENGTH - 1);
interp->opt_config.specialization_enabled = !is_env_enabled("PYTHON_SPECIALIZATION_OFF");
interp->opt_config.uops_optimize_enabled = !is_env_disabled("PYTHON_UOPS_OPTIMIZE");
if (interp != &runtime->_main_interpreter) {