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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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7
Python/generated_cases.c.h generated
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@ -5913,7 +5913,7 @@
int og_oparg = (oparg & ~255) | executor->vm_data.oparg;
next_instr = this_instr;
if (_PyJit_EnterExecutorShouldStopTracing(og_opcode)) {
if (_PyOpcode_Caches[_PyOpcode_Deopt[opcode]]) {
if (_PyOpcode_Caches[_PyOpcode_Deopt[og_opcode]]) {
PAUSE_ADAPTIVE_COUNTER(this_instr[1].counter);
}
opcode = og_opcode;
@ -12497,7 +12497,10 @@
tracer->prev_state.instr_frame = frame;
tracer->prev_state.instr_oparg = oparg;
tracer->prev_state.instr_stacklevel = PyStackRef_IsNone(frame->f_executable) ? 2 : STACK_LEVEL();
if (_PyOpcode_Caches[_PyOpcode_Deopt[opcode]]) {
if (_PyOpcode_Caches[_PyOpcode_Deopt[opcode]]
// Branch opcodes use the cache for branch history, not
// specialization counters. Don't reset it.
&& !IS_CONDITIONAL_JUMP_OPCODE(opcode)) {
(&next_instr[1])->counter = trigger_backoff_counter();
}
const _PyOpcodeRecordEntry *record_entry = &_PyOpcode_RecordEntries[opcode];