8000 gh-112320: Implement on-trace confidence tracking for branches by gvanrossum · Pull Request #112321 · python/cpython · GitHub
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gh-112320: Implement on-trace confidence tracking for branches #112321

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Merged
merged 7 commits into from
Dec 12, 2023
Merged

gh-112320: Implement on-trace confidence tracking for branches #112321

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a53ee93
Implement on-trace confidence tracking for branches
gvanrossum Nov 22, 2023
71d2238
Add news
gvanrossum Nov 22, 2023
c23ea95
Tweak uop debug output to show confidence
gvanrossum Nov 22, 2023
9a9a4b8
Merge branch 'main' into branch-confidence
gvanrossum Dec 9, 2023
caa6ab3
Track confidence as a scaled int
gvanrossum Dec 12, 2023
241b325
Remove outdated comment
gvanrossum Dec 12, 2023
828779d
Add test
gvanrossum Dec 12, 2023
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Track confidence as a scaled int
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@gvanrossum
gvanrossum committed Dec 12, 2023
commit caa6ab3ae9133b0ad3a199cf23887bac473c8006
15 changes: 9 additions & 6 deletions Python/optimizer.c
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Original file line number Diff line number Diff line change
Expand Up @@ -409,6 +409,9 @@ BRANCH_TO_GUARD[4][2] = {

#define TRACE_STACK_SIZE 5

#define CONFIDENCE_RANGE 1000
#define CONFIDENCE_CUTOFF 333

/* Returns 1 on success,
* 0 if it failed to produce a worthwhile trace,
* and -1 on an error.
Expand All @@ -431,7 +434,7 @@ translate_bytecode_to_trace(
_Py_CODEUNIT *instr;
} trace_stack[TRACE_STACK_SIZE];
int trace_stack_depth = 0;
float confidence = 1.0; // Adjusted by branch instructions
int confidence = CONFIDENCE_RANGE; // Adjusted by branch instructions

#ifdef Py_DEBUG
char *python_lltrace = Py_GETENV("PYTHON_LLTRACE");
Expand Down Expand Up @@ -544,20 +547,20 @@ translate_bytecode_to_trace(
int bitcount = _Py_popcount32(counter);
int jump_likely = bitcount > 8;
if (jump_likely) {
confidence *= bitcount / 16.0;
confidence = confidence * bitcount / 16;
}
else {
confidence *= (16 - bitcount) / 16.0;
confidence = confidence * (16 - bitcount) / 16;
}
// TODO: Tweak the confidence cutoff
if (confidence < 0.33) {
DPRINTF(2, "Confidence too low (%.3f)\n", confidence);
if (confidence < CONFIDENCE_CUTOFF) {
DPRINTF(2, "Confidence too low (%d)\n", confidence);
OPT_STAT_INC(low_confidence);
goto done;
}
uint32_t uopcode = BRANCH_TO_GUARD[opcode - POP_JUMP_IF_FALSE][jump_likely];
_Py_CODEUNIT *next_instr = instr + 1 + _PyOpcode_Caches[_PyOpcode_Deopt[opcode]];
DPRINTF(2, "%s(%d): counter=%x, bitcount=%d, likely=%d, confidence=%.3f, uopcode=%s\n",
DPRINTF(2, "%s(%d): counter=%x, bitcount=%d, likely=%d, confidence=%d, uopcode=%s\n",
_PyUOpName(opcode), oparg,
counter, bitcount, jump_likely, confidence, _PyUOpName(uopcode));
ADD_TO_TRACE(uopcode, max_length, 0, target);
Expand Down
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