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Enable fan-in heuristics at high opt, reduce method size threshold from 50 to 30 for all opt levels #22834

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Merged
merged 2 commits into from
Nov 6, 2025
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Enable fan-in heuristics at high opt, reduce method size threshold from 50 to 30 for all opt levels #22834

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b3f7fcd
Enable fan-in inlining heuristics at high opt
ymanton Sep 5, 2025
9a53761
Reduce fan-in min bytecode size threshold
ymanton Oct 27, 2025
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2 changes: 1 addition & 1 deletion runtime/compiler/control/J9Options.cpp
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Expand Up @@ -196,7 +196,7 @@ int32_t J9::Options::_maxIprofilingCount = TR_DEFAULT_INITIAL_COUNT; // 3000
int32_t J9::Options::_maxIprofilingCountInStartupMode = TR_QUICKSTART_INITIAL_COUNT; // 1000
int32_t J9::Options::_iprofilerFailRateThreshold = 70; // percent 1-100
int32_t J9::Options::_iprofilerFailHistorySize = 10; // percent 1-100
int32_t J9::Options::_iprofilerFaninMethodMinSize = 50; // bytecodes
int32_t J9::Options::_iprofilerFaninMethodMinSize = 30; // bytecodes

int32_t J9::Options::_compYieldStatsThreshold = 1000; // usec
int32_t J9::Options::_compYieldStatsHeartbeatPeriod = 0; // ms
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3 changes: 2 additions & 1 deletion runtime/compiler/optimizer/InlinerTempForJ9.cpp
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Expand Up @@ -2971,7 +2971,8 @@ TR_J9InlinerPolicy::adjustFanInSizeInWeighCallSite(int32_t& weight,

INLINE_fanInCallGraphFactor is an integer number divided by 100. This allows us to avoid using float numbers for specifying the factor.
*/
if (comp()->getMethodHotness() > warm)
static bool disableFanInAtHighOpt = feGetEnv("TR_disableFanInAtHighOpt") != NULL;
if (disableFanInAtHighOpt && comp()->getMethodHotness() > warm)
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@keithc-ca keithc-ca Nov 6, 2025

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Was || intended instead of && here? I would have expected that the behavior (when TR_disableFanInAtHighOpt is not present) would not change.

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@ymanton ymanton Nov 6, 2025

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We do want to change the default behaviour and revert to the old behaviour when the env var is set.

The env var isn't there to control the fan-in heuristic in general (that can be done via -Xjit), it's there to quickly revert just this part of the change in case it causes perf regressions or functional issues in the near future. Thanks for double checking it.

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@keithc-ca keithc-ca Nov 6, 2025 •
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But when the environment variable is not set, disableFanInAtHighOpt == false and the if condition is false.

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@ymanton ymanton Nov 6, 2025

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Right, that causes control to skip the return and execute the rest of the routine as intended.

Before:

  • Methods compiled at <=warm don't return here and execute the rest of the routine, and are thereby subject to the fan-in heuristic.
  • Methods compiled at >warm return here and aren't subjected to fan-in heuristic.

After:

  • By default no methods return here, they all execute the rest of the routine and are subjected to the fan-in heuristic.
  • If the env var is set, methods compiled at >warm return, are not subject to fan-in; methods <=warm don't return, are subject to fan-in as before.

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@nbhuiyan nbhuiyan Nov 6, 2025

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@keithc-ca That is intentional from my understanding. Now at higher opts, unless TR_disableFanInAtHighOpt is set, we do not do an early return from the method adjustFanInSizeInWeighCallSite. The behaviour prior to this change was that at opt levels > warm, adjustFanInSizeInWeighCallSite was disabled. This PR now allows things to proceed at higher opt levels, with the option to disable it at higher opt levels.

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@keithc-ca keithc-ca Nov 6, 2025

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Ok, thanks for the explanations.

return;

uint32_t thresholdSize = (!comp()->getOption(TR_InlinerFanInUseCalculatedSize)) ? getJ9InitialBytecodeSize(callee, 0, comp()) : size;
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