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[JSC] Optimize returned promise from async function when it does not have await#63356

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Constellation:eng/JSC-Optimize-returned-promise-from-async-function-when-it-does-not-have-await
Apr 23, 2026
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[JSC] Optimize returned promise from async function when it does not have await#63356
webkit-commit-queue merged 1 commit into
WebKit:mainfrom
Constellation:eng/JSC-Optimize-returned-promise-from-async-function-when-it-does-not-have-await

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@Constellation Constellation commented Apr 22, 2026 •
edited by webkit-early-warning-system
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19dc01a

[JSC] Optimize returned promise from async function when it does not have await
https://bugs.webkit.org/show_bug.cgi?id=313029
rdar://175369313

Reviewed by Yijia Huang.

Let's optimize returned promise from async function when we do not have
`await`. Currently, we are calling operationFulfillPromiseFirstResolving
for the created promise when resolving. But since we know that we do not
have `await`, we do not need to create a promise a-priori, and we can
just create and resolve a promise when returning. This is more efficient
since we can fold it into a fulfilled promise allocation when input is
proven as non-object.

Test: JSTests/stress/async-function-empty-resolved-promise.js

* JSTests/stress/async-function-empty-resolved-promise.js: Added.
(shouldBe):
(async empty):
(async emptyArrow):
(C.prototype.async emptyMethod):
(C):
(const.obj.async emptyShort):
(async onlyUsing):
(async onlyAwaitUsing):
(async returnsThenable):
(async throwsLiteral):
(async throwsError):
(thrower):
(async defaultThrower):
(async defaultThrowerBody):
(async run.async returnsPromise):
(async run):
* Source/JavaScriptCore/builtins/BuiltinNames.h:
* Source/JavaScriptCore/bytecode/LinkTimeConstant.h:
* Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:
(JSC::BytecodeGenerator::generate):
(JSC::BytecodeGenerator::BytecodeGenerator):
* Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp:
(JSC::FunctionNode::emitBytecode):
* Source/JavaScriptCore/dfg/DFGAbstractInterpreterInlines.h:
(JSC::DFG::AbstractInterpreter<AbstractStateType>::executeEffects):
* Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::handleIntrinsicCall):
* Source/JavaScriptCore/dfg/DFGClobberize.h:
(JSC::DFG::clobberize):
* Source/JavaScriptCore/dfg/DFGDoesGC.cpp:
(JSC::DFG::doesGC):
* Source/JavaScriptCore/dfg/DFGFixupPhase.cpp:
(JSC::DFG::FixupPhase::fixupNode):
* Source/JavaScriptCore/dfg/DFGNodeType.h:
* Source/JavaScriptCore/dfg/DFGOperations.cpp:
(JSC::DFG::JSC_DEFINE_JIT_OPERATION):
* Source/JavaScriptCore/dfg/DFGOperations.h:
* Source/JavaScriptCore/dfg/DFGPredictionPropagationPhase.cpp:
* Source/JavaScriptCore/dfg/DFGSafeToExecute.h:
(JSC::DFG::safeToExecute):
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp:
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT.h:
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* Source/JavaScriptCore/ftl/FTLCapabilities.cpp:
(JSC::FTL::canCompile):
* Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp:
(JSC::FTL::DFG::LowerDFGToB3::compileNode):
(JSC::FTL::DFG::LowerDFGToB3::compileCompareStrictEq):
* Source/JavaScriptCore/parser/Nodes.h:
(JSC::ScopeNode::isEmptyBody const):
* Source/JavaScriptCore/runtime/Intrinsic.h:
* Source/JavaScriptCore/runtime/JSGlobalObject.cpp:
(JSC::JSC_DEFINE_HOST_FUNCTION):
(JSC::JSGlobalObject::init):

Canonical link: https://commits.webkit.org/311883@main

697b279

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
❌ 🧪 style ✅ 🛠 ios ✅ 🛠 mac ✅ 🛠 wpe   🛠 win ⏳ 🛠 ios-apple
  🛠 ios-sim ✅ 🛠 mac-AS-debug   🧪 wpe-wk2   🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
  🧪 ios-wk2-wpt   🧪 api-mac-debug ✅ 🛠 gtk3-libwebrtc
✅ 🛠 🧪 jsc   🧪 api-ios ✅ 🧪 mac-wk1 ✅ 🛠 gtk
✅ 🛠 🧪 jsc-debug-arm64   🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
  🛠 vision   🧪 mac-AS-debug-wk2   🧪 api-gtk
  🛠 vision-sim ✅ 🧪 mac-wk2-stress   🛠 playstation
✅ 🛠 🧪 unsafe-merge   🧪 vision-wk2   🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
✅ 🛠 tv   🛠 mac-safer-cpp ✅ 🧪 jsc-armv7-tests
  🛠 tv-sim
  🛠 watch
  🛠 watch-sim

@Constellation Constellation requested a review from a team as a code owner April 22, 2026 21:13
@Constellation Constellation self-assigned this Apr 22, 2026
@Constellation Constellation added the JavaScriptCore For bugs in JavaScriptCore, the JS engine used by WebKit, other than kxmlcore issues. label Apr 22, 2026
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webkit-early-warning-system commented Apr 22, 2026 •
edited
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EWS run on previous version of this PR (hash 141712d)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
❌ 🧪 style ✅ 🛠 ios ✅ 🛠 mac ✅ 🛠 wpe   🛠 win ⏳ 🛠 ios-apple
  🛠 ios-sim ❌ 🛠 mac-AS-debug   🧪 wpe-wk2   🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
  🧪 ios-wk2-wpt ❌ 🧪 api-mac-debug   🛠 gtk3-libwebrtc
  🛠 🧪 jsc   🧪 api-ios ✅ 🧪 mac-wk1 ✅ 🛠 gtk
  🛠 🧪 jsc-debug-arm64   🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
  🛠 vision ❌ 🧪 mac-AS-debug-wk2   🧪 api-gtk
  🛠 vision-sim ✅ 🧪 mac-wk2-stress   🛠 playstation
  🧪 vision-wk2   🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
  🛠 tv   🛠 mac-safer-cpp ✅ 🧪 jsc-armv7-tests
  🛠 tv-sim
  🛠 watch
  🛠 watch-sim

@webkit-ews-buildbot webkit-ews-buildbot added the merging-blocked Applied to prevent a change from being merged label Apr 22, 2026
@Constellation Constellation removed the merging-blocked Applied to prevent a change from being merged label Apr 22, 2026
@Constellation Constellation force-pushed the eng/JSC-Optimize-returned-promise-from-async-function-when-it-does-not-have-await branch from 141712d to 7b190ec Compare April 22, 2026 22:11
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webkit-early-warning-system commented Apr 22, 2026 •
edited
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EWS run on previous version of this PR (hash 7b190ec)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
❌ 🧪 style   🛠 ios   🛠 mac   🛠 wpe   🛠 win ⏳ 🛠 ios-apple
  🛠 ios-sim ✅ 🛠 mac-AS-debug   🧪 wpe-wk2   🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
  🧪 ios-wk2-wpt   🧪 api-mac-debug   🛠 gtk3-libwebrtc
  🛠 🧪 jsc   🧪 api-ios   🧪 mac-wk1   🛠 gtk
  🛠 🧪 jsc-debug-arm64   🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
  🛠 vision   🧪 mac-AS-debug-wk2   🧪 api-gtk
  🛠 vision-sim   🧪 mac-wk2-stress   🛠 playstation
  🧪 vision-wk2   🧪 mac-intel-wk2   🛠 jsc-armv7
  🛠 tv   🛠 mac-safer-cpp   🧪 jsc-armv7-tests
  🛠 tv-sim
  🛠 watch
  🛠 watch-sim

@Constellation Constellation force-pushed the eng/JSC-Optimize-returned-promise-from-async-function-when-it-does-not-have-await branch from 7b190ec to 0ea821e Compare April 22, 2026 22:13
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webkit-early-warning-system commented Apr 22, 2026 •
edited
Loading

EWS run on previous version of this PR (hash 0ea821e)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
❌ 🧪 style ✅ 🛠 ios ✅ 🛠 mac ✅ 🛠 wpe ✅ 🛠 win ⏳ 🛠 ios-apple
✅ 🛠 ios-sim ✅ 🛠 mac-AS-debug ✅ 🧪 wpe-wk2 ✅ 🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl ✅ 🧪 ios-wk2 ✅ 🧪 api-mac ✅ 🧪 api-wpe ⏳ 🛠 vision-apple
✅ 🧪 ios-wk2-wpt ✅ 🧪 api-mac-debug ✅ 🛠 gtk3-libwebrtc
✅ 🛠 🧪 jsc ✅ 🧪 api-ios ✅ 🧪 mac-wk1 ✅ 🛠 gtk
✅ 🛠 🧪 jsc-debug-arm64 ✅ 🛠 ios-safer-cpp ✅ 🧪 mac-wk2 ✅ 🧪 gtk-wk2
✅ 🛠 vision ✅ 🧪 mac-AS-debug-wk2 ✅ 🧪 api-gtk
✅ 🛠 vision-sim ✅ 🧪 mac-wk2-stress ✅ 🛠 playstation
✅ 🧪 vision-wk2 ✅ 🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
✅ 🛠 tv ✅ 🛠 mac-safer-cpp ✅ 🧪 jsc-armv7-tests
✅ 🛠 tv-sim
✅ 🛠 watch
✅ 🛠 watch-sim

hyjorc1
hyjorc1 reviewed Apr 23, 2026
View reviewed changes
Comment thread Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp Outdated

JumpList slowCases;

FrozenValue* structure = m_graph.freezeStrong(globalObject->promiseStructure());
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@hyjorc1 hyjorc1 Apr 23, 2026

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Should we use

RegisteredStructure structure = m_graph.registerStructure(globalObject->promiseStructure());

which is same as the one used by compileCreatePromise?

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@Constellation Constellation Apr 23, 2026

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Sounds good, changed.

@Constellation Constellation force-pushed the eng/JSC-Optimize-returned-promise-from-async-function-when-it-does-not-have-await branch from 0ea821e to 697b279 Compare April 23, 2026 18:45
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webkit-early-warning-system commented Apr 23, 2026 •
edited
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EWS run on current version of this PR (hash 697b279)

Details

Misc iOS, visionOS, tvOS & watchOS macOS Linux Windows Apple Internal
❌ 🧪 style ✅ 🛠 ios ✅ 🛠 mac ✅ 🛠 wpe   🛠 win ⏳ 🛠 ios-apple
  🛠 ios-sim ✅ 🛠 mac-AS-debug   🧪 wpe-wk2   🧪 win-tests ⏳ 🛠 mac-apple
✅ 🧪 webkitperl   🧪 ios-wk2   🧪 api-mac   🧪 api-wpe ⏳ 🛠 vision-apple
  🧪 ios-wk2-wpt   🧪 api-mac-debug ✅ 🛠 gtk3-libwebrtc
✅ 🛠 🧪 jsc   🧪 api-ios ✅ 🧪 mac-wk1 ✅ 🛠 gtk
✅ 🛠 🧪 jsc-debug-arm64   🛠 ios-safer-cpp   🧪 mac-wk2   🧪 gtk-wk2
  🛠 vision   🧪 mac-AS-debug-wk2   🧪 api-gtk
  🛠 vision-sim ✅ 🧪 mac-wk2-stress   🛠 playstation
✅ 🛠 🧪 unsafe-merge   🧪 vision-wk2   🧪 mac-intel-wk2 ✅ 🛠 jsc-armv7
✅ 🛠 tv   🛠 mac-safer-cpp ✅ 🧪 jsc-armv7-tests
  🛠 tv-sim
  🛠 watch
  🛠 watch-sim

@Constellation Constellation added the unsafe-merge-queue Applied to send a pull request to merge-queue, but skip building and testing label Apr 23, 2026
@Constellation
[JSC] Optimize returned promise from async function when it does not …
19dc01a 
…have await

https://bugs.webkit.org/show_bug.cgi?id=313029
rdar://175369313

Reviewed by Yijia Huang.

Let's optimize returned promise from async function when we do not have
`await`. Currently, we are calling operationFulfillPromiseFirstResolving
for the created promise when resolving. But since we know that we do not
have `await`, we do not need to create a promise a-priori, and we can
just create and resolve a promise when returning. This is more efficient
since we can fold it into a fulfilled promise allocation when input is
proven as non-object.

Test: JSTests/stress/async-function-empty-resolved-promise.js

* JSTests/stress/async-function-empty-resolved-promise.js: Added.
(shouldBe):
(async empty):
(async emptyArrow):
(C.prototype.async emptyMethod):
(C):
(const.obj.async emptyShort):
(async onlyUsing):
(async onlyAwaitUsing):
(async returnsThenable):
(async throwsLiteral):
(async throwsError):
(thrower):
(async defaultThrower):
(async defaultThrowerBody):
(async run.async returnsPromise):
(async run):
* Source/JavaScriptCore/builtins/BuiltinNames.h:
* Source/JavaScriptCore/bytecode/LinkTimeConstant.h:
* Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:
(JSC::BytecodeGenerator::generate):
(JSC::BytecodeGenerator::BytecodeGenerator):
* Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp:
(JSC::FunctionNode::emitBytecode):
* Source/JavaScriptCore/dfg/DFGAbstractInterpreterInlines.h:
(JSC::DFG::AbstractInterpreter<AbstractStateType>::executeEffects):
* Source/JavaScriptCore/dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::handleIntrinsicCall):
* Source/JavaScriptCore/dfg/DFGClobberize.h:
(JSC::DFG::clobberize):
* Source/JavaScriptCore/dfg/DFGDoesGC.cpp:
(JSC::DFG::doesGC):
* Source/JavaScriptCore/dfg/DFGFixupPhase.cpp:
(JSC::DFG::FixupPhase::fixupNode):
* Source/JavaScriptCore/dfg/DFGNodeType.h:
* Source/JavaScriptCore/dfg/DFGOperations.cpp:
(JSC::DFG::JSC_DEFINE_JIT_OPERATION):
* Source/JavaScriptCore/dfg/DFGOperations.h:
* Source/JavaScriptCore/dfg/DFGPredictionPropagationPhase.cpp:
* Source/JavaScriptCore/dfg/DFGSafeToExecute.h:
(JSC::DFG::safeToExecute):
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT.cpp:
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT.h:
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* Source/JavaScriptCore/dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* Source/JavaScriptCore/ftl/FTLCapabilities.cpp:
(JSC::FTL::canCompile):
* Source/JavaScriptCore/ftl/FTLLowerDFGToB3.cpp:
(JSC::FTL::DFG::LowerDFGToB3::compileNode):
(JSC::FTL::DFG::LowerDFGToB3::compileCompareStrictEq):
* Source/JavaScriptCore/parser/Nodes.h:
(JSC::ScopeNode::isEmptyBody const):
* Source/JavaScriptCore/runtime/Intrinsic.h:
* Source/JavaScriptCore/runtime/JSGlobalObject.cpp:
(JSC::JSC_DEFINE_HOST_FUNCTION):
(JSC::JSGlobalObject::init):

Canonical link: https://commits.webkit.org/311883@main
@webkit-commit-queue webkit-commit-queue force-pushed the eng/JSC-Optimize-returned-promise-from-async-function-when-it-does-not-have-await branch from 697b279 to 19dc01a Compare April 23, 2026 19:58
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webkit-commit-queue commented Apr 23, 2026

Committed 311883@main (19dc01a): https://commits.webkit.org/311883@main

Reviewed commits have been landed. Closing PR #63356 and removing active labels.

@webkit-commit-queue webkit-commit-queue merged commit 19dc01a into WebKit:main Apr 23, 2026
@webkit-commit-queue webkit-commit-queue removed the unsafe-merge-queue Applied to send a pull request to merge-queue, but skip building and testing label Apr 23, 2026
@Constellation Constellation deleted the eng/JSC-Optimize-returned-promise-from-async-function-when-it-does-not-have-await branch April 23, 2026 21:32
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@hyjorc1 hyjorc1 hyjorc1 approved these changes

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