[JSC] Add emitBytecodeInConditionContext for optional chaining

[sosukesuzuki]

bfab895

[JSC] Add `emitBytecodeInConditionContext` for optional chaining
https://bugs.webkit.org/show_bug.cgi?id=310815

Reviewed by Yusuke Suzuki.

`if (a?.x)` emitted `mov Undefined` + `jfalse` on short-circuit, even
though undefined is always falsy. This wastes 2 instructions (8 -> 6)
and requires materializing the undefined constant.

Implement OptionalChainNode::emitBytecodeInConditionContext to route
the short-circuit bail-out directly to falseTarget instead of
materializing undefined. The optimization composes with existing
condition-context handling in LogicalNotNode, LogicalOpNode, and
ConditionalNode, so patterns like `if (!a?.x)`, `if (a?.x && b?.y)`,
`while (node?.next)`, and `a?.x ? 1 : 2` are optimized automatically.

`delete a?.x` is excluded since its short-circuit result is true, not
undefined.

Before:
    [ 1] jundefined_or_null arg1, ->12
    [ 4] get_by_id loc5, arg1, "x"
    [10] jmp ->15
    [12] mov loc5, Undefined
    [15] jfalse loc5, ->20
    [18] ret 1
    [20] ret 2

After:
    [ 1] jundefined_or_null arg1, ->15
    [ 4] get_by_id loc5, arg1, "x"
    [10] jfalse loc5, ->15
    [13] ret 1
    [15] ret 2

Test: JSTests/stress/optional-chaining-in-condition-context.js

* JSTests/stress/optional-chaining-in-condition-context.js: Added.
(shouldBe):
(testNested):
(testNot):
(testAnd):
(testOr):
(testTernary):
(testWhile):
(testDoWhile):
(testFor):
(testOptCall):
(testBracket):
(testDelete):
(testDeep5):
(testMixed):
(testPrimitive):
(testComplexLogic):
(testNestedTernary):
(testDoubleNot):
(testSideEffect):
(testBracketSideEffect):
(let.getterObj.get x):
(let.getterFalsy.get x):
(let.getterThrows.get x):
(testGetter):
(testGetterInTry):
(testProxy):
(testSymbol):
(testCompareUndef):
(testCompareNull):
(testCoalesce):
(testParenthesized):
(testIfElseChain):
(testSwitch):
(testPoly):
(testFinally):
(testGenerator):
(async testAsync):
(testThis):
(testInnerChain):
(testComma):
(get t):
(has):
* Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:
(JSC::BytecodeGenerator::pushOptionalChainTarget):
(JSC::BytecodeGenerator::discardOptionalChainTarget):
* Source/JavaScriptCore/bytecompiler/BytecodeGenerator.h:
* Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp:
(JSC::OptionalChainNode::emitBytecodeInConditionContext):
* Source/JavaScriptCore/parser/Nodes.h:

Canonical link: https://commits.webkit.org/312001@main

25a17af

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 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
✅ 🛠 🧪 merge	✅ 🛠 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-early-warning-system]

EWS run on previous version of this PR (hash f26a233)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	❌ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 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-early-warning-system]

EWS run on current version of this PR (hash 25a17af)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 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
✅ 🛠 🧪 merge	✅ 🛠 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-commit-queue]

Committed 312001@main (bfab895): https://commits.webkit.org/312001@main

Reviewed commits have been landed. Closing PR #61415 and removing active labels.