FixedVector(size, value) should not double-initialize non-POD elements

[cdumez]

422833b

`FixedVector(size, value)` should not double-initialize non-POD elements
https://bugs.webkit.org/show_bug.cgi?id=310963

Reviewed by Sam Weinig.

The `FixedVector(size_t, const T&)` constructor was first
default-constructing all elements via `Storage::create(size)`, then
copy-assigning over them with `fill(value)`. For non-POD types, this
means N default constructions + N copy assignments instead of just
N copy constructions.

Fix this by adding a `createFilled()` factory to `EmbeddedFixedVector`
backed by a new `TrailingArray` FillWith constructor that uses
`VectorTypeOperations::uninitializedFill`, matching what
`Vector(size, val)` already does.

Also add API test coverage for this constructor, which had none.

Test: Tools/TestWebKitAPI/Tests/WTF/FixedVector.cpp

* Source/WTF/wtf/EmbeddedFixedVector.h:
* Source/WTF/wtf/FixedVector.h:
(WTF::FixedVector::FixedVector):
* Source/WTF/wtf/TrailingArray.h:
(WTF::TrailingArray::TrailingArray):
* Tools/TestWebKitAPI/Tests/WTF/FixedVector.cpp:
(TestWebKitAPI::TEST(WTF_FixedVector, SizeAndValueConstructorPOD)):
(TestWebKitAPI::TEST(WTF_FixedVector, SizeAndValueConstructorNonPOD)):
(TestWebKitAPI::TEST(WTF_FixedVector, SizeAndValueConstructorZeroSize)):
(TestWebKitAPI::TEST(WTF_FixedVector, SizeAndValueConstructorSingleElement)):

Canonical link: https://commits.webkit.org/310167@main

96cea8f

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[webkit-early-warning-system]

EWS run on current version of this PR (hash 96cea8f)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows	Apple Internal
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win	🛠 ios-apple
✅ 🧪 bindings	✅ 🛠 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
✅ 🛠 🧪 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

[weinig]

I'd be tempted to add a FillWith type tag here too, as the constructor without it is always a confusion point for me.

[cdumez]

This is a fairly large change I suspect, especially because we'd want to align the similar Vector constructor as well. I will look into doing this separately.

[cdumez]

#61607

[webkit-commit-queue]

Committed 310167@main (422833b): https://commits.webkit.org/310167@main

Reviewed commits have been landed. Closing PR #61560 and removing active labels.