Bug 183357 – [WTF] Set canInitializeWithMemset = true if T is an integral type

• Component: New Bugs
• Status: RESOLVED FIXED

[Yusuke Suzuki]

[WTF] Set canInitializeWithMemset = true if T is an integral type

[Yusuke Suzuki]

Created attachment 335071 [details]
Patch

[EWS Watchlist]

Comment on attachment 335071 [details]
Patch

Attachment 335071 [details] did not pass win-ews (win):
Output: http://webkit-queues.webkit.org/results/6822587

New failing tests:
http/tests/preload/download_resources.html

[EWS Watchlist]

Created attachment 335079 [details]
Archive of layout-test-results from ews206 for win-future

The attached test failures were seen while running run-webkit-tests on the win-ews.
Bot: ews206  Port: win-future  Platform: CYGWIN_NT-6.1-2.9.0-0.318-5-3-x86_64-64bit

[Yusuke Suzuki]

Created attachment 335098 [details]
Patch

[Darin Adler]

Comment on attachment 335098 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=335098&action=review

> Source/WTF/wtf/Vector.h:71
> +    static void initializeIfNecessary(T*, T*) { }

I am not sure what "if necessary" means here. I think a C++ expert would call this initializeUnlessConstructorIsTrivial or initializeIfConstructorIsNonTrivial.

> Source/WTF/wtf/VectorTraits.h:52
> +        static const bool canInitializeWithMemset = std::is_integral<T>::value;

Why can’t we just set this to true? Are there types that return true for is_pod and can’t be initialized with memset?

[Yusuke Suzuki]

Comment on attachment 335098 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=335098&action=review

>> Source/WTF/wtf/Vector.h:71
>> +    static void initializeIfNecessary(T*, T*) { }
> 
> I am not sure what "if necessary" means here. I think a C++ expert would call this initializeUnlessConstructorIsTrivial or initializeIfConstructorIsNonTrivial.

Our Vector<> intentionally does not initialize backing store if T is POD (this is described in Vector.h constructor). This `initializeIfNecessary()` does that: do not initialize if T is POD.
`initializeIfNonPOD` would be fine I think. changed.

>> Source/WTF/wtf/VectorTraits.h:52
>> +        static const bool canInitializeWithMemset = std::is_integral<T>::value;
> 
> Why can’t we just set this to true? Are there types that return true for is_pod and can’t be initialized with memset?

I think it is OK: even `double` can be initialized with 0. Changed.

[Yusuke Suzuki]

Committed r229397: <https://trac.webkit.org/changeset/229397>

[Radar WebKit Bug Importer]

<rdar://problem/38266004>

[Radar WebKit Bug Importer]

<rdar://problem/38266005>