Hi all!
I’ve noticed that compile times for the WebKit project have started creeping up
again, so I and a few other WebKit contributors started looking into possible
compile time improvements using the tools listed in
<https://trac.webkit.org/wiki/AnalyzingBuildPerformance>. One cause of long
compile times is when a commonly-included header (like Document.h) includes
other headers (which include other headers, ad nauseam). Whereas much of the
time those includes can be avoided by forward declaring types, for types
(specifically enums) scoped within classes, this is impossible.
I attempted to address this in <https://github.com/WebKit/WebKit/pull/8867>,
which (on this machine) reduces the total compile time of Document.h in the
WebCore project from about 1000s to about 200s.
However, this change requires moving class-scoped enums out into the namespace
scope. E.g.:
> diff --git a/Source/WebCore/Modules/audiosession/DOMAudioSession.h
> b/Source/WebCore/Modules/audiosession/DOMAudioSession.h
> index 01bf6960d3a4..d84e1eae78d5 100644
> --- a/Source/WebCore/Modules/audiosession/DOMAudioSession.h
> +++ b/Source/WebCore/Modules/audiosession/DOMAudioSession.h
> @@ -36,14 +36,17 @@
>
> namespace WebCore {
>
> +enum class DOMAudioSessionType : uint8_t { Auto, Playback, Transient,
> TransientSolo, Ambient, PlayAndRecord };
> +enum class DOMAudioSessionState : uint8_t { Inactive, Active, Interrupted };
> +
> class DOMAudioSession final : public RefCounted<DOMAudioSession>, public
> ActiveDOMObject, public EventTarget, public
> AudioSession::InterruptionObserver {
> WTF_MAKE_ISO_ALLOCATED(DOMAudioSession);
> public:
> static Ref<DOMAudioSession> create(ScriptExecutionContext*);
> ~DOMAudioSession();
>
> - enum class Type : uint8_t { Auto, Playback, Transient, TransientSolo,
> Ambient, PlayAndRecord };
> - enum class State : uint8_t { Inactive, Active, Interrupted };
> + using Type = DOMAudioSessionType;
> + using State = DOMAudioSessionState;
>
> ExceptionOr<void> setType(Type);
> Type type() const;
So that these enums can be forward declared in Document.h, rather than
including the header wholesale.
However, this requires a significant coding style change, both to existing code
and new code, and as such, it should probably be discussed here. So, what do
people think? Is the change in coding style (moving class-scoped enums out into
namespace scope) worth doing if it means a significant increases in compile
speeds?
-Jer_______________________________________________
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