1073559 - sizeof(Maybe<T>) >= 16 on win32

Status: RESOLVED DUPLICATE of bug 1287006

(Core :: MFBT, defect)

Description

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I was looking at an nsCxPusher which contains a Maybe<nsAutoCxPusher> which itself contains a Maybe<nsJSAutoRequest> and a Maybe<nsJSAutoCompartment>. nsJSAutoRequest just contains a pointer, so its size is 4. But sizeof(Maybe<nsJSAutoRequest>) is 16, so it's 68% empty! The irony is that my nsCxPusher only had 4-byte alignment all along.

Comment 1

[Nathan Froyd [:froydnj]]

We ought to be using something like AlignedElem<sizeof(T)> instead of AlignedStorage2<T>; the only problem is that there exist compilers for which AlignedElem<> won't actually be aligned.  We could make MOZ_ALIGNED_DECL just #error out for those compilers, or we could choose between AlignedElem<> and AlignedStorage2<T> depending on the compiler.