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Bug 567530 - silence strict-aliasing warnings on threadsafe opt builds (r=igor)

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This commit is contained in:
Luke Wagner 2010-06-02 10:03:36 -07:00
parent 85dcf30556
commit db6f35351f
1 changed files with 21 additions and 2 deletions
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23
js/src/jstl.h
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@ -271,6 +271,18 @@ struct AlignedStorage
void *addr() { return u.bytes; }
};
template <class T>
struct AlignedStorage2
{
union U {
char bytes[sizeof(T)];
uint64 _;
} u;
const T *addr() const { return (const T *)u.bytes; }
T *addr() { return (T *)u.bytes; }
};
/*
* Small utility for lazily constructing objects without using dynamic storage.
* When a LazilyConstructed<T> is constructed, it is |empty()|, i.e., no value
@ -278,14 +290,17 @@ struct AlignedStorage
* LazilyConstructed<T> is destroyed. Upon calling |construct|, a T object will
* be constructed with the given arguments and that object will be destroyed
* when the owning LazilyConstructed<T> is destroyed.
*
* N.B. GCC seems to miss some optimizations with LazilyConstructed and may
* generate extra branches/loads/stores. Use with caution on hot paths.
*/
template <class T>
class LazilyConstructed
{
AlignedStorage<sizeof(T)> storage;
AlignedStorage2<T> storage;
bool constructed;
T &asT() { return *reinterpret_cast<T *>(storage.addr()); }
T &asT() { return *storage.addr(); }
public:
LazilyConstructed() { constructed = false; }
@ -332,6 +347,10 @@ class LazilyConstructed
};
/*
* N.B. GCC seems to miss some optimizations with Conditionally and may
* generate extra branches/loads/stores. Use with caution on hot paths.
*/
template <class T>
class Conditionally {
LazilyConstructed<T> t;