For std::copy to optimize a copy to memcpy, the valuetype must be both
trivially constructable and trivially copyable.
The new copy benchmarks highlighted an issue that std::copy'ing pairs
and vecs were not optimized to memcpy. For a 256 MiB buffer on my
laptop w/ GCC, the serial copy speeds were:
UInt8: 10.10 GiB/s
Vec<UInt8, 2> 3.12 GiB/s
Pair<UInt32, Float32> 6.92 GiB/s
After this patch, the optimization occurs and a bitwise copy occurs:
UInt8: 10.12 GiB/s
Vec<UInt8, 2> 9.66 GiB/s
Pair<UInt32, Float32> 9.88 GiB/s
Check were also added to the Vec and Pair unit tests to ensure that
this classes continue to be trivial.
The ArrayHandleSwizzle test was refactored a bit to eliminate a new
'possibly uninitialized memory' warning introduced with the default
Vec ctors.
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