Pad FixedPipelineState's size to 384 bytes to be a multiple of 16.
Compare the whole struct with std::memcmp and hash with CityHash. Using
CityHash instead of a naive hash should reduce the number of collisions.
Improve used type traits to ensure this operation is safe.
With these changes the improvements to the hashable pipeline state are:
Optimized structure
Hash: 89 ns
Comparison: 103 ns
Construction*: 164 ns
Struct size: 384 bytes
Original structure
Hash: 148 ns
Equal: 174 ns
Construction*: 281 ns
Size: 1384 bytes
* Attribute state initialization is not measured
These measures are averages taken with std::chrono::high_accuracy_clock
on MSVC shipped on Visual Studio 16.6.0 Preview 2.1.
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