This story dates back to the days when getVariantBitmask() was introduced. The purpose of this function was to allow the variant info to be extracted from the metadata, for use with item drops. This was later changed to state bitmask for reasons I don't clearly recall.
In the great 4.0 refactor, we now store variant magic numbers separately, so we don't need any generic bitmask to split up variant and state information anymore. Variant is now only ever serialized and never deserialized. The same thing goes for blockIDs. States are read from the world by matching the full stateID against a table of prefilled known blocks, so the variant doesn't need to be deserialized - only the state does, and the state metadata readers already do bit fuckery by themselves and don't need this mask - notice how little actual changes were required to get rid of this?
This is better for performance because these then don't need to be reevaluated every time they are called.
When encountering an unqualified function or constant reference, PHP will first try to locate a symbol in the current namespace by that name, and then fall back to the global namespace.
This short-circuits the check, which has substantial performance effects in some cases - in particular, ord(), chr() and strlen() show ~1500x faster calls when they are fully qualified.
However, this doesn't mean that PM is getting a massive amount faster. In real world terms, this translates to about 10-15% performance improvement.
But before anyone gets excited, you should know that the CodeOptimizer in the PreProcessor repo has been applying fully-qualified symbol optimizations to Jenkins builds for years, which is one of the reasons why Jenkins builds have better performance than home-built or source installations.
We're choosing to do this for the sake of future SafePHP integration and also to be able to get rid of the buggy CodeOptimizer, so that phar and source are more consistent.
This filters out over 200 invalid states which were previously considered just fine, including zero-width cakes, buttons with broken facing values, furnace/chest with crazy values, and more.
This will be needed to deal with things like chest/furnace which don't use 0 as a valid state (these both use facing horizontal for rotation, and vertical is invalid, so 0 would mean downwards facing which is invalid.
This is a major change to the way block metadata is handled within the PM core. This separates variant metadata (which really ought to be part of the ID) from state metadata, and in a couple of cases flattens separate states of blocks together.
The result of this is that invalid variants can be much more easily detected, and additionally state handling is much cleaner since meta is only needed at the serialize layer instead of throughout the code.
