Eliminate global flags#9095
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StringIO needs changes to support this, since it accesses and mutates RubyBasicObject.flags directly. |
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StringIO fixed in ruby/stringio#182 and pending release. |
This is a first step toward eliminating the global "flags" field in favor of type-specific flags.
The implementation of nil and false as a flag should not be visible from outside the object.
Only NEEDSIMPL is accessed from outside of RubyModule, by Kernel, but this flag is only used for visibility checking and may be eliminated at some point.
Frozen as a boolean would still consume a byte, so even if we eliminated the other two flags (nil and false) it would not save us any space compared to just leaving all three in a byte-sized flags field. And obviously without eliminating the other two flags, we still need to store them. We may revisit this if we can show that polymorphic "nil" and "false" tests show some benefit (and no detriment) but ultimately we won't get smaller than 8 bits of space for the unavoidable frozen flag.
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With compressed OOPS on HotSpot, we have 4 bytes of slack currently that can be used to store the full long hash. This may change with jruby#9095 and jruby#9091 land, which will greatly reduce the flag overhead of all objects.
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This is an experiment to remove or greatly reduce in size the global RubyBasicObject.flags field.
See #9088.