https://issues.dlang.org/show_bug.cgi?id=13061

          Issue ID: 13061
           Summary: [GC] investigate using compressed bitmaps for
                    attribute bits
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: nobody@puremagic.com
          Reporter: safety0ff.bugz@gmail.com

We're currently using a considerable amount of space storing bitmaps.
I suspect the  bit patterns within them are good candidates for compression.

The attributes which aren't aren't used during marking inner loop are good candidates for compression as they are less performance sensitive.

There's even room for improvement with the eagerly allocated "scan" bit set which are only used for deferred scanning of blocks when a deep heap graph is encountered.

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