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Consider using compact regions in GHC itself to reduce GC overhead

In make mode, GHC keeps a lot of in-memory data structures about modules it has built and interface files it has read. These data structures are long-lived and immutable (at least, per module/mutually recursive module group/package), so they may be candidates for storing in compact regions to reduce the work done by the GC.

Potential problem: if we rely heavily on lazy evaluation in these structures for the purpose of avoiding work that will never be needed, then we can't store them in a compact region (since the contents of a compact region must be fully evaluated).

Trac metadata
Trac field Value
Version 8.0.1
Type FeatureRequest
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
Differential revisions
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