Quadratic constructor tag allocation

With a large data type like:

data A = A0
  | A0001
  | A0002
...
  | A9999

GHC spends a lot of time allocating constructor tags. It accounts for half of allocations for large data types like this.

The hot piece of code is in mkDataCon:

   tag = assoc "mkDataCon" (tyConDataCons rep_tycon `zip` [fIRST_TAG..]) con

Previous discussion: https://mail.haskell.org/pipermail/ghc-devs/2017-October/014974.html

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Trac field	Value
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Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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