Unbox around runRW#

Because runRW# inlines so late, we don't end up unboxing around it. For example, suppose we write

f x = runST $ do
  mar <- newArray 100 x
  unsafeFreeze mar

This will compile to something like

f x = case runRW# (\s ->
        case newArray# 100# x s of { (# s', mar #) ->
        case unsafeFreezeArray# mar s' of { (# s'', ar# #) ->
          (# s'', Array ar# #) }}) of
         (# _, ar #) -> ar

We generally want to pull the constructor application out of the runRW# argument:

f x = case runRW# (\s ->
        case newArray# 100# x s of { (# s', mar #) ->
          unsafeFreezeArray# mar s' }) of
        (# _, ar# #) -> Array ar#

This exposes the Array constructor to case-of-case.

Trac metadata

Trac field	Value
Version	8.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler
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