Ben Gamari authored Dec 13, 2016 and Ben Gamari committed Dec 13, 2016

Ticket #9696 reported that `readRawBufferPtr` and `writeRawBufferPtr`
allocated unnecessarily. The binding is question was,
```
let {
  buf_s4VD [Dmd=<L,U(U)>] :: GHC.Ptr.Ptr GHC.Word.Word8
  [LclId, Unf=OtherCon []] =
      NO_CCS GHC.Ptr.Ptr! [ds1_s4Vy];
} in
  case
      GHC.IO.FD.$wreadRawBufferPtr
          Main.main5
          0#
          0#
          buf_s4VD
          Main.main4
          Main.main3
          GHC.Prim.void#
  of ...
```
The problem was that GHC apparently couldn't tell that
`readRawBufferPtr` would always demand the buffer. Here we simple add
bang patterns on all of the small arguments of these functions to ensure
that worker/wrappers can eliminate these allocations.

Test Plan: Look at STG produced by testcase in #9696, verify no
allocations

Reviewers: austin, hvr, simonmar

Reviewed By: simonmar

Subscribers: RyanGlScott, simonmar, thomie

Differential Revision: https://phabricator.haskell.org/D2813

GHC Trac Issues: #9696