Use ShortByteString for FastString

There are multiple reasons we want this:

- Fewer allocations: ByteString has 3 fields, ShortByteString just has one.
- ByteString memory is pinned:
  - This can cause fragmentation issues (see for example #13110) but also
  - makes using FastStrings in compact regions impossible.

Metric Decrease:
    T5837
    T12150
    T12234
    T12425

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/GHC/Data/StringBuffer.hs b/compiler/GHC/Data/StringBuffer.hs
index 8ac5d1ae07..daf599d5e7 100644
--- a/compiler/GHC/Data/StringBuffer.hs
+++ b/compiler/GHC/Data/StringBuffer.hs
@@ -200,7 +200,7 @@ nextChar (StringBuffer buf len (I# cur#)) =
   -- Getting our fingers dirty a little here, but this is performance-critical
   inlinePerformIO $ do
     withForeignPtr buf $ \(Ptr a#) -> do
-        case utf8DecodeChar# (a# `plusAddr#` cur#) of
+        case utf8DecodeCharAddr# (a# `plusAddr#` cur#) of
           (# c#, nBytes# #) ->
              let cur' = I# (cur# +# nBytes#) in
              return (C# c#, StringBuffer buf len cur')