Optimize dumping of consecutive whitespace.wip/andreask/opt_dumps

The naive way of putting out n characters of indent would be something
like `hPutStr hdl (replicate n ' ')`. However this is quite inefficient
as we allocate an absurd number of strings consisting of simply spaces
as we don't cache them.

To improve on this we now track if we can simply write ascii spaces via
hPutBuf instead. This is the case when running with -ddump-to-file where
we force the encoding to be UTF8.

This avoids both the cost of going through encoding as well as avoiding
allocation churn from all the white space. Instead we simply use hPutBuf
on a preallocated unlifted string.

When dumping stg like this:

> nofib/spectral/simple/Main.hs -fforce-recomp -ddump-stg-final -ddump-to-file -c +RTS -s

Allocations went from 1,778 MB to 1,702MB. About a 4% reduction of
allocation! I did not measure the difference in runtime but expect it
to be similar.

Bumps the haddock submodule since the interface of GHC's Pretty
slightly changed.

-------------------------
Metric Decrease:
    T12227
-------------------------

1 files changed, 15 insertions, 12 deletions

diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index a1075f1cdb..c4b28b1210 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -1344,7 +1344,7 @@ defaultFatalMessager = hPutStrLn stderr
 jsonLogAction :: LogAction
 jsonLogAction dflags reason severity srcSpan msg
   =
-    defaultLogActionHPutStrDoc dflags stdout
+    defaultLogActionHPutStrDoc dflags True stdout
       (withPprStyle (PprCode CStyle) (doc $$ text ""))
     where
       str = renderWithContext (initSDocContext dflags defaultUserStyle) msg
@@ -1367,9 +1367,9 @@ defaultLogAction dflags reason severity srcSpan msg
       SevWarning     -> printWarns
       SevError       -> printWarns
     where
-      printOut   = defaultLogActionHPrintDoc  dflags stdout
-      printErrs  = defaultLogActionHPrintDoc  dflags stderr
-      putStrSDoc = defaultLogActionHPutStrDoc dflags stdout
+      printOut   = defaultLogActionHPrintDoc  dflags False stdout
+      printErrs  = defaultLogActionHPrintDoc  dflags False stderr
+      putStrSDoc = defaultLogActionHPutStrDoc dflags False stdout
       -- Pretty print the warning flag, if any (#10752)
       message = mkLocMessageAnn flagMsg severity srcSpan msg
 
@@ -1409,16 +1409,19 @@ defaultLogAction dflags reason severity srcSpan msg
           | otherwise = ""
 
 -- | Like 'defaultLogActionHPutStrDoc' but appends an extra newline.
-defaultLogActionHPrintDoc :: DynFlags -> Handle -> SDoc -> IO ()
-defaultLogActionHPrintDoc dflags h d
- = defaultLogActionHPutStrDoc dflags h (d $$ text "")
-
-defaultLogActionHPutStrDoc :: DynFlags -> Handle -> SDoc -> IO ()
-defaultLogActionHPutStrDoc dflags h d
+defaultLogActionHPrintDoc :: DynFlags -> Bool -> Handle -> SDoc -> IO ()
+defaultLogActionHPrintDoc dflags asciiSpace h d
+ = defaultLogActionHPutStrDoc dflags asciiSpace h (d $$ text "")
+
+-- | The boolean arguments let's the pretty printer know if it can optimize indent
+-- by writing ascii ' ' characters without going through decoding.
+defaultLogActionHPutStrDoc :: DynFlags -> Bool -> Handle -> SDoc -> IO ()
+defaultLogActionHPutStrDoc dflags asciiSpace h d
   -- Don't add a newline at the end, so that successive
   -- calls to this log-action can output all on the same line
-  = printSDoc ctx Pretty.PageMode h d
-    where ctx = initSDocContext dflags defaultUserStyle
+  = printSDoc ctx (Pretty.PageMode asciiSpace) h d
+    where
+      ctx = initSDocContext dflags defaultUserStyle
 
 newtype FlushOut = FlushOut (IO ())