hadrian: Add enableTickyGhc helper

This took a bit of trial-and-error to get working so it seems worth
having in the tree.

hadrian/src/Flavour.hs

@@ -4,7 +4,7 @@ module Flavour
     -- * Flavour transformers
   , addArgs
   , splitSections, splitSectionsIf
-  , enableDebugInfo
+  , enableDebugInfo, enableTickyGhc
   ) where
 
 import Expression
@@ -80,6 +80,17 @@ enableDebugInfo = addArgs $ mconcat
     , builder (Cc CompileC) ? notStage0 ? arg "-g3"
     ]
 
+-- | Enable the ticky-ticky profiler in stage2 GHC
+enableTickyGhc :: Flavour -> Flavour
+enableTickyGhc =
+    addArgs $ foldMap enableTickyFor [ghc, compiler, base]
+  where
+    enableTickyFor pkg = stage1 ? package pkg ? mconcat
+      [ builder (Ghc CompileHs) ? ticky
+      , builder (Ghc LinkHs) ? ticky
+      ]
+    ticky = arg "-ticky" <> arg "-ticky-allocd"
+
 -- | Transform the input 'Flavour' so as to build with
 --   @-split-sections@ whenever appropriate. You can
 --   select which package gets built with split sections