hadrian: Add no_split_sections tranformer

This transformer reverts the effect of `split_sections`, which we intend
to use for platforms which don't support split sections.

In order to achieve this we have to modify the implemntation of the
split_sections transformer to store whether we are enabling
split_sections directly in the `Flavour` definition. This is because
otherwise there's no convenient way to turn off split_sections due to
having to pass additional linker scripts when merging objects.

(cherry picked from commit fec6638e2468c78f136f2363d8b3239a9bfd4f91)

6 files changed, 53 insertions, 25 deletions

diff --git a/hadrian/doc/flavours.md b/hadrian/doc/flavours.md
index 9aeabcc49d..af94fde32f 100644
--- a/hadrian/doc/flavours.md
+++ b/hadrian/doc/flavours.md
@@ -217,6 +217,10 @@ The supported transformers are listed below:
             library due to the long linking times that this causes).</td>
     </tr>
     <tr>
+        <td><code>no_split_sections</code></td>
+        <td>Disable section splitting for all libraries.</td>
+    </tr>
+    <tr>
         <td><code>thread_sanitizer</code></td>
         <td>Build the runtime system with ThreadSanitizer support</td>
     </tr>
diff --git a/hadrian/hadrian.cabal b/hadrian/hadrian.cabal
index b220f27462..0c1f3c63be 100644
--- a/hadrian/hadrian.cabal
+++ b/hadrian/hadrian.cabal
@@ -112,6 +112,7 @@ executable hadrian
                        , Settings.Builders.Ld
                        , Settings.Builders.Make
                        , Settings.Builders.MergeObjects
+                       , Settings.Builders.SplitSections
                        , Settings.Builders.RunTest
                        , Settings.Builders.Win32Tarballs
                        , Settings.Builders.Xelatex
diff --git a/hadrian/src/Flavour.hs b/hadrian/src/Flavour.hs
index f1e4aba881..9f8bd1d955 100644
--- a/hadrian/src/Flavour.hs
+++ b/hadrian/src/Flavour.hs
@@ -5,7 +5,7 @@ module Flavour
     -- * Flavour transformers
   , flavourTransformers
   , addArgs
-  , splitSections, splitSectionsIf
+  , splitSections
   , enableThreadSanitizer
   , enableDebugInfo, enableTickyGhc
   , viaLlvmBackend
@@ -37,7 +37,6 @@ import Text.Parsec.Char as P
 import Control.Monad.Except
 import UserSettings
 import Oracles.Flag
-import Oracles.Setting
 
 
 flavourTransformers :: Map String (Flavour -> Flavour)
@@ -46,6 +45,7 @@ flavourTransformers = M.fromList
     , "debug_info"       =: enableDebugInfo
     , "ticky_ghc"        =: enableTickyGhc
     , "split_sections"   =: splitSections
+    , "no_split_sections" =: noSplitSections
     , "thread_sanitizer" =: enableThreadSanitizer
     , "llvm"             =: viaLlvmBackend
     , "profiled_ghc"     =: enableProfiledGhc
@@ -181,31 +181,13 @@ enableHaddock =
       ]
 
 -- | Transform the input 'Flavour' so as to build with
---   @-split-sections@ whenever appropriate. You can
---   select which package gets built with split sections
---   by passing a suitable predicate. If the predicate holds
---   for a given package, then @split-sections@ is used when
---   building it. Note that this transformer doesn't do anything
+--   @-split-sections@ whenever appropriate.
+--   Note that this transformer doesn't do anything
 --   on darwin because on darwin platforms we always enable subsections
 --   via symbols.
-splitSectionsIf :: (Package -> Bool) -> Flavour -> Flavour
-splitSectionsIf pkgPredicate = addArgs $ do
-    pkg <- getPackage
-    osx <- expr isOsxTarget
-    not osx ? -- osx doesn't support split sections
-      pkgPredicate pkg ? mconcat -- Only apply to these packages
-        [ builder (Ghc CompileHs) ? arg "-split-sections"
-        , builder MergeObjects ? ifM (expr isWinTarget)
-            (pure ["-t", "driver/utils/merge_sections_pe.ld"])
-            (pure ["-t", "driver/utils/merge_sections.ld"])
-        ]
-
--- | Like 'splitSectionsIf', but with a fixed predicate: use
---   split sections for all packages but the GHC library.
-splitSections :: Flavour -> Flavour
-splitSections = splitSectionsIf (/=ghc)
--- Disable section splitting for the GHC library. It takes too long and
--- there is little benefit.
+splitSections, noSplitSections :: Flavour -> Flavour
+splitSections f = f { ghcSplitSections = True }
+noSplitSections f = f { ghcSplitSections = False }
 
 -- | Build GHC and libraries with ThreadSanitizer support. You likely want to
 -- configure with @--disable-large-address-space@ when using this.
diff --git a/hadrian/src/Flavour/Type.hs b/hadrian/src/Flavour/Type.hs
index 60021268fa..da236cbba3 100644
--- a/hadrian/src/Flavour/Type.hs
+++ b/hadrian/src/Flavour/Type.hs
@@ -43,6 +43,8 @@ data Flavour = Flavour {
     -- | Build the GHC executable against the threaded runtime system.
     ghcThreaded :: Stage -- ^ stage of the /built/ compiler
                 -> Bool,
+
+    ghcSplitSections :: Bool, -- ^ Whether to enable split sections
     -- | Whether to build docs and which ones
     --   (haddocks, user manual, haddock manual)
     ghcDocs :: Action DocTargets }
diff --git a/hadrian/src/Settings/Builders/SplitSections.hs b/hadrian/src/Settings/Builders/SplitSections.hs
new file mode 100644
index 0000000000..215d164b55
--- /dev/null
+++ b/hadrian/src/Settings/Builders/SplitSections.hs
@@ -0,0 +1,36 @@
+-- | Settings required when split-sections is enabled.
+module Settings.Builders.SplitSections where
+
+import Expression
+import Packages
+import Settings
+import Flavour.Type
+
+import Oracles.Setting
+
+-- | Does it make sense to enable or disable split sections?
+splitSectionsArgs :: Args
+splitSectionsArgs = do
+  pkg <- getPackage
+  osx <- expr isOsxTarget
+  notSt0 <- notStage0
+  flav <- expr flavour
+  if ( ghcSplitSections flav
+         -- Flavour enables split-sections
+    && not osx
+         -- OS X doesn't support split sections
+    && notSt0
+         -- Disable for stage 0 because we aren't going to ship
+         -- the resulting binaries and consequently there is no
+         -- reason to minimize size.
+    && (pkg /= ghc)
+         -- Disable section splitting for the GHC library.
+         -- It takes too long and there is little benefit.
+    ) then
+    ( mconcat
+        [ builder (Ghc CompileHs) ? arg "-fsplit-sections"
+        , builder MergeObjects ? ifM (expr isWinTarget)
+            (pure ["-t", "driver/utils/merge_sections_pe.ld"])
+            (pure ["-t", "driver/utils/merge_sections.ld"])
+        ]
+    ) else mempty
diff --git a/hadrian/src/Settings/Default.hs b/hadrian/src/Settings/Default.hs
index 312747141b..5df34a18c4 100644
--- a/hadrian/src/Settings/Default.hs
+++ b/hadrian/src/Settings/Default.hs
@@ -41,6 +41,7 @@ import Settings.Builders.Ar
 import Settings.Builders.Ld
 import Settings.Builders.Make
 import Settings.Builders.MergeObjects
+import Settings.Builders.SplitSections
 import Settings.Builders.RunTest
 import Settings.Builders.Xelatex
 import Settings.Packages
@@ -243,6 +244,7 @@ defaultFlavour = Flavour
     , ghcDebugged        = const False
     , ghcThreaded        = const True
     , ghcDebugAssertions = const False
+    , ghcSplitSections   = False
     , ghcDocs            = cmdDocsArgs }
 
 -- | Default logic for determining whether to build
@@ -279,6 +281,7 @@ defaultBuilderArgs = mconcat
     , validateBuilderArgs
     , xelatexBuilderArgs
     , win32TarballsArgs
+    , splitSectionsArgs
     -- Generic builders from the Hadrian library:
     , builder (Sphinx HtmlMode ) ? Hadrian.Builder.Sphinx.args HtmlMode
     , builder (Sphinx LatexMode) ? Hadrian.Builder.Sphinx.args LatexMode