From ce426964baf58f76ad4681d8a26f671c10ad4f7e Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Tue, 12 Jan 2010 22:58:53 +0000
Subject: [PATCH] Do some recompilation avoidance in GHC.loadModule
 GHC.loadModule compiles a module after it has been parsed
 and typechecked explicity. If we are compiling to object
 code and there is a valid object file already on disk, then
 we can skip the compilation step. This is useful in
 Haddock, when processing a package that uses Template
 Haskell and hence needs actual compilation, and the package
 has already been compiled.

As usual, the recomp avoidance can be disabled with -fforce-recomp.
---
 compiler/main/GHC.hs      |   24 +++++++++++++++++-------
 compiler/main/HscMain.lhs |   17 +++++++++++++++++
 2 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/compiler/main/GHC.hs b/compiler/main/GHC.hs
index c01a433..f8a4dbb 100644
--- a/compiler/main/GHC.hs
+++ b/compiler/main/GHC.hs
@@ -1115,25 +1115,35 @@ loadModule :: (TypecheckedMod mod, GhcMonad m) => mod -> m mod
 loadModule tcm = do
    let ms = modSummary tcm
    let mod = ms_mod_name ms
+   let loc = ms_location ms
    let (tcg, _details) = tm_internals tcm
    hpt_new <-
        withTempSession (\e -> e { hsc_dflags = ms_hspp_opts ms }) $ do
 
          let compilerBackend comp env ms' _ _mb_old_iface _ =
                withTempSession (\_ -> env) $
-                 hscBackend comp tcg ms'
-                            Nothing
+                 hscBackend comp tcg ms' Nothing
+
          hsc_env <- getSession
-         mod_info
-             <- compile' (compilerBackend hscNothingCompiler
-                         ,compilerBackend hscInteractiveCompiler
-                         ,compilerBackend hscBatchCompiler)
-                         hsc_env ms 1 1 Nothing Nothing
+         mod_info <- do
+             mb_linkable <- 
+                  case ms_obj_date ms of
+                     Just t | t > ms_hs_date ms  -> do
+                         l <- liftIO $ findObjectLinkable (ms_mod ms) 
+                                                  (ml_obj_file loc) t
+                         return (Just l)
+                     _otherwise -> return Nothing
+                                                
+             compile' (compilerBackend hscNothingCompiler
+                      ,compilerBackend hscInteractiveCompiler
+                      ,hscCheckRecompBackend hscBatchCompiler tcg)
+                      hsc_env ms 1 1 Nothing mb_linkable
          -- compile' shouldn't change the environment
          return $ addToUFM (hsc_HPT hsc_env) mod mod_info
    modifySession $ \e -> e{ hsc_HPT = hpt_new }
    return tcm
 
+
 -- | This is the way to get access to the Core bindings corresponding
 -- to a module. 'compileToCore' parses, typechecks, and
 -- desugars the module, then returns the resulting Core module (consisting of
diff --git a/compiler/main/HscMain.lhs b/compiler/main/HscMain.lhs
index 9f91b4d..d5ad093 100644
--- a/compiler/main/HscMain.lhs
+++ b/compiler/main/HscMain.lhs
@@ -24,6 +24,7 @@ module HscMain
     , hscCompileBatch       -- :: Compiler (HscStatus, ModIface, ModDetails)
     , hscCompileNothing     -- :: Compiler (HscStatus, ModIface, ModDetails)
     , hscCompileInteractive -- :: Compiler (InteractiveStatus, ModIface, ModDetails)
+    , hscCheckRecompBackend
     , HscStatus' (..)
     , InteractiveStatus, HscStatus
 
@@ -382,6 +383,22 @@ genericHscCompile compiler hscMessage
            -> do hscMessage mb_mod_index True mod_summary
                  hscRecompile compiler mod_summary mb_old_hash
 
+hscCheckRecompBackend :: HsCompiler a -> TcGblEnv -> Compiler a
+hscCheckRecompBackend compiler tc_result 
+                   hsc_env mod_summary source_unchanged mb_old_iface _m_of_n =
+   withTempSession (\_ -> hsc_env) $ do
+     (recomp_reqd, mb_checked_iface)
+         <- {-# SCC "checkOldIface" #-}
+            liftIO $ checkOldIface hsc_env mod_summary
+                                   source_unchanged mb_old_iface
+
+     let mb_old_hash = fmap mi_iface_hash mb_checked_iface
+     case mb_checked_iface of
+       Just iface | not recomp_reqd
+           -> hscNoRecomp compiler iface{ mi_globals = Just (tcg_rdr_env tc_result) }
+       _otherwise
+           -> hscBackend compiler tc_result mod_summary mb_old_hash
+
 genericHscRecompile :: GhcMonad m =>
                        HsCompiler a
                     -> ModSummary -> Maybe Fingerprint
-- 
1.7.10.4