DriverPipeline.hs 94.2 KB
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{-# OPTIONS -fno-cse #-}
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{-# LANGUAGE NamedFieldPuns #-}
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-- -fno-cse is needed for GLOBAL_VAR's to behave properly

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-----------------------------------------------------------------------------
--
-- GHC Driver
--
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-- (c) The University of Glasgow 2005
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--
-----------------------------------------------------------------------------

module DriverPipeline (
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        -- Run a series of compilation steps in a pipeline, for a
        -- collection of source files.
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   oneShot, compileFile,
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        -- Interfaces for the batch-mode driver
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   linkBinary,
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        -- Interfaces for the compilation manager (interpreted/batch-mode)
   preprocess,
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   compileOne, compileOne',
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   link,
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        -- Exports for hooks to override runPhase and link
   PhasePlus(..), CompPipeline(..), PipeEnv(..), PipeState(..),
   phaseOutputFilename, getPipeState, getPipeEnv,
   hscPostBackendPhase, getLocation, setModLocation, setDynFlags,
   runPhase, exeFileName,
   mkExtraObjToLinkIntoBinary, mkNoteObjsToLinkIntoBinary,
   maybeCreateManifest, runPhase_MoveBinary,
   linkingNeeded, checkLinkInfo
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  ) where

#include "HsVersions.h"

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import PipelineMonad
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import Packages
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import HeaderInfo
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import DriverPhases
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import SysTools
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import HscMain
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import Finder
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import HscTypes hiding ( Hsc )
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import Outputable
import Module
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import UniqFM           ( eltsUFM )
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import ErrUtils
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import DynFlags
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import Config
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import Panic
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import Util
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import StringBuffer     ( hGetStringBuffer )
import BasicTypes       ( SuccessFlag(..) )
import Maybes           ( expectJust )
import ParserCoreUtils  ( getCoreModuleName )
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import SrcLoc
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import FastString
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import LlvmCodeGen      ( llvmFixupAsm )
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import MonadUtils
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import Platform
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import TcRnTypes
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import Hooks
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import Exception
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import Data.IORef       ( readIORef )
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import System.Directory
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import System.FilePath
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import System.IO
import Control.Monad
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import Data.List        ( isSuffixOf )
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import Data.Maybe
import System.Environment
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import Data.Char
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-- ---------------------------------------------------------------------------
-- Pre-process
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-- | Just preprocess a file, put the result in a temp. file (used by the
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-- compilation manager during the summary phase).
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--
-- We return the augmented DynFlags, because they contain the result
-- of slurping in the OPTIONS pragmas
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preprocess :: HscEnv
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           -> (FilePath, Maybe Phase) -- ^ filename and starting phase
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           -> IO (DynFlags, FilePath)
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preprocess hsc_env (filename, mb_phase) =
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  ASSERT2(isJust mb_phase || isHaskellSrcFilename filename, text filename)
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  runPipeline anyHsc hsc_env (filename, fmap RealPhase mb_phase)
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        Nothing Temporary Nothing{-no ModLocation-} Nothing{-no stub-}
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-- ---------------------------------------------------------------------------
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-- | Compile
--
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-- Compile a single module, under the control of the compilation manager.
--
-- This is the interface between the compilation manager and the
-- compiler proper (hsc), where we deal with tedious details like
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-- reading the OPTIONS pragma from the source file, converting the
-- C or assembly that GHC produces into an object file, and compiling
-- FFI stub files.
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--
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-- NB.  No old interface can also mean that the source has changed.

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compileOne :: HscEnv
           -> ModSummary      -- ^ summary for module being compiled
           -> Int             -- ^ module N ...
           -> Int             -- ^ ... of M
           -> Maybe ModIface  -- ^ old interface, if we have one
           -> Maybe Linkable  -- ^ old linkable, if we have one
           -> SourceModified
           -> IO HomeModInfo   -- ^ the complete HomeModInfo, if successful

compileOne = compileOne' Nothing (Just batchMsg)

compileOne' :: Maybe TcGblEnv
            -> Maybe Messager
            -> HscEnv
            -> ModSummary      -- ^ summary for module being compiled
            -> Int             -- ^ module N ...
            -> Int             -- ^ ... of M
            -> Maybe ModIface  -- ^ old interface, if we have one
            -> Maybe Linkable  -- ^ old linkable, if we have one
            -> SourceModified
            -> IO HomeModInfo   -- ^ the complete HomeModInfo, if successful

compileOne' m_tc_result mHscMessage
            hsc_env0 summary mod_index nmods mb_old_iface maybe_old_linkable
            source_modified0
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 = do
   let dflags0     = ms_hspp_opts summary
       this_mod    = ms_mod summary
       src_flavour = ms_hsc_src summary
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       location    = ms_location summary
       input_fn    = expectJust "compile:hs" (ml_hs_file location)
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       input_fnpp  = ms_hspp_file summary
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       mod_graph   = hsc_mod_graph hsc_env0
       needsTH     = any (xopt Opt_TemplateHaskell . ms_hspp_opts) mod_graph
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       isDynWay    = any (== WayDyn) (ways dflags0)
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       isProfWay   = any (== WayProf) (ways dflags0)
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   -- #8180 - when using TemplateHaskell, switch on -dynamic-too so
   -- the linker can correctly load the object files.
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   let dflags1 = if needsTH && dynamicGhc && not isDynWay && not isProfWay
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                  then gopt_set dflags0 Opt_BuildDynamicToo
                  else dflags0

   debugTraceMsg dflags1 2 (text "compile: input file" <+> text input_fnpp)
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   let basename = dropExtension input_fn
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  -- We add the directory in which the .hs files resides) to the import path.
  -- This is needed when we try to compile the .hc file later, if it
  -- imports a _stub.h file that we created here.
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   let current_dir = takeDirectory basename
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       old_paths   = includePaths dflags1
       dflags      = dflags1 { includePaths = current_dir : old_paths }
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       hsc_env     = hsc_env0 {hsc_dflags = dflags}
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   -- Figure out what lang we're generating
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   let hsc_lang = hscTarget dflags
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   -- ... and what the next phase should be
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   let next_phase = hscPostBackendPhase dflags src_flavour hsc_lang
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   -- ... and what file to generate the output into
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   output_fn <- getOutputFilename next_phase
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                        Temporary basename dflags next_phase (Just location)
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   let extCore_filename = basename ++ ".hcr"
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   -- -fforce-recomp should also work with --make
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   let force_recomp = gopt Opt_ForceRecomp dflags
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       source_modified
         | force_recomp || isNothing maybe_old_linkable = SourceModified
         | otherwise = source_modified0
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       object_filename = ml_obj_file location
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   let always_do_basic_recompilation_check = case hsc_lang of
                                             HscInterpreted -> True
                                             _ -> False

   e <- genericHscCompileGetFrontendResult
            always_do_basic_recompilation_check
            m_tc_result mHscMessage
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            hsc_env summary source_modified mb_old_iface (mod_index, nmods)
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   case e of
       Left iface ->
           do details <- genModDetails hsc_env iface
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              MASSERT(isJust maybe_old_linkable)
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              return (HomeModInfo{ hm_details  = details,
                                   hm_iface    = iface,
                                   hm_linkable = maybe_old_linkable })

       Right (tc_result, mb_old_hash) ->
           -- run the compiler
           case hsc_lang of
               HscInterpreted ->
                   case ms_hsc_src summary of
                   HsBootFile ->
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                       do (iface, _changed, details) <- hscSimpleIface hsc_env tc_result mb_old_hash
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                          return (HomeModInfo{ hm_details  = details,
                                               hm_iface    = iface,
                                               hm_linkable = maybe_old_linkable })
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                   _ -> do guts0 <- hscDesugar hsc_env summary tc_result
                           guts <- hscSimplify hsc_env guts0
                           (iface, _changed, details, cgguts) <- hscNormalIface hsc_env extCore_filename guts mb_old_hash
                           (hasStub, comp_bc, modBreaks) <- hscInteractive hsc_env cgguts summary
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                           stub_o <- case hasStub of
                                     Nothing -> return []
                                     Just stub_c -> do
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                                         stub_o <- compileStub hsc_env stub_c
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                                         return [DotO stub_o]

                           let hs_unlinked = [BCOs comp_bc modBreaks]
                               unlinked_time = ms_hs_date summary
                             -- Why do we use the timestamp of the source file here,
                             -- rather than the current time?  This works better in
                             -- the case where the local clock is out of sync
                             -- with the filesystem's clock.  It's just as accurate:
                             -- if the source is modified, then the linkable will
                             -- be out of date.
                           let linkable = LM unlinked_time this_mod
                                          (hs_unlinked ++ stub_o)

                           return (HomeModInfo{ hm_details  = details,
                                                hm_iface    = iface,
                                                hm_linkable = Just linkable })
               HscNothing ->
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                   do (iface, _changed, details) <- hscSimpleIface hsc_env tc_result mb_old_hash
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                      let linkable = if isHsBoot src_flavour
                                     then maybe_old_linkable
                                     else Just (LM (ms_hs_date summary) this_mod [])
                      return (HomeModInfo{ hm_details  = details,
                                           hm_iface    = iface,
                                           hm_linkable = linkable })

               _ ->
                   case ms_hsc_src summary of
                   HsBootFile ->
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                       do (iface, changed, details) <- hscSimpleIface hsc_env tc_result mb_old_hash
                          hscWriteIface dflags iface changed summary
                          touchObjectFile dflags object_filename
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                          return (HomeModInfo{ hm_details  = details,
                                               hm_iface    = iface,
                                               hm_linkable = maybe_old_linkable })

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                   _ -> do guts0 <- hscDesugar hsc_env summary tc_result
                           guts <- hscSimplify hsc_env guts0
                           (iface, changed, details, cgguts) <- hscNormalIface hsc_env extCore_filename guts mb_old_hash
                           hscWriteIface dflags iface changed summary
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                           -- We're in --make mode: finish the compilation pipeline.
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                           let mod_name = ms_mod_name summary
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                           _ <- runPipeline StopLn hsc_env
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                                             (output_fn,
                                              Just (HscOut src_flavour mod_name (HscRecomp cgguts summary)))
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                                             (Just basename)
                                             Persistent
                                             (Just location)
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                                             Nothing
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                                 -- The object filename comes from the ModLocation
                           o_time <- getModificationUTCTime object_filename
                           let linkable = LM o_time this_mod [DotO object_filename]

                           return (HomeModInfo{ hm_details  = details,
                                                hm_iface    = iface,
                                                hm_linkable = Just linkable })
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-----------------------------------------------------------------------------
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-- stub .h and .c files (for foreign export support)

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-- The _stub.c file is derived from the haskell source file, possibly taking
-- into account the -stubdir option.
--
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-- The object file created by compiling the _stub.c file is put into a
-- temporary file, which will be later combined with the main .o file
-- (see the MergeStubs phase).
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compileStub :: HscEnv -> FilePath -> IO FilePath
compileStub hsc_env stub_c = do
        (_, stub_o) <- runPipeline StopLn hsc_env (stub_c,Nothing)  Nothing
                                   Temporary Nothing{-no ModLocation-} Nothing
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        return stub_o
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-- ---------------------------------------------------------------------------
-- Link
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link :: GhcLink                 -- interactive or batch
     -> DynFlags                -- dynamic flags
     -> Bool                    -- attempt linking in batch mode?
     -> HomePackageTable        -- what to link
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     -> IO SuccessFlag

-- For the moment, in the batch linker, we don't bother to tell doLink
-- which packages to link -- it just tries all that are available.
-- batch_attempt_linking should only be *looked at* in batch mode.  It
-- should only be True if the upsweep was successful and someone
-- exports main, i.e., we have good reason to believe that linking
-- will succeed.

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link ghcLink dflags
  = lookupHook linkHook l dflags ghcLink dflags
  where
    l LinkInMemory _ _ _
      = if cGhcWithInterpreter == "YES"
        then -- Not Linking...(demand linker will do the job)
             return Succeeded
        else panicBadLink LinkInMemory
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    l NoLink _ _ _
      = return Succeeded
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    l LinkBinary dflags batch_attempt_linking hpt
      = link' dflags batch_attempt_linking hpt
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    l LinkStaticLib dflags batch_attempt_linking hpt
      = link' dflags batch_attempt_linking hpt
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    l LinkDynLib dflags batch_attempt_linking hpt
      = link' dflags batch_attempt_linking hpt
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panicBadLink :: GhcLink -> a
panicBadLink other = panic ("link: GHC not built to link this way: " ++
                            show other)

link' :: DynFlags                -- dynamic flags
      -> Bool                    -- attempt linking in batch mode?
      -> HomePackageTable        -- what to link
      -> IO SuccessFlag

link' dflags batch_attempt_linking hpt
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   | batch_attempt_linking
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   = do
        let
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            staticLink = case ghcLink dflags of
                          LinkStaticLib -> True
                          _ -> platformBinariesAreStaticLibs (targetPlatform dflags)

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            home_mod_infos = eltsUFM hpt
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            -- the packages we depend on
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            pkg_deps  = concatMap (map fst . dep_pkgs . mi_deps . hm_iface) home_mod_infos
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            -- the linkables to link
            linkables = map (expectJust "link".hm_linkable) home_mod_infos
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        debugTraceMsg dflags 3 (text "link: linkables are ..." $$ vcat (map ppr linkables))
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        -- check for the -no-link flag
        if isNoLink (ghcLink dflags)
          then do debugTraceMsg dflags 3 (text "link(batch): linking omitted (-c flag given).")
                  return Succeeded
          else do
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        let getOfiles (LM _ _ us) = map nameOfObject (filter isObject us)
            obj_files = concatMap getOfiles linkables
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            exe_file = exeFileName staticLink dflags
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        linking_needed <- linkingNeeded dflags staticLink linkables pkg_deps
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        if not (gopt Opt_ForceRecomp dflags) && not linking_needed
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           then do debugTraceMsg dflags 2 (text exe_file <+> ptext (sLit "is up to date, linking not required."))
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                   return Succeeded
           else do
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        compilationProgressMsg dflags ("Linking " ++ exe_file ++ " ...")
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        -- Don't showPass in Batch mode; doLink will do that for us.
        let link = case ghcLink dflags of
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                LinkBinary    -> linkBinary
                LinkStaticLib -> linkStaticLibCheck
                LinkDynLib    -> linkDynLibCheck
                other         -> panicBadLink other
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        link dflags obj_files pkg_deps
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        debugTraceMsg dflags 3 (text "link: done")
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        -- linkBinary only returns if it succeeds
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        return Succeeded

   | otherwise
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   = do debugTraceMsg dflags 3 (text "link(batch): upsweep (partially) failed OR" $$
                                text "   Main.main not exported; not linking.")
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        return Succeeded
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linkingNeeded :: DynFlags -> Bool -> [Linkable] -> [PackageId] -> IO Bool
linkingNeeded dflags staticLink linkables pkg_deps = do
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        -- if the modification time on the executable is later than the
        -- modification times on all of the objects and libraries, then omit
        -- linking (unless the -fforce-recomp flag was given).
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  let exe_file = exeFileName staticLink dflags
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  e_exe_time <- tryIO $ getModificationUTCTime exe_file
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  case e_exe_time of
    Left _  -> return True
    Right t -> do
        -- first check object files and extra_ld_inputs
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        let extra_ld_inputs = [ f | FileOption _ f <- ldInputs dflags ]
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        e_extra_times <- mapM (tryIO . getModificationUTCTime) extra_ld_inputs
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        let (errs,extra_times) = splitEithers e_extra_times
        let obj_times =  map linkableTime linkables ++ extra_times
        if not (null errs) || any (t <) obj_times
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            then return True
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            else do

        -- next, check libraries. XXX this only checks Haskell libraries,
        -- not extra_libraries or -l things from the command line.
        let pkg_map = pkgIdMap (pkgState dflags)
            pkg_hslibs  = [ (libraryDirs c, lib)
                          | Just c <- map (lookupPackage pkg_map) pkg_deps,
                            lib <- packageHsLibs dflags c ]

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        pkg_libfiles <- mapM (uncurry (findHSLib dflags)) pkg_hslibs
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        if any isNothing pkg_libfiles then return True else do
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        e_lib_times <- mapM (tryIO . getModificationUTCTime)
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                          (catMaybes pkg_libfiles)
        let (lib_errs,lib_times) = splitEithers e_lib_times
        if not (null lib_errs) || any (t <) lib_times
           then return True
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           else checkLinkInfo dflags pkg_deps exe_file

-- Returns 'False' if it was, and we can avoid linking, because the
-- previous binary was linked with "the same options".
checkLinkInfo :: DynFlags -> [PackageId] -> FilePath -> IO Bool
checkLinkInfo dflags pkg_deps exe_file
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 | not (platformSupportsSavingLinkOpts (platformOS (targetPlatform dflags)))
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 -- ToDo: Windows and OS X do not use the ELF binary format, so
 -- readelf does not work there.  We need to find another way to do
 -- this.
 = return False -- conservatively we should return True, but not
                -- linking in this case was the behaviour for a long
                -- time so we leave it as-is.
 | otherwise
 = do
   link_info <- getLinkInfo dflags pkg_deps
   debugTraceMsg dflags 3 $ text ("Link info: " ++ link_info)
   m_exe_link_info <- readElfSection dflags ghcLinkInfoSectionName exe_file
   debugTraceMsg dflags 3 $ text ("Exe link info: " ++ show m_exe_link_info)
   return (Just link_info /= m_exe_link_info)

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platformSupportsSavingLinkOpts :: OS -> Bool
platformSupportsSavingLinkOpts os
  | os == OSSolaris2 = False -- see #5382
  | otherwise        = osElfTarget os

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ghcLinkInfoSectionName :: String
ghcLinkInfoSectionName = ".debug-ghc-link-info"
   -- if we use the ".debug" prefix, then strip will strip it by default
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findHSLib :: DynFlags -> [String] -> String -> IO (Maybe FilePath)
findHSLib dflags dirs lib = do
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  let batch_lib_file = if gopt Opt_Static dflags
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                       then "lib" ++ lib <.> "a"
                       else mkSOName (targetPlatform dflags) lib
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  found <- filterM doesFileExist (map (</> batch_lib_file) dirs)
  case found of
    [] -> return Nothing
    (x:_) -> return (Just x)

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-- -----------------------------------------------------------------------------
-- Compile files in one-shot mode.

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oneShot :: HscEnv -> Phase -> [(String, Maybe Phase)] -> IO ()
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oneShot hsc_env stop_phase srcs = do
  o_files <- mapM (compileFile hsc_env stop_phase) srcs
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  doLink (hsc_dflags hsc_env) stop_phase o_files
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compileFile :: HscEnv -> Phase -> (FilePath, Maybe Phase) -> IO FilePath
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compileFile hsc_env stop_phase (src, mb_phase) = do
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   exists <- doesFileExist src
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   when (not exists) $
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        throwGhcExceptionIO (CmdLineError ("does not exist: " ++ src))
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   let
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        dflags    = hsc_dflags hsc_env
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        split     = gopt Opt_SplitObjs dflags
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        mb_o_file = outputFile dflags
        ghc_link  = ghcLink dflags      -- Set by -c or -no-link
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        -- When linking, the -o argument refers to the linker's output.
        -- otherwise, we use it as the name for the pipeline's output.
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        output
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         -- If we are dong -fno-code, then act as if the output is
         -- 'Temporary'. This stops GHC trying to copy files to their
         -- final location.
         | HscNothing <- hscTarget dflags = Temporary
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         | StopLn <- stop_phase, not (isNoLink ghc_link) = Persistent
                -- -o foo applies to linker
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         | isJust mb_o_file = SpecificFile
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                -- -o foo applies to the file we are compiling now
         | otherwise = Persistent

        stop_phase' = case stop_phase of
                        As | split -> SplitAs
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                        _          -> stop_phase
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   ( _, out_file) <- runPipeline stop_phase' hsc_env
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                            (src, fmap RealPhase mb_phase) Nothing output
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                            Nothing{-no ModLocation-} Nothing
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   return out_file


doLink :: DynFlags -> Phase -> [FilePath] -> IO ()
doLink dflags stop_phase o_files
  | not (isStopLn stop_phase)
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  = return ()           -- We stopped before the linking phase
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  | otherwise
  = case ghcLink dflags of
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        NoLink        -> return ()
        LinkBinary    -> linkBinary         dflags o_files []
        LinkStaticLib -> linkStaticLibCheck dflags o_files []
        LinkDynLib    -> linkDynLibCheck    dflags o_files []
        other         -> panicBadLink other
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-- ---------------------------------------------------------------------------
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-- | Run a compilation pipeline, consisting of multiple phases.
--
-- This is the interface to the compilation pipeline, which runs
-- a series of compilation steps on a single source file, specifying
-- at which stage to stop.
--
-- The DynFlags can be modified by phases in the pipeline (eg. by
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-- OPTIONS_GHC pragmas), and the changes affect later phases in the
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-- pipeline.
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runPipeline
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  :: Phase                      -- ^ When to stop
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  -> HscEnv                     -- ^ Compilation environment
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  -> (FilePath,Maybe PhasePlus) -- ^ Input filename (and maybe -x suffix)
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  -> Maybe FilePath             -- ^ original basename (if different from ^^^)
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  -> PipelineOutput             -- ^ Output filename
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  -> Maybe ModLocation          -- ^ A ModLocation, if this is a Haskell module
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  -> Maybe FilePath             -- ^ stub object, if we have one
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  -> IO (DynFlags, FilePath)    -- ^ (final flags, output filename)
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runPipeline stop_phase hsc_env0 (input_fn, mb_phase)
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             mb_basename output maybe_loc maybe_stub_o
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    = do let
             dflags0 = hsc_dflags hsc_env0

             -- Decide where dump files should go based on the pipeline output
             dflags = dflags0 { dumpPrefix = Just (basename ++ ".") }
             hsc_env = hsc_env0 {hsc_dflags = dflags}

             (input_basename, suffix) = splitExtension input_fn
             suffix' = drop 1 suffix -- strip off the .
             basename | Just b <- mb_basename = b
                      | otherwise             = input_basename

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             -- If we were given a -x flag, then use that phase to start from
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             start_phase = fromMaybe (RealPhase (startPhase suffix')) mb_phase
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             isHaskell (RealPhase (Unlit _)) = True
             isHaskell (RealPhase (Cpp   _)) = True
             isHaskell (RealPhase (HsPp  _)) = True
             isHaskell (RealPhase (Hsc   _)) = True
             isHaskell (HscOut {})           = True
             isHaskell _                     = False
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             isHaskellishFile = isHaskell start_phase

             env = PipeEnv{ pe_isHaskellishFile = isHaskellishFile,
                            stop_phase,
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                            src_filename = input_fn,
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                            src_basename = basename,
                            src_suffix = suffix',
                            output_spec = output }

         -- We want to catch cases of "you can't get there from here" before
         -- we start the pipeline, because otherwise it will just run off the
         -- end.
         --
         -- There is a partial ordering on phases, where A < B iff A occurs
         -- before B in a normal compilation pipeline.

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         let happensBefore' = happensBefore dflags
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         case start_phase of
             RealPhase start_phase' ->
                 when (not (start_phase' `happensBefore'` stop_phase)) $
                       throwGhcExceptionIO (UsageError
                                   ("cannot compile this file to desired target: "
                                      ++ input_fn))
             HscOut {} -> return ()
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         debugTraceMsg dflags 4 (text "Running the pipeline")
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         r <- runPipeline' start_phase hsc_env env input_fn
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                           maybe_loc maybe_stub_o
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         -- If we are compiling a Haskell module, and doing
         -- -dynamic-too, but couldn't do the -dynamic-too fast
         -- path, then rerun the pipeline for the dyn way
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         let dflags = extractDynFlags hsc_env
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         -- NB: Currently disabled on Windows (ref #7134, #8228, and #5987)
         when (not $ platformOS (targetPlatform dflags) == OSMinGW32) $ do
           when isHaskellishFile $ whenCannotGenerateDynamicToo dflags $ do
               debugTraceMsg dflags 4
                   (text "Running the pipeline again for -dynamic-too")
               let dflags' = dynamicTooMkDynamicDynFlags dflags
               hsc_env' <- newHscEnv dflags'
               _ <- runPipeline' start_phase hsc_env' env input_fn
                                 maybe_loc maybe_stub_o
               return ()
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         return r

runPipeline'
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  :: PhasePlus                  -- ^ When to start
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  -> HscEnv                     -- ^ Compilation environment
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  -> PipeEnv
  -> FilePath                   -- ^ Input filename
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  -> Maybe ModLocation          -- ^ A ModLocation, if this is a Haskell module
  -> Maybe FilePath             -- ^ stub object, if we have one
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  -> IO (DynFlags, FilePath)    -- ^ (final flags, output filename)
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runPipeline' start_phase hsc_env env input_fn
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             maybe_loc maybe_stub_o
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  = do
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  -- Execute the pipeline...
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  let state = PipeState{ hsc_env, maybe_loc, maybe_stub_o = maybe_stub_o }
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  evalP (pipeLoop start_phase input_fn) env state
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-- ---------------------------------------------------------------------------
-- outer pipeline loop

-- | pipeLoop runs phases until we reach the stop phase
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pipeLoop :: PhasePlus -> FilePath -> CompPipeline (DynFlags, FilePath)
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pipeLoop phase input_fn = do
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  env <- getPipeEnv
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  dflags <- getDynFlags
  let happensBefore' = happensBefore dflags
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      stopPhase = stop_phase env
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  case phase of
   RealPhase realPhase | realPhase `eqPhase` stopPhase            -- All done
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     -> -- Sometimes, a compilation phase doesn't actually generate any output
        -- (eg. the CPP phase when -fcpp is not turned on).  If we end on this
        -- stage, but we wanted to keep the output, then we have to explicitly
        -- copy the file, remembering to prepend a {-# LINE #-} pragma so that
        -- further compilation stages can tell what the original filename was.
        case output_spec env of
        Temporary ->
            return (dflags, input_fn)
        output ->
            do pst <- getPipeState
               final_fn <- liftIO $ getOutputFilename
                                        stopPhase output (src_basename env)
                                        dflags stopPhase (maybe_loc pst)
               when (final_fn /= input_fn) $ do
                  let msg = ("Copying `" ++ input_fn ++"' to `" ++ final_fn ++ "'")
                      line_prag = Just ("{-# LINE 1 \"" ++ src_filename env ++ "\" #-}\n")
                  liftIO $ copyWithHeader dflags msg line_prag input_fn final_fn
               return (dflags, final_fn)


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     | not (realPhase `happensBefore'` stopPhase)
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        -- Something has gone wrong.  We'll try to cover all the cases when
        -- this could happen, so if we reach here it is a panic.
        -- eg. it might happen if the -C flag is used on a source file that
        -- has {-# OPTIONS -fasm #-}.
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     -> panic ("pipeLoop: at phase " ++ show realPhase ++
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           " but I wanted to stop at phase " ++ show stopPhase)
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   _
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     -> do liftIO $ debugTraceMsg dflags 4
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                                  (ptext (sLit "Running phase") <+> ppr phase)
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           (next_phase, output_fn) <- runHookedPhase phase input_fn dflags
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           r <- pipeLoop next_phase output_fn
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           case phase of
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               HscOut {} ->
                   whenGeneratingDynamicToo dflags $ do
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                       setDynFlags $ dynamicTooMkDynamicDynFlags dflags
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                       -- TODO shouldn't ignore result:
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                       _ <- pipeLoop phase input_fn
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                       return ()
               _ ->
                   return ()
           return r
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runHookedPhase :: PhasePlus -> FilePath -> DynFlags
               -> CompPipeline (PhasePlus, FilePath)
runHookedPhase pp input dflags =
  lookupHook runPhaseHook runPhase dflags pp input dflags

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-- -----------------------------------------------------------------------------
-- In each phase, we need to know into what filename to generate the
-- output.  All the logic about which filenames we generate output
-- into is embodied in the following function.
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phaseOutputFilename :: Phase{-next phase-} -> CompPipeline FilePath
phaseOutputFilename next_phase = do
  PipeEnv{stop_phase, src_basename, output_spec} <- getPipeEnv
  PipeState{maybe_loc, hsc_env} <- getPipeState
  let dflags = hsc_dflags hsc_env
  liftIO $ getOutputFilename stop_phase output_spec
                             src_basename dflags next_phase maybe_loc

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getOutputFilename
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  :: Phase -> PipelineOutput -> String
  -> DynFlags -> Phase{-next phase-} -> Maybe ModLocation -> IO FilePath
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getOutputFilename stop_phase output basename dflags next_phase maybe_location
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 | is_last_phase, Persistent   <- output = persistent_fn
 | is_last_phase, SpecificFile <- output = case outputFile dflags of
                                           Just f -> return f
                                           Nothing ->
                                               panic "SpecificFile: No filename"
 | keep_this_output                      = persistent_fn
 | otherwise                             = newTempName dflags suffix
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    where
          hcsuf      = hcSuf dflags
          odir       = objectDir dflags
          osuf       = objectSuf dflags
          keep_hc    = gopt Opt_KeepHcFiles dflags
          keep_s     = gopt Opt_KeepSFiles dflags
          keep_bc    = gopt Opt_KeepLlvmFiles dflags

          myPhaseInputExt HCc       = hcsuf
          myPhaseInputExt MergeStub = osuf
          myPhaseInputExt StopLn    = osuf
          myPhaseInputExt other     = phaseInputExt other

          is_last_phase = next_phase `eqPhase` stop_phase

          -- sometimes, we keep output from intermediate stages
          keep_this_output =
               case next_phase of
                       As      | keep_s     -> True
                       LlvmOpt | keep_bc    -> True
                       HCc     | keep_hc    -> True
                       _other               -> False

          suffix = myPhaseInputExt next_phase

          -- persistent object files get put in odir
          persistent_fn
             | StopLn <- next_phase = return odir_persistent
             | otherwise            = return persistent

          persistent = basename <.> suffix

          odir_persistent
             | Just loc <- maybe_location = ml_obj_file loc
             | Just d <- odir = d </> persistent
             | otherwise      = persistent
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-- -----------------------------------------------------------------------------
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-- | Each phase in the pipeline returns the next phase to execute, and the
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-- name of the file in which the output was placed.
--
-- We must do things dynamically this way, because we often don't know
-- what the rest of the phases will be until part-way through the
-- compilation: for example, an {-# OPTIONS -fasm #-} at the beginning
-- of a source file can change the latter stages of the pipeline from
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-- taking the LLVM route to using the native code generator.
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--
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runPhase :: PhasePlus   -- ^ Run this phase
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         -> FilePath    -- ^ name of the input file
         -> DynFlags    -- ^ for convenience, we pass the current dflags in
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         -> CompPipeline (PhasePlus,           -- next phase to run
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                          FilePath)            -- output filename
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        -- Invariant: the output filename always contains the output
        -- Interesting case: Hsc when there is no recompilation to do
        --                   Then the output filename is still a .o file
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-------------------------------------------------------------------------------
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-- Unlit phase
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runPhase (RealPhase (Unlit sf)) input_fn dflags
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  = do
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       output_fn <- phaseOutputFilename (Cpp sf)
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       let flags = [ -- The -h option passes the file name for unlit to
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                     -- put in a #line directive
                     SysTools.Option     "-h"
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                   , SysTools.Option $ escape $ normalise input_fn
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                   , SysTools.FileOption "" input_fn
                   , SysTools.FileOption "" output_fn
                   ]

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       liftIO $ SysTools.runUnlit dflags flags
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       return (RealPhase (Cpp sf), output_fn)
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  where
       -- escape the characters \, ", and ', but don't try to escape
       -- Unicode or anything else (so we don't use Util.charToC
       -- here).  If we get this wrong, then in
       -- Coverage.addTicksToBinds where we check that the filename in
       -- a SrcLoc is the same as the source filenaame, the two will
       -- look bogusly different. See test:
       -- libraries/hpc/tests/function/subdir/tough2.lhs
       escape ('\\':cs) = '\\':'\\': escape cs
       escape ('\"':cs) = '\\':'\"': escape cs
       escape ('\'':cs) = '\\':'\'': escape cs
       escape (c:cs)    = c : escape cs
       escape []        = []
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-------------------------------------------------------------------------------
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-- Cpp phase : (a) gets OPTIONS out of file
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--             (b) runs cpp if necessary
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runPhase (RealPhase (Cpp sf)) input_fn dflags0
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  = do
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       src_opts <- liftIO $ getOptionsFromFile dflags0 input_fn
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       (dflags1, unhandled_flags, warns)
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           <- liftIO $ parseDynamicFilePragma dflags0 src_opts
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       setDynFlags dflags1
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       liftIO $ checkProcessArgsResult dflags1 unhandled_flags
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       if not (xopt Opt_Cpp dflags1) then do
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           -- we have to be careful to emit warnings only once.
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           unless (gopt Opt_Pp dflags1) $
               liftIO $ handleFlagWarnings dflags1 warns
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           -- no need to preprocess CPP, just pass input file along
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           -- to the next phase of the pipeline.
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           return (RealPhase (HsPp sf), input_fn)
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        else do
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            output_fn <- phaseOutputFilename (HsPp sf)
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            liftIO $ doCpp dflags1 True{-raw-}
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                           input_fn output_fn
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            -- re-read the pragmas now that we've preprocessed the file
            -- See #2464,#3457
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            src_opts <- liftIO $ getOptionsFromFile dflags0 output_fn
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            (dflags2, unhandled_flags, warns)
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                <- liftIO $ parseDynamicFilePragma dflags0 src_opts
            liftIO $ checkProcessArgsResult dflags2 unhandled_flags
            unless (gopt Opt_Pp dflags2) $
                liftIO $ handleFlagWarnings dflags2 warns
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            -- the HsPp pass below will emit warnings
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            setDynFlags dflags2
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            return (RealPhase (HsPp sf), output_fn)
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-------------------------------------------------------------------------------
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-- HsPp phase
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runPhase (RealPhase (HsPp sf)) input_fn dflags
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  = do
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       if not (gopt Opt_Pp dflags) then
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           -- no need to preprocess, just pass input file along
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           -- to the next phase of the pipeline.
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          return (RealPhase (Hsc sf), input_fn)
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        else do
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            PipeEnv{src_basename, src_suffix} <- getPipeEnv
            let orig_fn = src_basename <.> src_suffix
            output_fn <- phaseOutputFilename (Hsc sf)
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            liftIO $ SysTools.runPp dflags
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                           ( [ SysTools.Option     orig_fn
                             , SysTools.Option     input_fn
                             , SysTools.FileOption "" output_fn
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                             ]
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                           )
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            -- re-read pragmas now that we've parsed the file (see #3674)
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            src_opts <- liftIO $ getOptionsFromFile dflags output_fn
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            (dflags1, unhandled_flags, warns)
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                <- liftIO $ parseDynamicFilePragma dflags src_opts
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            setDynFlags dflags1
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            liftIO $ checkProcessArgsResult dflags1 unhandled_flags
            liftIO $ handleFlagWarnings dflags1 warns
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            return (RealPhase (Hsc sf), output_fn)
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-----------------------------------------------------------------------------
-- Hsc phase

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-- Compilation of a single module, in "legacy" mode (_not_ under
-- the direction of the compilation manager).
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runPhase (RealPhase (Hsc src_flavour)) input_fn dflags0
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 = do   -- normal Hsc mode, not mkdependHS
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        PipeEnv{ stop_phase=stop,
                 src_basename=basename,
                 src_suffix=suff } <- getPipeEnv
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  -- we add the current directory (i.e. the directory in which
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  -- the .hs files resides) to the include path, since this is
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  -- what gcc does, and it's probably what you want.
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        let current_dir = takeDirectory basename
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            paths = includePaths dflags0
            dflags = dflags0 { includePaths = current_dir : paths }

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        setDynFlags dflags

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  -- gather the imports and module name
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        (hspp_buf,mod_name,imps,src_imps) <- liftIO $
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            case src_flavour of
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                ExtCoreFile -> do  -- no explicit imports in ExtCore input.
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                    m <- getCoreModuleName input_fn
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                    return (Nothing, mkModuleName m, [], [])
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                _           -> do
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                    buf <- hGetStringBuffer input_fn
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                    (src_imps,imps,L _ mod_name) <- getImports dflags buf input_fn (basename <.> suff)
                    return (Just buf, mod_name, imps, src_imps)
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  -- Take -o into account if present
  -- Very like -ohi, but we must *only* do this if we aren't linking
  -- (If we're linking then the -o applies to the linked thing, not to
  -- the object file for one module.)
  -- Note the nasty duplication with the same computation in compileFile above
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        location <- getLocation src_flavour mod_name
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        let o_file = ml_obj_file location -- The real object file
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  -- Figure out if the source has changed, for recompilation avoidance.
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  --
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  -- Setting source_unchanged to True means that M.o seems
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  -- to be up to date wrt M.hs; so no need to recompile unless imports have
  -- changed (which the compiler itself figures out).
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  -- Setting source_unchanged to False tells the compiler that M.o is out of
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  -- date wrt M.hs (or M.o doesn't exist) so we must recompile regardless.
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        src_timestamp <- liftIO $ getModificationUTCTime (basename <.> suff)
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        source_unchanged <- liftIO $
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          if not (isStopLn stop)
                -- SourceModified unconditionally if
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                --      (a) recompilation checker is off, or
                --      (b) we aren't going all the way to .o file (e.g. ghc -S)
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             then return SourceModified
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                -- Otherwise look at file modification dates
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             else do o_file_exists <- doesFileExist o_file
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                     if not o_file_exists
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                        then return SourceModified       -- Need to recompile
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                        else do t2 <- getModificationUTCTime o_file
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                                if t2 > src_timestamp
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                                  then return SourceUnmodified
                                  else return SourceModified
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        let extCore_filename = basename ++ ".hcr"
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        PipeState{hsc_env=hsc_env'} <- getPipeState
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  -- Tell the finder cache about this module
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        mod <- liftIO $ addHomeModuleToFinder hsc_env' mod_name location
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  -- Make the ModSummary to hand to hscMain
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        let
            mod_summary = ModSummary {  ms_mod       = mod,
                                        ms_hsc_src   = src_flavour,
                                        ms_hspp_file = input_fn,
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                                        ms_hspp_opts = dflags,
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                                        ms_hspp_buf  = hspp_buf,
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                                        ms_location  = location,
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                                        ms_hs_date   = src_timestamp,
                                        ms_obj_date  = Nothing,
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                                        ms_textual_imps = imps,
                                        ms_srcimps      = src_imps }
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  -- run the compiler!
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        result <- liftIO $ hscCompileOneShot hsc_env' extCore_filename
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                               mod_summary source_unchanged
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        return (HscOut src_flavour mod_name result,
                panic "HscOut doesn't have an input filename")

runPhase (HscOut src_flavour mod_name result) _ dflags = do
        location <- getLocation src_flavour mod_name
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        setModLocation location

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        let o_file = ml_obj_file location -- The real object file
            hsc_lang = hscTarget dflags
            next_phase = hscPostBackendPhase dflags src_flavour hsc_lang

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        case result of