DriverPipeline.hs

{-# OPTIONS -fno-cse #-}
{-# LANGUAGE NamedFieldPuns #-}
-- -fno-cse is needed for GLOBAL_VAR's to behave properly

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

module DriverPipeline (
        -- Run a series of compilation steps in a pipeline, for a
        -- collection of source files.
   oneShot, compileFile,

        -- Interfaces for the batch-mode driver
   linkBinary,

        -- Interfaces for the compilation manager (interpreted/batch-mode)
   preprocess,
   compile, compile',
   link,

  ) where

#include "HsVersions.h"

import Packages
import HeaderInfo
import DriverPhases
import SysTools
import HscMain
import Finder
import HscTypes
import Outputable
import Module
import UniqFM           ( eltsUFM )
import ErrUtils
import DynFlags
import StaticFlags      ( v_Ld_inputs, opt_PIC, opt_Static, WayName(..) )
import Config
import Panic
import Util
import StringBuffer     ( hGetStringBuffer )
import BasicTypes       ( SuccessFlag(..) )
import Maybes           ( expectJust )
import ParserCoreUtils  ( getCoreModuleName )
import SrcLoc
import FastString
import LlvmCodeGen      ( llvmFixupAsm )
import MonadUtils
import Platform

import Exception
import Data.IORef       ( readIORef )
import System.Directory
import System.FilePath
import System.IO
import Control.Monad
import Data.List        ( isSuffixOf )
import Data.Maybe
import System.Environment
import Data.Char

-- ---------------------------------------------------------------------------
-- Pre-process

-- | Just preprocess a file, put the result in a temp. file (used by the
-- compilation manager during the summary phase).
--
-- We return the augmented DynFlags, because they contain the result
-- of slurping in the OPTIONS pragmas

preprocess :: HscEnv
           -> (FilePath, Maybe Phase) -- ^ filename and starting phase
           -> IO (DynFlags, FilePath)
preprocess hsc_env (filename, mb_phase) =
  ASSERT2(isJust mb_phase || isHaskellSrcFilename filename, text filename)
  runPipeline anyHsc hsc_env (filename, mb_phase)
        Nothing Temporary Nothing{-no ModLocation-} Nothing{-no stub-}

-- ---------------------------------------------------------------------------

-- | Compile
--
-- 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
-- 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.
--
-- NB.  No old interface can also mean that the source has changed.

compile :: 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

compile = compile' (hscCompileNothing, hscCompileInteractive, hscCompileBatch)

compile' :: 
           (Compiler (HscStatus, ModIface, ModDetails),
            Compiler (InteractiveStatus, ModIface, ModDetails),
            Compiler (HscStatus, ModIface, ModDetails))
        -> 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

compile' (nothingCompiler, interactiveCompiler, batchCompiler)
        hsc_env0 summary mod_index nmods mb_old_iface maybe_old_linkable
        source_modified0
 = do
   let dflags0     = ms_hspp_opts summary
       this_mod    = ms_mod summary
       src_flavour = ms_hsc_src summary
       location    = ms_location summary
       input_fn    = expectJust "compile:hs" (ml_hs_file location)
       input_fnpp  = ms_hspp_file summary

   debugTraceMsg dflags0 2 (text "compile: input file" <+> text input_fnpp)

   let basename = dropExtension input_fn

  -- 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.
   let current_dir = case takeDirectory basename of
                     "" -> "." -- XXX Hack required for filepath-1.1 and earlier
                               -- (GHC 6.12 and earlier)
                     d -> d
       old_paths   = includePaths dflags0
       dflags      = dflags0 { includePaths = current_dir : old_paths }
       hsc_env     = hsc_env0 {hsc_dflags = dflags}

   -- Figure out what lang we're generating
   let hsc_lang = hscTarget dflags
   -- ... and what the next phase should be
   let next_phase = hscNextPhase dflags src_flavour hsc_lang
   -- ... and what file to generate the output into
   output_fn <- getOutputFilename next_phase
                        Temporary basename dflags next_phase (Just location)

   let dflags' = dflags { hscTarget = hsc_lang,
                                hscOutName = output_fn,
                                extCoreName = basename ++ ".hcr" }
   let hsc_env' = hsc_env { hsc_dflags = dflags' }

   -- -fforce-recomp should also work with --make
   let force_recomp = dopt Opt_ForceRecomp dflags
       source_modified
         | force_recomp || isNothing maybe_old_linkable = SourceModified
         | otherwise = source_modified0
       object_filename = ml_obj_file location

   let handleBatch HscNoRecomp
           = ASSERT (isJust maybe_old_linkable)
             return maybe_old_linkable

       handleBatch (HscRecomp hasStub _)
           | isHsBoot src_flavour
               = do when (isObjectTarget hsc_lang) $ -- interpreted reaches here too
                       liftIO $ touchObjectFile dflags' object_filename
                    return maybe_old_linkable

           | otherwise
               = do (hs_unlinked, unlinked_time) <-
                        case hsc_lang of
                          HscNothing ->
                            return ([], ms_hs_date summary)
                          -- We're in --make mode: finish the compilation pipeline.
                          _other -> do
                            maybe_stub_o <- case hasStub of
                               Nothing -> return Nothing
                               Just stub_c -> do
                                 stub_o <- compileStub hsc_env' stub_c
                                 return (Just stub_o)
                            _ <- runPipeline StopLn hsc_env' (output_fn,Nothing)
                                              (Just basename)
                                              Persistent
                                              (Just location)
                                              maybe_stub_o
                                  -- The object filename comes from the ModLocation
                            o_time <- getModificationTime object_filename
                            return ([DotO object_filename], o_time)
                    
                    let linkable = LM unlinked_time this_mod hs_unlinked
                    return (Just linkable)

       handleInterpreted HscNoRecomp
           = ASSERT (isJust maybe_old_linkable)
             return maybe_old_linkable
       handleInterpreted (HscRecomp _hasStub Nothing)
           = ASSERT (isHsBoot src_flavour)
             return maybe_old_linkable
       handleInterpreted (HscRecomp hasStub (Just (comp_bc, modBreaks)))
           = do stub_o <- case hasStub of
                            Nothing -> return []
                            Just stub_c -> do
                              stub_o <- compileStub hsc_env' stub_c
                              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 (Just linkable)

   let -- runCompiler :: Compiler result -> (result -> Maybe Linkable)
       --            -> m HomeModInfo
       runCompiler compiler handle
           = do (result, iface, details)
                    <- compiler hsc_env' summary source_modified mb_old_iface
                                (Just (mod_index, nmods))
                linkable <- handle result
                return (HomeModInfo{ hm_details  = details,
                                     hm_iface    = iface,
                                     hm_linkable = linkable })
   -- run the compiler
   case hsc_lang of
      HscInterpreted -> runCompiler interactiveCompiler handleInterpreted
      HscNothing     -> runCompiler nothingCompiler     handleBatch
      _other         -> runCompiler batchCompiler       handleBatch

-----------------------------------------------------------------------------
-- stub .h and .c files (for foreign export support)

-- The _stub.c file is derived from the haskell source file, possibly taking
-- into account the -stubdir option.
--
-- 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).

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

        return stub_o

-- ---------------------------------------------------------------------------
-- Link

link :: GhcLink                 -- interactive or batch
     -> DynFlags                -- dynamic flags
     -> Bool                    -- attempt linking in batch mode?
     -> HomePackageTable        -- what to link
     -> 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.

link LinkInMemory _ _ _
    = if cGhcWithInterpreter == "YES"
      then -- Not Linking...(demand linker will do the job)
           return Succeeded
      else panicBadLink LinkInMemory

link NoLink _ _ _
   = return Succeeded

link LinkBinary dflags batch_attempt_linking hpt
   = link' dflags batch_attempt_linking hpt

link LinkDynLib dflags batch_attempt_linking hpt
   = link' dflags batch_attempt_linking hpt

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
   | batch_attempt_linking
   = do
        let
            home_mod_infos = eltsUFM hpt

            -- the packages we depend on
            pkg_deps  = concatMap (map fst . dep_pkgs . mi_deps . hm_iface) home_mod_infos

            -- the linkables to link
            linkables = map (expectJust "link".hm_linkable) home_mod_infos

        debugTraceMsg dflags 3 (text "link: linkables are ..." $$ vcat (map ppr linkables))

        -- 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

        let getOfiles (LM _ _ us) = map nameOfObject (filter isObject us)
            obj_files = concatMap getOfiles linkables

            exe_file = exeFileName dflags

        linking_needed <- linkingNeeded dflags linkables pkg_deps

        if not (dopt Opt_ForceRecomp dflags) && not linking_needed
           then do debugTraceMsg dflags 2 (text exe_file <+> ptext (sLit "is up to date, linking not required."))
                   return Succeeded
           else do

        compilationProgressMsg dflags $ showSDoc $
            (ptext (sLit "Linking") <+> text exe_file <+> text "...")

        -- Don't showPass in Batch mode; doLink will do that for us.
        let link = case ghcLink dflags of
                LinkBinary  -> linkBinary
                LinkDynLib  -> linkDynLib
                other       -> panicBadLink other
        link dflags obj_files pkg_deps

        debugTraceMsg dflags 3 (text "link: done")

        -- linkBinary only returns if it succeeds
        return Succeeded

   | otherwise
   = do debugTraceMsg dflags 3 (text "link(batch): upsweep (partially) failed OR" $$
                                text "   Main.main not exported; not linking.")
        return Succeeded


linkingNeeded :: DynFlags -> [Linkable] -> [PackageId] -> IO Bool
linkingNeeded dflags linkables pkg_deps = do
        -- 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).
  let exe_file = exeFileName dflags
  e_exe_time <- tryIO $ getModificationTime exe_file
  case e_exe_time of
    Left _  -> return True
    Right t -> do
        -- first check object files and extra_ld_inputs
        extra_ld_inputs <- readIORef v_Ld_inputs
        e_extra_times <- mapM (tryIO . getModificationTime) extra_ld_inputs
        let (errs,extra_times) = splitEithers e_extra_times
        let obj_times =  map linkableTime linkables ++ extra_times
        if not (null errs) || any (t <) obj_times
            then return True
            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 ]

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

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

ghcLinkInfoSectionName :: String
ghcLinkInfoSectionName = ".debug-ghc-link-info"
   -- if we use the ".debug" prefix, then strip will strip it by default

findHSLib :: [String] -> String -> IO (Maybe FilePath)
findHSLib dirs lib = do
  let batch_lib_file = "lib" ++ lib <.> "a"
  found <- filterM doesFileExist (map (</> batch_lib_file) dirs)
  case found of
    [] -> return Nothing
    (x:_) -> return (Just x)

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

oneShot :: HscEnv -> Phase -> [(String, Maybe Phase)] -> IO ()
oneShot hsc_env stop_phase srcs = do
  o_files <- mapM (compileFile hsc_env stop_phase) srcs
  doLink (hsc_dflags hsc_env) stop_phase o_files

compileFile :: HscEnv -> Phase -> (FilePath, Maybe Phase) -> IO FilePath
compileFile hsc_env stop_phase (src, mb_phase) = do
   exists <- doesFileExist src
   when (not exists) $
        ghcError (CmdLineError ("does not exist: " ++ src))

   let
        dflags = hsc_dflags hsc_env
        split     = dopt Opt_SplitObjs dflags
        mb_o_file = outputFile dflags
        ghc_link  = ghcLink dflags      -- Set by -c or -no-link

        -- When linking, the -o argument refers to the linker's output.
        -- otherwise, we use it as the name for the pipeline's output.
        output
         | StopLn <- stop_phase, not (isNoLink ghc_link) = Persistent
                -- -o foo applies to linker
         | Just o_file <- mb_o_file = SpecificFile o_file
                -- -o foo applies to the file we are compiling now
         | otherwise = Persistent

        stop_phase' = case stop_phase of
                        As | split -> SplitAs
                        _          -> stop_phase

   ( _, out_file) <- runPipeline stop_phase' hsc_env
                            (src, mb_phase) Nothing output
                            Nothing{-no ModLocation-} Nothing
   return out_file


doLink :: DynFlags -> Phase -> [FilePath] -> IO ()
doLink dflags stop_phase o_files
  | not (isStopLn stop_phase)
  = return ()           -- We stopped before the linking phase

  | otherwise
  = case ghcLink dflags of
        NoLink     -> return ()
        LinkBinary -> linkBinary dflags o_files []
        LinkDynLib -> linkDynLib dflags o_files []
        other      -> panicBadLink other


-- ---------------------------------------------------------------------------

data PipelineOutput
  = Temporary
        -- ^ Output should be to a temporary file: we're going to
        -- run more compilation steps on this output later.
  | Persistent
        -- ^ We want a persistent file, i.e. a file in the current directory
        -- derived from the input filename, but with the appropriate extension.
        -- eg. in "ghc -c Foo.hs" the output goes into ./Foo.o.
  | SpecificFile FilePath
        -- ^ The output must go into the specified file.

-- | 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
-- OPTIONS_GHC pragmas), and the changes affect later phases in the
-- pipeline.
runPipeline
  :: Phase                      -- ^ When to stop
  -> HscEnv                     -- ^ Compilation environment
  -> (FilePath,Maybe Phase)     -- ^ Input filename (and maybe -x suffix)
  -> Maybe FilePath             -- ^ original basename (if different from ^^^)
  -> PipelineOutput             -- ^ Output filename
  -> Maybe ModLocation          -- ^ A ModLocation, if this is a Haskell module
  -> Maybe FilePath             -- ^ stub object, if we have one
  -> IO (DynFlags, FilePath)     -- ^ (final flags, output filename)

runPipeline stop_phase hsc_env0 (input_fn, mb_phase)
            mb_basename output maybe_loc maybe_stub_o
  = do
  let dflags0 = hsc_dflags hsc_env0
      (input_basename, suffix) = splitExtension input_fn
      suffix' = drop 1 suffix -- strip off the .
      basename | Just b <- mb_basename = b
               | otherwise             = input_basename

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

        -- If we were given a -x flag, then use that phase to start from
      start_phase = fromMaybe (startPhase suffix') mb_phase

  -- 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.

  when (not (start_phase `happensBefore` stop_phase)) $
        ghcError (UsageError
                    ("cannot compile this file to desired target: "
                       ++ input_fn))

  -- this is a function which will be used to calculate output file names
  -- as we go along (we partially apply it to some of its inputs here)
  let get_output_fn = getOutputFilename stop_phase output basename

  -- Execute the pipeline...
  let env   = PipeEnv{ stop_phase,
                       src_basename = basename,
                       src_suffix = suffix',
                       output_spec = output }

      state = PipeState{ hsc_env, maybe_loc, maybe_stub_o = maybe_stub_o }

  (state', output_fn) <- unP (pipeLoop start_phase input_fn) env state

  let PipeState{ hsc_env=hsc_env', maybe_loc } = state'
      dflags' = hsc_dflags hsc_env'

  -- 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 of
    Temporary ->
        return (dflags', output_fn)
    _other -> 
        do final_fn <- get_output_fn dflags' stop_phase maybe_loc
           when (final_fn /= output_fn) $ do
              let msg = ("Copying `" ++ output_fn ++"' to `" ++ final_fn ++ "'")
                  line_prag = Just ("{-# LINE 1 \"" ++ input_fn ++ "\" #-}\n")
              copyWithHeader dflags msg line_prag output_fn final_fn
           return (dflags', final_fn)

-- -----------------------------------------------------------------------------
-- The pipeline uses a monad to carry around various bits of information

-- PipeEnv: invariant information passed down
data PipeEnv = PipeEnv {
       stop_phase   :: Phase,       -- ^ Stop just before this phase
       src_basename :: String,      -- ^ basename of original input source
       src_suffix   :: String,      -- ^ its extension
       output_spec  :: PipelineOutput -- ^ says where to put the pipeline output
  }

-- PipeState: information that might change during a pipeline run
data PipeState = PipeState {
       hsc_env   :: HscEnv,
          -- ^ only the DynFlags change in the HscEnv.  The DynFlags change
          -- at various points, for example when we read the OPTIONS_GHC
          -- pragmas in the Cpp phase.
       maybe_loc :: Maybe ModLocation,
          -- ^ the ModLocation.  This is discovered during compilation,
          -- in the Hsc phase where we read the module header.
       maybe_stub_o :: Maybe FilePath
          -- ^ the stub object.  This is set by the Hsc phase if a stub
          -- object was created.  The stub object will be joined with
          -- the main compilation object using "ld -r" at the end.
  }

getPipeEnv :: CompPipeline PipeEnv
getPipeEnv = P $ \env state -> return (state, env)

getPipeState :: CompPipeline PipeState
getPipeState = P $ \_env state -> return (state, state)

getDynFlags :: CompPipeline DynFlags
getDynFlags = P $ \_env state -> return (state, hsc_dflags (hsc_env state))

setDynFlags :: DynFlags -> CompPipeline ()
setDynFlags dflags = P $ \_env state ->
  return (state{hsc_env= (hsc_env state){ hsc_dflags = dflags }}, ())

setModLocation :: ModLocation -> CompPipeline ()
setModLocation loc = P $ \_env state ->
  return (state{ maybe_loc = Just loc }, ())

setStubO :: FilePath -> CompPipeline ()
setStubO stub_o = P $ \_env state ->
  return (state{ maybe_stub_o = Just stub_o }, ())

newtype CompPipeline a = P { unP :: PipeEnv -> PipeState -> IO (PipeState, a) }

instance Monad CompPipeline where
  return a = P $ \_env state -> return (state, a)
  P m >>= k = P $ \env state -> do (state',a) <- m env state
                                   unP (k a) env state'

io :: IO a -> CompPipeline a
io m = P $ \_env state -> do a <- m; return (state, a)

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
  io $ getOutputFilename stop_phase output_spec
                         src_basename dflags next_phase maybe_loc

-- ---------------------------------------------------------------------------
-- outer pipeline loop

-- | pipeLoop runs phases until we reach the stop phase
pipeLoop :: Phase -> FilePath -> CompPipeline FilePath
pipeLoop phase input_fn = do
  PipeEnv{stop_phase} <- getPipeEnv
  PipeState{hsc_env}  <- getPipeState
  case () of
   _ | phase `eqPhase` stop_phase            -- All done
     -> return input_fn

     | not (phase `happensBefore` stop_phase)
        -- 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 #-}.
     -> panic ("pipeLoop: at phase " ++ show phase ++
           " but I wanted to stop at phase " ++ show stop_phase)

     | otherwise
     -> do io $ debugTraceMsg (hsc_dflags hsc_env) 4
                         (ptext (sLit "Running phase") <+> ppr phase)
           dflags <- getDynFlags
           (next_phase, output_fn) <- runPhase phase input_fn dflags
           pipeLoop next_phase output_fn

-- -----------------------------------------------------------------------------
-- 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.

getOutputFilename
  :: Phase -> PipelineOutput -> String
  -> DynFlags -> Phase{-next phase-} -> Maybe ModLocation -> IO FilePath
getOutputFilename stop_phase output basename
 = func
 where
        func dflags next_phase maybe_location
           | is_last_phase, Persistent <- output     = persistent_fn
           | is_last_phase, SpecificFile f <- output = return f
           | keep_this_output                        = persistent_fn
           | otherwise                               = newTempName dflags suffix
           where
                hcsuf      = hcSuf dflags
                odir       = objectDir dflags
                osuf       = objectSuf dflags
                keep_hc    = dopt Opt_KeepHcFiles dflags
                keep_s     = dopt Opt_KeepSFiles dflags
                keep_bc    = dopt 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


-- -----------------------------------------------------------------------------
-- | Each phase in the pipeline returns the next phase to execute, and the
-- 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
-- taking the via-C route to using the native code generator.
--
runPhase :: Phase       -- ^ Run this phase
         -> FilePath    -- ^ name of the input file
         -> DynFlags    -- ^ for convenience, we pass the current dflags in
         -> CompPipeline (Phase,               -- next phase to run
                          FilePath)            -- output filename

        -- 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


-------------------------------------------------------------------------------
-- Unlit phase

runPhase (Unlit sf) input_fn dflags
  = do
       output_fn <- phaseOutputFilename (Cpp sf)

       let unlit_flags = getOpts dflags opt_L
           flags = map SysTools.Option unlit_flags ++
                   [ -- The -h option passes the file name for unlit to
                     -- put in a #line directive
                     SysTools.Option     "-h"
                     -- cpp interprets \b etc as escape sequences,
                     -- so we use / for filenames in pragmas
                   , SysTools.Option $ reslash Forwards $ normalise input_fn
                   , SysTools.FileOption "" input_fn
                   , SysTools.FileOption "" output_fn
                   ]

       io $ SysTools.runUnlit dflags flags

       return (Cpp sf, output_fn)

-------------------------------------------------------------------------------
-- Cpp phase : (a) gets OPTIONS out of file
--             (b) runs cpp if necessary

runPhase (Cpp sf) input_fn dflags0
  = do
       src_opts <- io $ getOptionsFromFile dflags0 input_fn
       (dflags1, unhandled_flags, warns)
           <- io $ parseDynamicFilePragma dflags0 src_opts
       setDynFlags dflags1
       io $ checkProcessArgsResult unhandled_flags

       if not (xopt Opt_Cpp dflags1) then do
           -- we have to be careful to emit warnings only once.
           unless (dopt Opt_Pp dflags1) $ io $ handleFlagWarnings dflags1 warns

           -- no need to preprocess CPP, just pass input file along
           -- to the next phase of the pipeline.
           return (HsPp sf, input_fn)
        else do
            output_fn <- phaseOutputFilename (HsPp sf)
            io $ doCpp dflags1 True{-raw-} False{-no CC opts-} input_fn output_fn
            -- re-read the pragmas now that we've preprocessed the file
            -- See #2464,#3457
            src_opts <- io $ getOptionsFromFile dflags0 output_fn
            (dflags2, unhandled_flags, warns)
                <- io $ parseDynamicFilePragma dflags0 src_opts
            io $ checkProcessArgsResult unhandled_flags
            unless (dopt Opt_Pp dflags2) $ io $ handleFlagWarnings dflags2 warns
            -- the HsPp pass below will emit warnings

            setDynFlags dflags2

            return (HsPp sf, output_fn)

-------------------------------------------------------------------------------
-- HsPp phase

runPhase (HsPp sf) input_fn dflags
  = do
       if not (dopt Opt_Pp dflags) then
           -- no need to preprocess, just pass input file along
           -- to the next phase of the pipeline.
          return (Hsc sf, input_fn)
        else do
            let hspp_opts = getOpts dflags opt_F
            PipeEnv{src_basename, src_suffix} <- getPipeEnv
            let orig_fn = src_basename <.> src_suffix
            output_fn <- phaseOutputFilename (Hsc sf)
            io $ SysTools.runPp dflags
                           ( [ SysTools.Option     orig_fn
                             , SysTools.Option     input_fn
                             , SysTools.FileOption "" output_fn
                             ] ++
                             map SysTools.Option hspp_opts
                           )

            -- re-read pragmas now that we've parsed the file (see #3674)
            src_opts <- io $ getOptionsFromFile dflags output_fn
            (dflags1, unhandled_flags, warns)
                <- io $ parseDynamicFilePragma dflags src_opts
            setDynFlags dflags1
            io $ checkProcessArgsResult unhandled_flags
            io $ handleFlagWarnings dflags1 warns

            return (Hsc sf, output_fn)

-----------------------------------------------------------------------------
-- Hsc phase

-- Compilation of a single module, in "legacy" mode (_not_ under
-- the direction of the compilation manager).
runPhase (Hsc src_flavour) input_fn dflags0
 = do   -- normal Hsc mode, not mkdependHS

        PipeEnv{ stop_phase=stop,
                 src_basename=basename,
                 src_suffix=suff } <- getPipeEnv

  -- we add the current directory (i.e. the directory in which
  -- the .hs files resides) to the include path, since this is
  -- what gcc does, and it's probably what you want.
        let current_dir = case takeDirectory basename of
                     "" -> "." -- XXX Hack required for filepath-1.1 and earlier
                               -- (GHC 6.12 and earlier)
                     d -> d

            paths = includePaths dflags0
            dflags = dflags0 { includePaths = current_dir : paths }

        setDynFlags dflags

  -- gather the imports and module name
        (hspp_buf,mod_name,imps,src_imps) <- io $
            case src_flavour of
                ExtCoreFile -> do  -- no explicit imports in ExtCore input.
                    m <- getCoreModuleName input_fn
                    return (Nothing, mkModuleName m, [], [])

                _           -> do
                    buf <- hGetStringBuffer input_fn
                    (src_imps,imps,L _ mod_name) <- getImports dflags buf input_fn (basename <.> suff)
                    return (Just buf, mod_name, imps, src_imps)

  -- Build a ModLocation to pass to hscMain.
  -- The source filename is rather irrelevant by now, but it's used
  -- by hscMain for messages.  hscMain also needs
  -- the .hi and .o filenames, and this is as good a way
  -- as any to generate them, and better than most. (e.g. takes
  -- into accout the -osuf flags)
        location1 <- io $ mkHomeModLocation2 dflags mod_name basename suff

  -- Boot-ify it if necessary
        let location2 | isHsBoot src_flavour = addBootSuffixLocn location1
                      | otherwise            = location1


  -- Take -ohi into account if present
  -- This can't be done in mkHomeModuleLocation because
  -- it only applies to the module being compiles
        let ohi = outputHi dflags
            location3 | Just fn <- ohi = location2{ ml_hi_file = fn }
                      | otherwise      = location2

  -- 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
        let expl_o_file = outputFile dflags
            location4 | Just ofile <- expl_o_file
                      , isNoLink (ghcLink dflags)
                      = location3 { ml_obj_file = ofile }
                      | otherwise = location3

            o_file = ml_obj_file location4      -- The real object file

        setModLocation location4

  -- Figure out if the source has changed, for recompilation avoidance.
  --
  -- Setting source_unchanged to True means that M.o seems
  -- to be up to date wrt M.hs; so no need to recompile unless imports have
  -- changed (which the compiler itself figures out).
  -- Setting source_unchanged to False tells the compiler that M.o is out of
  -- date wrt M.hs (or M.o doesn't exist) so we must recompile regardless.
        src_timestamp <- io $ getModificationTime (basename <.> suff)

        let hsc_lang = hscTarget dflags
        source_unchanged <- io $
          if not (isStopLn stop)
                -- SourceModified unconditionally if
                --      (a) recompilation checker is off, or
                --      (b) we aren't going all the way to .o file (e.g. ghc -S)
             then return SourceModified
                -- Otherwise look at file modification dates
             else do o_file_exists <- doesFileExist o_file
                     if not o_file_exists
                        then return SourceModified       -- Need to recompile
                        else do t2 <- getModificationTime o_file
                                if t2 > src_timestamp
                                  then return SourceUnmodified
                                  else return SourceModified

  -- get the DynFlags