Replace HscTarget with Backend

They both have the same role and Backend name is more explicit.

Metric Decrease:
    T3064

Update Haddock submodule

25 files changed, 305 insertions, 249 deletions

diff --git a/compiler/GHC.hs b/compiler/GHC.hs
index d5d15143c2..f61c93ea2d 100644
--- a/compiler/GHC.hs
+++ b/compiler/GHC.hs
@@ -27,8 +27,8 @@ module GHC (
         needsTemplateHaskellOrQQ,
 
         -- * Flags and settings
-        DynFlags(..), GeneralFlag(..), Severity(..), HscTarget(..), gopt,
-        GhcMode(..), GhcLink(..), defaultObjectTarget,
+        DynFlags(..), GeneralFlag(..), Severity(..), Backend(..), gopt,
+        GhcMode(..), GhcLink(..),
         parseDynamicFlags,
         getSessionDynFlags, setSessionDynFlags,
         getProgramDynFlags, setProgramDynFlags, setLogAction,
@@ -302,6 +302,7 @@ import GHC.Runtime.Interpreter.Types
 import GHCi.RemoteTypes
 
 import GHC.Core.Ppr.TyThing  ( pprFamInst )
+import GHC.Driver.Backend
 import GHC.Driver.Main
 import GHC.Driver.Make
 import GHC.Driver.Hooks
@@ -1012,7 +1013,7 @@ desugarModule tcm = do
 --
 -- A module must be loaded before dependent modules can be typechecked.  This
 -- always includes generating a 'ModIface' and, depending on the
--- @DynFlags@\'s 'GHC.Driver.Session.hscTarget', may also include code generation.
+-- @DynFlags@\'s 'GHC.Driver.Session.backend', may also include code generation.
 --
 -- This function will always cause recompilation and will always overwrite
 -- previous compilation results (potentially files on disk).
diff --git a/compiler/GHC/Cmm/CLabel.hs b/compiler/GHC/Cmm/CLabel.hs
index 47487c7ebe..ab1ecede5f 100644
--- a/compiler/GHC/Cmm/CLabel.hs
+++ b/compiler/GHC/Cmm/CLabel.hs
@@ -129,6 +129,7 @@ import GHC.Types.CostCentre
 import GHC.Utils.Outputable
 import GHC.Data.FastString
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Platform
 import GHC.Types.Unique.Set
 import GHC.Utils.Misc
@@ -1255,7 +1256,7 @@ pprCLabel dflags = \case
 
   where
     platform = targetPlatform dflags
-    useNCG   = hscTarget dflags == HscAsm
+    useNCG   = backend dflags == NCG
 
     maybe_underscore :: SDoc -> SDoc
     maybe_underscore doc =
diff --git a/compiler/GHC/Cmm/Pipeline.hs b/compiler/GHC/Cmm/Pipeline.hs
index e28c880d44..876de8a41e 100644
--- a/compiler/GHC/Cmm/Pipeline.hs
+++ b/compiler/GHC/Cmm/Pipeline.hs
@@ -24,6 +24,7 @@ import GHC.Cmm.Dataflow.Collections
 
 import GHC.Types.Unique.Supply
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Utils.Error
 import GHC.Driver.Types
 import Control.Monad
@@ -171,7 +172,7 @@ cpsTop hsc_env proc =
         -- tablesNextToCode is off.  The latter is because we have no
         -- label to put on info tables for basic blocks that are not
         -- the entry point.
-        splitting_proc_points = hscTarget dflags /= HscAsm
+        splitting_proc_points = backend dflags /= NCG
                              || not (platformTablesNextToCode platform)
                              || -- Note [inconsistent-pic-reg]
                                 usingInconsistentPicReg
diff --git a/compiler/GHC/Cmm/Switch.hs b/compiler/GHC/Cmm/Switch.hs
index b8d7456b37..ee0d5a07df 100644
--- a/compiler/GHC/Cmm/Switch.hs
+++ b/compiler/GHC/Cmm/Switch.hs
@@ -8,14 +8,14 @@ module GHC.Cmm.Switch (
      switchTargetsToList, eqSwitchTargetWith,
 
      SwitchPlan(..),
-     targetSupportsSwitch,
+     backendSupportsSwitch,
      createSwitchPlan,
   ) where
 
 import GHC.Prelude
 
 import GHC.Utils.Outputable
-import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Cmm.Dataflow.Label (Label)
 
 import Data.Maybe
@@ -316,12 +316,12 @@ and slowed down all other cases making it not worthwhile.
 -}
 
 
--- | Does the target support switch out of the box? Then leave this to the
--- target!
-targetSupportsSwitch :: HscTarget -> Bool
-targetSupportsSwitch HscC = True
-targetSupportsSwitch HscLlvm = True
-targetSupportsSwitch _ = False
+-- | Does the backend support switch out of the box? Then leave this to the
+-- backend!
+backendSupportsSwitch :: Backend -> Bool
+backendSupportsSwitch ViaC = True
+backendSupportsSwitch LLVM = True
+backendSupportsSwitch _    = False
 
 -- | This function creates a SwitchPlan from a SwitchTargets value, breaking it
 -- down into smaller pieces suitable for code generation.
diff --git a/compiler/GHC/Cmm/Switch/Implement.hs b/compiler/GHC/Cmm/Switch/Implement.hs
index 3279c5ab05..a91809e585 100644
--- a/compiler/GHC/Cmm/Switch/Implement.hs
+++ b/compiler/GHC/Cmm/Switch/Implement.hs
@@ -35,7 +35,7 @@ import GHC.Utils.Monad (concatMapM)
 cmmImplementSwitchPlans :: DynFlags -> CmmGraph -> UniqSM CmmGraph
 cmmImplementSwitchPlans dflags g
     -- Switch generation done by backend (LLVM/C)
-    | targetSupportsSwitch (hscTarget dflags) = return g
+    | backendSupportsSwitch (backend dflags) = return g
     | otherwise = do
     blocks' <- concatMapM (visitSwitches (targetPlatform dflags)) (toBlockList g)
     return $ ofBlockList (g_entry g) blocks'
diff --git a/compiler/GHC/Driver/Backend.hs b/compiler/GHC/Driver/Backend.hs
index 8f227d2a2b..845a5f36c0 100644
--- a/compiler/GHC/Driver/Backend.hs
+++ b/compiler/GHC/Driver/Backend.hs
@@ -5,18 +5,82 @@ module GHC.Driver.Backend
    ( Backend (..)
    , platformDefaultBackend
    , platformNcgSupported
+   , backendProducesObject
+   , backendRetainsAllBindings
    )
 where
 
 import GHC.Prelude
 import GHC.Platform
 
--- | Backend
+-- | Code generation backends.
+--
+-- GHC supports several code generation backends serving different purposes
+-- (producing machine code, producing ByteCode for the interpreter) and
+-- supporting different platforms.
+--
 data Backend
-   = NCG           -- ^ Native code generator backend
-   | LLVM          -- ^ LLVM backend
-   | ViaC          -- ^ Via-C backend
-   | Interpreter   -- ^ Interpreter
+   = NCG           -- ^ Native code generator backend.
+                   --
+                   -- Compiles Cmm code into textual assembler, then relies on
+                   -- an external assembler toolchain to produce machine code.
+                   --
+                   -- Only supports a few platforms (X86, PowerPC, SPARC).
+                   --
+                   -- See "GHC.CmmToAsm".
+
+
+   | LLVM          -- ^ LLVM backend.
+                   --
+                   -- Compiles Cmm code into LLVM textual IR, then relies on
+                   -- LLVM toolchain to produce machine code.
+                   --
+                   -- It relies on LLVM support for the calling convention used
+                   -- by the NCG backend to produce code objects ABI compatible
+                   -- with it (see "cc 10" or "ghccc" calling convention in
+                   -- https://llvm.org/docs/LangRef.html#calling-conventions).
+                   --
+                   -- Support a few platforms (X86, AArch64, s390x, ARM).
+                   --
+                   -- See "GHC.CmmToLlvm"
+
+
+   | ViaC          -- ^ Via-C backend.
+                   --
+                   -- Compiles Cmm code into C code, then relies on a C compiler
+                   -- to produce machine code.
+                   --
+                   -- It produces code objects that are *not* ABI compatible
+                   -- with those produced by NCG and LLVM backends.
+                   --
+                   -- Produced code is expected to be less efficient than the
+                   -- one produced by NCG and LLVM backends because STG
+                   -- registers are not pinned into real registers.  On the
+                   -- other hand, it supports more target platforms (those
+                   -- having a valid C toolchain).
+                   --
+                   -- See "GHC.CmmToC"
+
+
+   | Interpreter   -- ^ ByteCode interpreter.
+                   --
+                   -- Produce ByteCode objects (BCO, see "GHC.ByteCode") that
+                   -- can be interpreted. It is used by GHCi.
+                   --
+                   -- Currently some extensions are not supported (unboxed
+                   -- tuples/sums, foreign primops).
+                   --
+                   -- See "GHC.CoreToByteCode"
+
+
+   | NoBackend     -- ^ No code generated.
+                   --
+                   -- Use this to disable code generation. It is particularly
+                   -- useful when GHC is used as a library for other purpose
+                   -- than generating code (e.g. to generate documentation with
+                   -- Haddock) or when the user requested it (via -fno-code) for
+                   -- some reason.
+
    deriving (Eq,Ord,Show,Read)
 
 -- | Default backend to use for the given platform.
@@ -41,3 +105,27 @@ platformNcgSupported platform = if
          ArchPPC_64 {} -> True
          ArchSPARC     -> True
          _             -> False
+
+-- | Will this backend produce an object file on the disk?
+backendProducesObject :: Backend -> Bool
+backendProducesObject ViaC        = True
+backendProducesObject NCG         = True
+backendProducesObject LLVM        = True
+backendProducesObject Interpreter = False
+backendProducesObject NoBackend   = False
+
+-- | Does this backend retain *all* top-level bindings for a module,
+-- rather than just the exported bindings, in the TypeEnv and compiled
+-- code (if any)?
+--
+-- Interpreter backend does this, so that GHCi can call functions inside a
+-- module.
+--
+-- When no backend is used we also do it, so that Haddock can get access to the
+-- GlobalRdrEnv for a module after typechecking it.
+backendRetainsAllBindings :: Backend -> Bool
+backendRetainsAllBindings Interpreter = True
+backendRetainsAllBindings NoBackend   = True
+backendRetainsAllBindings ViaC        = False
+backendRetainsAllBindings NCG         = False
+backendRetainsAllBindings LLVM        = False
diff --git a/compiler/GHC/Driver/Backpack.hs b/compiler/GHC/Driver/Backpack.hs
index 8dfd865a2b..acde752f66 100644
--- a/compiler/GHC/Driver/Backpack.hs
+++ b/compiler/GHC/Driver/Backpack.hs
@@ -162,15 +162,15 @@ withBkpSession cid insts deps session_type do_this = do
       (case session_type of
         -- Make sure to write interfaces when we are type-checking
         -- indefinite packages.
-        TcSession | hscTarget dflags /= HscNothing
+        TcSession | backend dflags /= NoBackend
                   -> flip gopt_set Opt_WriteInterface
                   | otherwise -> id
         CompSession -> id
         ExeSession -> id) $
       dflags {
-        hscTarget   = case session_type of
-                        TcSession -> HscNothing
-                        _ -> hscTarget dflags,
+        backend   = case session_type of
+                        TcSession -> NoBackend
+                        _ -> backend dflags,
         homeUnitInstantiations = insts,
                                  -- if we don't have any instantiation, don't
                                  -- fill `homeUnitInstanceOfId` as it makes no
@@ -505,8 +505,7 @@ mkBackpackMsg = do
           showMsg msg reason =
             backpackProgressMsg level dflags $
                 showModuleIndex mod_index ++
-                msg ++ showModMsg dflags (hscTarget dflags)
-                                  (recompileRequired recomp) mod_summary
+                msg ++ showModMsg dflags (recompileRequired recomp) mod_summary
                     ++ reason
       in case recomp of
             MustCompile -> showMsg "Compiling " ""
diff --git a/compiler/GHC/Driver/CodeOutput.hs b/compiler/GHC/Driver/CodeOutput.hs
index f0bfcb76ed..5cc502a715 100644
--- a/compiler/GHC/Driver/CodeOutput.hs
+++ b/compiler/GHC/Driver/CodeOutput.hs
@@ -23,6 +23,7 @@ import GHC.CmmToLlvm    ( llvmCodeGen )
 import GHC.Types.Unique.Supply ( mkSplitUniqSupply )
 
 import GHC.Driver.Finder    ( mkStubPaths )
+import GHC.Driver.Backend
 import GHC.CmmToC           ( writeC )
 import GHC.Cmm.Lint         ( cmmLint )
 import GHC.Cmm              ( RawCmmGroup )
@@ -94,13 +95,13 @@ codeOutput dflags this_mod filenm location foreign_stubs foreign_fps pkg_deps
                 }
 
         ; stubs_exist <- outputForeignStubs dflags this_mod location foreign_stubs
-        ; a <- case hscTarget dflags of
-                 HscAsm         -> outputAsm dflags this_mod location filenm
-                                             linted_cmm_stream
-                 HscC           -> outputC dflags filenm linted_cmm_stream pkg_deps
-                 HscLlvm        -> outputLlvm dflags filenm linted_cmm_stream
-                 HscInterpreted -> panic "codeOutput: HscInterpreted"
-                 HscNothing     -> panic "codeOutput: HscNothing"
+        ; a <- case backend dflags of
+                 NCG         -> outputAsm dflags this_mod location filenm
+                                          linted_cmm_stream
+                 ViaC        -> outputC dflags filenm linted_cmm_stream pkg_deps
+                 LLVM        -> outputLlvm dflags filenm linted_cmm_stream
+                 Interpreter -> panic "codeOutput: Interpreter"
+                 NoBackend   -> panic "codeOutput: NoBackend"
         ; return (filenm, stubs_exist, foreign_fps, a)
         }
 
diff --git a/compiler/GHC/Driver/Main.hs b/compiler/GHC/Driver/Main.hs
index a743e0f1ba..b2a0f887e0 100644
--- a/compiler/GHC/Driver/Main.hs
+++ b/compiler/GHC/Driver/Main.hs
@@ -149,6 +149,7 @@ import GHC.Runtime.Loader   ( initializePlugins )
 import GHC.StgToCmm.Types (CgInfos (..), ModuleLFInfos)
 
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Utils.Error
 
 import GHC.Utils.Outputable
@@ -784,7 +785,7 @@ finish :: ModSummary
 finish summary tc_result mb_old_hash = do
   hsc_env <- getHscEnv
   let dflags = hsc_dflags hsc_env
-      target = hscTarget dflags
+      bcknd  = backend dflags
       hsc_src = ms_hsc_src summary
 
   -- Desugar, if appropriate
@@ -802,7 +803,7 @@ finish summary tc_result mb_old_hash = do
   -- interface file.
   case mb_desugar of
       -- Just cause we desugared doesn't mean we are generating code, see above.
-      Just desugared_guts | target /= HscNothing -> do
+      Just desugared_guts | bcknd /= NoBackend -> do
           plugins <- liftIO $ readIORef (tcg_th_coreplugins tc_result)
           simplified_guts <- hscSimplify' plugins desugared_guts
 
@@ -830,11 +831,12 @@ finish summary tc_result mb_old_hash = do
 
         liftIO $ hscMaybeWriteIface dflags iface mb_old_iface_hash (ms_location summary)
 
-        return $ case (target, hsc_src) of
-          (HscNothing, _) -> HscNotGeneratingCode iface details
-          (_, HsBootFile) -> HscUpdateBoot iface details
-          (_, HsigFile) -> HscUpdateSig iface details
-          _ -> panic "finish"
+        return $ case bcknd of
+          NoBackend -> HscNotGeneratingCode iface details
+          _         -> case hsc_src of
+                        HsBootFile -> HscUpdateBoot iface details
+                        HsigFile   -> HscUpdateSig iface details
+                        _          -> panic "finish"
 
 {-
 Note [Writing interface files]
@@ -853,10 +855,10 @@ hscMaybeWriteIface, but only once per compilation (twice with dynamic-too).
 hscMaybeWriteIface :: DynFlags -> ModIface -> Maybe Fingerprint -> ModLocation -> IO ()
 hscMaybeWriteIface dflags iface old_iface location = do
     let force_write_interface = gopt Opt_WriteInterface dflags
-        write_interface = case hscTarget dflags of
-                            HscNothing      -> False
-                            HscInterpreted  -> False
-                            _               -> True
+        write_interface = case backend dflags of
+                            NoBackend    -> False
+                            Interpreter  -> False
+                            _            -> True
         no_change = old_iface == Just (mi_iface_hash (mi_final_exts iface))
 
     when (write_interface || force_write_interface) $
@@ -901,8 +903,7 @@ batchMsg hsc_env mod_index recomp mod_summary =
         showMsg msg reason =
             compilationProgressMsg dflags $
             (showModuleIndex mod_index ++
-            msg ++ showModMsg dflags (hscTarget dflags)
-                              (recompileRequired recomp) mod_summary)
+            msg ++ showModMsg dflags (recompileRequired recomp) mod_summary)
                 ++ reason
 
 --------------------------------------------------------------
diff --git a/compiler/GHC/Driver/Make.hs b/compiler/GHC/Driver/Make.hs
index 6fb5fe9c72..e59a78904d 100644
--- a/compiler/GHC/Driver/Make.hs
+++ b/compiler/GHC/Driver/Make.hs
@@ -40,6 +40,7 @@ import qualified GHC.Runtime.Linker as Linker
 import GHC.Driver.Phases
 import GHC.Driver.Pipeline
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Utils.Error
 import GHC.Driver.Finder
 import GHC.Driver.Monad
@@ -274,7 +275,7 @@ data LoadHowMuch
 --
 -- This function implements the core of GHC's @--make@ mode.  It preprocesses,
 -- compiles and loads the specified modules, avoiding re-compilation wherever
--- possible.  Depending on the target (see 'GHC.Driver.Session.hscTarget') compiling
+-- possible.  Depending on the backend (see 'DynFlags.backend' field) compiling
 -- and loading may result in files being created on disk.
 --
 -- Calls the 'defaultWarnErrLogger' after each compiling each module, whether
@@ -1516,7 +1517,7 @@ upsweep mHscMessage old_hpt stable_mods cleanup sccs = do
                         -- Add any necessary entries to the static pointer
                         -- table. See Note [Grand plan for static forms] in
                         -- GHC.Iface.Tidy.StaticPtrTable.
-                when (hscTarget (hsc_dflags hsc_env4) == HscInterpreted) $
+                when (backend (hsc_dflags hsc_env4) == Interpreter) $
                     liftIO $ hscAddSptEntries hsc_env4
                                  [ spt
                                  | Just linkable <- pure $ hm_linkable mod_info
@@ -1575,24 +1576,25 @@ upsweep_mod hsc_env mHscMessage old_hpt (stable_obj, stable_bco) summary mod_ind
             -- We're using the dflags for this module now, obtained by
             -- applying any options in its LANGUAGE & OPTIONS_GHC pragmas.
             dflags = ms_hspp_opts summary
-            prevailing_target = hscTarget (hsc_dflags hsc_env)
-            local_target      = hscTarget dflags
+            prevailing_backend = backend (hsc_dflags hsc_env)
+            local_backend      = backend dflags
 
             -- If OPTIONS_GHC contains -fasm or -fllvm, be careful that
             -- we don't do anything dodgy: these should only work to change
             -- from -fllvm to -fasm and vice-versa, or away from -fno-code,
             -- otherwise we could end up trying to link object code to byte
             -- code.
-            target = if prevailing_target /= local_target
-                        && (not (isObjectTarget prevailing_target)
-                            || not (isObjectTarget local_target))
-                        && not (prevailing_target == HscNothing)
-                        && not (prevailing_target == HscInterpreted)
-                        then prevailing_target
-                        else local_target
-
-            -- store the corrected hscTarget into the summary
-            summary' = summary{ ms_hspp_opts = dflags { hscTarget = target } }
+            bcknd = case (prevailing_backend,local_backend) of
+               (LLVM,NCG) -> NCG
+               (NCG,LLVM) -> LLVM
+               (NoBackend,b)
+                  | backendProducesObject b -> b
+               (Interpreter,b)
+                  | backendProducesObject b -> b
+               _ -> prevailing_backend
+
+            -- store the corrected backend into the summary
+            summary' = summary{ ms_hspp_opts = dflags { backend = bcknd } }
 
             -- The old interface is ok if
             --  a) we're compiling a source file, and the old HPT
@@ -1623,9 +1625,9 @@ upsweep_mod hsc_env mHscMessage old_hpt (stable_obj, stable_bco) summary mod_ind
                   compileOne' Nothing mHscMessage hsc_env summary' mod_index nmods
                              Nothing mb_linkable src_modified
 
-            -- With the HscNothing target we create empty linkables to avoid
-            -- recompilation.  We have to detect these to recompile anyway if
-            -- the target changed since the last compile.
+            -- With NoBackend we create empty linkables to avoid recompilation.
+            -- We have to detect these to recompile anyway if the backend changed
+            -- since the last compile.
             is_fake_linkable
                | Just hmi <- old_hmi, Just l <- hm_linkable hmi =
                   null (linkableUnlinked l)
@@ -1658,8 +1660,8 @@ upsweep_mod hsc_env mHscMessage old_hpt (stable_obj, stable_bco) summary mod_ind
                 -- object is stable, but we need to load the interface
                 -- off disk to make a HMI.
 
-          | not (isObjectTarget target), is_stable_bco,
-            (target /= HscNothing) `implies` not is_fake_linkable ->
+          | not (backendProducesObject bcknd), is_stable_bco,
+            (bcknd /= NoBackend) `implies` not is_fake_linkable ->
                 ASSERT(isJust old_hmi) -- must be in the old_hpt
                 let Just hmi = old_hmi in do
                 liftIO $ debugTraceMsg (hsc_dflags hsc_env) 5
@@ -1667,11 +1669,11 @@ upsweep_mod hsc_env mHscMessage old_hpt (stable_obj, stable_bco) summary mod_ind
                 return hmi
                 -- BCO is stable: nothing to do
 
-          | not (isObjectTarget target),
+          | not (backendProducesObject bcknd),
             Just hmi <- old_hmi,
             Just l <- hm_linkable hmi,
             not (isObjectLinkable l),
-            (target /= HscNothing) `implies` not is_fake_linkable,
+            (bcknd /= NoBackend) `implies` not is_fake_linkable,
             linkableTime l >= ms_hs_date summary -> do
                 liftIO $ debugTraceMsg (hsc_dflags hsc_env) 5
                            (text "compiling non-stable BCO mod:" <+> ppr this_mod_name)
@@ -1688,7 +1690,7 @@ upsweep_mod hsc_env mHscMessage old_hpt (stable_obj, stable_bco) summary mod_ind
           -- separately and generated a new interface, that we must
           -- read from the disk.
           --
-          | isObjectTarget target,
+          | backendProducesObject bcknd,
             Just obj_date <- mb_obj_date,
             obj_date >= hs_date -> do
                 case old_hmi of
@@ -1728,7 +1730,7 @@ possible.
 When GHC is invoked with -fno-code no object files or linked output will be
 generated. As many errors and warnings as possible will be generated, as if
 -fno-code had not been passed. The session DynFlags will have
-hscTarget == HscNothing.
+backend == NoBackend.
 
 -fwrite-interface
 ~~~~~~~~~~~~~~~~
@@ -2109,15 +2111,11 @@ downsweep hsc_env old_summaries excl_mods allow_dup_roots
        -- for dependencies of modules that have -XTemplateHaskell,
        -- otherwise those modules will fail to compile.
        -- See Note [-fno-code mode] #8025
-       map1 <- if hscTarget dflags == HscNothing
-         then enableCodeGenForTH
-           (defaultObjectTarget dflags)
-           map0
-         else if hscTarget dflags == HscInterpreted
-           then enableCodeGenForUnboxedTuplesOrSums
-             (defaultObjectTarget dflags)
-             map0
-           else return map0
+       let default_backend = platformDefaultBackend (targetPlatform dflags)
+       map1 <- case backend dflags of
+         NoBackend   -> enableCodeGenForTH default_backend map0
+         Interpreter -> enableCodeGenForUnboxedTuplesOrSums default_backend map0
+         _           -> return map0
        if null errs
          then pure $ concat $ nodeMapElts map1
          else pure $ map Left errs
@@ -2200,7 +2198,7 @@ downsweep hsc_env old_summaries excl_mods allow_dup_roots
 -- the specified target, disable optimization and change the .hi
 -- and .o file locations to be temporary files.
 -- See Note [-fno-code mode]
-enableCodeGenForTH :: HscTarget
+enableCodeGenForTH :: Backend
   -> NodeMap [Either ErrorMessages ModSummary]
   -> IO (NodeMap [Either ErrorMessages ModSummary])
 enableCodeGenForTH =
@@ -2208,7 +2206,7 @@ enableCodeGenForTH =
   where
     condition = isTemplateHaskellOrQQNonBoot
     should_modify (ModSummary { ms_hspp_opts = dflags }) =
-      hscTarget dflags == HscNothing &&
+      backend dflags == NoBackend &&
       -- Don't enable codegen for TH on indefinite packages; we
       -- can't compile anything anyway! See #16219.
       homeUnitIsDefinite dflags
@@ -2220,7 +2218,7 @@ enableCodeGenForTH =
 --
 -- This is used in order to load code that uses unboxed tuples
 -- or sums into GHCi while still allowing some code to be interpreted.
-enableCodeGenForUnboxedTuplesOrSums :: HscTarget
+enableCodeGenForUnboxedTuplesOrSums :: Backend
   -> NodeMap [Either ErrorMessages ModSummary]
   -> IO (NodeMap [Either ErrorMessages ModSummary])
 enableCodeGenForUnboxedTuplesOrSums =
@@ -2233,7 +2231,7 @@ enableCodeGenForUnboxedTuplesOrSums =
     unboxed_tuples_or_sums d =
       xopt LangExt.UnboxedTuples d || xopt LangExt.UnboxedSums d
     should_modify (ModSummary { ms_hspp_opts = dflags }) =
-      hscTarget dflags == HscInterpreted
+      backend dflags == Interpreter
 
 -- | Helper used to implement 'enableCodeGenForTH' and
 -- 'enableCodeGenForUnboxedTuples'. In particular, this enables
@@ -2246,10 +2244,10 @@ enableCodeGenWhen
   -> (ModSummary -> Bool)
   -> TempFileLifetime
   -> TempFileLifetime
-  -> HscTarget
+  -> Backend
   -> NodeMap [Either ErrorMessages ModSummary]
   -> IO (NodeMap [Either ErrorMessages ModSummary])
-enableCodeGenWhen condition should_modify staticLife dynLife target nodemap =
+enableCodeGenWhen condition should_modify staticLife dynLife bcknd nodemap =
   traverse (traverse (traverse enable_code_gen)) nodemap
   where
     enable_code_gen ms
@@ -2282,7 +2280,7 @@ enableCodeGenWhen condition should_modify staticLife dynLife target nodemap =
           ms
           { ms_location =
               ms_location {ml_hi_file = hi_file, ml_obj_file = o_file}
-          , ms_hspp_opts = updOptLevel 0 $ dflags {hscTarget = target}
+          , ms_hspp_opts = updOptLevel 0 $ dflags {backend = bcknd}
           }
       | otherwise = return ms
 
@@ -2433,7 +2431,7 @@ checkSummaryTimestamp
       not (gopt Opt_ForceRecomp (hsc_dflags hsc_env)) = do
            -- update the object-file timestamp
            obj_timestamp <-
-             if isObjectTarget (hscTarget (hsc_dflags hsc_env))
+             if backendProducesObject (backend (hsc_dflags hsc_env))
                  || obj_allowed -- bug #1205
                  then liftIO $ getObjTimestamp location is_boot
                  else return Nothing
@@ -2609,7 +2607,7 @@ makeNewModSummary hsc_env MakeNewModSummary{..} = do
   -- when the user asks to load a source file by name, we only
   -- use an object file if -fobject-code is on.  See #1205.
   obj_timestamp <- liftIO $
-      if isObjectTarget (hscTarget dflags)
+      if backendProducesObject (backend dflags)
          || nms_obj_allowed -- bug #1205
           then getObjTimestamp nms_location nms_is_boot
           else return Nothing
diff --git a/compiler/GHC/Driver/Pipeline.hs b/compiler/GHC/Driver/Pipeline.hs
index 81a141afee..336a3bc447 100644
--- a/compiler/GHC/Driver/Pipeline.hs
+++ b/compiler/GHC/Driver/Pipeline.hs
@@ -53,6 +53,7 @@ import GHC.Utils.Outputable
 import GHC.Unit.Module
 import GHC.Utils.Error
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Utils.Panic
 import GHC.Utils.Misc
 import GHC.Data.StringBuffer ( hGetStringBuffer, hPutStringBuffer )
@@ -183,25 +184,25 @@ compileOne' m_tc_result mHscMessage
    -- hscIncrementalCompile)
    let hsc_env' = hsc_env{ hsc_dflags = plugin_dflags }
 
-   case (status, hsc_lang) of
+   case (status, bcknd) of
         (HscUpToDate iface hmi_details, _) ->
             -- TODO recomp014 triggers this assert. What's going on?!
             -- ASSERT( isJust mb_old_linkable || isNoLink (ghcLink dflags) )
             return $! HomeModInfo iface hmi_details mb_old_linkable
-        (HscNotGeneratingCode iface hmi_details, HscNothing) ->
+        (HscNotGeneratingCode iface hmi_details, NoBackend) ->
             let mb_linkable = if isHsBootOrSig src_flavour
                                 then Nothing
                                 -- TODO: Questionable.
                                 else Just (LM (ms_hs_date summary) this_mod [])
             in return $! HomeModInfo iface hmi_details mb_linkable
         (HscNotGeneratingCode _ _, _) -> panic "compileOne HscNotGeneratingCode"
-        (_, HscNothing) -> panic "compileOne HscNothing"
-        (HscUpdateBoot iface hmi_details, HscInterpreted) -> do
+        (_, NoBackend) -> panic "compileOne NoBackend"
+        (HscUpdateBoot iface hmi_details, Interpreter) -> do
             return $! HomeModInfo iface hmi_details Nothing
         (HscUpdateBoot iface hmi_details, _) -> do
             touchObjectFile dflags object_filename
             return $! HomeModInfo iface hmi_details Nothing
-        (HscUpdateSig iface hmi_details, HscInterpreted) -> do
+        (HscUpdateSig iface hmi_details, Interpreter) -> do
             let !linkable = LM (ms_hs_date summary) this_mod []
             return $! HomeModInfo iface hmi_details (Just linkable)
         (HscUpdateSig iface hmi_details, _) -> do
@@ -229,7 +230,7 @@ compileOne' m_tc_result mHscMessage
                      hscs_mod_details = hmi_details,
                      hscs_partial_iface = partial_iface,
                      hscs_old_iface_hash = mb_old_iface_hash,
-                     hscs_iface_dflags = iface_dflags }, HscInterpreted) -> do
+                     hscs_iface_dflags = iface_dflags }, Interpreter) -> do
             -- In interpreted mode the regular codeGen backend is not run so we
             -- generate a interface without codeGen info.
             final_iface <- mkFullIface hsc_env'{hsc_dflags=iface_dflags} partial_iface Nothing
@@ -285,7 +286,7 @@ compileOne' m_tc_result mHscMessage
 
        src_flavour = ms_hsc_src summary
        mod_name = ms_mod_name summary
-       next_phase = hscPostBackendPhase src_flavour hsc_lang
+       next_phase = hscPostBackendPhase src_flavour bcknd
        object_filename = ml_obj_file location
 
        -- #8180 - when using TemplateHaskell, switch on -dynamic-too so
@@ -320,8 +321,8 @@ compileOne' m_tc_result mHscMessage
                   -- to re-summarize all the source files.
        hsc_env     = hsc_env0 {hsc_dflags = dflags}
 
-       -- Figure out what lang we're generating
-       hsc_lang = hscTarget dflags
+       -- Figure out which backend we're using
+       bcknd = backend dflags
 
        -- -fforce-recomp should also work with --make
        force_recomp = gopt Opt_ForceRecomp dflags
@@ -329,8 +330,8 @@ compileOne' m_tc_result mHscMessage
          | force_recomp = SourceModified
          | otherwise = source_modified0
 
-       always_do_basic_recompilation_check = case hsc_lang of
-                                             HscInterpreted -> True
+       always_do_basic_recompilation_check = case bcknd of
+                                             Interpreter -> True
                                              _ -> False
 
 -----------------------------------------------------------------------------
@@ -562,7 +563,7 @@ compileFile hsc_env stop_phase (src, mb_phase) = do
          -- If we are doing -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 TFL_CurrentModule
+         | NoBackend <- backend dflags = Temporary TFL_CurrentModule
          | StopLn <- stop_phase, not (isNoLink ghc_link) = Persistent
                 -- -o foo applies to linker
          | isJust mb_o_file = SpecificFile
@@ -1144,8 +1145,7 @@ runPhase (HscOut src_flavour mod_name result) _ dflags = do
         setModLocation location
 
         let o_file = ml_obj_file location -- The real object file
-            hsc_lang = hscTarget dflags
-            next_phase = hscPostBackendPhase src_flavour hsc_lang
+            next_phase = hscPostBackendPhase src_flavour (backend dflags)
 
         case result of
             HscNotGeneratingCode _ _ ->
@@ -1209,8 +1209,7 @@ runPhase (RealPhase CmmCpp) input_fn dflags
        return (RealPhase Cmm, output_fn)
 
 runPhase (RealPhase Cmm) input_fn dflags
-  = do let hsc_lang = hscTarget dflags
-       let next_phase = hscPostBackendPhase HsSrcFile hsc_lang
+  = do let next_phase = hscPostBackendPhase HsSrcFile (backend dflags)
        output_fn <- phaseOutputFilename next_phase
        PipeState{hsc_env} <- getPipeState
        liftIO $ hscCompileCmmFile hsc_env input_fn output_fn
@@ -1355,7 +1354,7 @@ runPhase (RealPhase (As with_cpp)) input_fn dflags
   = do
         -- LLVM from version 3.0 onwards doesn't support the OS X system
         -- assembler, so we use clang as the assembler instead. (#5636)
-        let as_prog | hscTarget dflags == HscLlvm &&
+        let as_prog | backend dflags == LLVM &&
                       platformOS (targetPlatform dflags) == OSDarwin
                     = GHC.SysTools.runClang
                     | otherwise = GHC.SysTools.runAs
@@ -2060,7 +2059,7 @@ doCpp dflags raw input_fn output_fn = do
                        ])
 
 getBackendDefs :: DynFlags -> IO [String]
-getBackendDefs dflags | hscTarget dflags == HscLlvm = do
+getBackendDefs dflags | backend dflags == LLVM = do
     llvmVer <- figureLlvmVersion dflags
     return $ case fmap llvmVersionList llvmVer of
                Just [m] -> [ "-D__GLASGOW_HASKELL_LLVM__=" ++ format (m,0) ]
@@ -2199,7 +2198,7 @@ joinObjectFiles dflags o_files output_fn = do
 writeInterfaceOnlyMode :: DynFlags -> Bool
 writeInterfaceOnlyMode dflags =
  gopt Opt_WriteInterface dflags &&
- HscNothing == hscTarget dflags
+ NoBackend == backend dflags
 
 -- | Figure out if a source file was modified after an output file (or if we
 -- anyways need to consider the source file modified since the output is gone).
@@ -2214,16 +2213,16 @@ sourceModified dest_file src_timestamp = do
              return (t2 <= src_timestamp)
 
 -- | What phase to run after one of the backend code generators has run
-hscPostBackendPhase :: HscSource -> HscTarget -> Phase
+hscPostBackendPhase :: HscSource -> Backend -> Phase
 hscPostBackendPhase HsBootFile _    =  StopLn
 hscPostBackendPhase HsigFile _      =  StopLn
-hscPostBackendPhase _ hsc_lang =
-  case hsc_lang of
-        HscC           -> HCc
-        HscAsm         -> As False
-        HscLlvm        -> LlvmOpt
-        HscNothing     -> StopLn
-        HscInterpreted -> StopLn
+hscPostBackendPhase _ bcknd =
+  case bcknd of
+        ViaC        -> HCc
+        NCG         -> As False
+        LLVM        -> LlvmOpt
+        NoBackend   -> StopLn
+        Interpreter -> StopLn
 
 touchObjectFile :: DynFlags -> FilePath -> IO ()
 touchObjectFile dflags path = do
diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index 7d5c72ba74..82be1ab02e 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -47,8 +47,6 @@ module GHC.Driver.Session (
         FlagSpec(..),
         HasDynFlags(..), ContainsDynFlags(..),
         RtsOptsEnabled(..),
-        HscTarget(..), isObjectTarget, defaultObjectTarget,
-        targetRetainsAllBindings,
         GhcMode(..), isOneShot,
         GhcLink(..), isNoLink,
         PackageFlag(..), PackageArg(..), ModRenaming(..),
@@ -445,7 +443,20 @@ instance Outputable SafeHaskellMode where
 data DynFlags = DynFlags {
   ghcMode               :: GhcMode,
   ghcLink               :: GhcLink,
-  hscTarget             :: HscTarget,
+  backend               :: !Backend,
+   -- ^ The backend to use (if any).
+   --
+   -- Whenever you change the backend, also make sure to set 'ghcLink' to
+   -- something sensible.
+   --
+   -- 'NoBackend' can be used to avoid generating any output, however, note that:
+   --
+   --  * If a program uses Template Haskell the typechecker may need to run code
+   --    from an imported module.  To facilitate this, code generation is enabled
+   --    for modules imported by modules that use template haskell, using the
+   --    default backend for the platform.
+   --    See Note [-fno-code mode].
+
 
   -- formerly Settings
   ghcNameVersion    :: {-# UNPACK #-} !GhcNameVersion,
@@ -1003,45 +1014,6 @@ versionedAppDir appname platform = do
 versionedFilePath :: PlatformMini -> FilePath
 versionedFilePath platform = uniqueSubdir platform
 
--- | The target code type of the compilation (if any).
---
--- Whenever you change the target, also make sure to set 'ghcLink' to
--- something sensible.
---
--- 'HscNothing' can be used to avoid generating any output, however, note
--- that:
---
---  * If a program uses Template Haskell the typechecker may need to run code
---    from an imported module.  To facilitate this, code generation is enabled
---    for modules imported by modules that use template haskell.
---    See Note [-fno-code mode].
---
-data HscTarget
-  = HscC           -- ^ Generate C code.
-  | HscAsm         -- ^ Generate assembly using the native code generator.
-  | HscLlvm        -- ^ Generate assembly using the llvm code generator.
-  | HscInterpreted -- ^ Generate bytecode.  (Requires 'LinkInMemory')
-  | HscNothing     -- ^ Don't generate any code.  See notes above.
-  deriving (Eq, Show)
-
--- | Will this target result in an object file on the disk?
-isObjectTarget :: HscTarget -> Bool
-isObjectTarget HscC     = True
-isObjectTarget HscAsm   = True
-isObjectTarget HscLlvm  = True
-isObjectTarget _        = False
-
--- | Does this target retain *all* top-level bindings for a module,
--- rather than just the exported bindings, in the TypeEnv and compiled
--- code (if any)?  In interpreted mode we do this, so that GHCi can
--- call functions inside a module.  In HscNothing mode we also do it,
--- so that Haddock can get access to the GlobalRdrEnv for a module
--- after typechecking it.
-targetRetainsAllBindings :: HscTarget -> Bool
-targetRetainsAllBindings HscInterpreted = True
-targetRetainsAllBindings HscNothing     = True
-targetRetainsAllBindings _              = False
-
 -- | The 'GhcMode' tells us whether we're doing multi-module
 -- compilation (controlled via the "GHC" API) or one-shot
 -- (single-module) compilation.  This makes a difference primarily to
@@ -1149,19 +1121,6 @@ instance Outputable PackageFlag where
     ppr (ExposePackage n arg rn) = text n <> braces (ppr arg <+> ppr rn)
     ppr (HidePackage str) = text "-hide-package" <+> text str
 
--- | The 'HscTarget' value corresponding to the default way to create
--- object files on the current platform.
-
-defaultHscTarget :: Platform -> HscTarget
-defaultHscTarget platform
-  | platformUnregisterised platform        = HscC
-  | NCG <- platformDefaultBackend platform = HscAsm
-  | otherwise = HscLlvm
-
-defaultObjectTarget :: DynFlags -> HscTarget
-defaultObjectTarget dflags = defaultHscTarget
-  (targetPlatform dflags)
-
 data DynLibLoader
   = Deployable
   | SystemDependent
@@ -1272,7 +1231,7 @@ defaultDynFlags mySettings llvmConfig =
      DynFlags {
         ghcMode                 = CompManager,
         ghcLink                 = LinkBinary,
-        hscTarget               = defaultHscTarget (sTargetPlatform mySettings),
+        backend                 = platformDefaultBackend (sTargetPlatform mySettings),
         verbosity               = 0,
         optLevel                = 0,
         debugLevel              = 0,
@@ -2492,9 +2451,9 @@ dynamic_flags_deps = [
   , make_ord_flag defGhcFlag "keep-s-files"
         (NoArg (setGeneralFlag Opt_KeepSFiles))
   , make_ord_flag defGhcFlag "keep-llvm-file"
-        (NoArg $ setObjTarget HscLlvm >> setGeneralFlag Opt_KeepLlvmFiles)
+        (NoArg $ setObjBackend LLVM >> setGeneralFlag Opt_KeepLlvmFiles)
   , make_ord_flag defGhcFlag "keep-llvm-files"
-        (NoArg $ setObjTarget HscLlvm >> setGeneralFlag Opt_KeepLlvmFiles)
+        (NoArg $ setObjBackend LLVM >> setGeneralFlag Opt_KeepLlvmFiles)
      -- This only makes sense as plural
   , make_ord_flag defGhcFlag "keep-tmp-files"
         (NoArg (setGeneralFlag Opt_KeepTmpFiles))
@@ -2667,7 +2626,7 @@ dynamic_flags_deps = [
   , make_ord_flag defGhcFlag "ddump-asm-expanded"
         (setDumpFlag Opt_D_dump_asm_expanded)
   , make_ord_flag defGhcFlag "ddump-llvm"
-        (NoArg $ setObjTarget HscLlvm >> setDumpFlag' Opt_D_dump_llvm)
+        (NoArg $ setObjBackend LLVM >> setDumpFlag' Opt_D_dump_llvm)
   , make_ord_flag defGhcFlag "ddump-deriv"
         (setDumpFlag Opt_D_dump_deriv)
   , make_ord_flag defGhcFlag "ddump-ds"
@@ -3060,24 +3019,24 @@ dynamic_flags_deps = [
 
         ------ Compiler flags -----------------------------------------------
 
-  , make_ord_flag defGhcFlag "fasm"             (NoArg (setObjTarget HscAsm))
+  , make_ord_flag defGhcFlag "fasm"             (NoArg (setObjBackend NCG))
   , make_ord_flag defGhcFlag "fvia-c"           (NoArg
          (deprecate $ "The -fvia-c flag does nothing; " ++
                       "it will be removed in a future GHC release"))
   , make_ord_flag defGhcFlag "fvia-C"           (NoArg
          (deprecate $ "The -fvia-C flag does nothing; " ++
                       "it will be removed in a future GHC release"))
-  , make_ord_flag defGhcFlag "fllvm"            (NoArg (setObjTarget HscLlvm))
+  , make_ord_flag defGhcFlag "fllvm"            (NoArg (setObjBackend LLVM))
 
   , make_ord_flag defFlag "fno-code"         (NoArg ((upd $ \d ->
-                  d { ghcLink=NoLink }) >> setTarget HscNothing))
+                  d { ghcLink=NoLink }) >> setBackend NoBackend))
   , make_ord_flag defFlag "fbyte-code"
       (noArgM $ \dflags -> do
-        setTarget HscInterpreted
+        setBackend Interpreter
         pure $ gopt_set dflags Opt_ByteCode)
   , make_ord_flag defFlag "fobject-code"     $ NoArg $ do
       dflags <- liftEwM getCmdLineState
-      setTarget $ defaultObjectTarget dflags
+      setBackend $ platformDefaultBackend (targetPlatform dflags)
 
   , make_dep_flag defFlag "fglasgow-exts"
       (NoArg enableGlasgowExts) "Use individual extensions instead"
@@ -4590,24 +4549,24 @@ canonicalizeModuleIfHome dflags mod
                       then canonicalizeHomeModule dflags (moduleName mod)
                       else mod
 
--- If we're linking a binary, then only targets that produce object
+-- If we're linking a binary, then only backends that produce object
 -- code are allowed (requests for other target types are ignored).
-setTarget :: HscTarget -> DynP ()
-setTarget l = upd $ \ dfs ->
-  if ghcLink dfs /= LinkBinary || isObjectTarget l
-  then dfs{ hscTarget = l }
+setBackend :: Backend -> DynP ()
+setBackend l = upd $ \ dfs ->
+  if ghcLink dfs /= LinkBinary || backendProducesObject l
+  then dfs{ backend = l }
   else dfs
 
 -- Changes the target only if we're compiling object code.  This is
 -- used by -fasm and -fllvm, which switch from one to the other, but
 -- not from bytecode to object-code.  The idea is that -fasm/-fllvm
 -- can be safely used in an OPTIONS_GHC pragma.
-setObjTarget :: HscTarget -> DynP ()
-setObjTarget l = updM set
+setObjBackend :: Backend -> DynP ()
+setObjBackend l = updM set
   where
    set dflags
-     | isObjectTarget (hscTarget dflags)
-       = return $ dflags { hscTarget = l }
+     | backendProducesObject (backend dflags)
+       = return $ dflags { backend = l }
      | otherwise = return dflags
 
 setOptLevel :: Int -> DynFlags -> DynP DynFlags
@@ -4615,7 +4574,7 @@ setOptLevel n dflags = return (updOptLevel n dflags)
 
 checkOptLevel :: Int -> DynFlags -> Either String DynFlags
 checkOptLevel n dflags
-   | hscTarget dflags == HscInterpreted && n > 0
+   | backend dflags == Interpreter && n > 0
      = Left "-O conflicts with --interactive; -O ignored."
    | otherwise
      = Right dflags
@@ -4953,31 +4912,32 @@ makeDynFlagsConsistent dflags
           warn    = "-dynamic-too is not supported on Windows"
       in loop dflags' warn
 
-   -- Via-C backend only supports unregisterised convention. Switch to a backend
+   -- Via-C backend only supports unregisterised ABI. Switch to a backend
    -- supporting it if possible.
- | hscTarget dflags == HscC &&
+ | backend dflags == ViaC &&
    not (platformUnregisterised (targetPlatform dflags))
     = case platformDefaultBackend (targetPlatform dflags) of
-         NCG  -> let dflags' = dflags { hscTarget = HscAsm }
+         NCG ->  let dflags' = dflags { backend = NCG }
                      warn = "Target platform doesn't use unregisterised ABI, so using native code generator rather than compiling via C"
                  in loop dflags' warn
-         LLVM -> let dflags' = dflags { hscTarget = HscLlvm }
+         LLVM -> let dflags' = dflags { backend = LLVM }
                      warn = "Target platform doesn't use unregisterised ABI, so using LLVM rather than compiling via C"
                  in loop dflags' warn
-         _    -> pgmError "Compiling via C is only supported with unregisterised ABI but target platform doesn't use it."
- | gopt Opt_Hpc dflags && hscTarget dflags == HscInterpreted
+         _    -> pgmError "Compiling via C only supports unregisterised ABI but target platform doesn't use it."
+
+ | gopt Opt_Hpc dflags && backend dflags == Interpreter
     = let dflags' = gopt_unset dflags Opt_Hpc
           warn = "Hpc can't be used with byte-code interpreter. Ignoring -fhpc."
       in loop dflags' warn
 
- | hscTarget dflags `elem` [HscAsm, HscLlvm] &&
+ | backend dflags `elem` [NCG, LLVM] &&
    platformUnregisterised (targetPlatform dflags)
-    = loop (dflags { hscTarget = HscC })
+    = loop (dflags { backend = ViaC })
            "Target platform uses unregisterised ABI, so compiling via C"
 
- | hscTarget dflags == HscAsm &&
+ | backend dflags == NCG &&
    not (platformNcgSupported $ targetPlatform dflags)
-      = let dflags' = dflags { hscTarget = HscLlvm }
+      = let dflags' = dflags { backend = LLVM }
             warn = "Native code generator doesn't support target platform, so using LLVM"
         in loop dflags' warn
 
@@ -4995,7 +4955,7 @@ makeDynFlagsConsistent dflags
  | LinkInMemory <- ghcLink dflags
  , not (gopt Opt_ExternalInterpreter dflags)
  , hostIsProfiled
- , isObjectTarget (hscTarget dflags)
+ , backendProducesObject (backend dflags)
  , WayProf `Set.notMember` ways dflags
     = loop dflags{ways = Set.insert WayProf (ways dflags)}
          "Enabling -prof, because -fobject-code is enabled and GHCi is profiled"
diff --git a/compiler/GHC/Driver/Types.hs b/compiler/GHC/Driver/Types.hs
index 5671079723..4029ab1c2c 100644
--- a/compiler/GHC/Driver/Types.hs
+++ b/compiler/GHC/Driver/Types.hs
@@ -192,6 +192,7 @@ import GHC.Core.DataCon
 import GHC.Core.PatSyn
 import GHC.Builtin.Names ( gHC_PRIM, ioTyConName, printName, mkInteractiveModule )
 import GHC.Builtin.Types
+import GHC.Driver.Backend
 import GHC.Driver.CmdLine
 import GHC.Driver.Session
 import GHC.Runtime.Linker.Types ( DynLinker, Linkable(..), Unlinked(..), SptEntry(..) )
@@ -2997,8 +2998,8 @@ instance Outputable ModSummary where
              char '}'
             ]
 
-showModMsg :: DynFlags -> HscTarget -> Bool -> ModSummary -> String
-showModMsg dflags target recomp mod_summary = showSDoc dflags $
+showModMsg :: DynFlags -> Bool -> ModSummary -> String
+showModMsg dflags recomp mod_summary = showSDoc dflags $
    if gopt Opt_HideSourcePaths dflags
       then text mod_str
       else hsep $
@@ -3017,10 +3018,10 @@ showModMsg dflags target recomp mod_summary = showSDoc dflags $
     mod      = moduleName (ms_mod mod_summary)
     mod_str  = showPpr dflags mod ++ hscSourceString (ms_hsc_src mod_summary)
     dyn_file = op $ msDynObjFilePath mod_summary dflags
-    obj_file = case target of
-                HscInterpreted | recomp -> "interpreted"
-                HscNothing              -> "nothing"
-                _                       -> (op $ msObjFilePath mod_summary)
+    obj_file = case backend dflags of
+                Interpreter | recomp -> "interpreted"
+                NoBackend            -> "nothing"
+                _                    -> (op $ msObjFilePath mod_summary)
 
 {-
 ************************************************************************
@@ -3171,7 +3172,7 @@ isObjectLinkable l = not (null unlinked) && all isObject unlinked
   where unlinked = linkableUnlinked l
         -- A linkable with no Unlinked's is treated as a BCO.  We can
         -- generate a linkable with no Unlinked's as a result of
-        -- compiling a module in HscNothing mode, and this choice
+        -- compiling a module in NoBackend mode, and this choice
         -- happens to work well with checkStability in module GHC.
 
 linkableObjs :: Linkable -> [FilePath]
diff --git a/compiler/GHC/HsToCore.hs b/compiler/GHC/HsToCore.hs
index af67088e51..13f5ca5dd4 100644
--- a/compiler/GHC/HsToCore.hs
+++ b/compiler/GHC/HsToCore.hs
@@ -23,6 +23,7 @@ import GHC.Prelude
 import GHC.HsToCore.Usage
 import GHC.Driver.Session
 import GHC.Driver.Types
+import GHC.Driver.Backend
 import GHC.Hs
 import GHC.Tc.Types
 import GHC.Tc.Utils.Monad  ( finalSafeMode, fixSafeInstances )
@@ -123,7 +124,7 @@ deSugar hsc_env
                      (const ()) $
      do { -- Desugar the program
         ; let export_set = availsToNameSet exports
-              target     = hscTarget dflags
+              bcknd      = backend dflags
               hpcInfo    = emptyHpcInfo other_hpc_info
 
         ; (binds_cvr, ds_hpc_info, modBreaks)
@@ -153,7 +154,7 @@ deSugar hsc_env
      do {       -- Add export flags to bindings
           keep_alive <- readIORef keep_var
         ; let (rules_for_locals, rules_for_imps) = partition isLocalRule all_rules
-              final_prs = addExportFlagsAndRules target export_set keep_alive
+              final_prs = addExportFlagsAndRules bcknd export_set keep_alive
                                                  rules_for_locals (fromOL all_prs)
 
               final_pgm = combineEvBinds ds_ev_binds final_prs
@@ -288,9 +289,9 @@ deSugarExpr hsc_env tc_expr = do {
 -}
 
 addExportFlagsAndRules
-    :: HscTarget -> NameSet -> NameSet -> [CoreRule]
+    :: Backend -> NameSet -> NameSet -> [CoreRule]
     -> [(Id, t)] -> [(Id, t)]
-addExportFlagsAndRules target exports keep_alive rules prs
+addExportFlagsAndRules bcknd exports keep_alive rules prs
   = mapFst add_one prs
   where
     add_one bndr = add_rules name (add_export name bndr)
@@ -326,7 +327,7 @@ addExportFlagsAndRules target exports keep_alive rules prs
         -- isExternalName separates the user-defined top-level names from those
         -- introduced by the type checker.
     is_exported :: Name -> Bool
-    is_exported | targetRetainsAllBindings target = isExternalName
+    is_exported | backendRetainsAllBindings bcknd = isExternalName
                 | otherwise                       = (`elemNameSet` exports)
 
 {-
diff --git a/compiler/GHC/HsToCore/Coverage.hs b/compiler/GHC/HsToCore/Coverage.hs
index edd67e5b17..b52b4ac209 100644
--- a/compiler/GHC/HsToCore/Coverage.hs
+++ b/compiler/GHC/HsToCore/Coverage.hs
@@ -24,6 +24,7 @@ import GHC.Hs
 import GHC.Unit
 import GHC.Utils.Outputable as Outputable
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Core.ConLike
 import Control.Monad
 import GHC.Types.SrcLoc
@@ -1050,7 +1051,7 @@ coveragePasses dflags =
 
 -- | Should we produce 'Breakpoint' ticks?
 breakpointsEnabled :: DynFlags -> Bool
-breakpointsEnabled dflags = hscTarget dflags == HscInterpreted
+breakpointsEnabled dflags = backend dflags == Interpreter
 
 -- | Tickishs that only make sense when their source code location
 -- refers to the current file. This might not always be true due to
diff --git a/compiler/GHC/Iface/Load.hs b/compiler/GHC/Iface/Load.hs
index de4ef89283..3d8a1f47ef 100644
--- a/compiler/GHC/Iface/Load.hs
+++ b/compiler/GHC/Iface/Load.hs
@@ -41,6 +41,7 @@ import {-# SOURCE #-} GHC.IfaceToCore
    , tcIfaceAnnotations, tcIfaceCompleteSigs )
 
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Iface.Syntax
 import GHC.Iface.Env
 import GHC.Driver.Types
@@ -592,12 +593,12 @@ dontLeakTheHPT thing_inside = do
          -- instantiation of a signature might reside in the HPT, so
          -- this case breaks the assumption that EPS interfaces only
          -- refer to other EPS interfaces. We can detect when we're in
-         -- typechecking-only mode by using hscTarget==HscNothing, and
+         -- typechecking-only mode by using backend==NoBackend, and
          -- in that case we don't empty the HPT.  (admittedly this is
          -- a bit of a hack, better suggestions welcome). A number of
          -- tests in testsuite/tests/backpack break without this
          -- tweak.
-         !hpt | hscTarget hsc_dflags == HscNothing = hsc_HPT
+         !hpt | backend hsc_dflags == NoBackend = hsc_HPT
               | otherwise = emptyHomePackageTable
        in
        HscEnv {  hsc_targets      = panic "cleanTopEnv: hsc_targets"
diff --git a/compiler/GHC/Iface/Make.hs b/compiler/GHC/Iface/Make.hs
index b43fe30bb3..bb383f6a57 100644
--- a/compiler/GHC/Iface/Make.hs
+++ b/compiler/GHC/Iface/Make.hs
@@ -46,6 +46,7 @@ import GHC.Core.FamInstEnv
 import GHC.Tc.Utils.Monad
 import GHC.Hs
 import GHC.Driver.Types
+import GHC.Driver.Backend
 import GHC.Driver.Session
 import GHC.Types.Var.Env
 import GHC.Types.Var
@@ -144,7 +145,7 @@ updateDecl decls (Just CgInfos{ cgNonCafs = NonCaffySet non_cafs, cgLFInfos = lf
 
 -- | Make an interface from the results of typechecking only.  Useful
 -- for non-optimising compilation, or where we aren't generating any
--- object code at all ('HscNothing').
+-- object code at all ('NoBackend').
 mkIfaceTc :: HscEnv
           -> SafeHaskellMode    -- The safe haskell mode
           -> ModDetails         -- gotten from mkBootModDetails, probably
@@ -301,8 +302,8 @@ mkIface_ hsc_env
      -- scope available. (#5534)
      maybeGlobalRdrEnv :: GlobalRdrEnv -> Maybe GlobalRdrEnv
      maybeGlobalRdrEnv rdr_env
-         | targetRetainsAllBindings (hscTarget dflags) = Just rdr_env
-         | otherwise                                   = Nothing
+         | backendRetainsAllBindings (backend dflags) = Just rdr_env
+         | otherwise                                  = Nothing
 
      ifFamInstTcName = ifFamInstFam
 
diff --git a/compiler/GHC/Iface/Recomp.hs b/compiler/GHC/Iface/Recomp.hs
index 58d9dd05af..4d680f4aca 100644
--- a/compiler/GHC/Iface/Recomp.hs
+++ b/compiler/GHC/Iface/Recomp.hs
@@ -23,6 +23,7 @@ import GHC.Types.Annotations
 import GHC.Core
 import GHC.Tc.Utils.Monad
 import GHC.Hs
+import GHC.Driver.Backend
 import GHC.Driver.Types
 import GHC.Driver.Finder
 import GHC.Driver.Session
@@ -169,7 +170,7 @@ check_old_iface hsc_env mod_summary src_modified maybe_iface
             -- If the source has changed and we're in interactive mode,
             -- avoid reading an interface; just return the one we might
             -- have been supplied with.
-            True | not (isObjectTarget $ hscTarget dflags) ->
+            True | not (backendProducesObject $ backend dflags) ->
                 return (MustCompile, maybe_iface)
 
             -- Try and read the old interface for the current module
diff --git a/compiler/GHC/Iface/Tidy.hs b/compiler/GHC/Iface/Tidy.hs
index 5121c11681..3c3fb4b488 100644
--- a/compiler/GHC/Iface/Tidy.hs
+++ b/compiler/GHC/Iface/Tidy.hs
@@ -18,6 +18,7 @@ import GHC.Prelude
 
 import GHC.Tc.Types
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Core
 import GHC.Core.Unfold
 import GHC.Core.FVs
@@ -383,10 +384,10 @@ tidyProgram hsc_env  (ModGuts { mg_module    = mod
              sptCreateStaticBinds hsc_env mod tidy_binds
         ; let { spt_init_code = sptModuleInitCode mod spt_entries
               ; add_spt_init_code =
-                  case hscTarget dflags of
+                  case backend dflags of
                     -- If we are compiling for the interpreter we will insert
                     -- any necessary SPT entries dynamically
-                    HscInterpreted -> id
+                    Interpreter -> id
                     -- otherwise add a C stub to do so
                     _              -> (`appendStubC` spt_init_code)
 
diff --git a/compiler/GHC/Runtime/Eval.hs b/compiler/GHC/Runtime/Eval.hs
index e88dfc3277..6871073eea 100644
--- a/compiler/GHC/Runtime/Eval.hs
+++ b/compiler/GHC/Runtime/Eval.hs
@@ -1256,7 +1256,7 @@ showModule mod_summary =
     withSession $ \hsc_env -> do
         interpreted <- moduleIsBootOrNotObjectLinkable mod_summary
         let dflags = hsc_dflags hsc_env
-        return (showModMsg dflags (hscTarget dflags) interpreted mod_summary)
+        return (showModMsg dflags interpreted mod_summary)
 
 moduleIsBootOrNotObjectLinkable :: GhcMonad m => ModSummary -> m Bool
 moduleIsBootOrNotObjectLinkable mod_summary = withSession $ \hsc_env ->
diff --git a/compiler/GHC/Runtime/Linker/Types.hs b/compiler/GHC/Runtime/Linker/Types.hs
index 429a658042..7899feae9e 100644
--- a/compiler/GHC/Runtime/Linker/Types.hs
+++ b/compiler/GHC/Runtime/Linker/Types.hs
@@ -71,7 +71,7 @@ data Linkable = LM {
     --
     -- INVARIANT: A valid linkable always has at least one 'Unlinked' item.
     -- If this list is empty, the Linkable represents a fake linkable, which
-    -- is generated in HscNothing mode to avoid recompiling modules.
+    -- is generated with no backend is used to avoid recompiling modules.
     --
     -- ToDo: Do items get removed from this list when they get linked?
  }
diff --git a/compiler/GHC/StgToCmm.hs b/compiler/GHC/StgToCmm.hs
index 04ce004df4..40a43b3e06 100644
--- a/compiler/GHC/StgToCmm.hs
+++ b/compiler/GHC/StgToCmm.hs
@@ -37,6 +37,7 @@ import GHC.Driver.Session
 import GHC.Utils.Error
 
 import GHC.Driver.Types
+import GHC.Driver.Backend
 import GHC.Types.CostCentre
 import GHC.Types.Id
 import GHC.Types.Id.Info
@@ -165,7 +166,7 @@ cgTopBinding dflags (StgTopStringLit id str) = do
   -- emit either a CmmString literal or dump the string in a file and emit a
   -- CmmFileEmbed literal.
   -- See Note [Embedding large binary blobs] in GHC.CmmToAsm.Ppr
-  let isNCG    = hscTarget dflags == HscAsm
+  let isNCG    = backend dflags == NCG
       isSmall  = fromIntegral (BS.length str) <= binBlobThreshold dflags
       asString = binBlobThreshold dflags == 0 || isSmall
 
diff --git a/compiler/GHC/StgToCmm/Prim.hs b/compiler/GHC/StgToCmm/Prim.hs
index afbcc34836..c3a14f9b1c 100644
--- a/compiler/GHC/StgToCmm/Prim.hs
+++ b/compiler/GHC/StgToCmm/Prim.hs
@@ -37,6 +37,7 @@ import GHC.StgToCmm.Heap
 import GHC.StgToCmm.Prof ( costCentreFrom )
 
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Platform
 import GHC.Types.Basic
 import GHC.Cmm.BlockId
@@ -1594,12 +1595,8 @@ emitPrimOp dflags primop = case primop of
     [_, CmmLit (CmmInt n _) ] -> isJust (exactLog2 n)
     _                         -> False
 
-  ncg = case hscTarget dflags of
-           HscAsm -> True
-           _      -> False
-  llvm = case hscTarget dflags of
-           HscLlvm -> True
-           _       -> False
+  ncg  = backend dflags == NCG
+  llvm = backend dflags == LLVM
   x86ish = case platformArch platform of
              ArchX86    -> True
              ArchX86_64 -> True
@@ -2169,7 +2166,7 @@ vecElemProjectCast _        _        _   =  Nothing
 
 checkVecCompatibility :: DynFlags -> PrimOpVecCat -> Length -> Width -> FCode ()
 checkVecCompatibility dflags vcat l w = do
-    when (hscTarget dflags /= HscLlvm) $ do
+    when (backend dflags /= LLVM) $ do
         sorry $ unlines ["SIMD vector instructions require the LLVM back-end."
                          ,"Please use -fllvm."]
     check vecWidth vcat l w
diff --git a/compiler/GHC/Tc/Gen/Foreign.hs b/compiler/GHC/Tc/Gen/Foreign.hs
index df699b9b78..902829fb68 100644
--- a/compiler/GHC/Tc/Gen/Foreign.hs
+++ b/compiler/GHC/Tc/Gen/Foreign.hs
@@ -57,6 +57,7 @@ import GHC.Core.TyCon
 import GHC.Tc.Utils.TcType
 import GHC.Builtin.Names
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Utils.Outputable as Outputable
 import GHC.Platform
 import GHC.Types.SrcLoc
@@ -474,31 +475,31 @@ checkSafe, noCheckSafe :: Bool
 checkSafe   = True
 noCheckSafe = False
 
--- Checking a supported backend is in use
-
-checkCOrAsmOrLlvm :: HscTarget -> Validity
-checkCOrAsmOrLlvm HscC    = IsValid
-checkCOrAsmOrLlvm HscAsm  = IsValid
-checkCOrAsmOrLlvm HscLlvm = IsValid
+-- | Checking a supported backend is in use
+checkCOrAsmOrLlvm :: Backend -> Validity
+checkCOrAsmOrLlvm ViaC = IsValid
+checkCOrAsmOrLlvm NCG  = IsValid
+checkCOrAsmOrLlvm LLVM = IsValid
 checkCOrAsmOrLlvm _
   = NotValid (text "requires unregisterised, llvm (-fllvm) or native code generation (-fasm)")
 
-checkCOrAsmOrLlvmOrInterp :: HscTarget -> Validity
-checkCOrAsmOrLlvmOrInterp HscC           = IsValid
-checkCOrAsmOrLlvmOrInterp HscAsm         = IsValid
-checkCOrAsmOrLlvmOrInterp HscLlvm        = IsValid
-checkCOrAsmOrLlvmOrInterp HscInterpreted = IsValid
+-- | Checking a supported backend is in use
+checkCOrAsmOrLlvmOrInterp :: Backend -> Validity
+checkCOrAsmOrLlvmOrInterp ViaC        = IsValid
+checkCOrAsmOrLlvmOrInterp NCG         = IsValid
+checkCOrAsmOrLlvmOrInterp LLVM        = IsValid
+checkCOrAsmOrLlvmOrInterp Interpreter = IsValid
 checkCOrAsmOrLlvmOrInterp _
   = NotValid (text "requires interpreted, unregisterised, llvm or native code generation")
 
-checkCg :: (HscTarget -> Validity) -> TcM ()
+checkCg :: (Backend -> Validity) -> TcM ()
 checkCg check = do
     dflags <- getDynFlags
-    let target = hscTarget dflags
-    case target of
-      HscNothing -> return ()
+    let bcknd = backend dflags
+    case bcknd of
+      NoBackend -> return ()
       _ ->
-        case check target of
+        case check bcknd of
           IsValid      -> return ()
           NotValid err -> addErrTc (text "Illegal foreign declaration:" <+> err)
 
diff --git a/compiler/GHC/Tc/Gen/Sig.hs b/compiler/GHC/Tc/Gen/Sig.hs
index aee53733f4..7d253f079d 100644
--- a/compiler/GHC/Tc/Gen/Sig.hs
+++ b/compiler/GHC/Tc/Gen/Sig.hs
@@ -43,6 +43,7 @@ import GHC.Core.Type ( mkTyVarBinders )
 import GHC.Core.Multiplicity
 
 import GHC.Driver.Session
+import GHC.Driver.Backend
 import GHC.Types.Var ( TyVar, Specificity(..), tyVarKind, binderVars )
 import GHC.Types.Id  ( Id, idName, idType, idInlinePragma, setInlinePragma, mkLocalId )
 import GHC.Builtin.Names( mkUnboundName )
@@ -817,10 +818,10 @@ tcImpPrags prags
     -- we don't want complaints about lack of INLINABLE pragmas
     not_specialising dflags
       | not (gopt Opt_Specialise dflags) = True
-      | otherwise = case hscTarget dflags of
-                      HscNothing -> True
-                      HscInterpreted -> True
-                      _other         -> False
+      | otherwise = case backend dflags of
+                      NoBackend   -> True
+                      Interpreter -> True
+                      _other      -> False
 
 tcImpSpec :: (Name, Sig GhcRn) -> TcM [TcSpecPrag]
 tcImpSpec (name, prag)