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Hannes Siebenhandl pushed to branch wip/fendor/no-code-output-constr at Glasgow Haskell Compiler / GHC

Commits:

c3f5364b

by fendor at 2026-06-23T10:39:42+02:00

Introduce 'NoCodeOutput' constructor to avoid partial `backendCodeOutput`

This makes `backendCodeOutput` total, but forces us to explicitly handle
the new `NoCodeOutput` case when using it.
Thus, we add some new `panic`'s when generating files.

The advantage is that `backendCodeOutput` can be used for checking
capabilities without requiring a prior check via `backendWritesFiles`.

04d96784

by Matthew Pickering at 2026-06-23T10:40:39+02:00

Add failing test for `-finfo-table-map` and bytecode backend

If you compile a module using the bytecode backend, with
-finfo-table-map, then the info table map doesn't get populated for the
module.

This is because the -finfo-table-map code path is implemented mostly in
the StgToCmm phase which isn't run when creating bytecode.

Ticket #27039

8 changed files:

compiler/GHC/Driver/Backend.hs
compiler/GHC/Driver/CodeOutput.hs
compiler/GHC/Driver/Main/Compile.hs
compiler/GHC/Driver/Pipeline.hs
testsuite/tests/ghci/scripts/all.T
+ testsuite/tests/ghci/scripts/bytecodeIPE.hs
+ testsuite/tests/ghci/scripts/bytecodeIPE.script
+ testsuite/tests/ghci/scripts/bytecodeIPE.stdout

Changes:

compiler/GHC/Driver/Backend.hs

@@ -117,7 +117,6 @@ import GHC.Driver.Phases
  import GHC.Utils.Error
 -import GHC.Utils.Panic
  import GHC.Driver.Pipeline.Monad
  import GHC.Platform
@@ -374,6 +373,7 @@ data DefunctionalizedCodeOutput
    | ViaCCodeOutput
    | LlvmCodeOutput
    | JSCodeOutput
 +  | NoCodeOutput
  -- | Names a function that tells the driver what should happen after
@@ -773,8 +773,8 @@ backendCodeOutput (Named NCG)         = NcgCodeOutput
  backendCodeOutput (Named LLVM)        = LlvmCodeOutput
  backendCodeOutput (Named ViaC)        = ViaCCodeOutput
  backendCodeOutput (Named JavaScript)  = JSCodeOutput
 -backendCodeOutput (Named Bytecode) = panic "backendCodeOutput: bytecodeBackend"
 -backendCodeOutput (Named NoBackend)   = panic "backendCodeOutput: noBackend"
 +backendCodeOutput (Named Bytecode)    = NoCodeOutput
 +backendCodeOutput (Named NoBackend)   = NoCodeOutput
  backendUseJSLinker :: Backend -> Bool
  backendUseJSLinker (Named NCG)         = False

compiler/GHC/Driver/CodeOutput.hs

@@ -63,6 +63,7 @@ import GHC.Types.Unique.Supply ( UniqueTag(..) )
  import System.IO
  import Data.Set (Set)
  import qualified Data.Set as Set
 +import GHC.Plugins (panic)
  {-
  ************************************************************************
@@ -129,6 +130,7 @@ codeOutput logger tmpfs llvm_config dflags unit_state this_mod filenm location g
                   ViaCCodeOutput -> outputC logger dflags filenm dus1 final_stream pkg_deps
                   LlvmCodeOutput -> outputLlvm logger llvm_config dflags filenm dus1 final_stream
                   JSCodeOutput   -> outputJS logger llvm_config dflags filenm final_stream
 +                 NoCodeOutput   -> panic "codeOutput: expected code output backend but got NoCodeOutput"
          ; stubs_exist <- outputForeignStubs logger tmpfs dflags unit_state this_mod location stubs
          ; return (filenm, stubs_exist, foreign_fps, a)
+         }

compiler/GHC/Driver/Main/Compile.hs

@@ -670,6 +670,8 @@ hscGenHardCode hsc_env cgguts mod_loc output_filename = do
          -- next withTiming after this will be "Assembler" (hard code only).
          withTiming logger (text "CodeGen"<+>brackets (ppr this_mod)) (const ())
           $ case backendCodeOutput (backend dflags) of
 +            NoCodeOutput ->
 +              panic "hscGenHardCode: expected code output backend but got NoCodeOutput"
              JSCodeOutput ->
                do
                let js_config = initStgToJSConfig dflags

compiler/GHC/Driver/Pipeline.hs

@@ -743,6 +743,8 @@ compileEmptyStub dflags hsc_env basename location mod_name = do
    let home_unit = hsc_home_unit hsc_env
    case backendCodeOutput (backend dflags) of
 +    NoCodeOutput ->
 +      panic "compileEmptyStub: expected code output backend but got NoCodeOutput"
      JSCodeOutput -> do
        empty_stub <- newTempName logger tmpfs (tmpDir dflags) TFL_CurrentModule "js"
        let src = ppr (mkHomeModule home_unit mod_name) <+> text "= 0;"

testsuite/tests/ghci/scripts/all.T

@@ -385,6 +385,14 @@ test('ListTuplePunsPpr', normal, ghci_script, ['ListTuplePunsPpr.script'])
  test('ListTuplePunsPprNoAbbrevTuple', [limit_stdout_lines(14)], ghci_script, ['ListTuplePunsPprNoAbbrevTuple.script'])
  test('T24459', normal, ghci_script, ['T24459.script'])
  test('T24632', normal, ghci_script, ['T24632.script'])
 +# bytecode backend doesn't support '-finfo-table-map' (#27039)
 +test('bytecodeIPE',
 +     [ extra_hc_opts('-finfo-table-map')
 +     , extra_files(['bytecodeIPE.hs'])
 +     , req_rts_linker
 +     , when(arch('wasm32') or arch('javascript'), skip)
 +     ],
 +     ghci_script, ['bytecodeIPE.script'])
  # Test package renaming in GHCi session
  test('GhciPackageRename',

testsuite/tests/ghci/scripts/bytecodeIPE.hs

 +module BytecodeIPE where
++
 +import Data.Maybe (isJust)
 +import GHC.InfoProv (whereFrom)
++
 +marker :: String
 +marker = id "bytecode-stub-init"
 +{-# NOINLINE marker #-}
++
 +-- `whereFrom` only succeeds if the module's IPE initializer ran.
 +probe :: IO Bool
 +probe = isJust <$> whereFrom marker

testsuite/tests/ghci/scripts/bytecodeIPE.script

	1	+:load bytecodeIPE.hs
	2	+probe

testsuite/tests/ghci/scripts/bytecodeIPE.stdout

+False