Matthew Pickering pushed to branch wip/bytecode-determinism at Glasgow Haskell Compiler / GHC Commits: b96b7645 by Matthew Pickering at 2026-02-09T17:13:24+00:00 determinism: Use a deterministic renaming when writing bytecode files Now when writing the bytecode file, a counter and substitution are used to provide deterministic keys to local variables (rather than relying on uniques). This change ensures that `.gbc` are produced deterministically. Fixes #26499 - - - - - 1 changed file: - compiler/GHC/ByteCode/Serialize.hs Changes: ===================================== compiler/GHC/ByteCode/Serialize.hs ===================================== @@ -48,6 +48,7 @@ import GHC.Utils.Logger import GHC.Linker.Types import System.IO.Unsafe (unsafeInterleaveIO) import GHC.Utils.Outputable +import GHC.Types.Name.Env {- Note [Overview of persistent bytecode] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -382,8 +383,13 @@ putViaBinName :: WriteBinHandle -> Name -> IO () putViaBinName bh nm = case findUserDataWriter Proxy bh of BinaryWriter f -> f bh $ BinName nm +data BytecodeNameEnv = ByteCodeNameEnv { _bytecode_next_id :: !Word64 + , _bytecode_name_subst :: NameEnv Word64 + } + addBinNameWriter :: WriteBinHandle -> IO WriteBinHandle -addBinNameWriter bh' = +addBinNameWriter bh' = do + env_ref <- newIORef (ByteCodeNameEnv 0 emptyNameEnv) evaluate $ flip addWriterToUserData bh' $ BinaryWriter @@ -394,10 +400,17 @@ addBinNameWriter bh' = put_ bh nm | otherwise -> do putByte bh 1 - put_ bh - $ occNameFS (occName nm) - `appendFS` mkFastString - (show $ nameUnique nm) + key <- getBinNameKey env_ref nm + -- Delimit the OccName from the deterministic counter to keep the + -- encoding injective, avoiding collisions like "foo1" vs "foo#1". + put_ bh (occNameFS (occName nm) `appendFS` mkFastString ('#' : show key)) + where + -- Find a deterministic key for local names. This + getBinNameKey ref name = do + atomicModifyIORef ref (\b@(ByteCodeNameEnv next subst) -> + case lookupNameEnv subst name of + Just idx -> (b, idx) + Nothing -> (ByteCodeNameEnv (next + 1) (extendNameEnv subst name next), next)) addBinNameReader :: HscEnv -> ReadBinHandle -> IO ReadBinHandle addBinNameReader HscEnv {..} bh' = do @@ -423,9 +436,6 @@ addBinNameReader HscEnv {..} bh' = do -- Note [Serializing Names in bytecode] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --- NOTE: This approach means that bytecode objects are not deterministic. --- We need to revisit this in order to make the output deterministic. --- -- The bytecode related types contain various Names which we need to -- serialize. Unfortunately, we can't directly use the Binary instance -- of Name: it is only meant to be used for serializing external Names @@ -433,9 +443,8 @@ addBinNameReader HscEnv {..} bh' = do -- -- We also need to maintain the invariant that: any pair of internal -- Names with equal/different uniques must also be deserialized to --- have the same equality. So normally uniques aren't supposed to be --- serialized, but for this invariant to work, we do append uniques to --- OccNames of internal Names, so that they can be uniquely identified --- by OccName alone. When deserializing, we check a global cached --- mapping from OccName to Unique, and create the real Name with the --- right Unique if it's already deserialized at least once. +-- have the same equality. Therefore when we write the names to the interface, we +-- use an incrementing counter to give each local name it's own unique number. A substitution +-- is maintained to give each occurence of the Name the same unique key. When the interface +-- is read, a reverse mapping is used from these unique keys to a Name. +-- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b96b7645c5621419393e240ee0690dff... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/b96b7645c5621419393e240ee0690dff... You're receiving this email because of your account on gitlab.haskell.org.