Matthew Pickering pushed to branch wip/gbc-files at Glasgow Haskell Compiler / GHC
Commits:
57febb55 by Matthew Pickering at 2025-10-03T09:08:21+00:00
Apply 3 suggestion(s) to 2 file(s)
Co-authored-by: Rodrigo Mesquita
- - - - -
2 changed files:
- compiler/GHC/ByteCode/Serialize.hs
- compiler/GHC/Driver/Main.hs
Changes:
=====================================
compiler/GHC/ByteCode/Serialize.hs
=====================================
@@ -40,18 +40,11 @@ import System.IO.Unsafe (unsafeInterleaveIO)
{- Note [Overview of persistent bytecode]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-GHC can produce a .gbc file, which is a serialised representation of a bytecode object.
+By default, when using the interpreter, a Haskell module is first compiled to bytecode (which lives in memory) and then executed by the RTS interpreter. However, when dealing with many modules compiling to bytecode from scratch every time is expensive. This is especially relevant for interpreter-heavy workflows on large projects where changes are incremental or non-existent (e.g. running the project in the debugger).
-By passing the flag `-fwrite-bytecode`, then when using the bytecode backend,
-a .gbc file will be written to the output directory.
+In light of this, GHC can produce so-called `.gbc` files, which contain a serialized representation of the bytecode objects in a Haskell module. These files are written by enabling the flag `-fwrite-bytecode` when using the interpreter.
-The primary use case for the file is to avoid having to recompile when using
-GHCi. Instead, the driver will look for the interface and .gbc file and load
-those to avoid recompiling.
-
-* This can save a lot of time if you have many modules. Even compared to `-fwrite-if-simplified-core`.
-* The source code might not be available, but you may still want to run the bytecode rather than
- native object code (for example, for debugging).
+The driver will always look for both the interface and the `.gbc` file and load those to avoid unnecessary recompilation. This can save a lot of time if you have many modules. Even compared to `-fwrite-if-simplified-core`.
.gbc files are standalone, in the sense that they can be loaded into the interpreter
without having the interface file or source files available. In the future you could
=====================================
compiler/GHC/Driver/Main.hs
=====================================
@@ -877,7 +877,7 @@ hscRecompStatus
, text "BCO core linkable", ppr bc_core_linkable
, text "Object Linkable", ppr obj_linkable])
- let just_o = justObjects <$> obj_linkable
+ let just_o = justObjects <$> obj_linkable
bytecode_or_object_code
| gopt Opt_WriteByteCode lcl_dflags = justBytecode <$> definitely_bc
@@ -2215,7 +2215,7 @@ generateAndWriteByteCode hsc_env cgguts mod_location = do
{-
Note [-fwrite-bytecode is not the default]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`-fwrite-bytecode` is not enabled by default because previously using `-fbyte-code` would
not write anything at all to disk. For example, GHCi would not write anything to the directory
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/57febb55de1dd512cf3e9dda032a7e6a...
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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/57febb55de1dd512cf3e9dda032a7e6a...
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