Interface Files with Core Definitions

This commit adds three new flags

* -fwrite-if-simplified-core: Writes the whole core program into an interface
  file
* -fbyte-code-and-object-code: Generate both byte code and object code
  when compiling a file
* -fprefer-byte-code: Prefer to use byte-code if it's available when
  running TH splices.

The goal for including the core bindings in an interface file is to be able to restart the compiler pipeline
at the point just after simplification and before code generation. Once compilation is
restarted then code can be created for the byte code backend.
This can significantly speed up
start-times for projects in GHCi. HLS already implements its own version of these extended interface
files for this reason.

Preferring to use byte-code means that we can avoid some potentially
expensive code generation steps (see #21700)

* Producing object code is much slower than producing bytecode, and normally you
  need to compile with `-dynamic-too` to produce code in the static and dynamic way, the
  dynamic way just for Template Haskell execution when using a dynamically linked compiler.

* Linking many large object files, which happens once per splice, can be quite
  expensive compared to linking bytecode.

And you can get GHC to compile the necessary byte code so
`-fprefer-byte-code` has access to it by using
`-fbyte-code-and-object-code`.

Fixes #21067

1 files changed, 14 insertions, 3 deletions

diff --git a/compiler/GHC/Unit/Module/ModIface.hs b/compiler/GHC/Unit/Module/ModIface.hs
index 76cfff2b9f..1d5280f4fa 100644
--- a/compiler/GHC/Unit/Module/ModIface.hs
+++ b/compiler/GHC/Unit/Module/ModIface.hs
@@ -200,6 +200,11 @@ data ModIface_ (phase :: ModIfacePhase)
                 -- Ditto data constructors, class operations, except that
                 -- the hash of the parent class/tycon changes
 
+        mi_extra_decls :: Maybe [IfaceBindingX IfaceMaybeRhs IfaceTopBndrInfo],
+                -- ^ Extra variable definitions which are **NOT** exposed but when
+                -- combined with mi_decls allows us to restart code generation.
+                -- See Note [Interface Files with Core Definitions] and Note [Interface File with Core: Sharing RHSs]
+
         mi_globals  :: !(Maybe GlobalRdrEnv),
                 -- ^ Binds all the things defined at the top level in
                 -- the /original source/ code for this module. which
@@ -349,6 +354,7 @@ instance Binary ModIface where
                  mi_warns     = warns,
                  mi_anns      = anns,
                  mi_decls     = decls,
+                 mi_extra_decls = extra_decls,
                  mi_insts     = insts,
                  mi_fam_insts = fam_insts,
                  mi_rules     = rules,
@@ -392,6 +398,7 @@ instance Binary ModIface where
         lazyPut bh warns
         lazyPut bh anns
         put_ bh decls
+        put_ bh extra_decls
         put_ bh insts
         put_ bh fam_insts
         lazyPut bh rules
@@ -423,6 +430,7 @@ instance Binary ModIface where
         warns       <- {-# SCC "bin_warns" #-} lazyGet bh
         anns        <- {-# SCC "bin_anns" #-} lazyGet bh
         decls       <- {-# SCC "bin_tycldecls" #-} get bh
+        extra_decls <- get bh
         insts       <- {-# SCC "bin_insts" #-} get bh
         fam_insts   <- {-# SCC "bin_fam_insts" #-} get bh
         rules       <- {-# SCC "bin_rules" #-} lazyGet bh
@@ -446,6 +454,7 @@ instance Binary ModIface where
                  mi_fixities    = fixities,
                  mi_warns       = warns,
                  mi_decls       = decls,
+                 mi_extra_decls = extra_decls,
                  mi_globals     = Nothing,
                  mi_insts       = insts,
                  mi_fam_insts   = fam_insts,
@@ -494,6 +503,7 @@ emptyPartialModIface mod
                mi_fam_insts   = [],
                mi_rules       = [],
                mi_decls       = [],
+               mi_extra_decls = Nothing,
                mi_globals     = Nothing,
                mi_hpc         = False,
                mi_trust       = noIfaceTrustInfo,
@@ -541,12 +551,13 @@ emptyIfaceHashCache _occ = Nothing
 -- avoid major space leaks.
 instance (NFData (IfaceBackendExts (phase :: ModIfacePhase)), NFData (IfaceDeclExts (phase :: ModIfacePhase))) => NFData (ModIface_ phase) where
   rnf (ModIface f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12
-                f13 f14 f15 f16 f17 f18 f19 f20 f21 f22 f23) =
+                f13 f14 f15 f16 f17 f18 f19 f20 f21 f22 f23 f24) =
     rnf f1 `seq` rnf f2 `seq` f3 `seq` f4 `seq` f5 `seq` f6 `seq` rnf f7 `seq` f8 `seq`
-    f9 `seq` rnf f10 `seq` rnf f11 `seq` f12 `seq` rnf f13 `seq` rnf f14 `seq` rnf f15 `seq`
-    rnf f16 `seq` f17 `seq` rnf f18 `seq` rnf f19 `seq` f20 `seq` f21 `seq` f22 `seq` rnf f23
+    f9 `seq` rnf f10 `seq` rnf f11 `seq` rnf f12 `seq` f13 `seq` rnf f14 `seq` rnf f15 `seq` rnf f16 `seq`
+    rnf f17 `seq` f18 `seq` rnf f19 `seq` rnf f20 `seq` f21 `seq` f22 `seq` f23 `seq` rnf f24
     `seq` ()
 
+
 instance NFData (ModIfaceBackend) where
   rnf (ModIfaceBackend f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13)
     = rnf f1 `seq` rnf f2 `seq` rnf f3 `seq` rnf f4 `seq`