Allow top-level string literals in Core (#8472)

This commits relaxes the invariants of the Core syntax so that a
top-level variable can be bound to a primitive string literal of type
Addr#.

This commit:

* Relaxes the invatiants of the Core, and allows top-level bindings whose
  type is Addr# as long as their RHS is either a primitive string literal or
  another variable.

* Allows the simplifier and the full-laziness transformer to float out
  primitive string literals to the top leve.

* Introduces the new StgGenTopBinding type to accomodate top-level Addr#
  bindings.

* Introduces a new type of labels in the object code, with the suffix "_bytes",
  for exported top-level Addr# bindings.

* Makes some built-in rules more robust. This was necessary to keep them
  functional after the above changes.

This is a continuation of D2554.

Rebasing notes:
This had two slightly suspicious performance regressions:

* T12425: bytes allocated regressed by roughly 5%
* T4029: bytes allocated regressed by a bit over 1%
* T13035: bytes allocated regressed by a bit over 5%

These deserve additional investigation.

Rebased by: bgamari.

Test Plan: ./validate --slow

Reviewers: goldfire, trofi, simonmar, simonpj, austin, hvr, bgamari

Reviewed By: trofi, simonpj, bgamari

Subscribers: trofi, simonpj, gridaphobe, thomie

Differential Revision: https://phabricator.haskell.org/D2605

GHC Trac Issues: #8472

1 files changed, 4 insertions, 3 deletions

diff --git a/compiler/ghci/ByteCodeAsm.hs b/compiler/ghci/ByteCodeAsm.hs
index 817e379003..9eb730ff1a 100644
--- a/compiler/ghci/ByteCodeAsm.hs
+++ b/compiler/ghci/ByteCodeAsm.hs
@@ -89,9 +89,10 @@ bcoFreeNames bco
 
 -- Top level assembler fn.
 assembleBCOs
-  :: HscEnv -> [ProtoBCO Name] -> [TyCon] -> Maybe ModBreaks
+  :: HscEnv -> [ProtoBCO Name] -> [TyCon] -> [RemotePtr ()]
+  -> Maybe ModBreaks
   -> IO CompiledByteCode
-assembleBCOs hsc_env proto_bcos tycons modbreaks = do
+assembleBCOs hsc_env proto_bcos tycons top_strs modbreaks = do
   itblenv <- mkITbls hsc_env tycons
   bcos    <- mapM (assembleBCO (hsc_dflags hsc_env)) proto_bcos
   (bcos',ptrs) <- mallocStrings hsc_env bcos
@@ -99,7 +100,7 @@ assembleBCOs hsc_env proto_bcos tycons modbreaks = do
     { bc_bcos = bcos'
     , bc_itbls =  itblenv
     , bc_ffis = concat (map protoBCOFFIs proto_bcos)
-    , bc_strs = ptrs
+    , bc_strs = top_strs ++ ptrs
     , bc_breaks = modbreaks
     }