Remote GHCi, -fexternal-interpreter

Summary:
(Apologies for the size of this patch, I couldn't make a smaller one
that was validate-clean and also made sense independently)

(Some of this code is derived from GHCJS.)

This commit adds support for running interpreted code (for GHCi and
TemplateHaskell) in a separate process.  The functionality is
experimental, so for now it is off by default and enabled by the flag
-fexternal-interpreter.

Reaosns we want this:

* compiling Template Haskell code with -prof does not require
  building the code without -prof first

* when GHC itself is profiled, it can interpret unprofiled code, and
  the same applies to dynamic linking.  We would no longer need to
  force -dynamic-too with TemplateHaskell, and we can load ordinary
  objects into a dynamically-linked GHCi (and vice versa).

* An unprofiled GHCi can load and run profiled code, which means it
  can use the stack-trace functionality provided by profiling without
  taking the performance hit on the compiler that profiling would
  entail.

Amongst other things; see
https://ghc.haskell.org/trac/ghc/wiki/RemoteGHCi for more details.

Notes on the implementation are in Note [Remote GHCi] in the new
module compiler/ghci/GHCi.hs.  It probably needs more documenting,
feel free to suggest things I could elaborate on.

Things that are not currently implemented for -fexternal-interpreter:

* The GHCi debugger
* :set prog, :set args in GHCi
* `recover` in Template Haskell
* Redirecting stdin/stdout for the external process

These are all doable, I just wanted to get to a working validate-clean
patch first.

I also haven't done any benchmarking yet.  I expect there to be slight hit
to link times for byte code and some penalty due to having to
serialize/deserialize TH syntax, but I don't expect it to be a serious
problem.  There's also lots of low-hanging fruit in the byte code
generator/linker that we could exploit to speed things up.

Test Plan:
* validate
* I've run parts of the test suite with
EXTRA_HC_OPTS=-fexternal-interpreter, notably tests/ghci and tests/th.
There are a few failures due to the things not currently implemented
(see above).

Reviewers: simonpj, goldfire, ezyang, austin, alanz, hvr, niteria, bgamari, gibiansky, luite

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1562

1 files changed, 0 insertions, 5 deletions

diff --git a/compiler/basicTypes/BasicTypes.hs b/compiler/basicTypes/BasicTypes.hs
index 4133eac35f..f8d4e8fe3e 100644
--- a/compiler/basicTypes/BasicTypes.hs
+++ b/compiler/basicTypes/BasicTypes.hs
@@ -86,8 +86,6 @@ module BasicTypes(
 
         FractionalLit(..), negateFractionalLit, integralFractionalLit,
 
-        HValue(..),
-
         SourceText,
 
         IntWithInf, infinity, treatZeroAsInf, mkIntWithInf, intGtLimit
@@ -99,7 +97,6 @@ import SrcLoc ( Located,unLoc )
 import StaticFlags( opt_PprStyle_Debug )
 import Data.Data hiding (Fixity)
 import Data.Function (on)
-import GHC.Exts (Any)
 
 {-
 ************************************************************************
@@ -1165,8 +1162,6 @@ instance Ord FractionalLit where
 instance Outputable FractionalLit where
   ppr = text . fl_text
 
-newtype HValue = HValue Any
-
 {-
 ************************************************************************
 *                                                                      *