Maintain cost-centre stacks in the interpreter

Summary:
Breakpoints become SCCs, so we have detailed call-stack info for
interpreted code.  Currently this only works when GHC is compiled with
-prof, but D1562 (Remote GHCi) removes this constraint so that in the
future call stacks will be available without building your own GHCi.

How can you get a stack trace?

* programmatically: GHC.Stack.currentCallStack
* I've added an experimental :where command that shows the stack when
  stopped at a breakpoint
* `error` attaches a call stack automatically, although since calls to
  `error` are often lifted out to the top level, this is less useful
  than it might be (ImplicitParams still works though).
* Later we might attach call stacks to all exceptions

Other related changes in this diff:

* I reduced the number of places that get ticks attached for
  breakpoints.  In particular there was a breakpoint around the whole
  declaration, which was often redundant because it bound no variables.
  This reduces clutter in the stack traces and speeds up compilation.

* I tidied up some RealSrcSpan stuff in InteractiveUI, and made a few
  other small cleanups

Test Plan: validate

Reviewers: ezyang, bgamari, austin, hvr

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1595

GHC Trac Issues: #11047

1 files changed, 4 insertions, 3 deletions

diff --git a/compiler/ghci/ByteCodeInstr.hs b/compiler/ghci/ByteCodeInstr.hs
index 4f2b82ba27..74c4f9692e 100644
--- a/compiler/ghci/ByteCodeInstr.hs
+++ b/compiler/ghci/ByteCodeInstr.hs
@@ -13,6 +13,7 @@ module ByteCodeInstr (
 #include "../includes/MachDeps.h"
 
 import ByteCodeTypes
+import GHCi.RemoteTypes
 import StgCmmLayout     ( ArgRep(..) )
 import PprCore
 import Outputable
@@ -124,7 +125,7 @@ data BCInstr
 
    -- For doing calls to C (via glue code generated by libffi)
    | CCALL            Word16    -- stack frame size
-                      (Ptr ())  -- addr of the glue code
+                      RemotePtr -- addr of the glue code
                       Word16    -- whether or not the call is interruptible
                                 -- (XXX: inefficient, but I don't know
                                 -- what the alignment constraints are.)
@@ -139,7 +140,7 @@ data BCInstr
    | RETURN_UBX ArgRep -- return an unlifted value, here's its rep
 
    -- Breakpoints
-   | BRK_FUN          (MutableByteArray# RealWorld) Word16 BreakInfo
+   | BRK_FUN          (MutableByteArray# RealWorld) Word16 BreakInfo RemotePtr
 
 -- -----------------------------------------------------------------------------
 -- Printing bytecode instructions
@@ -239,7 +240,7 @@ instance Outputable BCInstr where
    ppr ENTER                 = text "ENTER"
    ppr RETURN                = text "RETURN"
    ppr (RETURN_UBX pk)       = text "RETURN_UBX  " <+> ppr pk
-   ppr (BRK_FUN _breakArray index info) = text "BRK_FUN" <+> text "<array>" <+> ppr index <+> ppr info
+   ppr (BRK_FUN _breakArray index info _cc) = text "BRK_FUN" <+> text "<array>" <+> ppr index <+> ppr info <+> text "<cc>"
 
 -- -----------------------------------------------------------------------------
 -- The stack use, in words, of each bytecode insn.  These _must_ be