Source notes (CorePrep and Stg support)

This is basically just about continuing maintaining source notes after
the Core stage. Unfortunately, this is more involved as it might seem,
as there are more restrictions on where ticks are allowed to show up.

Notes:

* We replace the StgTick / StgSCC constructors with a unified StgTick
  that can carry any tickish.

* For handling constructor or lambda applications, we generally float
  ticks out.

* Note that thanks to the NonLam placement, we know that source notes
  can never appear on lambdas. This means that as long as we are
  careful to always use mkTick, we will never violate CorePrep
  invariants.

* This is however not automatically true for eta expansion, which
  needs to somewhat awkwardly strip, then re-tick the expression in
  question.

* Where CorePrep floats out lets, we make sure to wrap them in the
  same spirit as FloatOut.

* Detecting selector thunks becomes a bit more involved, as we can run
  into ticks at multiple points.

(From Phabricator D169)

1 files changed, 17 insertions, 4 deletions

diff --git a/compiler/codeGen/StgCmmExpr.hs b/compiler/codeGen/StgCmmExpr.hs
index b2b64f8650..9097e7fa12 100644
--- a/compiler/codeGen/StgCmmExpr.hs
+++ b/compiler/codeGen/StgCmmExpr.hs
@@ -66,10 +66,7 @@ cgExpr (StgOpApp (StgPrimOp SeqOp) [StgVarArg a, _] _res_ty) =
 
 cgExpr (StgOpApp op args ty) = cgOpApp op args ty
 cgExpr (StgConApp con args)  = cgConApp con args
-cgExpr (StgSCC cc tick push expr) = do { emitSetCCC cc tick push; cgExpr expr }
-cgExpr (StgTick m n expr) = do dflags <- getDynFlags
-                               emit (mkTickBox dflags m n)
-                               cgExpr expr
+cgExpr (StgTick t e)         = cgTick t >> cgExpr e
 cgExpr (StgLit lit)       = do cmm_lit <- cgLit lit
                                emitReturn [CmmLit cmm_lit]
 
@@ -852,3 +849,19 @@ emitEnter fun = do
        ; return (ReturnedTo lret off)
        }
   }
+
+------------------------------------------------------------------------
+--              Ticks
+------------------------------------------------------------------------
+
+-- | Generate Cmm code for a tick. Depending on the type of Tickish,
+-- this will either generate actual Cmm instrumentation code, or
+-- simply pass on the annotation as a @CmmTickish@.
+cgTick :: Tickish Id -> FCode ()
+cgTick tick
+  = do { dflags <- getDynFlags
+       ; case tick of
+           ProfNote   cc t p -> emitSetCCC cc t p
+           HpcTick    m n    -> emit (mkTickBox dflags m n)
+           _other            -> return () -- ignore
+       }