Add a CSE pass to Stg (#9291)wip/T9291

This CSE pass only targets data constructor applications. This is
probably the best we can do, as function calls and primitive operations
might have side-effects.

Introduces the flag -fstg-cse, enabled by default with -O.

Differential Revision: https://phabricator.haskell.org/D2871

2 files changed, 25 insertions, 0 deletions

diff --git a/compiler/basicTypes/Id.hs b/compiler/basicTypes/Id.hs
index 1b84acda75..84cafa3902 100644
--- a/compiler/basicTypes/Id.hs
+++ b/compiler/basicTypes/Id.hs
@@ -28,6 +28,10 @@ module Id (
         -- * The main types
         Var, Id, isId,
 
+        -- * In and Out variants
+        InVar,  InId,
+        OutVar, OutId,
+
         -- ** Simple construction
         mkGlobalId, mkVanillaGlobal, mkVanillaGlobalWithInfo,
         mkLocalId, mkLocalCoVar, mkLocalIdOrCoVar,
@@ -114,6 +118,8 @@ import BasicTypes
 
 -- Imported and re-exported
 import Var( Id, CoVar, DictId,
+            InId,  InVar,
+            OutId, OutVar,
             idInfo, idDetails, globaliseId, varType,
             isId, isLocalId, isGlobalId, isExportedId )
 import qualified Var
diff --git a/compiler/basicTypes/Var.hs b/compiler/basicTypes/Var.hs
index e783efea0d..3f78c2800f 100644
--- a/compiler/basicTypes/Var.hs
+++ b/compiler/basicTypes/Var.hs
@@ -37,6 +37,10 @@ module Var (
         Var, CoVar, Id, NcId, DictId, DFunId, EvVar, EqVar, EvId, IpId,
         TyVar, TypeVar, KindVar, TKVar, TyCoVar,
 
+        -- * In and Out variants
+        InVar,  InCoVar,  InId,  InTyVar,
+        OutVar, OutCoVar, OutId, OutTyVar,
+
         -- ** Taking 'Var's apart
         varName, varUnique, varType,
 
@@ -150,6 +154,21 @@ type EqVar  = EvId      -- Boxed equality evidence
 type TyCoVar = Id       -- Type, *or* coercion variable
                         --   predicate: isTyCoVar
 
+
+{- Many passes apply a substitution, and it's very handy to have type
+   synonyms to remind us whether or not the subsitution has been applied -}
+
+type InVar      = Var
+type InTyVar    = TyVar
+type InCoVar    = CoVar
+type InId       = Id
+type OutVar     = Var
+type OutTyVar   = TyVar
+type OutCoVar   = CoVar
+type OutId      = Id
+
+
+
 {- Note [Evidence: EvIds and CoVars]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 * An EvId (evidence Id) is a term-level evidence variable