Add a CSE pass to Stg (#9291)

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 for now. It
might also be a good candiate for -O2.

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

1 files changed, 22 insertions, 2 deletions

diff --git a/compiler/stgSyn/StgSyn.hs b/compiler/stgSyn/StgSyn.hs
index 3ec37eefff..64c8448421 100644
--- a/compiler/stgSyn/StgSyn.hs
+++ b/compiler/stgSyn/StgSyn.hs
@@ -24,8 +24,11 @@ module StgSyn (
         combineStgBinderInfo,
 
         -- a set of synonyms for the most common (only :-) parameterisation
-        StgArg,
-        StgBinding, StgExpr, StgRhs, StgAlt,
+        StgArg, StgBinding, StgExpr, StgRhs, StgAlt,
+
+        -- a set of synonyms to distinguish in- and out variants
+        InStgArg,  InStgBinding,  InStgExpr,  InStgRhs,  InStgAlt,
+        OutStgArg, OutStgBinding, OutStgExpr, OutStgRhs, OutStgAlt,
 
         -- StgOp
         StgOp(..),
@@ -551,7 +554,24 @@ type StgExpr     = GenStgExpr     Id Id
 type StgRhs      = GenStgRhs      Id Id
 type StgAlt      = GenStgAlt      Id Id
 
+{- 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.
+   See CoreSyn for precedence in Core land
+-}
+
+type InStgBinding  = StgBinding
+type InStgArg      = StgArg
+type InStgExpr     = StgExpr
+type InStgRhs      = StgRhs
+type InStgAlt      = StgAlt
+type OutStgBinding = StgBinding
+type OutStgArg     = StgArg
+type OutStgExpr    = StgExpr
+type OutStgRhs     = StgRhs
+type OutStgAlt     = StgAlt
+
 {-
+
 ************************************************************************
 *                                                                      *
 \subsubsection[UpdateFlag-datatype]{@UpdateFlag@}