Implement same argument reduction, as well as CSE (currently disabled)

compiler/src/l3/CPSOptimizer.scala

@@ -107,18 +107,32 @@ abstract class CPSOptimizer[T <: CPSTreeModule { type Name = Symbol }]
       val newState = s.withExp(name, prim, replacedArgs)
       lazy val shrunkBody = shrink(body, newState)
 
+      // Dead code elim
       if (s.dead(name) && !impure(prim)) {
         shrunkBody
       } else {
         val allLitOpt = replacedArgs.map(_.asLiteral)
         val isAllLit = allLitOpt.forall(_.isDefined)
         lazy val asLit = allLitOpt.map(_.get)
-        if (isAllLit && vEvaluator.isDefinedAt((prim, asLit))) {
-          val newNewState = newState.withASubst(name, vEvaluator((prim, asLit)))
-          val newBody = shrink(body, newNewState)
-          newBody
+        if (false && s.eInvEnv.isDefinedAt((prim, replacedArgs))) {
+          val preComputedAtom = s.eInvEnv((prim, replacedArgs))
+          shrink(body, newState.withASubst(name, preComputedAtom))
         } else {
-          LetP(name, prim, replacedArgs, shrunkBody)
+          // Constant folding
+          if (isAllLit && vEvaluator.isDefinedAt((prim, asLit))) {
+            val newNewState = newState.withASubst(name, vEvaluator((prim, asLit)))
+            val newBody = shrink(body, newNewState)
+            newBody
+          } else {
+            lazy val x = replacedArgs(0)
+            lazy val y = replacedArgs(1)
+            if (replacedArgs.length == 2 && x == y && sameArgReduce.isDefinedAt((prim, x))) {
+              val newNewState = newState.withASubst(name, sameArgReduce((prim, x)))
+              shrink(body, newNewState)
+            } else {
+              LetP(name, prim, replacedArgs, shrunkBody)
+            }
+          }
         }
       }
     }