preliminary ternary substitution simplification

src/Convert.hs

@@ -20,6 +20,7 @@ import qualified Convert.Interface
 import qualified Convert.IntTypes
 import qualified Convert.KWArgs
 import qualified Convert.Logic
+import qualified Convert.Mux
 import qualified Convert.NamedBlock
 import qualified Convert.NestPI
 import qualified Convert.Package
@@ -47,6 +48,7 @@ phases excludes =
     , Convert.Enum.convert
     , Convert.IntTypes.convert
     , Convert.KWArgs.convert
+    , Convert.Mux.convert
     , Convert.PackedArray.convert
     , Convert.StarPort.convert
     , Convert.StmtBlock.convert

src/Convert/Mux.hs

@@ -0,0 +1,65 @@
+{- sv2v
+ - Author: Zachary Snow <zach@zachjs.com>
+ -
+ - Elaboration of ternary expressions where the condition references a
+ - localparam.
+ -
+ - Our conversions generate a lot of ternary expressions. This conversion
+ - attempts to make the code output a bit cleaner. Note that we can only do this
+ - simplification on localparams because parameters can be overridden at
+ - instantiation.
+ -
+ - This conversion applies the heuristic that it will only make substitutions
+ - into a ternary condition if making substitutions immediately enables the
+ - expression to be simplified further.
+ -}
+
+module Convert.Mux (convert) where
+
+import Control.Monad.State
+import qualified Data.Map.Strict as Map
+
+import Convert.Traverse
+import Language.SystemVerilog.AST
+
+type Info = Map.Map Identifier Expr
+
+convert :: [AST] -> [AST]
+convert = map $ traverseDescriptions convertDescription
+
+convertDescription :: Description -> Description
+convertDescription =
+    scopedConversion traverseDeclM traverseModuleItemM traverseStmtM Map.empty
+
+traverseDeclM :: Decl -> State Info Decl
+traverseDeclM decl = do
+    case decl of
+        Localparam _ x e -> modify $ Map.insert x e
+        _ -> return ()
+    return decl
+
+traverseModuleItemM :: ModuleItem -> State Info ModuleItem
+traverseModuleItemM item = traverseExprsM traverseExprM item
+
+traverseStmtM :: Stmt -> State Info Stmt
+traverseStmtM stmt = traverseStmtExprsM traverseExprM stmt
+
+traverseExprM :: Expr -> State Info Expr
+traverseExprM = traverseNestedExprsM $ stately convertExpr
+
+convertExpr :: Info -> Expr -> Expr
+convertExpr info (Mux cc aa bb) =
+    if before == after
+        then Mux cc aa bb
+        else simplify $ Mux after aa bb
+    where
+        before = traverseNestedExprs substitute (simplify cc)
+        after = simplify before
+        substitute :: Expr -> Expr
+        substitute (Ident x) =
+            case Map.lookup x info of
+                Nothing -> Ident x
+                Just e-> e
+        substitute other = other
+convertExpr _ other = other
+

src/Language/SystemVerilog/AST/Expr.hs

@@ -125,6 +125,7 @@ simplify (orig @ (Call Nothing "$clog2" (Args [Just (Number n)] []))) =
     case readNumber n of
         Nothing -> orig
         Just x -> Number $ show $ clog2 x
+simplify (Mux (Number "0") e _) = e
 simplify (Mux (BinOp Ge c1 c2) e1 e2) =
     case (c1', c2') of
         (Number a, Number b) ->

sv2v.cabal

@@ -64,6 +64,7 @@ executable sv2v
     Convert.IntTypes
     Convert.KWArgs
     Convert.Logic
+    Convert.Mux
     Convert.NamedBlock
     Convert.NestPI
     Convert.Package