From 39457f6c85fc9764d714d52317edcd4300fd82b8 Mon Sep 17 00:00:00 2001
From: Grzegorz Kossakowski <grzegorz.kossakowski@gmail.com>
Date: Wed, 1 Feb 2012 17:26:11 +0100
Subject: Convert values to Int in switchable patterns.

Further improvements to how -Yvirtpatmat
handles switch-like patterns that can be
translated to switch tables.

First of all, we added a check whether
a type of an expression we pattern match
on is in the set of allowed types for
switch patterns.

If yes, we translate a pattern to switch
one by converting both an expression we
pattern match on and literals in a pattern
to an Int.

I borrowed an idea of converting to Ints
from both old pattern matcher implementation
and from how javac handles it.
---
 .../tools/nsc/typechecker/PatMatVirtualiser.scala  | 62 ++++++++++++++--------
 1 file changed, 41 insertions(+), 21 deletions(-)

diff --git a/src/compiler/scala/tools/nsc/typechecker/PatMatVirtualiser.scala b/src/compiler/scala/tools/nsc/typechecker/PatMatVirtualiser.scala
index cf5985eeee..b1e02cb062 100644
--- a/src/compiler/scala/tools/nsc/typechecker/PatMatVirtualiser.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/PatMatVirtualiser.scala
@@ -1128,10 +1128,22 @@ defined class Foo */
     //   }
     // }
 
+    private val switchableTpes = Set(ByteClass.tpe, ShortClass.tpe, IntClass.tpe, CharClass.tpe)
+
     def emitSwitch(scrut: Tree, scrutSym: Symbol, cases: List[List[TreeMaker]], pt: Type): Option[Tree] = if (!optimizingCodeGen) None else {
       def sequence[T](xs: List[Option[T]]): Option[List[T]] =
         if (xs exists (_.isEmpty)) None else Some(xs.flatten)
 
+      def isSwitchableTpe(tpe: Type): Boolean =
+        switchableTpes contains tpe
+      def switchableConstToInt(x: Tree): Tree = {
+        val Literal(const) = x
+        const.tag match {
+          case IntTag => x
+          case ByteTag | ShortTag | CharTag => Literal(Constant(const.intValue))
+        }
+      }
+
       val caseDefs = cases map { makers =>
         removeSubstOnly(makers) match {
           // default case (don't move this to unfold, as it may only occur on the top level, not as an alternative -- well, except in degenerate matches)
@@ -1139,12 +1151,12 @@ defined class Foo */
             Some(CaseDef(Ident(nme.WILDCARD), EmptyTree, btm.substitution(body)))
           // constant
           case (EqualityTestTreeMaker(_, const@SwitchablePattern(), _)) :: (btm@BodyTreeMaker(body, _)) :: Nil =>
-            Some(CaseDef(const, EmptyTree, btm.substitution(body)))
+            Some(CaseDef(switchableConstToInt(const), EmptyTree, btm.substitution(body)))
           // alternatives
           case AlternativesTreeMaker(_, altss, _) :: (btm@BodyTreeMaker(body, _)) :: Nil => // assert(currLabel.isEmpty && nextLabel.isEmpty)
             val caseConstants = altss map {
               case EqualityTestTreeMaker(_, const@SwitchablePattern(), _) :: Nil =>
-                Some(const)
+                Some(switchableConstToInt(const))
               case _ =>
                 None
             }
@@ -1158,27 +1170,35 @@ defined class Foo */
         }
       }
 
-      sequence(caseDefs) map { caseDefs =>
-        import CODE._
-        val caseDefsWithDefault = {
-          def isDefault(x: CaseDef): Boolean = x match { 
-            case CaseDef(Ident(nme.WILDCARD), EmptyTree, _) => true
-            case _ => false
-          }
-          val hasDefault = caseDefs exists isDefault
-          if (hasDefault) caseDefs else {
-            val default = atPos(scrut.pos) { DEFAULT ==> MATCHERROR(REF(scrutSym)) }
-            caseDefs :+ default
+      if (!isSwitchableTpe(scrut.tpe))
+        None
+      else {
+        sequence(caseDefs) map { caseDefs =>
+          import CODE._
+          val caseDefsWithDefault = {
+            def isDefault(x: CaseDef): Boolean = x match {
+              case CaseDef(Ident(nme.WILDCARD), EmptyTree, _) => true
+              case _ => false
+            }
+            val hasDefault = caseDefs exists isDefault
+            if (hasDefault) caseDefs else {
+              val default = atPos(scrut.pos) { DEFAULT ==> MATCHERROR(REF(scrutSym)) }
+              caseDefs :+ default
+            }
           }
+          val matcher = BLOCK(
+            if (scrut.tpe != IntClass.tpe) {
+              scrutSym setInfo IntClass.tpe
+              VAL(scrutSym) === (scrut DOT nme.toInt)
+            } else {
+              VAL(scrutSym) === scrut
+            },
+            Match(REF(scrutSym), caseDefsWithDefault) // match on scrutSym, not scrut to avoid duplicating scrut
+          )
+          // matcher filter (tree => tree.tpe == null) foreach println
+          // treeBrowser browse matcher
+          matcher // set type to avoid recursion in typedMatch
         }
-        val matcher = BLOCK(
-          VAL(scrutSym) === scrut, // TODO: type test for switchable type if patterns allow switch but the scrutinee doesn't
-          Match(REF(scrutSym), caseDefsWithDefault) // match on scrutSym, not scrut to avoid duplicating scrut
-        )
-
-        // matcher filter (tree => tree.tpe == null) foreach println
-        // treeBrowser browse matcher
-        matcher // set type to avoid recursion in typedMatch
       }
     }
 
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