Merge pull request #2848 from dotty-staging/change/patmat-optimize

Add option -Yno-patmat-opt to disable pm optimizations

Author: smarter

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -90,6 +90,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val Yheartbeat = BooleanSetting("-Yheartbeat", "show heartbeat stack trace of compiler operations.")
   val Yprintpos = BooleanSetting("-Yprintpos", "show tree positions.")
   val YnoDeepSubtypes = BooleanSetting("-Yno-deep-subtypes", "throw an exception on deep subtyping call stacks.")
+  val YnoPatmatOpt = BooleanSetting("-Yno-patmat-opt", "disable all pattern matching optimizations.")
   val YplainPrinter = BooleanSetting("-Yplain-printer", "Pretty-print using a plain printer.")
   val YprintSyms = BooleanSetting("-Yprint-syms", "when printing trees print info in symbols instead of corresponding info in trees.")
   val YprintDebug = BooleanSetting("-Yprint-debug", "when printing trees, print some extra information useful for debugging.")

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -687,12 +687,12 @@ object PatternMatcher {
       val refCount = varRefCount(plan)
       val LetPlan(topSym, _) = plan
 
-      def toDrop(sym: Symbol) =
-        initializer.contains(sym) &&
-        isPatmatGenerated(sym) &&
-        refCount(sym) <= 1 &&
-        sym != topSym &&
-        isPureExpr(initializer(sym))
+      def toDrop(sym: Symbol) = initializer.get(sym) match {
+        case Some(rhs) =>
+          isPatmatGenerated(sym) && refCount(sym) <= 1 && sym != topSym && isPureExpr(rhs)
+        case none =>
+          false
+      }
 
       object Inliner extends PlanTransform {
         override val treeMap = new TreeMap {
@@ -924,10 +924,11 @@ object PatternMatcher {
     def translateMatch(tree: Match): Tree = {
       var plan = matchPlan(tree)
       patmatch.println(i"Plan for $tree: ${show(plan)}")
-      for ((title, optimization) <- optimizations) {
-        plan = optimization(plan)
-        patmatch.println(s"After $title: ${show(plan)}")
-      }
+      if (!ctx.settings.YnoPatmatOpt.value)
+        for ((title, optimization) <- optimizations) {
+          plan = optimization(plan)
+          patmatch.println(s"After $title: ${show(plan)}")
+        }
       val result = emit(plan)
       checkSwitch(tree, result)
       result