Implemented handling of <label> DefDefs in backend.

1 files changed, 185 insertions, 0 deletions

diff --git a/src/dotty/tools/backend/jvm/LabelDefs.scala b/src/dotty/tools/backend/jvm/LabelDefs.scala
new file mode 100644
index 000000000..0e50e9366
--- /dev/null
+++ b/src/dotty/tools/backend/jvm/LabelDefs.scala
@@ -0,0 +1,185 @@
+package dotty.tools.backend.jvm
+
+import dotty.tools.dotc.ast.tpd
+import dotty.tools.dotc.core.Contexts.Context
+import dotty.tools.dotc.core.Types
+import dotty.tools.dotc.transform.TreeTransforms.{TransformerInfo, TreeTransform, MiniPhase, MiniPhaseTransform}
+import dotty.tools.dotc.ast.tpd
+import dotty.tools.dotc
+import dotty.tools.dotc.backend.jvm.DottyPrimitives
+import dotty.tools.dotc.core.Flags.FlagSet
+import dotty.tools.dotc.transform.Erasure
+import dotty.tools.dotc.transform.SymUtils._
+import java.io.{File => JFile}
+
+import scala.collection.generic.Clearable
+import scala.collection.mutable
+import scala.collection.mutable.{ListBuffer, ArrayBuffer}
+import scala.reflect.ClassTag
+import scala.reflect.internal.util.WeakHashSet
+import scala.reflect.io.{Directory, PlainDirectory, AbstractFile}
+import scala.tools.asm.{ClassVisitor, FieldVisitor, MethodVisitor}
+import scala.tools.nsc.backend.jvm.{BCodeHelpers, BackendInterface}
+import dotty.tools.dotc.core._
+import Periods._
+import SymDenotations._
+import Contexts._
+import Types._
+import Symbols._
+import Denotations._
+import Phases._
+import java.lang.AssertionError
+import dotty.tools.dotc.util.Positions.Position
+import Decorators._
+import tpd._
+import StdNames.nme
+
+/**
+ * Verifies that each Label DefDef has only a single address to jump back and
+ * reorders them such that they are not nested and this address is a fall-through address for JVM
+ *
+ * ei such code
+ *
+ *
+ * <label> def foo(i: Int) = {
+ *   <label> def bar = 0
+ *   <label> def dough(i: Int) = if(i == 0) bar else foo(i-1)
+ *   dough(i)
+ *   }
+ *
+ * foo(100)
+ *
+ * will get rewritten to
+ *
+ *                                                  \
+ * <label> def foo(i: Int) = dough(i)
+ * <label> def dough(i: Int) = if(i == 0) bar else foo(i-1)
+ * <label> def bar = 2
+ *   foo(100)
+ *
+ *   Proposed way to generate this pattern in backend is:
+ *
+ *  foo(100)
+ *  <jump foo>
+ *  <label> def foo(i: Int) = dough(i)
+ *  // <jump a>                           // unreachable
+ *  <label> def dough(i: Int) = if(i == 0) bar else foo(i-1)
+ *  // <jump a>                           // unreachable
+ *  <label> def bar = 2
+ *  // <jump a>                           // unreachable
+ *  <asm point a>
+ *
+ *    Unreachable jumps will be eliminated by local dead code analysis.
+ *    After JVM is smart enough to remove next-line jumps
+ *
+ * Note that Label DefDefs can be only nested in Block, otherwise no one would be able to call them
+ * Other DefDefs are eliminated
+ */
+class LabelDefs extends MiniPhaseTransform {
+  def phaseName: String = "labelDef"
+
+  val queue = new ArrayBuffer[Tree]()
+
+
+
+  override def transformBlock(tree: tpd.Block)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
+    collectLabelDefs.clear
+    val newStats = collectLabelDefs.transformStats(tree.stats)
+    val newExpr = collectLabelDefs.transform(tree.expr)
+    val labelCalls = collectLabelDefs.labelCalls
+    val entryPoints = collectLabelDefs.parentLabelCalls
+    val labelDefs = collectLabelDefs.labelDefs
+
+    // make sure that for every label there's a single location it should return and single entry point
+    // if theres already a location that it returns to that's a failure
+    val disallowed = new mutable.HashMap[Symbol, Tree]()
+    queue.sizeHint(labelCalls.size + entryPoints.size)
+    def moveLabels(entryPoint: Tree): List[Tree] = {
+      if((entryPoint.symbol is Flags.Label) && labelDefs.contains(entryPoint.symbol)) {
+        val visitedNow = new mutable.HashMap[Symbol, Tree]()
+        val treesToAppend = new ArrayBuffer[Tree]() // order matters. parents should go first
+        queue.clear()
+
+        var visited = 0
+        queue += entryPoint
+        while (visited < queue.size) {
+          val owningLabelDefSym = queue(visited).symbol
+          val owningLabelDef = labelDefs(owningLabelDefSym)
+          for (call <- labelCalls(owningLabelDefSym))
+            if (disallowed.contains(call.symbol)) {
+              val oldCall = disallowed(call.symbol)
+              ctx.error(s"Multiple return locations for Label $oldCall and $call", call.symbol.pos)
+            } else {
+              if ((!visitedNow.contains(call.symbol)) && labelDefs.contains(call.symbol)) {
+                val df = labelDefs(call.symbol)
+                visitedNow.put(call.symbol, labelDefs(call.symbol))
+                queue += call
+              }
+            }
+          if(!treesToAppend.contains(owningLabelDef))
+            treesToAppend += owningLabelDef
+          visited += 1
+        }
+        disallowed ++= visitedNow
+
+        treesToAppend.toList
+      } else Nil
+    }
+
+    cpy.Block(tree)(entryPoints.flatMap(moveLabels).toList ++ newStats, newExpr)
+
+  }
+
+  val collectLabelDefs = new TreeMap() {
+
+    // label calls from this DefDef
+    var parentLabelCalls: mutable.Set[Tree] = new mutable.HashSet[Tree]()
+    var isInsideLabel = false
+    var isInsideBlock = false
+
+    def shouldMoveLabel = !isInsideBlock
+
+    // labelSymbol -> Defining tree
+    val labelDefs = new mutable.HashMap[Symbol, Tree]()
+    // owner -> all calls by this owner
+    val labelCalls = new mutable.HashMap[Symbol, mutable.Set[Tree]]()
+    val labelCallCounts = new mutable.HashMap[Symbol, Int]()
+
+    def clear = {
+      parentLabelCalls.clear()
+      labelDefs.clear()
+      labelCalls.clear()
+    }
+
+    override def transform(tree: tpd.Tree)(implicit ctx: Context): tpd.Tree = tree match {
+      case t: Template => t
+      case t: Block => 
+        val tmp = isInsideBlock
+        isInsideBlock = true
+        val r = super.transform(t)
+        isInsideBlock = tmp
+        r
+      case t: DefDef =>
+        assert(t.symbol is Flags.Label)
+        val st = parentLabelCalls
+        parentLabelCalls = new mutable.HashSet[Tree]()
+        val tmp = isInsideLabel
+        isInsideLabel = true
+        val r = super.transform(tree)
+        isInsideLabel = tmp
+        labelCalls(r.symbol) = parentLabelCalls
+        parentLabelCalls = st
+        if(shouldMoveLabel) {
+        labelDefs(r.symbol) = r
+        EmptyTree
+        } else r
+      case t: Apply if t.symbol is Flags.Label =>
+        parentLabelCalls = parentLabelCalls + t
+        labelCallCounts.get(t.symbol)
+        super.transform(tree)
+      case _ =>
+        super.transform(tree)
+
+    }
+  }
+}