Improved the peephole optimizer to use liveness.

2 files changed, 33 insertions, 8 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/opt/ClosureElimination.scala b/src/compiler/scala/tools/nsc/backend/opt/ClosureElimination.scala
index 70bea2d44a..0897b94a15 100644
--- a/src/compiler/scala/tools/nsc/backend/opt/ClosureElimination.scala
+++ b/src/compiler/scala/tools/nsc/backend/opt/ClosureElimination.scala
@@ -25,8 +25,9 @@ abstract class ClosureElimination extends SubComponent {
   override def newPhase(p: Phase) = new ClosureEliminationPhase(p)
 
   /** A simple peephole optimizer. */
-  val peephole = new PeepholeOpt( (i1, i2) =>
-    (i1, i2) match {
+  val peephole = new PeepholeOpt {
+
+    def peep(bb: BasicBlock, i1: Instruction, i2: Instruction) = (i1, i2) match {
       case (CONSTANT(c), DROP(_)) =>
         if (c.tag == UnitTag)
           Some(List(i2))
@@ -37,7 +38,21 @@ abstract class ClosureElimination extends SubComponent {
         if (x eq y) Some(Nil) else None
 
       case (STORE_LOCAL(x), LOAD_LOCAL(y)) if (x == y) =>
-        Some(List(DUP(x.kind), STORE_LOCAL(x)))
+        var liveOut = liveness.out(bb)
+        if (!liveOut(x)) {
+          log("store/load to a dead local? " + x)
+          val instrs = bb.getArray
+          var idx = instrs.length - 1
+          while (idx > 0 && (instrs(idx) ne i2)) {
+            liveOut = liveness.interpret(liveOut, instrs(idx))
+            idx -= 1
+          }
+          if (!liveOut(x)) {
+            println("removing dead store/load " + x)
+            Some(Nil)
+          } else None
+        } else
+          Some(List(DUP(x.kind), STORE_LOCAL(x)))
 
       case (LOAD_LOCAL(_), DROP(_)) | (DUP(_), DROP(_)) =>
         Some(Nil)
@@ -52,7 +67,8 @@ abstract class ClosureElimination extends SubComponent {
           Some(DROP(REFERENCE(definitions.ObjectClass)) :: Nil);
 
       case _ => None
-    });
+    }
+  }
 
   /** The closure elimination phase.
    */
@@ -85,7 +101,7 @@ abstract class ClosureElimination extends SubComponent {
     def analyzeClass(cls: IClass): Unit = if (settings.Xcloselim.value) {
       cls.methods.foreach { m =>
         analyzeMethod(m)
-        peephole.transformMethod(m);
+        peephole(m);
      }}
 
 
@@ -202,12 +218,20 @@ abstract class ClosureElimination extends SubComponent {
 
 
   /** Peephole optimization. */
-  class PeepholeOpt(peep: (Instruction, Instruction) => Option[List[Instruction]]) {
+  abstract class PeepholeOpt {
 
     private var method: IMethod = null
 
-    def transformMethod(m: IMethod): Unit = if (m.code ne null) {
+    /** Concrete implementations will perform their optimizations here */
+    def peep(bb: BasicBlock, i1: Instruction, i2: Instruction): Option[List[Instruction]]
+
+    var liveness: global.icodes.liveness.LivenessAnalysis = null
+
+    def apply(m: IMethod): Unit = if (m.code ne null) {
       method = m
+      liveness = new global.icodes.liveness.LivenessAnalysis
+      liveness.init(m)
+      liveness.run
       for (b <- m.code.blocks)
         transformBlock(b)
     }
@@ -225,7 +249,7 @@ abstract class ClosureElimination extends SubComponent {
         redo = false;
 
         while (t != Nil) {
-          peep(h, t.head) match {
+          peep(b, h, t.head) match {
             case Some(newInstrs) =>
               newInstructions = seen.reverse ::: newInstrs ::: t.tail;
               redo = true;
diff --git a/src/compiler/scala/tools/nsc/backend/opt/DeadCodeElimination.scala b/src/compiler/scala/tools/nsc/backend/opt/DeadCodeElimination.scala
index e365b3bc08..589425298f 100644
--- a/src/compiler/scala/tools/nsc/backend/opt/DeadCodeElimination.scala
+++ b/src/compiler/scala/tools/nsc/backend/opt/DeadCodeElimination.scala
@@ -47,6 +47,7 @@ abstract class DeadCodeElimination extends SubComponent {
       cls.methods.foreach { m =>
         this.method = m
         dieCodeDie(m)
+        global.closureElimination.peephole(m)
       }
     }