Cleanups and performance fixes in Nullness analysis

1 files changed, 29 insertions, 57 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/analysis/NullnessAnalyzer.scala b/src/compiler/scala/tools/nsc/backend/jvm/analysis/NullnessAnalyzer.scala
index f6d249db7b..f9ac12eb4d 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/analysis/NullnessAnalyzer.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/analysis/NullnessAnalyzer.scala
@@ -33,56 +33,34 @@ import BytecodeUtils._
  */
 
 /**
- * Type to represent nullness of values.
- */
-sealed trait Nullness {
-  final def merge(other: Nullness) = if (this == other) this else Unknown
-}
-case object NotNull extends Nullness
-case object Unknown extends Nullness
-case object Null    extends Nullness
-
-/**
  * Represents the nullness state for a local variable or stack value.
  *
- * Note that nullness of primitive values is not tracked, it will be always [[Unknown]].
+ * Note that nullness of primitive values is not tracked, it will be always unknown.
  */
-sealed trait NullnessValue extends Value {
-  /**
-   * The nullness of this value.
-   */
-  def nullness: Nullness
-
-  /**
-   * True if this value is a long or double. The Analyzer framework needs to know
-   * the size of each value when interpreting instructions, see `Frame.execute`.
-   */
-  def isSize2: Boolean
+sealed abstract class NullnessValue(final val isSize2: Boolean) extends Value {
   /**
    * The size of the slot described by this value. Cannot be 0 because no values are allocated
    * for void-typed slots, see NullnessInterpreter.newValue.
    **/
   def getSize: Int = if (isSize2) 2 else 1
 
-  def merge(other: NullnessValue) = NullnessValue(nullness merge other.nullness, isSize2)
+  def merge(other: NullnessValue) = {
+    if (this eq other) this
+    else if (this eq UnknownValue2) this // the only possible value of size two
+    else UnknownValue1
+  }
+
+  final override def equals(other: Any) = this eq other.asInstanceOf[Object]
 }
 
-object NullValue     extends NullnessValue { def nullness = Null;    def isSize2 = false; override def toString = "Null"     }
-object UnknownValue1 extends NullnessValue { def nullness = Unknown; def isSize2 = false; override def toString = "Unknown1" }
-object UnknownValue2 extends NullnessValue { def nullness = Unknown; def isSize2 = true;  override def toString = "Unknown2" }
-object NotNullValue  extends NullnessValue { def nullness = NotNull; def isSize2 = false; override def toString = "NotNull"  }
+object NullValue     extends NullnessValue(isSize2 = false) { override def toString = "Null"     }
+object UnknownValue1 extends NullnessValue(isSize2 = false) { override def toString = "Unknown1" }
+object UnknownValue2 extends NullnessValue(isSize2 = true ) { override def toString = "Unknown2" }
+object NotNullValue  extends NullnessValue(isSize2 = false) { override def toString = "NotNull"  }
 
 object NullnessValue {
-  def apply(nullness: Nullness, isSize2: Boolean): NullnessValue = {
-    if      (nullness == Null)    NullValue
-    else if (nullness == NotNull) NotNullValue
-    else if (isSize2)             UnknownValue2
-    else                          UnknownValue1
-  }
-
-  def apply(nullness: Nullness, insn: AbstractInsnNode): NullnessValue = {
-    apply(nullness, isSize2 = BytecodeUtils.instructionResultSize(insn) == 2)
-  }
+  def unknown(isSize2: Boolean) = if (isSize2) UnknownValue2 else UnknownValue1
+  def unknown(insn: AbstractInsnNode) = if (BytecodeUtils.instructionResultSize(insn) == 2) UnknownValue2 else UnknownValue1
 }
 
 final class NullnessInterpreter extends Interpreter[NullnessValue](Opcodes.ASM5) {
@@ -97,29 +75,25 @@ final class NullnessInterpreter extends Interpreter[NullnessValue](Opcodes.ASM5)
     // (2) `tp` may also be `null`. When creating the initial frame, the analyzer invokes
     //     `newValue(null)` for each local variable. We have to return a value of size 1.
     if (tp == Type.VOID_TYPE) null // (1)
-    else NullnessValue(Unknown, isSize2 = tp != null /*(2)*/ && tp.getSize == 2 )
+    else NullnessValue.unknown(isSize2 = tp != null /*(2)*/ && tp.getSize == 2 )
   }
 
   override def newParameterValue(isInstanceMethod: Boolean, local: Int, tp: Type): NullnessValue = {
     // For instance methods, the `this` parameter is known to be not null.
-    if (isInstanceMethod && local == 0) NullnessValue(NotNull, isSize2 = false)
+    if (isInstanceMethod && local == 0) NotNullValue
     else super.newParameterValue(isInstanceMethod, local, tp)
   }
 
-  def newOperation(insn: AbstractInsnNode): NullnessValue = {
-    val nullness = (insn.getOpcode: @switch) match {
-      case Opcodes.ACONST_NULL => Null
-
-      case Opcodes.LDC => insn.asInstanceOf[LdcInsnNode].cst match {
-        case _: String | _: Type => NotNull
-        case _ => Unknown
-      }
+  def newOperation(insn: AbstractInsnNode): NullnessValue = (insn.getOpcode: @switch) match {
+    case Opcodes.ACONST_NULL => NullValue
 
-      case _ => Unknown
+    case Opcodes.LDC => insn.asInstanceOf[LdcInsnNode].cst match {
+      case _: String | _: Type => NotNullValue
+      case _ => NullnessValue.unknown(insn)
     }
 
     // for Opcodes.NEW, we use Unknown. The value will become NotNull after the constructor call.
-    NullnessValue(nullness, insn)
+    case _ => NullnessValue.unknown(insn)
   }
 
   def copyOperation(insn: AbstractInsnNode, value: NullnessValue): NullnessValue = value
@@ -128,26 +102,24 @@ final class NullnessInterpreter extends Interpreter[NullnessValue](Opcodes.ASM5)
     case Opcodes.CHECKCAST => value
 
     case Opcodes.NEWARRAY |
-         Opcodes.ANEWARRAY => NullnessValue(NotNull, isSize2 = false)
+         Opcodes.ANEWARRAY => NotNullValue
 
-    case _ => NullnessValue(Unknown, insn)
+    case _ => NullnessValue.unknown(insn)
   }
 
   def binaryOperation(insn: AbstractInsnNode, value1: NullnessValue, value2: NullnessValue): NullnessValue = {
-    NullnessValue(Unknown, insn)
+    NullnessValue.unknown(insn)
   }
 
-  def ternaryOperation(insn: AbstractInsnNode, value1: NullnessValue, value2: NullnessValue, value3: NullnessValue): NullnessValue = {
-    NullnessValue(Unknown, isSize2 = false)
-  }
+  def ternaryOperation(insn: AbstractInsnNode, value1: NullnessValue, value2: NullnessValue, value3: NullnessValue): NullnessValue = UnknownValue1
 
   def naryOperation(insn: AbstractInsnNode, values: util.List[_ <: NullnessValue]): NullnessValue = (insn.getOpcode: @switch) match {
     case Opcodes.MULTIANEWARRAY =>
-      NullnessValue(NotNull, isSize2 = false)
+      NotNullValue
 
     case _ =>
       // TODO: use a list of methods that are known to return non-null values
-      NullnessValue(Unknown, insn)
+      NullnessValue.unknown(insn)
   }
 
   def returnOperation(insn: AbstractInsnNode, value: NullnessValue, expected: NullnessValue): Unit = ()