Cleanup asm-to-string debug helpers

Introduces methods for textifying classes, methods, InsnLists and
individual AbstractInsnNodes.

Author: lrytz

src/compiler/scala/tools/nsc/backend/jvm/AsmUtils.scala

@@ -5,10 +5,11 @@
 
 package scala.tools.nsc.backend.jvm
 
-import scala.tools.asm.tree.{AbstractInsnNode, ClassNode, MethodNode}
-import java.io.PrintWriter
+import scala.tools.asm.tree.{InsnList, AbstractInsnNode, ClassNode, MethodNode}
+import java.io.{StringWriter, PrintWriter}
 import scala.tools.asm.util.{TraceClassVisitor, TraceMethodVisitor, Textifier}
 import scala.tools.asm.ClassReader
+import scala.collection.convert.decorateAsScala._
 
 object AsmUtils {
 
@@ -36,19 +37,12 @@ object AsmUtils {
 
   def traceMethod(mnode: MethodNode): Unit = {
     println(s"Bytecode for method ${mnode.name}")
-    val p = new Textifier
-    val tracer = new TraceMethodVisitor(p)
-    mnode.accept(tracer)
-    val w = new PrintWriter(System.out)
-    p.print(w)
-    w.flush()
+    println(textify(mnode))
   }
 
   def traceClass(cnode: ClassNode): Unit = {
     println(s"Bytecode for class ${cnode.name}")
-    val w = new PrintWriter(System.out)
-    cnode.accept(new TraceClassVisitor(w))
-    w.flush()
+    println(textify(cnode))
   }
 
   def traceClass(bytes: Array[Byte]): Unit = traceClass(readClass(bytes))
@@ -59,8 +53,56 @@ object AsmUtils {
     node
   }
 
-  def instructionString(instruction: AbstractInsnNode): String = instruction.getOpcode match {
-    case -1 => instruction.toString
-    case op => scala.tools.asm.util.Printer.OPCODES(op)
+  /**
+   * Returns a human-readable representation of the cnode ClassNode.
+   */
+  def textify(cnode: ClassNode): String = {
+    val trace = new TraceClassVisitor(new PrintWriter(new StringWriter))
+    cnode.accept(trace)
+    val sw = new StringWriter
+    val pw = new PrintWriter(sw)
+    trace.p.print(pw)
+    sw.toString
   }
+
+  /**
+   * Returns a human-readable representation of the code in the mnode MethodNode.
+   */
+  def textify(mnode: MethodNode): String = {
+    val trace = new TraceClassVisitor(new PrintWriter(new StringWriter))
+    mnode.accept(trace)
+    val sw = new StringWriter
+    val pw = new PrintWriter(sw)
+    trace.p.print(pw)
+    sw.toString
+  }
+
+  /**
+   * Returns a human-readable representation of the given instruction.
+   */
+  def textify(insn: AbstractInsnNode): String = {
+    val trace = new TraceMethodVisitor(new Textifier)
+    insn.accept(trace)
+    val sw = new StringWriter
+    val pw = new PrintWriter(sw)
+    trace.p.print(pw)
+    sw.toString.trim
+  }
+
+  /**
+   * Returns a human-readable representation of the given instruction sequence.
+   */
+  def textify(insns: Iterator[AbstractInsnNode]): String = {
+    val trace = new TraceMethodVisitor(new Textifier)
+    insns.foreach(_.accept(trace))
+    val sw: StringWriter = new StringWriter
+    val pw: PrintWriter = new PrintWriter(sw)
+    trace.p.print(pw)
+    sw.toString.trim
+  }
+
+  /**
+   * Returns a human-readable representation of the given instruction sequence.
+   */
+  def textify(insns: InsnList): String = textify(insns.iterator().asScala)
 }

test/files/run/icode-reader-dead-code.check

@@ -1,4 +1,7 @@
 Bytecode for method f
+
+  // access flags 0x11
+  public final f()I
    L0
     LINENUMBER 4 L0
     ICONST_1
@@ -7,7 +10,11 @@ Bytecode for method f
     LOCALVARIABLE this Lp/A; L0 L1 0
     MAXSTACK = 1
     MAXLOCALS = 1
+
 Bytecode for method f
+
+  // access flags 0x11
+  public final f()I
    L0
     LINENUMBER 4 L0
     ICONST_1
@@ -17,3 +24,4 @@ Bytecode for method f
     LOCALVARIABLE this Lp/A; L0 L1 0
     MAXSTACK = 1
     MAXLOCALS = 1
+