additional documentation for GenBCode

Author: magarciaEPFL

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

@@ -240,7 +240,7 @@ abstract class BCodeHelpers extends BCodeTypes with BytecodeWriters {
 
   /*
    * Populates the InnerClasses JVM attribute with `refedInnerClasses`.
-   * In additiona to inner classes mentioned somewhere in `jclass` (where `jclass` is a class file being emitted)
+   * In addition to inner classes mentioned somewhere in `jclass` (where `jclass` is a class file being emitted)
    * `refedInnerClasses` should contain those inner classes defined as direct member classes of `jclass`
    * but otherwise not mentioned in `jclass`.
    *
@@ -1000,6 +1000,9 @@ abstract class BCodeHelpers extends BCodeTypes with BytecodeWriters {
 
   trait BCClassGen extends BCInnerClassGen {
 
+    // Used as threshold above which a tableswitch bytecode instruction is preferred over a lookupswitch.
+    // There's a space tradeoff between these multi-branch instructions (details in the JVM spec).
+    // The particular value in use for `MIN_SWITCH_DENSITY` reflects a heuristic.
     val MIN_SWITCH_DENSITY = 0.7
 
     /*

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

@@ -43,7 +43,7 @@ abstract class GenBCode extends BCodeSyncAndTry {
   class BCodePhase(prev: Phase) extends StdPhase(prev) {
 
     override def name = phaseName
-    override def description = "Generate bytecode from ASTs"
+    override def description = "Generate bytecode from ASTs using the ASM library"
     override def erasedTypes = true
 
     private var bytecodeWriter  : BytecodeWriter   = null

src/compiler/scala/tools/nsc/transform/CleanUp.scala

@@ -406,6 +406,8 @@ abstract class CleanUp extends Transform with ast.TreeDSL {
       if (entryPoints != null) &&
          genBCode.isJavaEntryPoint(tree.symbol, currentUnit)
       =>
+        // collecting symbols for entry points here (as opposed to GenBCode where they are used)
+        // has the advantage of saving an additional pass over all ClassDefs.
         entryPoints ::= tree.symbol
         super.transform(tree)