Use a java static to throw IndexOutOfBoundsException #7086

cb372 · 2018-08-16T10:20:21Z

Follow-up to #6972.

As suggested by @retronym, this reduces the bytecode fixed cost of the synthetic productElement and productElementName implementations in case classes.

Measured the difference using a simple case class:

case class FiveFields(a: Int, b: Int, c: Int, d: Int, e: Int)

Before (2.13.0-pre-b739165):

-rw-r--r--  1 chris  staff  2207 Aug 16 11:11 FiveFields$.class
-rw-r--r--  1 chris  staff  6291 Aug 16 11:11 FiveFields.class

After:

-rw-r--r--  1 chris  staff  2207 Aug 16 22:54 FiveFields$.class
-rw-r--r--  1 chris  staff  6186 Aug 16 22:54 FiveFields.class

So a saving of 105 bytes.

The new bytecode looks like this:

  public java.lang.String productElementName(int);
    Code:
       0: iload_1
       1: istore_2
       2: iload_2
       3: tableswitch   { // 0 to 4
                     0: 36
                     1: 41
                     2: 46
                     3: 51
                     4: 56
               default: 61
          }
      36: ldc           #104                // String a
      38: goto          71
      41: ldc           #105                // String b
      43: goto          71
      46: ldc           #106                // String c
      48: goto          71
      51: ldc           #107                // String d
      53: goto          71
      56: ldc           #108                // String e
      58: goto          71
      61: iload_1
      62: invokestatic  #101                // Method scala/runtime/Statics.ioobe:(I)Ljava/lang/Object;
      65: checkcast     #110                // class java/lang/String
      68: goto          71
      71: areturn

If we care about saving another 3 bytes, we could make the ioobe return String instead of having it generic. That happens to work because it's only called in these two places (productElement, which returns Any, and productElementName, which returns String) but it seems a bit naughty.

Also removed the synthetic productElementName for case objects. A bridge method is generated instead, but it's slightly smaller than the synthetic so we save about 16 bytes on case objects.

hrhino · 2018-08-16T12:51:39Z

src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala

    def createSwitchMethod(name: Name, range: Seq[Int], returnType: Type)(f: Int => Tree) = {
      createMethod(name, List(IntTpe), returnType) { m =>
        val arg0    = Ident(m.firstParam)
-        val default = DEFAULT ==> Throw(IndexOutOfBoundsExceptionClass.tpe_*, fn(arg0, nme.toString_))
+        val default = DEFAULT ==> callStaticsGenericMethod("aioobe", returnType)(arg0)


you should add a val aioobe = "aioobe" to nme in StdNames rather than calling newTermName every time.

hrhino · 2018-08-16T12:52:43Z

src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala

+      Apply(TypeApply(gen.mkAttributedRef(method), List(TypeTree(returnType))), args.toList)
+    }
+
+    def callStaticsGenericMethod(name: String, returnType: Type)(args: Tree*): Tree =


... and then you won't be needing this.

olafurpg · 2018-08-16T12:58:00Z

Nice! Another possible avenue to shave off further bytes is to skip generating productElementName for case object. Case objects inevitably throw ArrayIndexOutOfBoundsException when productArity == 0 so the default implementation in Product should do the right thing.

cb372 · 2018-08-16T21:13:18Z

Just noticed that we should actually throw IndexOutOfBoundsException (not ArrayIndexOutOfBoundsException), to match what is thrown by the implementation in Product.

Fixing now.

mkeskells · 2018-08-17T07:10:47Z

src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala

@@ -76,10 +76,15 @@ trait MethodSynthesis {
    def forwardMethod(original: Symbol, newMethod: Symbol)(transformArgs: List[Tree] => List[Tree]): Tree =
      createMethod(original)(m => gen.mkMethodCall(newMethod, transformArgs(m.paramss.head map Ident)))

+    def callStaticsGenericMethod(name: TermName, returnType: Type)(args: Tree*): Tree = {


why is args a vararg - its always one param?

The method is based on this method in SyntheticMethods. Over there it made more sense for it to have varargs.

To be honest, this method is only used in one place so we could just inline it if you're worried about performance. I would either do that, or leave it as it is for the sake of readability, but I don't have a strong opinion either way.

I don't think inlining it would be too bad, personally.

mkeskells · 2018-08-17T07:14:53Z

src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala

@@ -307,13 +314,13 @@ trait SyntheticMethods extends ast.TreeDSL {
      Any_equals -> (() => equalsDerivedValueClassMethod)
    )

-    def caseClassMethods = productMethods ++ /*productNMethods ++*/ Seq(
+    def caseClassMethods = productClassMethods ++ /*productNMethods ++*/ Seq(


we can remove the intermediate collections easily here either in this PR or another - just to remove some CPU/memory in the compile

yeah, I'm poking at this file; there's some room for improvement

lrytz · 2018-11-02T14:35:36Z

@cb372 I reviewed this and pushed my review feedback as a commit. If it LGTY we can squash and merge.

cb372 · 2018-11-02T20:19:01Z

@lrytz Thanks for the feedback. Your changes LGTM.

The Travis build failed with a StackOverflowError in the typer. I'm not sure if that's caused by the changes in this PR? I just ran the tests locally and I couldn't reproduce it.

This reduces the bytecode cost of the synthetic `productElement` and `productElementName` implementations in case classes.

cb372 · 2018-11-02T20:26:39Z

Squashed and rebased. Will see if Travis is any happier this time.

lrytz · 2018-11-02T20:50:47Z

You can ignore travis for now, scala/scala-dev#570

scala-jenkins added this to the 2.13.0-RC1 milestone Aug 16, 2018

cb372 force-pushed the static-aioobe branch from 18dfdc7 to c79d258 Compare August 16, 2018 11:14

hrhino reviewed Aug 16, 2018

View reviewed changes

cb372 changed the title ~~Use a java static to throw ArrayIndexOutOfBoundsException~~ Use a java static to throw IndexOutOfBoundsException Aug 16, 2018

mkeskells reviewed Aug 17, 2018

View reviewed changes

cb372 force-pushed the static-aioobe branch from 868e7e2 to 08123b1 Compare August 20, 2018 10:38

lrytz force-pushed the static-aioobe branch from 08123b1 to af424d1 Compare November 2, 2018 14:35

lrytz force-pushed the static-aioobe branch from af424d1 to e33452e Compare November 2, 2018 14:36

lrytz self-assigned this Nov 2, 2018

Use a java static to throw IndexOutOfBoundsException

5279463

This reduces the bytecode cost of the synthetic `productElement` and `productElementName` implementations in case classes.

cb372 force-pushed the static-aioobe branch from e33452e to 5279463 Compare November 2, 2018 20:25

lrytz approved these changes Nov 2, 2018

View reviewed changes

lrytz merged commit 30123af into scala:2.13.x Nov 2, 2018

cb372 deleted the static-aioobe branch November 2, 2018 21:24

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Use a java static to throw IndexOutOfBoundsException #7086

Use a java static to throw IndexOutOfBoundsException #7086

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Use a java static to throw IndexOutOfBoundsException #7086

Use a java static to throw IndexOutOfBoundsException #7086

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