Eliminate store-load pairs with multiple branches #61
Description
Matches generate "result" variables that could be elided:
class C { def f(x: String) = println(x match { case "hai" => x.trim }) } compiles to
public f(Ljava/lang/String;)V L0 LINENUMBER 2 L0 GETSTATIC scala/Predef$.MODULE$ : Lscala/Predef$; L1 LINENUMBER 3 L1 LDC "hai" ALOAD 1 INVOKEVIRTUAL java/lang/Object.equals (Ljava/lang/Object;)Z IFEQ L2 ALOAD 1 INVOKEVIRTUAL java/lang/String.trim ()Ljava/lang/String; ASTORE 2 GOTO L3 L2 FRAME SAME1 scala/Predef$ NEW scala/MatchError DUP ALOAD 1 INVOKESPECIAL scala/MatchError.<init> (Ljava/lang/Object;)V ATHROW L3 FRAME FULL [C java/lang/String java/lang/String] [scala/Predef$] ALOAD 2 INVOKEVIRTUAL scala/Predef$.println (Ljava/lang/Object;)V RETURN The ASTORE 2 and ALOAD 2 can be eliminated:
- for each producer of
ALOAD 2(which is anASTORE 2), the next instruction has to be- the
ALOAD, or - an unconditional jump to a label whose next instruction is the
ALOAD
- the