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https://issues.apache.org/jira/browse/GROOVY-10314?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17429602#comment-17429602
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Daniel Sun commented on GROOVY-10314:
-------------------------------------
I compiled the script via groovyc and decompiled with javap, here is what
groovyc generated for {{test}} method. As we could see, ASM does not optimize
the bytecode for us, there are still many {{nop}} in the bytecode.
{code:java}
public java.lang.Object test();
descriptor: ()Ljava/lang/Object;
flags: (0x0001) ACC_PUBLIC
Code:
stack=2, locals=3, args_size=1
0: aload_0
1: ldc #47 // String hello
3: invokedynamic #53, 0 // InvokeDynamic
#1:invoke:(LTestGroovy10314;Ljava/lang/String;)Ljava/lang/Object;
8: astore_1
9: nop
10: aload_0
11: ldc #55 // String world
13: invokedynamic #53, 0 // InvokeDynamic
#1:invoke:(LTestGroovy10314;Ljava/lang/String;)Ljava/lang/Object;
18: pop
19: nop
20: aload_1
21: areturn
22: nop
23: nop
24: athrow
25: nop
26: nop
27: nop
28: nop
29: nop
30: nop
31: nop
32: nop
33: athrow
34: nop
35: nop
36: athrow
37: astore_2
38: aload_0
39: ldc #55 // String world
41: invokedynamic #53, 0 // InvokeDynamic
#1:invoke:(LTestGroovy10314;Ljava/lang/String;)Ljava/lang/Object;
46: pop
47: aload_2
48: athrow
49: nop
50: athrow
Exception table:
from to target type
0 10 37 any
20 22 37 any
StackMapTable: number_of_entries = 5
frame_type = 255 /* full_frame */
offset_delta = 22
locals = []
stack = [ class java/lang/Throwable ]
frame_type = 66 /* same_locals_1_stack_item */
stack = [ class java/lang/Throwable ]
frame_type = 72 /* same_locals_1_stack_item */
stack = [ class java/lang/Throwable ]
frame_type = 255 /* full_frame */
offset_delta = 2
locals = [ class TestGroovy10314 ]
stack = [ class java/lang/Throwable ]
frame_type = 255 /* full_frame */
offset_delta = 11
locals = []
stack = [ class java/lang/Throwable ]
LineNumberTable:
line 3: 0
line 5: 10
line 7: 49
LocalVariableTable:
Start Length Slot Name Signature
0 49 0 this LTestGroovy10314;
{code}
> finally block produces long sequence of nop instructions
> --------------------------------------------------------
>
> Key: GROOVY-10314
> URL: https://issues.apache.org/jira/browse/GROOVY-10314
> Project: Groovy
> Issue Type: Bug
> Components: class generator, Compiler
> Reporter: Eric Milles
> Priority: Minor
> Labels: bytecode
>
> Consider the following:
> {code:groovy}
> def test() {
> try {
> print 'hello'
> } finally {
> print ' world'
> }
> }
> {code}
> For any non-void method where the {{try}}/{{finally}} is part of the return
> value, a long sequence of {{nop}} bytecode instructions is produced. The
> sample code from GROOVY-4721 produces 18 {{nop}} in a row.
> {code}
> // Method descriptor #42 ()Ljava/lang/Object;
> // Stack: 2, Locals: 3
> public java.lang.Object test();
> 0 aload_0 [this]
> 1 ldc <String "hello"> [47]
> 3 invokedynamic 1 invoke(Scratch, java.lang.String) : java.lang.Object
> [53]
> 8 astore_1
> 9 nop
> 10 aload_0 [this]
> 11 ldc <String " world"> [55]
> 13 invokedynamic 1 invoke(Scratch, java.lang.String) : java.lang.Object
> [53]
> 18 pop
> 19 nop
> 20 aload_1
> 21 areturn
> 22 nop
> 23 nop
> 24 athrow
> 25 nop
> 26 nop
> 27 nop
> 28 nop
> 29 nop
> 30 nop
> 31 nop
> 32 nop
> 33 athrow
> 34 nop
> 35 nop
> 36 athrow
> 37 astore_2
> 38 aload_0 [this]
> 39 ldc <String " world"> [55]
> 41 invokedynamic 1 invoke(Scratch, java.lang.String) : java.lang.Object
> [53]
> 46 pop
> 47 aload_2
> 48 athrow
> 49 nop
> 50 athrow
> Exception Table:
> [pc: 0, pc: 10] -> 37 when : any
> [pc: 20, pc: 22] -> 37 when : any
> Line numbers:
> [pc: 0, line: 3]
> [pc: 10, line: 5]
> [pc: 49, line: 7]
> Local variable table:
> [pc: 0, pc: 49] local: this index: 0 type: Scratch
> {code}
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