On Fri, 4 Oct 2024 12:05:02 GMT, Shaojin Wen <s...@openjdk.org> wrote:
> java.base should provide best practices for Class File API
>
> 1. Use fluent coding style
> 2. Use aconst_null instead of oadConstant(null)
> 3. use astore intead of 'storeLocal(REFERENCE'
> 4. use aload instead of 'loadLocal(REFERENCE'
> 5. 'lload/lstore' instead of 'loadLocal(LONG)/storeLocal(LONG)'
Using a fluent coding style can reduce the code size, such as the following code
import java.lang.classfile.CodeBuilder;
public class Demo {
public static void f0(CodeBuilder cb) {
cb.aload(0);
cb.aload(1);
}
public static void f1(CodeBuilder cb) {
cb.aload(0)
.aload(1);
}
}
Compile Java code and view bytecode
javac --enable-preview --release 24 Demo.java
javap -c Demo
The bytecode is as follows
public class Demo {
public Demo();
Code:
0: aload_0
1: invokespecial #1 // Method
java/lang/Object."<init>":()V
4: return
public static void f0(java.lang.classfile.CodeBuilder);
Code:
0: aload_0
1: iconst_0
2: invokeinterface #7, 2 // InterfaceMethod
java/lang/classfile/CodeBuilder.aload:(I)Ljava/lang/classfile/CodeBuilder;
7: pop
8: aload_0
9: iconst_1
10: invokeinterface #7, 2 // InterfaceMethod
java/lang/classfile/CodeBuilder.aload:(I)Ljava/lang/classfile/CodeBuilder;
15: pop
16: return
public static void f1(java.lang.classfile.CodeBuilder);
Code:
0: aload_0
1: iconst_0
2: invokeinterface #7, 2 // InterfaceMethod
java/lang/classfile/CodeBuilder.aload:(I)Ljava/lang/classfile/CodeBuilder;
7: iconst_1
8: invokeinterface #7, 2 // InterfaceMethod
java/lang/classfile/CodeBuilder.aload:(I)Ljava/lang/classfile/CodeBuilder;
13: pop
14: return
}
We can see that method `f0` does not use the fluent code style, and the
generated bytecode has redundant pop and aload_0 operations.
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PR Comment: https://git.openjdk.org/jdk/pull/21355#issuecomment-2393963891
