Re: [jdt-dev] How does this code work ?

["Sankaran, Srikanth" <srikanth.sankaran@xxxxxxxxxxxxx>]

It seems you need a branch and so a different stackmap frame for verification to catch such problems.

 

I have raised https://github.com/eclipse-jdt/eclipse.jdt.core/issues/2476 with a test case where we do get a verify error.

 

Thanks

Srikanth

 

From: jdt-dev <jdt-dev-bounces@xxxxxxxxxxx> On Behalf Of Sankaran, Srikanth via jdt-dev
Sent: Wednesday, May 22, 2024 11:33 AM
To: jdt-dev@xxxxxxxxxxx
Cc: Sankaran, Srikanth <srikanth.sankaran@xxxxxxxxxxxxx>
Subject: [jdt-dev] How does this code work ?

 

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I have been staring at this code for a while now wondering how the bad code generated still works:

 

public class X {

       public static void main(String[] args) {

             

              foo(String.class, switch (42) {

              default -> {

                     try {

                           yield 42;

                     } finally {

 

                     }

              }

              });

       }

      

       static void foo(Class<?> c, int v) {

              System.out.println(c);

              System.out.println(v);

       }

}

 

 

On master, we generate the following code:

 

  public static void main(java.lang.String[]);

    descriptor: ([Ljava/lang/String;)V

    flags: (0x0009) ACC_PUBLIC, ACC_STATIC

    Code:

      stack=2, locals=3, args_size=1

         0: ldc           #16                 // class java/lang/String

         2: astore_1                        <<ß-------------------- Class Object being stored into String See LVT slot 1 below.

         3: bipush        42

         5: istore_2

         6: aload_1                             <<ß-------------------- aload loads an object statically typed String, but at bci 8 we invoke a method that expects a Class object

         7: iload_2

         8: invokestatic  #18                 // Method foo:(Ljava/lang/Class;I)V

        11: return

      LineNumberTable:

        line 4: 0

        line 7: 3

        line 4: 8

        line 13: 11

      LocalVariableTable:

        Start  Length  Slot  Name   Signature

            0      12     0  args   [Ljava/lang/String;

            3       5     1  yieldValue0   Ljava/lang/String;  <<ß---------------------- String typed local

            6       2     2  secretYieldValue   I

 

What am I overlooking ??

 

Srikanth