RFR: 8332106: VerifyError when using switch pattern in this(...) or super(…)

[Aggelos Biboudis]

On Mon, 13 May 2024 14:37:49 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> Considering code like:
> 
> public class Test {
> 
>     public Test(int i) {
>     }
> 
>     public Test(Object o) {
>         this(o instanceof R(String s) ? s.length() : -1);
>     }
> 
>     public static void main(String... args) {}
> 
>     record R(String s) {}
> }
> 
> 
> Running this crashes:
> 
> $ java .../Test.java
> Exception in thread "main" java.lang.VerifyError: Stack map does not match the one at exception handler 36
> Exception Details:
>   Location:
>     Test.<init>(Ljava/lang/Object;)V @36: astore_2
>   Reason:
>     Type uninitializedThis (current frame, locals[0]) is not assignable to 'Test' (stack map, locals[0])
>   Current Frame:
>     bci: @14
>     flags: { flagThisUninit }
>     locals: { uninitializedThis, 'java/lang/Object', top, 'Test$R' }
>     stack: { 'java/lang/Throwable' }
>   Stackmap Frame:
>     bci: @36
>     flags: { }
>     locals: { 'Test', 'java/lang/Object' }
>     stack: { 'java/lang/Throwable' }
>   Bytecode:
>     0000000: 2a2b c100 0799 0018 2bc0 0007 4e2d b600
>     0000010: 093a 0419 044d 2cb6 000d a700 0402 b700
>     0000020: 13a7 0011 4dbb 001a 592c b600 1c2c b700
>     0000030: 1fbf b1                                
>   Exception Handler Table:
>     bci [14, 17] => handler: 36
>   Stackmap Table:
>     same_locals_1_stack_item_frame(@29,UninitializedThis)
>     full_frame(@30,{UninitializedThis,Object[#2]},{UninitializedThis,Integer})
>     full_frame(@36,{Object[#20],Object[#2]},{Object[#24]})
>     same_frame(@50)
> 
>         at java.base/java.lang.Class.forName0(Native Method)
>         at java.base/java.lang.Class.forName(Class.java:534)
>         at java.base/java.lang.Class.forName(Class.java:513)
>         at jdk.compiler/com.sun.tools.javac.launcher.Main.execute(Main.java:432)
>         at jdk.compiler/com.sun.tools.javac.launcher.Main.run(Main.java:208)
>         at jdk.compiler/com.sun.tools.javac.launcher.Main.main(Main.java:135)
> 
> 
> The reason is that there is a synthetic catch generated wrapping the record accessors inside the pattern matching. The range where the exception this catch is catching is before the real `this(...)` `invokespecial`, and hence the `this` is still an "uninitialized this". But the code for the catch is generated at the end of the constructor, when `this` is already initialized, and javac generates the stack maps as if `this` was initialized.
> 
> In general, the pattern matching code can be both before and after the `this` has been initialized. But, I don't think a stack map frame can be generated for the handler originating in places with both "uninitialized this " and (...

test/langtools/tools/javac/patterns/UninitializedThisException.java line 38:

> 36: import java.util.function.Supplier;
> 37: 
> 38: public class UninitializedThisException {

nit: It would be nice to have a test for `super(...)` as well even though I am confident that it works. Feel free to ignore if there is no need for an extra test.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/19217#discussion_r1599664579