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Just spotted a minor bytecode generation error. I'll try to attach a simple test project. When this project is built after clean everithing is ok. But when class D is recompiled incrementally a double checkcast instruction is emmited.
Created attachment 29635 [details] Test project
Created attachment 29636 [details] Correct bytecode
Created attachment 29637 [details] Incorrect bytecode with double checkcast
Good find, indeed the cast is overkill after the generic cast conversion. Fixed in latest. Added GenericTypeTest#test874. No plan to backport to 3.1.2 since really not severe. Fixed
Verified for 3.2 M4 using build I20051213-0010
In fact, GenericTypeTests#test874 already passes with M3. So, it seems that the problem is fixed but we currently need to investigate in order to know precisely which changes has done it => reopen until clarified...
Note also that test passes with 3.1.2 (ie. there's only one checkcast)
It feels like this regression got introduced after M3; and given it isn't in 3.1.2, it would point at the unification of generic and parameterized bindings. Need to understand what exactly occurred there; i.e. is fix really needed, or is it working around another issue ?
The original testcase didn't fail in 3.1.2&3.2M3, since the return type is generic type (instead of parameterized type - pre binding unification); consequently, no generic cast is inserted as generic type interestingly doesn't have its tagbits saying HasTypeVariable true (!?). In 3.2, it works as expected. Here is another testcase which would fail in 3.1.2&3.2M3: class A {} class D extends A {} abstract class B<T> { public T label(String s) { return null; } } final class C extends B<A> { public static C instance(String s) { return new C(); } @Override public String toString() { return "SUCCESS"; } } public class X { public static void main(String[] args) { D d = (D)C.instance("X").label("Y"); System.out.println(d); } } It would issue a double checkcast D inside X#main(). Added GenericTypeTest#test878
Fixed buildnotes (re-inserted), and tagged for M4. Frederic - pls verify it.
Verified in build I20051214-1600. output is: // Method descriptor #15 ([Ljava/lang/String;)V // Stack: 2, Locals: 2 public static void main(java.lang.String[] args); 0 ldc <String "X"> [16] 2 invokestatic C.instance(java.lang.String) : C [17] 5 ldc <String "Y"> [23] 7 invokevirtual C.label(java.lang.String) : java.lang.Object [25] 10 checkcast D [29] 13 astore_1 [d] 14 getstatic java.lang.System.out : java.io.PrintStream [31] 17 aload_1 [d] 18 invokevirtual java.io.PrintStream.println(java.lang.Object) : void [37] 21 return
