Bad stack map frame when using conditional with different array types

Issue #236 resolved
Jesper Öqvist created an issue

ExtendJ 8.0.1-234-g7a7bcbc Java SE 8

When building Stack Map Frames, ExtendJ does not compute the common supertype of two array types correctly. In this case, the compiler should compute the type [Ljava/lang/Number as the common supertype of [Ljava/lang/Number and [Ljava/lang/Float in stack[2] of the merge frame after the conditional expression. Instead, ExtendJ computes java/lang/Object as the common supertype.

// Test that the correct verification types are generated for a conditional
// expression with two different array types.
public class Test {
  public static void main(String[] args) {
    new Test().run(true);
    new Test().run(false);

  void run(boolean b) {
    Float[] floats = new Float[3];
    System.out.println(process(b ? new Number[20] : floats));

  int process(Object o) {
    return -1;

  int process(Number[] n) {
    return 20;

Expected result: should print 20, 20.

Actual result: fails to run with this error:

    [junit] [FAIL] runTest[run/conditional_04](tests.extendj.TestJava7)
    [junit] Error output files differ expected:<[]> but was:<[Error: A JNI error has occurred, please check your installation and try again
    [junit] Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
    [junit] Exception Details:
    [junit]   Location:
    [junit] @22: invokevirtual
    [junit]   Reason:
    [junit]     Type 'java/lang/Object' (current frame, stack[2]) is not assignable to '[Ljava/lang/Number;'
    [junit]   Current Frame:
    [junit]     bci: @22
    [junit]     flags: { }
    [junit]     locals: { 'Test', integer, '[Ljava/lang/Float;' }
    [junit]     stack: { 'java/io/PrintStream', 'Test', 'java/lang/Object' }
    [junit]   Bytecode:
    [junit]     0x0000000: 06bd 001e 4db2 0024 2a1b 9900 0b10 14bd
    [junit]     0x0000010: 0026 a700 042c b600 2ab6 0030 b1
    [junit]   Stackmap Table:
    [junit]     full_frame(@21,{Object[#2],Integer,Object[#50]},{Object[#44],Object[#2]})
    [junit]     full_frame(@22,{Object[#2],Integer,Object[#50]},{Object[#44],Object[#2],Object[#4]})
    [junit]     at java.lang.Class.getDeclaredMethods0(Native Method)
    [junit]     at java.lang.Class.privateGetDeclaredMethods(
    [junit]     at java.lang.Class.privateGetMethodRecursive(
    [junit]     at java.lang.Class.getMethod0(
    [junit]     at java.lang.Class.getMethod(
    [junit]     at sun.launcher.LauncherHelper.validateMainClass(
    [junit]     at sun.launcher.LauncherHelper.checkAndLoadMain(]>

Comments (1)

  1. Jesper Öqvist reporter

    Fix error in array verification type construction

    Common supertypes for array verification types were not computed correctly, leading to too loose verification types in stack map frames.

    fixes #236 (bitbucket)

    → <<cset 487581b77faf>>

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