Erroneous for-loops in Java?

Question

I observed erroneous behaviour running the following java-code:

public class Prototype {   public static void main(String[] args) {     final int start = Integer.MAX_VALUE/2;     final int end = Integer.MAX_VALUE;     {       long b = 0;       for (int i = start; i < end; i++) {         b++;       }       System.out.println(b);     }     {       long b = 0;       for (int i = start; i < end; i++) {         b++;       }       System.out.println(b);     }   } } 

Both loops do exactly the same. Nevertheless, the second one outputs a non-deterministic erroneous value. I'm running the code on Linux using Version:

java version "1.6.0_25" Java(TM) SE Runtime Environment (build 1.6.0_25-b06) Java HotSpot(TM) 64-Bit Server VM (build 20.0-b11, mixed mode) 

Sample Output:

1073741811 141312 

Can you reproduce it? Is it a bug?

Edit: Strange

final int end = Integer.MAX_VALUE - 1; 

works fine.

Answer 1

I'm able to reproduce it with the .class file produced by Eclipse, but not when compiling on the command line with javac.

The bytecode generated differs:

javac output

public static void main(java.lang.String[]);   Code:    0:   lconst_0    1:   lstore_3    2:   ldc #2; //int 1073741823    4:   istore  5    6:   iload   5    8:   ldc #3; //int 2147483647    10:  if_icmpge   23    13:  lload_3    14:  lconst_1    15:  ladd    16:  lstore_3    17:  iinc    5, 1    20:  goto    6    23:  getstatic   #4; //Field java/lang/System.out:Ljava/io/PrintStream;    26:  lload_3    27:  invokevirtual   #5; //Method java/io/PrintStream.println:(J)V    30:  lconst_0    31:  lstore_3    32:  ldc #2; //int 1073741823    34:  istore  5    36:  iload   5    38:  ldc #3; //int 2147483647    40:  if_icmpge   53    43:  lload_3    44:  lconst_1    45:  ladd    46:  lstore_3    47:  iinc    5, 1    50:  goto    36    53:  getstatic   #4; //Field java/lang/System.out:Ljava/io/PrintStream;    56:  lload_3    57:  invokevirtual   #5; //Method java/io/PrintStream.println:(J)V    60:  return 

For something easier to read, here is the Grimp output produced by Soot:

    java.lang.String[] r0;     long l0, l2;     int i1, i3;      r0 := @parameter0;     l0 = 0L;     i1 = 1073741823;   label0:     if i1 >= 2147483647 goto label1;      l0 = l0 + 1L;     i1 = i1 + 1;     goto label0;   label1:     java.lang.System.out.println(l0);     l2 = 0L;     i3 = 1073741823;   label2:     if i3 >= 2147483647 goto label3;      l2 = l2 + 1L;     i3 = i3 + 1;     goto label2;   label3:     java.lang.System.out.println(l2);     return; 

Eclipse compiler output

public static void main(java.lang.String[]);   Code:    0:   ldc #16; //int 1073741823    2:   istore_1    3:   ldc #17; //int 2147483647    5:   istore_2    6:   lconst_0    7:   lstore_3    8:   ldc #16; //int 1073741823    10:  istore  5    12:  goto    22    15:  lload_3    16:  lconst_1    17:  ladd    18:  lstore_3    19:  iinc    5, 1    22:  iload   5    24:  ldc #17; //int 2147483647    26:  if_icmplt   15    29:  getstatic   #18; //Field java/lang/System.out:Ljava/io/PrintStream;    32:  lload_3    33:  invokevirtual   #24; //Method java/io/PrintStream.println:(J)V    36:  lconst_0    37:  lstore_3    38:  ldc #16; //int 1073741823    40:  istore  5    42:  goto    52    45:  lload_3    46:  lconst_1    47:  ladd    48:  lstore_3    49:  iinc    5, 1    52:  iload   5    54:  ldc #17; //int 2147483647    56:  if_icmplt   45    59:  getstatic   #18; //Field java/lang/System.out:Ljava/io/PrintStream;    62:  lload_3    63:  invokevirtual   #24; //Method java/io/PrintStream.println:(J)V    66:  return 

Grimp output:

    java.lang.String[] r0;     int i0, i1, i3, i5;     long l2, l4;      r0 := @parameter0;     i0 = 1073741823;     i1 = 2147483647;     l2 = 0L;     i3 = 1073741823;     goto label1;   label0:     l2 = l2 + 1L;     i3 = i3 + 1;   label1:     if i3 < 2147483647 goto label0;      java.lang.System.out.println(l2);     l4 = 0L;     i5 = 1073741823;     goto label3;   label2:     l4 = l4 + 1L;     i5 = i5 + 1;   label3:     if i5 < 2147483647 goto label2;      java.lang.System.out.println(l4);     return; 

Interestingly, the javac-produced version uses if_icmpge as an exit condition (>= 2147483647) on an int, which shouldn't make sense (the equal does, but not the greater than). Both look correct, though, so I'd suspect a JVM bug.