C2 optimization bug ?

[Ulf Zibis]

Below you see 2 code snippets, im exactly doing the same if boolean 
validateNonSurrogates is set to false by constant value.

In the 1. example, I'm wondering, why register values are copied around 
and from/to the stack on each loop:

   0x00b88930: mov    %ebx,0x4(%esp)
   0x00b88934: mov    %eax,0x34(%esp)    ;*aload_0
   ...
   0x00b88940: mov    %ecx,%eax
   ...
   0x00b88952: mov    $0x2,%ecx
   0x00b88957: mov    0x34(%esp),%eax    ;*invokestatic charCount
                                         ; - 
java.lang.Character::charCount at 26 (line 2946)
   0x00b8895b: add    %ecx,%esi          ;*iadd
   ...

Even in the 2nd example it is not comprehensible, why the base address 
of int[] codePoints is repetitively loaded from the stack on each loop:

   0x00b84e0e: mov    0x4(%esp),%edi



========================== Example 1:

             n += Character.charCount(codePoints, 0, codePoints.length, 
false);


     public static int charCount(int codePoint, boolean 
validateNonSurrogates) {
         if (isBMPCodePoint(codePoint)) {
             if (!validateNonSurrogates || !isSurrogate((char)codePoint))
                 return 1;
         } else if (isSupplementaryCodePoint(codePoint))
             return 2;
         return 0;
     }

     public static int charCount(int[] codePoints, int offset, int 
count, boolean validateNonSurrogates) {
         checkBoundsOnCount(codePoints.length, offset, count);
         int n = 0;
         for (int i = offset; i < offset + count; i++) {
             int m = charCount(codePoints[i], validateNonSurrogates);
             if (m == 0)
                 throw new IllegalArgumentException("At position "+i);
             n += m;
         }
         return n;
     }


   0x00b88930: mov    %ebx,0x4(%esp)
   0x00b88934: mov    %eax,0x34(%esp)    ;*aload_0
                                         ; - 
java.lang.Character::charCount at 21 (line 2946)
   0x00b88938: mov    0x4(%esp),%ebx
   0x00b8893c: mov    0xc(%ebx,%ebp,4),%ecx  ;*iaload
                                         ; - 
java.lang.Character::charCount at 24 (line 2946)
   0x00b88940: mov    %ecx,%eax
   0x00b88942: shr    $0x10,%eax         ;*iushr
                                         ; - 
java.lang.Character::isBMPCodePoint at 3 (line 2737)
                                         ; - 
java.lang.Character::charCount at 1 (line 2907)
                                         ; - 
java.lang.Character::charCount at 26 (line 2946)
   0x00b88945: test   %eax,%eax
   0x00b88947: je     0x00b88973         ;*ifeq
                                         ; - 
java.lang.Character::charCount at 4 (line 2907)
                                         ; - 
java.lang.Character::charCount at 26 (line 2946)
   0x00b88949: cmp    $0x11,%eax
   0x00b8894c: jge    0x00b889bf         ;*if_icmpge
                                         ; - 
java.lang.Character::isValidCodePoint at 6 (line 2713)
                                         ; - 
java.lang.Character::isSupplementaryCodePoint at 8 (line 2768)
                                         ; - 
java.lang.Character::charCount at 22 (line 2910)
                                         ; - 
java.lang.Character::charCount at 26 (line 2946)
   0x00b88952: mov    $0x2,%ecx
   0x00b88957: mov    0x34(%esp),%eax    ;*invokestatic charCount
                                         ; - 
java.lang.Character::charCount at 26 (line 2946)
   0x00b8895b: add    %ecx,%esi          ;*iadd
                                         ; - 
java.lang.Character::charCount at 68 (line 2949)
   0x00b8895d: inc    %ebp               ;*iinc
                                         ; - 
java.lang.Character::charCount at 71 (line 2945)
   0x00b8895e: cmp    %edx,%ebp
   0x00b88960: jl     0x00b88930         ;*if_icmpge
                                         ; - 
java.lang.Character::charCount at 18 (line 2945)

========================== Example 2:

             n += Character.charCount(codePoints, 0, codePoints.length);

     public static int charCount(int[] codePoints, int offset, int count) {
         checkBoundsOnCount(codePoints.length, offset, count);
         int n = 0;
         for (int i = offset; i < offset + count; i++) {
             int c = codePoints[i];
             if (Character.isBMPCodePoint(c))
                 n += 1;
             else if (Character.isSupplementaryCodePoint(c))
                 n += 2;
             else
                 throw new IllegalArgumentException("At position "+i);
         }
         return n;
     }

   0x00b84e0e: mov    0x4(%esp),%edi
   0x00b84e12: mov    0xc(%edi,%edx,4),%ebp
   0x00b84e16: shr    $0x10,%ebp         ;*iushr
                                         ; - 
java.lang.Character::isBMPCodePoint at 3 (line 2737)
                                         ; - 
java.lang.Character::charCount at 28 (line 2958)
   0x00b84e19: test   %ebp,%ebp
   0x00b84e1b: je     0x00b84f21         ;*ifeq
                                         ; - 
java.lang.Character::charCount at 31 (line 2958)
   0x00b84e21: cmp    $0x11,%ebp
   0x00b84e24: jge    0x00b84eee         ;*if_icmpge
                                         ; - 
java.lang.Character::isValidCodePoint at 6 (line 2713)
                                         ; - 
java.lang.Character::isSupplementaryCodePoint at 8 (line 2768)
                                         ; - 
java.lang.Character::charCount at 42 (line 2960)
   0x00b84e2a: add    $0x2,%eax          ;*goto
                                         ; - 
java.lang.Character::charCount at 51 (line 2961)
   0x00b84e2d: inc    %edx               ;*iinc
                                         ; - 
java.lang.Character::charCount at 82 (line 2956)
   0x00b84e2e: cmp    %ecx,%edx
   0x00b84e30: jl     0x00b84e0e


-Ulf