A DESCRIPTION OF THE REQUEST :
1.) Compare last lines from EXPECTED section against ACTUAL.
    Loop termination doesn't need to compare the counter against constant -1.
2.) At PC 0x00b8838a in compiled code you can see superfluous comparison.
3.) Additionally the swapping of counter n between %ebx and %ecx seems superfluous boilerplate.
4.) Pushing all values o1, o2, v1 liberately to stack seems avoidable if registers were better assigned, e.g. %eax is never used.

Using JDK7 fastdebug build b84.

JUSTIFICATION :
1.) Especially short loops would perform better.
2.-4.) Could perform better too and saves footprint.


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -

_> load v2[o2+n] in %ebp
  0x00b88404: movzwl 0xc(%esi,%ecx,2),%ebp ;*caload
                                        ; - java.lang.String::equals4@80 (line 1146)
_> load v1[o1+n] in %ebx
  0x00b88409: movzwl 0xc(%edx,%ecx,2),%ebx ;*caload
                                        ; - java.lang.String::equals4@73 (line 1146)
  0x00b8840e: cmp %ebp,%ebx
  0x00b88410: jne 0x00b8841d ;*if_icmpeq
                                        ; - java.lang.String::equals4@81 (line 1146)
_> decrement --> n--
  0x00b88412: dec %ecx ;*iinc
                                        ; - java.lang.String::equals4@60 (line 1144)
_> break while_1 if n < 0
  0x00b88413: jge 0x00b88404 ;*ifeq
                                        ; - java.lang.String::equals4@33 (line 1141)
  0x00b88418:


ACTUAL -

- this in %edx
- anotherString in %ebp
_> load count --> countLocal in %edi
  0x00b882ff: mov 0x10(%edx),%edi ;*getfield count
                                        ; - java.lang.String::equals4@20 (line 1139)
_> load anotherString.count in %ecx
  0x00b88302: mov 0x10(%ebp),%ecx
  0x00b88305: cmp %ecx,%edi
  0x00b88307: jne 0x00b8841d ;*if_icmpne
                                        ; - java.lang.String::equals4@29 (line 1140)
_> return true if countLocal == 0 (seems to be superfluous)
  0x00b8830d: test %edi,%edi
  0x00b8830f: je 0x00b88418 ;*ifeq
                                        ; - java.lang.String::equals4@33 (line 1141)
_> copy countLocal --> n-- in %ebx
  0x00b88315: mov %edi,%ebx
  0x00b88317: dec %ebx ;*iinc
                                        ; - java.lang.String::equals4@60 (line 1144)
_> break while() (return true) if n < 0
  0x00b88318: test %ebx,%ebx
  0x00b8831a: jl 0x00b88418 ;*iflt
                                        ; - java.lang.String::equals4@64 (line 1144)
_> load anotherString.offset --> o2 in %ecx + 0x4(%esp)
  0x00b88320: mov 0xc(%ebp),%ecx ;*getfield offset
                                        ; - java.lang.String::equals4@55 (line 1143)
  0x00b88323: mov %ecx,0x4(%esp)
_> move anotherString from %ebp in %ecx
  0x00b88327: mov %ebp,%ecx
_> load value --> v1 in %esi + 0x8(%esp)
  0x00b88329: mov 0x8(%edx),%esi ;*getfield value
                                        ; - java.lang.String::equals4@37 (line 1142)
  0x00b8832c: mov %esi,0x8(%esp)
_> load offset --> o1 in %ebp + 0xc(%esp)
  0x00b88330: mov 0xc(%edx),%ebp ;*getfield offset
                                        ; - java.lang.String::equals4@49 (line 1143)
  0x00b88333: mov %ebp,0xc(%esp)
_> load anotherString.value --> v2 in %ebp
  0x00b88337: mov 0x8(%ecx),%ebp ;*getfield value
                                        ; - java.lang.String::equals4@43 (line 1142)
_> copy v1.length in %ecx via %esi
  0x00b8833a: mov 0x8(%esi),%ecx ; implicit exception: dispatches to 0x00b88428
_> copy countLocal to %esi
  0x00b8833d: mov %edi,%esi
_> check o1 + countLocal - 1 < v1.length
  0x00b8833f: add 0xc(%esp),%esi
  0x00b88343: dec %esi
  0x00b88344: cmp %ecx,%esi
  0x00b88346: jae 0x00b88428

_> copy v2.length in %edx via %ebp
  0x00b8834c: mov 0x8(%ebp),%edx ; implicit exception: dispatches to 0x00b88428
_> copy countLocal to %ecx
  0x00b8834f: mov %edi,%ecx
_> check o2 + countLocal - 1 < v2.length
  0x00b88351: add 0x4(%esp),%ecx
  0x00b88355: dec %ecx
  0x00b88356: cmp %edx,%ecx
  0x00b88358: jae 0x00b88428

_> copy &v2[o2] in %esi via %ecx
  0x00b8835e: mov 0x4(%esp),%ecx
  0x00b88362: lea 0x0(%ebp,%ecx,2),%esi
_> copy &v1[o1] in %edx via %ecx
  0x00b88366: mov 0x8(%esp),%ebp
  0x00b8836a: mov 0xc(%esp),%ecx
  0x00b8836e: lea 0x0(%ebp,%ecx,2),%edx
_> decrement countLocal -= 2 in %edi
  0x00b88372: add $0xfffffffe,%edi ;*aload
                                        ; - java.lang.String::equals4@67 (line 1146)
_> load v2[o2+n] in %ebp
  0x00b88375: movzwl 0xc(%esi,%ebx,2),%ebp ;*caload
                                        ; - java.lang.String::equals4@80 (line 1146)
_> load v1[o1+n] in %ecx
  0x00b8837a: movzwl 0xc(%edx,%ebx,2),%ecx ;*caload
                                        ; - java.lang.String::equals4@73 (line 1146)
  0x00b8837f: cmp %ebp,%ecx
  0x00b88381: jne 0x00b8841d ;*if_icmpeq
                                        ; - java.lang.String::equals4@81 (line 1146)
_> decrement --> n-- via %ecx
  0x00b88387: mov %ebx,%ecx
  0x00b88389: dec %ecx ;*iinc
                                        ; - java.lang.String::equals4@60 (line 1144)
_> break while_1 if n <= countLocal (occurs always, so cmp is superfluos)
  0x00b8838a: cmp %edi,%ecx
  0x00b8838c: jle 0x00b88392 (n equals countLocal after 1st loop iteration)
  0x00b8838e: mov %ecx,%ebx
  0x00b88390: jmp 0x00b88375 (...so this line will never be reached)
  0x00b88392:
  .....
  .....
  .....
_> load v2[o2+n] in %ebp
  0x00b88404: movzwl 0xc(%esi,%ecx,2),%ebp ;*caload
                                        ; - java.lang.String::equals4@80 (line 1146)
_> load v1[o1+n] in %ebx
  0x00b88409: movzwl 0xc(%edx,%ecx,2),%ebx ;*caload
                                        ; - java.lang.String::equals4@73 (line 1146)
  0x00b8840e: cmp %ebp,%ebx
  0x00b88410: jne 0x00b8841d ;*if_icmpeq
                                        ; - java.lang.String::equals4@81 (line 1146)
_> decrement --> n--
  0x00b88412: dec %ecx ;*iinc
                                        ; - java.lang.String::equals4@60 (line 1144)
_> break while_1 if n <= -1
  0x00b88413: cmp $0xffffffff,%ecx
  0x00b88416: jg 0x00b88404 ;*ifeq
                                        ; - java.lang.String::equals4@33 (line 1141)
  0x00b88418:



---------- BEGIN SOURCE ----------

    public boolean equals4(Object anObject) {
        ...;
            int n = count;
            if (n == anotherString.count) { // 3rd check lengths
                if (n != 0) { // 4th avoid loading registers from members if length == 0
                    char[] v1 = value, v2 = anotherString.value;
                    int o1 = offset, o2 = anotherString.offset;
                    while (--n >= 0) // only decrement 1 register
                        // to benefit from CPU's complex addressing modes
                        if (v1[o1+n] != v2[o2+n]) // compare the chars backwards
                            return false;
                }
                return true;
            }
        ...;
    }


---------- END SOURCE ----------