x86 JIT: break; produces jne to loops end, when return false gives je to next comparison. My guess is that the number of jumps taken hurt performance by impairing the instruction pipeline.

x86JIT_break_VS_return_false

x86 version with break;

                            if (*((void**)firstPointer + 0) != *((void**)secondPointer + 0)) break;
010B3577  mov         eax,dword ptr [ebp-10h]  
                        {
                            if (*((void**)firstPointer + 0) != *((void**)secondPointer + 0)) break;
010B357A  mov         eax,dword ptr [eax]  
010B357C  mov         edx,dword ptr [ebp-14h]  
010B357F  cmp         eax,dword ptr [edx]  
010B3581  jne         010B360F  
                            if (*((void**)firstPointer + 1) != *((void**)secondPointer + 1)) break;
010B3587  mov         eax,dword ptr [ebp-10h]  
010B358A  mov         eax,dword ptr [eax+4]  
010B358D  mov         edx,dword ptr [ebp-14h]  
010B3590  cmp         eax,dword ptr [edx+4]  
010B3593  jne         010B360F  
                            if (*((void**)firstPointer + 2) != *((void**)secondPointer + 2)) break;
010B3595  mov         eax,dword ptr [ebp-10h]  
010B3598  mov         edx,4  
010B359D  add         edx,edx  
010B359F  mov         eax,dword ptr [eax+edx]  
010B35A2  mov         edx,dword ptr [ebp-14h]  
010B35A5  mov         ecx,4  
010B35AA  add         ecx,ecx  
010B35AC  cmp         eax,dword ptr [edx+ecx]  
010B35AF  jne         010B360F  
                            if (*((void**)firstPointer + 3) != *((void**)secondPointer + 3)) break;
010B35B1  mov         eax,dword ptr [ebp-10h]  
010B35B4  mov         edx,3  
010B35B9  mov         ecx,4  
010B35BE  imul        edx,ecx  
010B35C1  mov         eax,dword ptr [eax+edx]  
010B35C4  mov         edx,dword ptr [ebp-14h]  
010B35C7  mov         ecx,3  
010B35CC  mov         ebx,4  
010B35D1  imul        ecx,ebx  
010B35D4  cmp         eax,dword ptr [edx+ecx]  
010B35D7  jne         010B360F  
                            if (*((void**)firstPointer + 4) != *((void**)secondPointer + 4)) break;
010B35D9  mov         eax,dword ptr [ebp-10h]  
010B35DC  mov         edx,4  
010B35E1  shl         edx,2  
010B35E4  mov         eax,dword ptr [eax+edx]  
010B35E7  mov         edx,dword ptr [ebp-14h]  
010B35EA  mov         ecx,4  
010B35EF  shl         ecx,2  
010B35F2  cmp         eax,dword ptr [edx+ecx]  
010B35F5  jne         010B360F  

                            firstPointer += step;
010B35F7  mov         eax,dword ptr [ebp-18h]  
010B35FA  add         dword ptr [ebp-10h],eax  
                            secondPointer += step;
010B35FD  mov         eax,dword ptr [ebp-18h]  
010B3600  add         dword ptr [ebp-14h],eax  
                    {
                        while (firstPointer < firstPointerLimit)
010B3603  mov         eax,dword ptr [ebp-10h]  
010B3606  cmp         eax,dword ptr [ebp-1Ch]  
010B3609  jb          010B3577  
                        }
                        if (firstPointer < firstPointerLimit) // the upper loop ended with break;
010B360F  mov         eax,dword ptr [ebp-10h]  
010B3612  cmp         eax,dword ptr [ebp-1Ch]  
010B3615  jae         010B361F  
                        {
                            return false;
010B3617  xor         edx,edx  
010B3619  mov         dword ptr [ebp-20h],edx  
010B361C  nop  
010B361D  jmp         010B3655  
                        }
                        
x86 with return false;
if (*((void**)firstPointer + 0) != *((void**)secondPointer + 0)) return false;
02A73583  xor         edx,edx  
02A73585  mov         dword ptr [ebp-20h],edx  
02A73588  nop  
02A73589  jmp         02A73672  
                            if (*((void**)firstPointer + 1) != *((void**)secondPointer + 1)) return false;
02A7358E  mov         eax,dword ptr [ebp-10h]  
02A73591  mov         eax,dword ptr [eax+4]  
02A73594  mov         edx,dword ptr [ebp-14h]  
02A73597  cmp         eax,dword ptr [edx+4]  
02A7359A  je          02A735A7  
02A7359C  xor         edx,edx  
02A7359E  mov         dword ptr [ebp-20h],edx  
02A735A1  nop  
02A735A2  jmp         02A73672  
                            if (*((void**)firstPointer + 2) != *((void**)secondPointer + 2)) return false;
02A735A7  mov         eax,dword ptr [ebp-10h]  
02A735AA  mov         edx,4  
02A735AF  add         edx,edx  
02A735B1  mov         eax,dword ptr [eax+edx]  
02A735B4  mov         edx,dword ptr [ebp-14h]  
02A735B7  mov         ecx,4  
02A735BC  add         ecx,ecx  
02A735BE  cmp         eax,dword ptr [edx+ecx]  
02A735C1  je          02A735CE  
02A735C3  xor         edx,edx  
02A735C5  mov         dword ptr [ebp-20h],edx  
02A735C8  nop  
02A735C9  jmp         02A73672  
                            if (*((void**)firstPointer + 3) != *((void**)secondPointer + 3)) return false;
02A735CE  mov         eax,dword ptr [ebp-10h]  
02A735D1  mov         edx,3  
02A735D6  mov         ecx,4  
02A735DB  imul        edx,ecx  
02A735DE  mov         eax,dword ptr [eax+edx]  
02A735E1  mov         edx,dword ptr [ebp-14h]  
02A735E4  mov         ecx,3  
02A735E9  mov         ebx,4  
02A735EE  imul        ecx,ebx  
02A735F1  cmp         eax,dword ptr [edx+ecx]  
02A735F4  je          02A735FE  
02A735F6  xor         edx,edx  
02A735F8  mov         dword ptr [ebp-20h],edx  
02A735FB  nop  
02A735FC  jmp         02A73672  
                            if (*((void**)firstPointer + 4) != *((void**)secondPointer + 4)) return false;
02A735FE  mov         eax,dword ptr [ebp-10h]  
02A73601  mov         edx,4  
02A73606  shl         edx,2  
02A73609  mov         eax,dword ptr [eax+edx]  
02A7360C  mov         edx,dword ptr [ebp-14h]  
02A7360F  mov         ecx,4  
02A73614  shl         ecx,2  
02A73617  cmp         eax,dword ptr [edx+ecx]  
02A7361A  je          02A73624  
02A7361C  xor         edx,edx  
02A7361E  mov         dword ptr [ebp-20h],edx  
02A73621  nop  
02A73622  jmp         02A73672  

                            firstPointer += step;
02A73624  mov         eax,dword ptr [ebp-18h]  
02A73627  add         dword ptr [ebp-10h],eax  
                            secondPointer += step;
02A7362A  mov         eax,dword ptr [ebp-18h]  
02A7362D  add         dword ptr [ebp-14h],eax