A strange bit of code in MacroAssembler::multiply_128_x_128_loop

[Vladimir Kozlov]

It restores counter after:

   subl(idx, 2);
   jcc(Assembler::negative, L_check_1);

The value could be 1,2,3 before this point (idx & 3 before).
After 'sub 2': -1, 0, 1.

So we have to restore to positive values before subtracting 1.

Vladimir

On 4/10/15 8:12 AM, Daniel D. Daugherty wrote:
> Adding in the Compiler team since this is the MacroAssembler...
>
> Dan
>
>
> On 4/10/15 9:06 AM, Andrew Haley wrote:
>> This is for x86:
>>
>>    addl (idx, 0x2);
>>    andl (idx, 0x1);
>>    subl(idx, 1);
>>    jcc(Assembler::negative, L_post_third_loop_done);
>>
>> I'm trying to guess what the "addl (idx, 0x2)" instruction was supposed to do.
>> I don't think it has any effect now.
>>
>> Andrew.
>