Re: [Qemu-devel] [PATCH 5/6] target-ppc: support for 32-bit carry and overflow

[Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>]

Richard Henderson <rth@twiddle.net> writes:

> On 02/16/2017 04:08 PM, Nikunj A Dadhania wrote:
>> Richard Henderson <rth@twiddle.net> writes:
>>
>>> On 02/14/2017 02:05 PM, Nikunj A Dadhania wrote:
>>>> Yes, you are right. I had a discussion with Paul Mackerras yesterday, he
>>>> explained to me in detail about the bits. I am working on the revised
>>>> implementation. Will detail it in the commit message.
>>>
>>> As you're working on this, consider changing the definition of cpu_ov such that
>>> the MSB is OV and bit 31 is OV32.
>>>
>>> E.g.
>>>
>>>
>>>   static inline void gen_op_arith_compute_ov(DisasContext *ctx, TCGv arg0,
>>>                                              TCGv arg1, TCGv arg2, int sub)
>>>   {
>>>       TCGv t0 = tcg_temp_new();
>>>
>>>       tcg_gen_xor_tl(cpu_ov, arg0, arg2);
>>>       tcg_gen_xor_tl(t0, arg1, arg2);
>>>       if (sub) {
>>>           tcg_gen_and_tl(cpu_ov, cpu_ov, t0);
>>>       } else {
>>>           tcg_gen_andc_tl(cpu_ov, cpu_ov, t0);
>>>       }
>>>       tcg_temp_free(t0);
>>>       if (NARROW_MODE(ctx)) {
>>>           tcg_gen_ext32s_tl(cpu_ov, cpu_ov);
>>>       }
>>> -    tcg_gen_shri_tl(cpu_ov, cpu_ov, TARGET_LONG_BITS - 1);
>>>       tcg_gen_or_tl(cpu_so, cpu_so, cpu_ov);
>>>   }
>>>
>>>
>>> is all that is required for arithmetic to compute OV and OV32 into those two bits.
>>
>> How about the below?
>>
>> @@ -809,10 +809,11 @@ static inline void gen_op_arith_compute_ov(DisasContext *ctx, TCGv arg0,
>>          tcg_gen_andc_tl(cpu_ov, cpu_ov, t0);
>>      }
>>      tcg_temp_free(t0);
>> +    tcg_gen_extract_tl(cpu_ov32, cpu_ov, 31, 1);
>> +    tcg_gen_extract_tl(cpu_ov, cpu_ov, 63, 1);
>>      if (NARROW_MODE(ctx)) {
>> -        tcg_gen_ext32s_tl(cpu_ov, cpu_ov);
>> +        tcg_gen_mov_tl(cpu_ov, cpu_ov32);
>>      }
>> -    tcg_gen_shri_tl(cpu_ov, cpu_ov, TARGET_LONG_BITS - 1);
>>      tcg_gen_or_tl(cpu_so, cpu_so, cpu_ov);
>>  }
>
> Why do you want to extract these bits?

Convinient to copy that to XER later.

Regards
Nikunj