Re: [PATCH, rs6000] Add a combine pattern for CA minus one [PR95737]

[HAO CHEN GUI via Gcc-patches]

On 19/1/2022 下午 3:52, Andrew Pinski wrote:
> On Tue, Jan 18, 2022 at 11:13 PM HAO CHEN GUI via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Hi,
>>    This patch adds a combine pattern for "CA minus one". As CA only has two
>> values (0 or 1), we could convert following pattern
>>       (sign_extend:DI (plus:SI (reg:SI 98 ca)
>>                 (const_int -1 [0xffffffffffffffff]))))
>> to
>>        (plus:DI (reg:DI 98 ca)
>>             (const_int -1 [0xffffffffffffffff])))
>>     With this patch, it eliminates one unnecessary sign extend. Also in 
>> rs6000,
>> regclass of CA register is set to NO_REGS. So CA is not in hard register set
>> and it can't match register_operand. The patch changes it to any_operand.
>>
>>     Bootstrapped and tested on powerpc64-linux BE and LE with no regressions.
>> Is this okay for trunk? Any recommendations? Thanks a lot.
>>
>> ChangeLog
>> 2022-01-19 Haochen Gui <guih...@linux.ibm.com>
>>
>> gcc/
>>         * config/rs6000/predicates.md (ca_operand): Match any_operand as CA
>>         register is not in hard register set.
>>         * config/rs6000/rs6000.md (extenddi_ca_minus_one): Define.
>>
>> gcc/testsuite/
>>         * gcc.target/powerpc/pr95737.c: New.
>>
>>
>> patch.diff
>> diff --git a/gcc/config/rs6000/predicates.md 
>> b/gcc/config/rs6000/predicates.md
>> index c65dfb91f3d..cd2ae1dc8e0 100644
>> --- a/gcc/config/rs6000/predicates.md
>> +++ b/gcc/config/rs6000/predicates.md
>> @@ -188,7 +188,7 @@ (define_predicate "vlogical_operand"
>>
>>  ;; Return 1 if op is the carry register.
>>  (define_predicate "ca_operand"
>> -  (match_operand 0 "register_operand")
>> +  (match_operand 0 "any_operand")
>>  {
>>    if (SUBREG_P (op))
>>      op = SUBREG_REG (op);
>> diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
>> index 6ecb0bd6142..f1b09aad3b5 100644
>> --- a/gcc/config/rs6000/rs6000.md
>> +++ b/gcc/config/rs6000/rs6000.md
>> @@ -2358,6 +2358,21 @@ (define_insn "subf<mode>3_carry_in_xx"
>>    "subfe %0,%0,%0"
>>    [(set_attr "type" "add")])
>>
>> +(define_insn_and_split "*extenddi_ca_minus_one"
>> +  [(set (match_operand:DI 0 "gpc_reg_operand")
>> +       (sign_extend:DI (plus:SI (match_operand:SI 1 "ca_operand")
>> +                                (const_int -1))))]
>> +  ""
>> +  "#"
>> +  ""
>> +  [(parallel [(set (match_dup 0)
>> +                  (plus:DI (match_dup 2)
>> +                           (const_int -1)))
>> +             (clobber (match_dup 2))])]
>> +{
>> +  operands[2] = copy_rtx (operands[1]);
>> +  PUT_MODE (operands[2], DImode);
>> +})
> 
> There are a few things missing I think for this to be correct.
> I think it should be:
> (define_insn_and_split "*extenddi_ca_minus_one"
>   [(set (match_operand:DI 0 "gpc_reg_operand" "=r")
>        (sign_extend:DI (plus:SI (reg:SI CA_REGNO)
>                                  (const_int -1))))]
>   ""
>   "#"
>   "&& reload_completed"
>   [(parallel [(set (match_dup 0)
>                   (plus:DI (reg:DI CA_REGNO)
>                            (const_int -1)))
>              (clobber (reg:DI CA_REGNO))])]
> {})
> 
> There is no reason to change ca_operand either since
> subf<mode>3_carry_in_xx already hard codes the CA_REGNO too; you can
Yes, we can directly use CA_REGNO. It makes the pattern compact.
But why it needs reload_completed? Could you explain it?

Thanks.
Gui Haochen

> just use it directly like above.
> 
> Sorry for the incorrect whitespace formatting though.
> 
> Thanks,
> Andrew Pinski
> 
>>
>>  (define_insn "@neg<mode>2"
>>    [(set (match_operand:GPR 0 "gpc_reg_operand" "=r")
>> diff --git a/gcc/testsuite/gcc.target/powerpc/pr95737.c 
>> b/gcc/testsuite/gcc.target/powerpc/pr95737.c
>> new file mode 100644
>> index 00000000000..94320f23423
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/powerpc/pr95737.c
>> @@ -0,0 +1,10 @@
>> +/* PR target/95737 */
>> +/* { dg-do compile { target lp64 } } */
>> +/* { dg-options "-O2 -mdejagnu-cpu=power8" } */
>> +/* { dg-final { scan-assembler-not {\mextsw\M} } } */
>> +
>> +
>> +unsigned long long negativeLessThan (unsigned long long a, unsigned long 
>> long b)
>> +{
>> +   return -(a < b);
>> +}