Re: Re: [PATCH 2/4] [ifcvt] if convert x=c ? y+z : y by RISC-V Zicond like insns

["Fei Gao" <gaofei@eswincomputing.com>]

On 2023-11-20 14:59  Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
>
>On 10/30/23 01:25, Fei Gao wrote:
>> Conditional add, if zero
>> rd = (rc == 0) ? (rs1 + rs2) : rs1
>> -->
>> czero.nez rd, rs2, rc
>> add rd, rs1, rd
>>
>> Conditional add, if non-zero
>> rd = (rc != 0) ? (rs1 + rs2) : rs1
>> -->
>> czero.eqz rd, rs2, rc
>> add rd, rs1, rd
>>
>> Co-authored-by: Xiao Zeng<zengxiao@eswincomputing.com>
>>
>> gcc/ChangeLog:
>>
>>          * ifcvt.cc (noce_emit_czero): helper for noce_try_cond_zero_arith
>>          (noce_try_cond_zero_arith): handler for condtional zero op
>>          (noce_process_if_block): add noce_try_cond_zero_arith with hook control
>>
>> gcc/testsuite/ChangeLog:
>>
>>          * gcc.target/riscv/zicond_ifcvt_opt.c: New test.
>> ---
>>   gcc/ifcvt.cc                                  | 112 +++++++++++++++
>>   .../gcc.target/riscv/zicond_ifcvt_opt.c       | 130 ++++++++++++++++++
>>   2 files changed, 242 insertions(+)
>>   create mode 100644 gcc/testsuite/gcc.target/riscv/zicond_ifcvt_opt.c
>>
>> diff --git a/gcc/ifcvt.cc b/gcc/ifcvt.cc
>> index a0af553b9ff..4f98c1c7bf9 100644
>> --- a/gcc/ifcvt.cc
>> +++ b/gcc/ifcvt.cc
>> @@ -781,12 +781,14 @@ static bool noce_try_store_flag_constants (struct noce_if_info *);
>>   static bool noce_try_store_flag_mask (struct noce_if_info *);
>>   static rtx noce_emit_cmove (struct noce_if_info *, rtx, enum rtx_code, rtx,
>>       rtx, rtx, rtx, rtx = NULL, rtx = NULL);
>> +static rtx noce_emit_czero (struct noce_if_info *, enum rtx_code, rtx, rtx);
>>   static bool noce_try_cmove (struct noce_if_info *);
>>   static bool noce_try_cmove_arith (struct noce_if_info *);
>>   static rtx noce_get_alt_condition (struct noce_if_info *, rtx, rtx_insn **);
>>   static bool noce_try_minmax (struct noce_if_info *);
>>   static bool noce_try_abs (struct noce_if_info *);
>>   static bool noce_try_sign_mask (struct noce_if_info *);
>> +static bool noce_try_cond_zero_arith (struct noce_if_info *);
>>  
>>   /* Return the comparison code for reversed condition for IF_INFO,
>>      or UNKNOWN if reversing the condition is not possible.  */
>> @@ -1831,6 +1833,32 @@ noce_emit_cmove (struct noce_if_info *if_info, rtx x, enum rtx_code code,
>>       return NULL_RTX;
>>   }
>>  
>> +static rtx
>> +noce_emit_czero (struct noce_if_info *if_info, enum rtx_code czero_code, rtx z, rtx target)
>Every function needs a comment describing what the function does, it's
>return value(s) and its arguments.  There are many examples in ifcvt.cc
>you can use to guide you.  I might start with something like this:
>
>/* Emit a conditional zero, returning the location of the result
>    or NULL_RTX upon failure.
>
>    IF_INFO describes the if-conversion scenario under consideration.
>    CZERO_CODE selects the condition (EQ/NE).
>    Z is the nonzero operand of the conditional move
>    TARGET is the desired output register.  */
>
>Or something like that.  I would suggest renaming "Z" to something more
>meaningful. 
Hi Jeff

Thanks for your patients. All comments regarding coding style have been addressed in new patches.

>
>
>
>>  
>> +/* Convert x = c ? y + z : y or x = c ? y : y + z. */
>> +
>> +static bool
>> +noce_try_cond_zero_arith (struct noce_if_info *if_info)
>The function comment really should be improved.  For example it doesn't
>indicate what the return value is.
>
>> +
>> +  /* cond must be EQ or NEQ comparision of a reg and 0.  */
>In general when you refer to a variable in a comment, do so in upper
>case.  Use NE rather than NEQ as the former is how most code refers to a
>not-equal rtx code.
>
>
>> +  if (GET_CODE (cond) != NE && GET_CODE (cond) != EQ)
>> +    return false;
>> +  if (!REG_P (XEXP (cond, 0)) || !rtx_equal_p (XEXP (cond, 1), const0_rtx))
>> +    return false;
>> +
>> +  /* check y + z:y*/
>> +  if (GET_CODE (a) == PLUS && REG_P (XEXP (a, 0)) && REG_P (XEXP (a, 1))
>> +      && REG_P (b) && rtx_equal_p (XEXP (a, 0), b))
>Write comments as complete sentences.
>
>> +    {
>> +      common = b;
>> +      z = XEXP (a, 1);
>Rather than "z" use a more descriptive variable name.
>
>
>> +
>> +  /* If we have x = c ? x + z : x, use a new reg to avoid modifying x  */
>> +  if (common && rtx_equal_p (common, if_info->x))
>> +    target = gen_reg_rtx (mode);
>> +  else
>> +    target = if_info->x;
>if-conversion runs both before and after register allocation.  So you
>have to handle the case where you can not generate new registers.  Use
>can_create_pseudo_p () to test for that.  You may need to fail if you
>can't generate a new register. 
1. In find_if_header function, I found the following piece of codes:
if (!reload_completed && noce_find_if_block(...)), and find_if_header must 
be called before noce_try_cond_zero_arith().

2. In noce_try_strore_flag_constants, new registers are also generated
without can_create_pseudo_p() check.

So I guess no need to add can_create_pseudo_p() here.

>
>> +
>> +  target = noce_emit_czero (if_info, czero_code, z, target);
>> +  if (!target)
>> +    {
>> +      end_sequence ();
>> +      return false;
>> +    }
>> +
>> +  target = expand_simple_binop (mode, PLUS, common, target, if_info->x, 0,
>> +	OPTAB_DIRECT);
>I think you want OPTAB_WIDEN and in the other calls.
>
>> @@ -3975,6 +4085,8 @@ noce_process_if_block (struct noce_if_info *if_info)
>>   goto success;
>>         if (noce_try_store_flag_mask (if_info))
>>   goto success;
>> +      if (targetm.have_cond_zero () && noce_try_cond_zero_arith (if_info))
>> +	goto success;
>Replace targetm.have_cond_zero with HAVE_conditional_move since that's
>the RTL primitive we're building from. 
Done. 

>
>
>>
>> +**test_ADD_ceqz:
>> +**	czero\.eqz	a3,a2,a3
>> +**	add	a0,a1,a3
>> +**	ret
>Please don't use explicit registers unless you know they will always be
>correct.  In this sequence there's no guarantee the register allocator
>will put the result of the czero.eqz into $a3.  Use a suitable regexp
>instead to match a variety of registers.  This will be an issue for all
>your new tests. 
Done.

BR, 
Fei
>
>
>
>Jeff