Re: [PATCH V6] rs6000: Optimize cmp on rotated 16bits constant

[Jiufu Guo <guojiufu@linux.ibm.com>]

Hi,

Jiufu Guo via Gcc-patches <gcc-patches@gcc.gnu.org> writes:

> Hi,
>
> Segher Boessenkool <segher@kernel.crashing.org> writes:
>
>> Hi!
>>
>> Sorry for the tardiness.
>>
>> On Mon, Aug 29, 2022 at 11:42:16AM +0800, Jiufu Guo wrote:
>>> When checking eq/ne with a constant which has only 16bits, it can be
>>> optimized to check the rotated data.  By this, the constant building
>>> is optimized.
>>> 
>>> As the example in PR103743:
>>> For "in == 0x8000000000000000LL", this patch generates:
>>>         rotldi %r3,%r3,16
>>>         cmpldi %cr0,%r3,32768
>>> instead:
>>>         li %r9,-1
>>>         rldicr %r9,%r9,0,0
>>>         cmpd %cr0,%r3,%r9
>>
>> FWIW, I find the winnt assembler syntax very hard to read, and I doubt
>> I am the only one.
> Oh, sorry about that.  I will avoid to add '-mregnames' to dump asm. :)
> BTW, what options are you used to dump asm code? 
>>
>> So you're doing
>>   rotldi 3,3,16 ; cmpldi 3,0x8000
>> instead of
>>   li 9,-1 ; rldicr 9,9,0,0 ; cmpd 3,9
>>
>>> +/* Check if C can be rotated from an immediate which starts (as 64bit integer)
>>> +   with at least CLZ bits zero.
>>> +
>>> +   Return the number by which C can be rotated from the immediate.
>>> +   Return -1 if C can not be rotated as from.  */
>>> +
>>> +int
>>> +rotate_from_leading_zeros_const (unsigned HOST_WIDE_INT c, int clz)
>>
>> The name does not say what the function does.  Can you think of a better
>> name?
>>
>> Maybe it is better to not return magic values anyway?  So perhaps
>>
>> bool
>> can_be_done_as_compare_of_rotate (unsigned HOST_WIDE_INT c, int clz, int *rot)
>>
>> (with *rot written if the return value is true).
> Thanks for your suggestion!
> It is checking if a constant can be rotated from/to a value which has
> only few tailing nonzero bits (all leading bits are zeros). 
>
> So, I'm thinking to name the function as something like:
> can_be_rotated_to_lowbits.
>
>>
>>> +  /* case c. xx10.....0xx: rotate 'clz + 1' bits firstly, then check case b.
>>
>> s/firstly/first/
> Thanks! 
>>
>>> +/* Check if C can be rotated from an immediate operand of cmpdi or cmpldi.  */
>>> +
>>> +bool
>>> +compare_rotate_immediate_p (unsigned HOST_WIDE_INT c)
>>
>> No _p please, this function is not a predicate (at least, the name does
>> not say what it tests).  So a better name please.  This matters even
>> more for extern functions (like this one) because the function
>> implementation is always farther away so you do not easily have all
>> interface details in mind.  Good names help :-)
> Thanks! Name is always a matter. :)
>
> Maybe we can name this funciton as "can_be_rotated_as_compare_operand",
> or "is_constant_rotateable_for_compare", because this function checks
> "if a constant can be rotated to/from an immediate operand of
> cmpdi/cmpldi". 
>
>>
>>> +(define_code_iterator eqne [eq ne])
>>> +(define_code_attr EQNE [(eq "EQ") (ne "NE")])
>>
>> Just <CODE> or <CODE:eqne> should work?
> Great! Thanks for point out this! <eqne:CODE> works.
>>
>> Please fix these things.  Almost there :-)
>
> I updated the patch as below. Bootstraping and regtesting is ongoing.
> Thanks again for your careful and insight review!

Bootstrap and regtests pass on ppc64{,le}.

BR,
Jeff (Jiufu)

>
>
> BR,
> Jeff (Jiufu)
>
> ----------
> When checking eq/ne with a constant which has only 16bits, it can be
> optimized to check the rotated data.  By this, the constant building
> is optimized.
>
> As the example in PR103743:
> For "in == 0x8000000000000000LL", this patch generates:
>         rotldi 3,3,1 ; cmpldi 0,3,1
> instead of:
>         li 9,-1 ; rldicr 9,9,0,0 ; cmpd 0,3,9
>
> Compare with previous version:
> This patch refactor the code according to review comments.
> e.g. updating function names/comments/code.
>
>
> 	PR target/103743
>
> gcc/ChangeLog:
>
> 	* config/rs6000/rs6000-protos.h (can_be_rotated_to_lowbits): New.
> 	(can_be_rotated_as_compare_operand): New.
> 	* config/rs6000/rs6000.cc (can_be_rotated_to_lowbits): New definition.
> 	(can_be_rotated_as_compare_operand): New definition.
> 	* config/rs6000/rs6000.md (*rotate_on_cmpdi): New define_insn_and_split.
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.target/powerpc/pr103743.c: New test.
> 	* gcc.target/powerpc/pr103743_1.c: New test.
>
> ---
>  gcc/config/rs6000/rs6000-protos.h             |  2 +
>  gcc/config/rs6000/rs6000.cc                   | 56 +++++++++++
>  gcc/config/rs6000/rs6000.md                   | 63 +++++++++++-
>  gcc/testsuite/gcc.target/powerpc/pr103743.c   | 52 ++++++++++
>  gcc/testsuite/gcc.target/powerpc/pr103743_1.c | 95 +++++++++++++++++++
>  5 files changed, 267 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr103743.c
>  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr103743_1.c
>
> diff --git a/gcc/config/rs6000/rs6000-protos.h b/gcc/config/rs6000/rs6000-protos.h
> index d0d89320ef6..9626917e359 100644
> --- a/gcc/config/rs6000/rs6000-protos.h
> +++ b/gcc/config/rs6000/rs6000-protos.h
> @@ -35,6 +35,8 @@ extern bool xxspltib_constant_p (rtx, machine_mode, int *, int *);
>  extern int vspltis_shifted (rtx);
>  extern HOST_WIDE_INT const_vector_elt_as_int (rtx, unsigned int);
>  extern bool macho_lo_sum_memory_operand (rtx, machine_mode);
> +extern bool can_be_rotated_to_lowbits (unsigned HOST_WIDE_INT, int, int *);
> +extern bool can_be_rotated_as_compare_operand (unsigned HOST_WIDE_INT);
>  extern int num_insns_constant (rtx, machine_mode);
>  extern int small_data_operand (rtx, machine_mode);
>  extern bool mem_operand_gpr (rtx, machine_mode);
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index b3a609f3aa3..2b0df8479f0 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -14925,6 +14925,62 @@ rs6000_reverse_condition (machine_mode mode, enum rtx_code code)
>      return reverse_condition (code);
>  }
>  
> +/* Check if C (as 64bit integer) can be rotated to a constant which constains
> +   nonzero bits at LOWBITS only.
> +
> +   Return true if C can be rotated to such constant.  And *ROT is written to
> +   the number by which C is rotated.
> +   Return false otherwise.  */
> +
> +bool
> +can_be_rotated_to_lowbits (unsigned HOST_WIDE_INT c, int lowbits, int *rot)
> +{
> +  int clz = HOST_BITS_PER_WIDE_INT - lowbits;
> +
> +  /* case a. 0..0xxx: already at least clz zeros.  */
> +  int lz = clz_hwi (c);
> +  if (lz >= clz)
> +    {
> +      *rot = 0;
> +      return true;
> +    }
> +
> +  /* case b. 0..0xxx0..0: at least clz zeros.  */
> +  int tz = ctz_hwi (c);
> +  if (lz + tz >= clz)
> +    {
> +      *rot = HOST_BITS_PER_WIDE_INT - tz;
> +      return true;
> +    }
> +
> +  /* case c. xx10.....0xx: rotate 'clz - 1' bits first, then check case b.
> +	       ^bit -> Vbit, , then zeros are at head or tail.
> +	     00...00xxx100, 'clz - 1' >= 'bits of xxxx'.  */
> +  const int rot_bits = lowbits + 1;
> +  unsigned HOST_WIDE_INT rc = (c >> rot_bits) | (c << (clz - 1));
> +  tz = ctz_hwi (rc);
> +  if (clz_hwi (rc) + tz >= clz)
> +    {
> +      *rot = HOST_BITS_PER_WIDE_INT - (tz + rot_bits);
> +      return true;
> +    }
> +
> +  return false;
> +}
> +
> +/* Check if C can be rotated to an immediate operand of cmpdi or cmpldi.  */
> +
> +bool
> +can_be_rotated_as_compare_operand (unsigned HOST_WIDE_INT c)
> +{
> +  int rot = 0;
> +  /* leading 48 zeros + 16 lowbits (cmpldi),
> +     or leading 49 ones + 15 lowbits (cmpdi).  */
> +  bool res = can_be_rotated_to_lowbits (~c, 15, &rot)
> +	     || can_be_rotated_to_lowbits (c, 16, &rot);
> +  return res && rot > 0;
> +}
> +
>  /* Generate a compare for CODE.  Return a brand-new rtx that
>     represents the result of the compare.  */
>  
> diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
> index 4bd1dfd3da9..dabfe5dfdfd 100644
> --- a/gcc/config/rs6000/rs6000.md
> +++ b/gcc/config/rs6000/rs6000.md
> @@ -7765,6 +7765,68 @@ (define_insn "*movsi_from_df"
>    "xscvdpsp %x0,%x1"
>    [(set_attr "type" "fp")])
>  
> +
> +(define_code_iterator eqne [eq ne])
> +
> +;; "i == C" ==> "rotl(i,N) == rotl(C,N)"
> +(define_insn_and_split "*rotate_on_cmpdi"
> +  [(set (pc)
> +	(if_then_else (eqne (match_operand:DI 1 "gpc_reg_operand" "r")
> +			    (match_operand:DI 2 "const_int_operand" "n"))
> +		      (label_ref (match_operand 0 ""))
> +		      (pc)))
> +  (clobber (match_scratch:DI 3 "=r"))
> +  (clobber (match_scratch:CCUNS 4 "=y"))]
> +  "TARGET_POWERPC64 && num_insns_constant (operands[2], DImode) > 1
> +   && can_be_rotated_as_compare_operand (UINTVAL (operands[2]))"
> +   "#"
> +   "&& 1"
> +  [(pc)]
> +{
> +  rtx note = find_reg_note (curr_insn, REG_BR_PROB, 0);
> +  bool sgn = false;
> +  unsigned HOST_WIDE_INT C = INTVAL (operands[2]);
> +  int rot;
> +  if (!can_be_rotated_to_lowbits (C, 16, &rot))
> +    {
> +      /* cmpdi */
> +      sgn = true;
> +      bool res = can_be_rotated_to_lowbits (~C, 15, &rot);
> +      gcc_assert (res);
> +    }
> +  rtx n = GEN_INT (rot);
> +
> +  /* i' = rotl (i, n) */
> +  rtx op0 = can_create_pseudo_p () ? gen_reg_rtx (DImode) : operands[3];
> +  emit_insn (gen_rtx_SET (op0, gen_rtx_ROTATE (DImode, operands[1], n)));
> +
> +  /* C' = rotl (C, n) */
> +  rtx op1 = GEN_INT ((C << rot) | (C >> (HOST_BITS_PER_WIDE_INT - rot)));
> +
> +  /* i' ==  C' */
> +  machine_mode comp_mode = sgn ? CCmode : CCUNSmode;
> +  rtx cc = can_create_pseudo_p () ? gen_reg_rtx (comp_mode) : operands[4];
> +  PUT_MODE (cc, comp_mode);
> +  emit_insn (gen_rtx_SET (cc, gen_rtx_COMPARE (comp_mode, op0, op1)));
> +  rtx cmp = gen_rtx_<eqne:CODE> (CCmode, cc, const0_rtx);
> +  rtx loc_ref = gen_rtx_LABEL_REF (VOIDmode, operands[0]);
> +  emit_jump_insn (gen_rtx_SET (pc_rtx,
> +			       gen_rtx_IF_THEN_ELSE (VOIDmode, cmp,
> +						     loc_ref, pc_rtx)));
> +
> +  /* keep the probability info for the prediction of the branch insn.  */
> +  if (note)
> +    {
> +      profile_probability prob
> +	= profile_probability::from_reg_br_prob_note (XINT (note, 0));
> +
> +      add_reg_br_prob_note (get_last_insn (), prob);
> +    }
> +
> +  DONE;
> +}
> +)
> +
>  ;; Split a load of a large constant into the appropriate two-insn
>  ;; sequence.
>  
> @@ -13453,7 +13515,6 @@ (define_expand "@ctr<mode>"
>  ;; rs6000_legitimate_combined_insn prevents combine creating any of
>  ;; the ctr<mode> insns.
>  
> -(define_code_iterator eqne [eq ne])
>  (define_code_attr bd [(eq "bdz") (ne "bdnz")])
>  (define_code_attr bd_neg [(eq "bdnz") (ne "bdz")])
>  
> diff --git a/gcc/testsuite/gcc.target/powerpc/pr103743.c b/gcc/testsuite/gcc.target/powerpc/pr103743.c
> new file mode 100644
> index 00000000000..41c686bb4cb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr103743.c
> @@ -0,0 +1,52 @@
> +/* { dg-options "-O2" } */
> +/* { dg-do compile { target has_arch_ppc64 } } */
> +
> +/* { dg-final { scan-assembler-times {\mcmpldi\M} 10  } } */
> +/* { dg-final { scan-assembler-times {\mcmpdi\M} 4  } } */
> +/* { dg-final { scan-assembler-times {\mrotldi\M} 14  } } */
> +
> +int foo (int a);
> +
> +int __attribute__ ((noinline)) udi_fun (unsigned long long in)
> +{
> +  if (in == (0x8642000000000000ULL))
> +    return foo (1);
> +  if (in == (0x7642000000000000ULL))
> +    return foo (12);
> +  if (in == (0x8000000000000000ULL))
> +    return foo (32);
> +  if (in == (0x8700000000000091ULL))
> +    return foo (33);
> +  if (in == (0x8642FFFFFFFFFFFFULL))
> +    return foo (46);
> +  if (in == (0x7642FFFFFFFFFFFFULL))
> +    return foo (51);
> +  if (in == (0x7567000000ULL))
> +    return foo (9);
> +  if (in == (0xFFF8567FFFFFFFFFULL))
> +    return foo (19);
> +
> +  return 0;
> +}
> +
> +int __attribute__ ((noinline)) di_fun (long long in)
> +{
> +  if (in == (0x8642000000000000LL))
> +    return foo (1);
> +  if (in == (0x7642000000000000LL))
> +    return foo (12);
> +  if (in == (0x8000000000000000LL))
> +    return foo (32);
> +  if (in == (0x8700000000000091LL))
> +    return foo (33);
> +  if (in == (0x8642FFFFFFFFFFFFLL))
> +    return foo (46);
> +  if (in == (0x7642FFFFFFFFFFFFLL))
> +    return foo (51);
> +  if (in == (0x7567000000LL))
> +    return foo (9);
> +  if (in == (0xFFF8567FFFFFFFFFLL))
> +    return foo (19);
> +
> +  return 0;
> +}
> diff --git a/gcc/testsuite/gcc.target/powerpc/pr103743_1.c b/gcc/testsuite/gcc.target/powerpc/pr103743_1.c
> new file mode 100644
> index 00000000000..e128aae7574
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr103743_1.c
> @@ -0,0 +1,95 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -std=c99" } */
> +
> +int
> +foo (int a)
> +{
> +  return a + 6;
> +}
> +
> +int __attribute__ ((noipa)) udi_fun (unsigned long long in)
> +{
> +  if (in == (0x8642000000000000ULL))
> +    return foo (1);
> +  if (in == (0x7642000000000000ULL))
> +    return foo (12);
> +  if (in == (0x8000000000000000ULL))
> +    return foo (32);
> +  if (in == (0x8700000000000091ULL))
> +    return foo (33);
> +  if (in == (0x8642FFFFFFFFFFFFULL))
> +    return foo (46);
> +  if (in == (0x7642FFFFFFFFFFFFULL))
> +    return foo (51);
> +  if (in == (0x7567000000ULL))
> +    return foo (9);
> +  if (in == (0xFFF8567FFFFFFFFFULL))
> +    return foo (19);
> +  
> +  return 0;
> +}
> +
> +int __attribute__ ((noipa)) di_fun (long long in)
> +{
> +  if (in == (0x8642000000000000LL))
> +    return foo (1);
> +  if (in == (0x7642000000000000LL))
> +    return foo (12);
> +  if (in == (0x8000000000000000LL))
> +    return foo (32);
> +  if (in == (0x8700000000000091LL))
> +    return foo (33);
> +  if (in == (0x8642FFFFFFFFFFFFLL))
> +    return foo (46);
> +  if (in == (0x7642FFFFFFFFFFFFLL))
> +    return foo (51);
> +  return 0;
> +}
> +
> +int
> +main ()
> +{
> +  int e = 0;
> +  if (udi_fun (6) != 0)
> +    e++;
> +  if (udi_fun (0x8642000000000000ULL) != foo (1))
> +    e++;
> +  if (udi_fun (0x7642000000000000ULL) != foo (12))
> +    e++;
> +  if (udi_fun (0x8000000000000000ULL) != foo (32))
> +    e++;
> +  if (udi_fun (0x8700000000000091ULL) != foo (33))
> +    e++;
> +  if (udi_fun (0x8642FFFFFFFFFFFFULL) != foo (46))
> +    e++;
> +  if (udi_fun (0x7642FFFFFFFFFFFFULL) != foo (51))
> +    e++;
> +  if (udi_fun (0x7567000000ULL) != foo (9))
> +    e++;
> +  if (udi_fun (0xFFF8567FFFFFFFFFULL) != foo (19))
> +    e++;
> +
> +  if (di_fun (6) != 0)
> +    e++;
> +  if (di_fun (0x8642000000000000LL) != foo (1))
> +    e++;
> +  if (di_fun (0x7642000000000000LL) != foo (12))
> +    e++;
> +  if (di_fun (0x8000000000000000LL) != foo (32))
> +    e++;
> +  if (di_fun (0x8700000000000091LL) != foo (33))
> +    e++;
> +  if (di_fun (0x8642FFFFFFFFFFFFLL) != foo (46))
> +    e++;
> +  if (di_fun (0x7642FFFFFFFFFFFFLL) != foo (51))
> +    e++;
> +  if (udi_fun (0x7567000000LL) != foo (9))
> +    e++;
> +  if (udi_fun (0xFFF8567FFFFFFFFFLL) != foo (19))
> +    e++;
> +
> +  if (e)
> +    __builtin_abort ();
> +  return 0;
> +}
> +