Re: [PATCH] Add 3 target hooks for memset

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On 5/20/21 10:49 PM, H.J. Lu wrote:
> On Wed, May 19, 2021 at 5:55 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>>
>> On Wed, May 19, 2021 at 2:25 AM Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>>
>>> On Tue, May 18, 2021 at 9:16 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>
>>>> Add TARGET_READ_MEMSET_VALUE and TARGET_GEN_MEMSET_VALUE to support
>>>> target instructions to duplicate QImode value to TImode/OImode/XImode
>>>> value for memmset.
>>>>
>>>>         PR middle-end/90773
>>>>         * builtins.c (builtin_memset_read_str): Call
>>>>         targetm.read_memset_value.
>>>>         (builtin_memset_gen_str): Call targetm.gen_memset_value.
>>>>         * target.def (read_memset_value): New hook.
>>>>         (gen_memset_value): Likewise.
>>>>         * targhooks.c: Inclue "builtins.h".
>>>>         (default_read_memset_value): New function.
>>>>         (default_gen_memset_value): Likewise.
>>>>         * targhooks.h (default_read_memset_value): New prototype.
>>>>         (default_gen_memset_value): Likewise.
>>>>         * doc/tm.texi.in: Add TARGET_READ_MEMSET_VALUE and
>>>>         TARGET_GEN_MEMSET_VALUE hooks.
>>>>         * doc/tm.texi: Regenerated.
>>>> ---
>>>>  gcc/builtins.c     | 47 ++++----------------------------------
>>>>  gcc/doc/tm.texi    | 16 +++++++++++++
>>>>  gcc/doc/tm.texi.in |  4 ++++
>>>>  gcc/target.def     | 20 +++++++++++++++++
>>>>  gcc/targhooks.c    | 56 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>  gcc/targhooks.h    |  4 ++++
>>>>  6 files changed, 104 insertions(+), 43 deletions(-)
>>>>
>>>> diff --git a/gcc/builtins.c b/gcc/builtins.c
>>>> index e1b284846b1..f78a36478ef 100644
>>>> --- a/gcc/builtins.c
>>>> +++ b/gcc/builtins.c
>>>> @@ -6584,24 +6584,11 @@ expand_builtin_strncpy (tree exp, rtx target)
>>>>     previous iteration.  */
>>>>
>>>>  rtx
>>>> -builtin_memset_read_str (void *data, void *prevp,
>>>> +builtin_memset_read_str (void *data, void *prev,
>>>>                          HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
>>>>                          scalar_int_mode mode)
>>>>  {
>>>> -  by_pieces_prev *prev = (by_pieces_prev *) prevp;
>>>> -  if (prev != nullptr && prev->data != nullptr)
>>>> -    {
>>>> -      /* Use the previous data in the same mode.  */
>>>> -      if (prev->mode == mode)
>>>> -       return prev->data;
>>>> -    }
>>>> -
>>>> -  const char *c = (const char *) data;
>>>> -  char *p = XALLOCAVEC (char, GET_MODE_SIZE (mode));
>>>> -
>>>> -  memset (p, *c, GET_MODE_SIZE (mode));
>>>> -
>>>> -  return c_readstr (p, mode);
>>>> +  return targetm.read_memset_value ((const char *) data, prev, mode);
>>>>  }
>>>>
>>>>  /* Callback routine for store_by_pieces.  Return the RTL of a register
>>>> @@ -6611,37 +6598,11 @@ builtin_memset_read_str (void *data, void *prevp,
>>>>     nullptr, it has the RTL info from the previous iteration.  */
>>>>
>>>>  static rtx
>>>> -builtin_memset_gen_str (void *data, void *prevp,
>>>> +builtin_memset_gen_str (void *data, void *prev,
>>>>                         HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
>>>>                         scalar_int_mode mode)
>>>>  {
>>>> -  rtx target, coeff;
>>>> -  size_t size;
>>>> -  char *p;
>>>> -
>>>> -  by_pieces_prev *prev = (by_pieces_prev *) prevp;
>>>> -  if (prev != nullptr && prev->data != nullptr)
>>>> -    {
>>>> -      /* Use the previous data in the same mode.  */
>>>> -      if (prev->mode == mode)
>>>> -       return prev->data;
>>>> -
>>>> -      target = simplify_gen_subreg (mode, prev->data, prev->mode, 0);
>>>> -      if (target != nullptr)
>>>> -       return target;
>>>> -    }
>>>> -
>>>> -  size = GET_MODE_SIZE (mode);
>>>> -  if (size == 1)
>>>> -    return (rtx) data;
>>>> -
>>>> -  p = XALLOCAVEC (char, size);
>>>> -  memset (p, 1, size);
>>>> -  coeff = c_readstr (p, mode);
>>>> -
>>>> -  target = convert_to_mode (mode, (rtx) data, 1);
>>>> -  target = expand_mult (mode, target, coeff, NULL_RTX, 1);
>>>> -  return force_reg (mode, target);
>>>> +  return targetm.gen_memset_value ((rtx) data, prev, mode);
>>>>  }
>>>>
>>>>  /* Expand expression EXP, which is a call to the memset builtin.  Return
>>>> diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
>>>> index 85ea9395560..51385044e76 100644
>>>> --- a/gcc/doc/tm.texi
>>>> +++ b/gcc/doc/tm.texi
>>>> @@ -11868,6 +11868,22 @@ This function prepares to emit a conditional comparison within a sequence
>>>>   @var{bit_code} is @code{AND} or @code{IOR}, which is the op on the compares.
>>>>  @end deftypefn
>>>>
>>>> +@deftypefn {Target Hook} rtx TARGET_READ_MEMSET_VALUE (const char *@var{c}, void *@var{prev}, scalar_int_mode @var{mode})
>>>> +This function returns the RTL of a constant integer corresponding to
>>>> +target reading @code{GET_MODE_SIZE (@var{mode})} bytes from the stringn
>>>> +constant @var{str}.  If @var{prev} is not @samp{nullptr}, it contains
>>>> +the RTL information from the previous interation.
>>>> +@end deftypefn
>>>> +
>>>> +@deftypefn {Target Hook} rtx TARGET_GEN_MEMSET_VALUE (rtx @var{data}, void *@var{prev}, scalar_int_mode @var{mode})
>>>> +This function returns the RTL of a register containing
>>>> +@code{GET_MODE_SIZE (@var{mode})} consecutive copies of the unsigned
>>>> +char value given in the RTL register @var{data}.  For example, if
>>>> +@var{mode} is 4 bytes wide, return the RTL for 0x01010101*@var{data}.
>>>> +If @var{PREV} is not @samp{nullptr}, it is the RTL information from
>>>> +the previous iteration.
>>>> +@end deftypefn
>>>> +
>>>>  @deftypefn {Target Hook} unsigned TARGET_LOOP_UNROLL_ADJUST (unsigned @var{nunroll}, class loop *@var{loop})
>>>>  This target hook returns a new value for the number of times @var{loop}
>>>>  should be unrolled. The parameter @var{nunroll} is the number of times
>>>> diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
>>>> index d8e3de14af1..8d4c3949fbf 100644
>>>> --- a/gcc/doc/tm.texi.in
>>>> +++ b/gcc/doc/tm.texi.in
>>>> @@ -7956,6 +7956,10 @@ lists.
>>>>
>>>>  @hook TARGET_GEN_CCMP_NEXT
>>>>
>>>> +@hook TARGET_READ_MEMSET_VALUE
>>>> +
>>>> +@hook TARGET_GEN_MEMSET_VALUE
>>>> +
>>>>  @hook TARGET_LOOP_UNROLL_ADJUST
>>>>
>>>>  @defmac POWI_MAX_MULTS
>>>> diff --git a/gcc/target.def b/gcc/target.def
>>>> index bbaf6b4f3a0..c9aca40fa88 100644
>>>> --- a/gcc/target.def
>>>> +++ b/gcc/target.def
>>>> @@ -2694,6 +2694,26 @@ DEFHOOK
>>>>   rtx, (rtx_insn **prep_seq, rtx_insn **gen_seq, rtx prev, int cmp_code, tree op0, tree op1, int bit_code),
>>>>   NULL)
>>>>
>>>> +DEFHOOK
>>>> +(read_memset_value,
>>>> + "This function returns the RTL of a constant integer corresponding to\n\
>>>> +target reading @code{GET_MODE_SIZE (@var{mode})} bytes from the stringn\n\
>>>> +constant @var{str}.  If @var{prev} is not @samp{nullptr}, it contains\n\
>>>
>>> where is 'str' defined?  I can't really tell what's the difference
>>
>> Fixed with
>>
>> diff --git a/gcc/target.def b/gcc/target.def
>> index c9aca40fa88..4c3a5fcc634 100644
>> --- a/gcc/target.def
>> +++ b/gcc/target.def
>> @@ -2699,8 +2699,8 @@ DEFHOOK
>>   "This function returns the RTL of a constant integer corresponding to\n\
>>  target reading @code{GET_MODE_SIZE (@var{mode})} bytes from the string\n\
>>  constant @var{str}.  If @var{prev} is not @samp{nullptr}, it contains\n\
>> -the RTL information from the previous interation.",
>> - rtx, (const char *c, void *prev, scalar_int_mode mode),
>> +the RTL information from the previous iteration.",
>> + rtx, (const char *str, void *prev, scalar_int_mode mode),
>>   default_read_memset_value)
>>
>>  DEFHOOK
>>
>>> from read_memset_value
>>> and gen_memset_value.
>>
>> The difference is that input of read_memset_value is a string constant
>> like "123" and input of gen_memset_value is an RTL register.
>>
>>> Somehow I feel that an optab for the "splat" operation similar
>>> to vec_duplicate might be a better way to expose this - of course
>>> that doesn't handle the "prev" thing.
>>
>> The x86 backend has ix86_expand_vector_init_duplicate () to
>> broadcast QImode to TImode/OImode/XImode:
>>
>> /* A subroutine of ix86_expand_vector_init.  Store into TARGET a vector
>>    with all elements equal to VAR.  Return true if successful.  */
>>
>> bool
>> ix86_expand_vector_init_duplicate (bool mmx_ok, machine_mode mode,
>>                                    rtx target, rtx val)
>>
>>> So how's this the right point of abstraction to the target?
>>
>> I can add 2 target hooks, one for scratch register and one for
>> broadcasting QImode to TImode/OImode/XImode.   Then I can
>> move x86 codes to the middle-end.
>>
> 
> Here is the patch to add 3 target hooks:
> 
>  -- Target Hook: rtx TARGET_READ_MEMSET_VALUE (const char *C,
>           scalar_int_mode MODE)
>      This function returns the RTL of a constant integer corresponding
>      to target reading 'GET_MODE_SIZE (MODE)' bytes from the string
>      constant C.
> 
>  -- Target Hook: rtx TARGET_GEN_MEMSET_VALUE (rtx DATA, scalar_int_mode
>           MODE)
>      This function returns the RTL of a register containing
>      'GET_MODE_SIZE (MODE)' consecutive copies of the unsigned char
>      value given in the RTL register DATA.  For example, if MODE is 4
>      bytes wide, return the RTL for 0x01010101*DATA.
> 
>  -- Target Hook: rtx TARGET_GEN_MEMSET_VALUE_FROM_PREV (void *PREV,
>           scalar_int_mode MODE)
>      This function returns the RTL of a register in MODE generated from
>      PREV in the previous iteration.
> 
> with
> 
> /* Return the RTL of a register in MODE generated from PREV in the
>    previous iteration.  */
> 
> static rtx
> gen_memset_value_from_prev (void *prevp, scalar_int_mode mode)
> {
>   by_pieces_prev *prev = (by_pieces_prev *) prevp;
>   rtx value;
>   if (prev != nullptr && prev->data != nullptr)
>     {
>       /* Use the previous data in the same mode.  */
>       if (prev->mode == mode)
>         return prev->data;
> 
>       value = targetm.gen_memset_value_from_prev (prevp, mode);
>     }
>   else
>     value = nullptr;
>   return value;
> }
> 
> /* Callback routine for store_by_pieces.  Read GET_MODE_BITSIZE (MODE)
>    bytes from constant string DATA + OFFSET and return it as target
>    constant.  If PREV isn't nullptr, it has the RTL info from the
>    previous iteration.  */
> 
> rtx
> builtin_memset_read_str (void *data, void *prev,
>                          HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
>                          scalar_int_mode mode)
> {
>   const char *str = (const char *) data;
> 
>   /* Don't use the previous value if size is 1.  */
>   if (GET_MODE_SIZE (mode) == 1)
>     return default_read_memset_value (str, mode);
> 
>   rtx value = gen_memset_value_from_prev (prev, mode);
>   if (value)
>     return value;
> 
>   return targetm.read_memset_value (str, mode);
> }
> 
> /* Callback routine for store_by_pieces.  Return the RTL of a register
>    containing GET_MODE_SIZE (MODE) consecutive copies of the unsigned
>    char value given in the RTL register data.  For example, if mode is
>    4 bytes wide, return the RTL for 0x01010101*data.  If PREV isn't
>    nullptr, it has the RTL info from the previous iteration.  */
> 
> static rtx
> builtin_memset_gen_str (void *datap, void *prev,
>                         HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
>                         scalar_int_mode mode)
> {
>   rtx data = (rtx) datap;
> 
>   /* Don't use the previous value if size is 1.  */
>   if (GET_MODE_SIZE (mode) == 1)
>     return data;
> 
>   rtx value = gen_memset_value_from_prev (prev, mode);
>   if (value)
>     return value;
> 
>   return targetm.gen_memset_value (data, mode);
> }> +/* Default implementation of TARGET_GEN_MEMSET_VALUE.  */
> +
> +rtx
> +default_gen_memset_value (rtx data, scalar_int_mode mode)
> +{
> +  rtx target, coeff;
> +  size_t size;
> +  char *p;
> +
> +  size = GET_MODE_SIZE (mode);
> +  if (size == 1)
> +    return data;
> +
> +  p = XALLOCAVEC (char, size);
> +  memset (p, 1, size);
> +  coeff = c_readstr (p, mode);
> +
> +  target = convert_to_mode (mode, data, 1);
> +  target = expand_mult (mode, target, coeff, NULL_RTX, 1);


Note this formula does not work for data = -1 for instance,
since 0x01010101U * -1 = 0xFEFEFEFFU
but memset(str, n, -1) set it to 0xFFFFFFFFU, right?

So are we sure that the value of "data" is always in the range [0..255] ?


Bernd.