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Re: [PATCH v2 3/9] Introduce can_vector_compare_p function


> Am 26.08.2019 um 15:06 schrieb Richard Biener <richard.guenther@gmail.com>:
> 
> On Mon, Aug 26, 2019 at 1:54 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>> 
>>> Am 26.08.2019 um 10:49 schrieb Richard Biener <richard.guenther@gmail.com>:
>>> 
>>> On Fri, Aug 23, 2019 at 1:35 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>>>> 
>>>>> Am 23.08.2019 um 13:24 schrieb Richard Biener <richard.guenther@gmail.com>:
>>>>> 
>>>>> On Fri, Aug 23, 2019 at 12:43 PM Richard Sandiford
>>>>> <richard.sandiford@arm.com> wrote:
>>>>>> 
>>>>>> Ilya Leoshkevich <iii@linux.ibm.com> writes:
>>>>>>> @@ -3819,6 +3820,82 @@ can_compare_p (enum rtx_code code, machine_mode mode,
>>>>>>> return 0;
>>>>>>> }
>>>>>>> 
>>>>>>> +/* can_vector_compare_p presents fake rtx binary operations to the the back-end
>>>>>>> +   in order to determine its capabilities.  In order to avoid creating fake
>>>>>>> +   operations on each call, values from previous calls are cached in a global
>>>>>>> +   cached_binops hash_table.  It contains rtxes, which can be looked up using
>>>>>>> +   binop_keys.  */
>>>>>>> +
>>>>>>> +struct binop_key {
>>>>>>> +  enum rtx_code code;        /* Operation code.  */
>>>>>>> +  machine_mode value_mode;   /* Result mode.     */
>>>>>>> +  machine_mode cmp_op_mode;  /* Operand mode.    */
>>>>>>> +};
>>>>>>> +
>>>>>>> +struct binop_hasher : pointer_hash_mark<rtx>, ggc_cache_remove<rtx> {
>>>>>>> +  typedef rtx value_type;
>>>>>>> +  typedef binop_key compare_type;
>>>>>>> +
>>>>>>> +  static hashval_t
>>>>>>> +  hash (enum rtx_code code, machine_mode value_mode, machine_mode cmp_op_mode)
>>>>>>> +  {
>>>>>>> +    inchash::hash hstate (0);
>>>>>>> +    hstate.add_int (code);
>>>>>>> +    hstate.add_int (value_mode);
>>>>>>> +    hstate.add_int (cmp_op_mode);
>>>>>>> +    return hstate.end ();
>>>>>>> +  }
>>>>>>> +
>>>>>>> +  static hashval_t
>>>>>>> +  hash (const rtx &ref)
>>>>>>> +  {
>>>>>>> +    return hash (GET_CODE (ref), GET_MODE (ref), GET_MODE (XEXP (ref, 0)));
>>>>>>> +  }
>>>>>>> +
>>>>>>> +  static bool
>>>>>>> +  equal (const rtx &ref1, const binop_key &ref2)
>>>>>>> +  {
>>>>>>> +    return (GET_CODE (ref1) == ref2.code)
>>>>>>> +        && (GET_MODE (ref1) == ref2.value_mode)
>>>>>>> +        && (GET_MODE (XEXP (ref1, 0)) == ref2.cmp_op_mode);
>>>>>>> +  }
>>>>>>> +};
>>>>>>> +
>>>>>>> +static GTY ((cache)) hash_table<binop_hasher> *cached_binops;
>>>>>>> +
>>>>>>> +static rtx
>>>>>>> +get_cached_binop (enum rtx_code code, machine_mode value_mode,
>>>>>>> +               machine_mode cmp_op_mode)
>>>>>>> +{
>>>>>>> +  if (!cached_binops)
>>>>>>> +    cached_binops = hash_table<binop_hasher>::create_ggc (1024);
>>>>>>> +  binop_key key = { code, value_mode, cmp_op_mode };
>>>>>>> +  hashval_t hash = binop_hasher::hash (code, value_mode, cmp_op_mode);
>>>>>>> +  rtx *slot = cached_binops->find_slot_with_hash (key, hash, INSERT);
>>>>>>> +  if (!*slot)
>>>>>>> +    *slot = gen_rtx_fmt_ee (code, value_mode, gen_reg_rtx (cmp_op_mode),
>>>>>>> +                         gen_reg_rtx (cmp_op_mode));
>>>>>>> +  return *slot;
>>>>>>> +}
>>>>>> 
>>>>>> Sorry, I didn't mean anything this complicated.  I just meant that
>>>>>> we should have a single cached rtx that we can change via PUT_CODE and
>>>>>> PUT_MODE_RAW for each new query, rather than allocating a new rtx each
>>>>>> time.
>>>>>> 
>>>>>> Something like:
>>>>>> 
>>>>>> static GTY ((cache)) rtx cached_binop;
>>>>>> 
>>>>>> rtx
>>>>>> get_cached_binop (machine_mode mode, rtx_code code, machine_mode op_mode)
>>>>>> {
>>>>>> if (cached_binop)
>>>>>>  {
>>>>>>    PUT_CODE (cached_binop, code);
>>>>>>    PUT_MODE_RAW (cached_binop, mode);
>>>>>>    PUT_MODE_RAW (XEXP (cached_binop, 0), op_mode);
>>>>>>    PUT_MODE_RAW (XEXP (cached_binop, 1), op_mode);
>>>>>>  }
>>>>>> else
>>>>>>  {
>>>>>>    rtx reg1 = gen_raw_REG (op_mode, LAST_VIRTUAL_REGISTER + 1);
>>>>>>    rtx reg2 = gen_raw_REG (op_mode, LAST_VIRTUAL_REGISTER + 2);
>>>>>>    cached_binop = gen_rtx_fmt_ee (code, mode, reg1, reg2);
>>>>>>  }
>>>>>> return cached_binop;
>>>>>> }
>>>>> 
>>>>> Hmm, maybe we need  auto_rtx (code) that constructs such
>>>>> RTX on the stack instead of wasting a GC root (and causing
>>>>> issues for future threading of GCC ;)).
>>>> 
>>>> Do you mean something like this?
>>>> 
>>>> union {
>>>> char raw[rtx_code_size[code]];
>>>> rtx rtx;
>>>> } binop;
>>>> 
>>>> Does this exist already (git grep auto.*rtx / rtx.*auto doesn't show
>>>> anything useful), or should I implement this?
>>> 
>>> It doesn't exist AFAIK, I thought about using alloca like
>>> 
>>> rtx tem;
>>> rtx_alloca (tem, PLUS);
>>> 
>>> and due to using alloca rtx_alloca has to be a macro like
>>> 
>>> #define rtx_alloca(r, code) r = (rtx)alloca (RTX_CODE_SIZE(code));
>>> memset (r, 0, RTX_HDR_SIZE); PUT_CODE (r, code);
>>> 
>>> maybe C++ can help making this prettier but of course
>>> since we use alloca we have to avoid opening new scopes.
>>> 
>>> I guess templates like with auto_vec doesn't work unless
>>> we can make RTX_CODE_SIZE constant-evaluated.
>>> 
>>> Richard.
>> 
>> I ended up with the following change:
>> 
>> diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
>> index a667cdab94e..97aa2144e95 100644
>> --- a/gcc/emit-rtl.c
>> +++ b/gcc/emit-rtl.c
>> @@ -466,17 +466,25 @@ set_mode_and_regno (rtx x, machine_mode mode, unsigned int regno)
>>   set_regno_raw (x, regno, nregs);
>> }
>> 
>> -/* Generate a new REG rtx.  Make sure ORIGINAL_REGNO is set properly, and
>> +/* Initialize a REG rtx.  Make sure ORIGINAL_REGNO is set properly, and
>>    don't attempt to share with the various global pieces of rtl (such as
>>    frame_pointer_rtx).  */
>> 
>> -rtx
>> -gen_raw_REG (machine_mode mode, unsigned int regno)
>> +void
>> +init_raw_REG (rtx x, machine_mode mode, unsigned int regno)
>> {
>> -  rtx x = rtx_alloc (REG MEM_STAT_INFO);
>>   set_mode_and_regno (x, mode, regno);
>>   REG_ATTRS (x) = NULL;
>>   ORIGINAL_REGNO (x) = regno;
>> +}
>> +
>> +/* Generate a new REG rtx.  */
>> +
>> +rtx
>> +gen_raw_REG (machine_mode mode, unsigned int regno)
>> +{
>> +  rtx x = rtx_alloc (REG MEM_STAT_INFO);
>> +  init_raw_REG (x, mode, regno);
>>   return x;
>> }
>> 
>> diff --git a/gcc/gengenrtl.c b/gcc/gengenrtl.c
>> index 5c78fabfb50..bb2087da258 100644
>> --- a/gcc/gengenrtl.c
>> +++ b/gcc/gengenrtl.c
>> @@ -231,8 +231,7 @@ genmacro (int idx)
>>   puts (")");
>> }
>> 
>> -/* Generate the code for the function to generate RTL whose
>> -   format is FORMAT.  */
>> +/* Generate the code for functions to generate RTL whose format is FORMAT.  */
>> 
>> static void
>> gendef (const char *format)
>> @@ -240,22 +239,18 @@ gendef (const char *format)
>>   const char *p;
>>   int i, j;
>> 
>> -  /* Start by writing the definition of the function name and the types
>> +  /* Write the definition of the init function name and the types
>>      of the arguments.  */
>> 
>> -  printf ("static inline rtx\ngen_rtx_fmt_%s_stat (RTX_CODE code, machine_mode mode", format);
>> +  puts ("static inline void");
>> +  printf ("init_rtx_fmt_%s (rtx rt, machine_mode mode", format);
>>   for (p = format, i = 0; *p != 0; p++)
>>     if (*p != '0')
>>       printf (",\n\t%sarg%d", type_from_format (*p), i++);
>> +  puts (")");
>> 
>> -  puts (" MEM_STAT_DECL)");
>> -
>> -  /* Now write out the body of the function itself, which allocates
>> -     the memory and initializes it.  */
>> +  /* Now write out the body of the init function itself.  */
>>   puts ("{");
>> -  puts ("  rtx rt;");
>> -  puts ("  rt = rtx_alloc (code PASS_MEM_STAT);\n");
>> -
>>   puts ("  PUT_MODE_RAW (rt, mode);");
>> 
>>   for (p = format, i = j = 0; *p ; ++p, ++i)
>> @@ -266,16 +261,56 @@ gendef (const char *format)
>>     else
>>       printf ("  %s (rt, %d) = arg%d;\n", accessor_from_format (*p), i, j++);
>> 
>> -  puts ("\n  return rt;\n}\n");
>> +  puts ("}\n");
>> +
>> +  /* Write the definition of the gen function name and the types
>> +     of the arguments.  */
>> +
>> +  puts ("static inline rtx");
>> +  printf ("gen_rtx_fmt_%s_stat (RTX_CODE code, machine_mode mode", format);
>> +  for (p = format, i = 0; *p != 0; p++)
>> +    if (*p != '0')
>> +      printf (",\n\t%sarg%d", type_from_format (*p), i++);
>> +  puts (" MEM_STAT_DECL)");
>> +
>> +  /* Now write out the body of the function itself, which allocates
>> +     the memory and initializes it.  */
>> +  puts ("{");
>> +  puts ("  rtx rt;\n");
>> +
>> +  puts ("  rt = rtx_alloc (code PASS_MEM_STAT);");
>> +  printf ("  init_rtx_fmt_%s (rt, mode", format);
>> +  for (p = format, i = 0; *p != 0; p++)
>> +    if (*p != '0')
>> +      printf (", arg%d", i++);
>> +  puts (");\n");
>> +
>> +  puts ("  return rt;\n}\n");
>> +
>> +  /* Write the definition of gen macro.  */
>> +
>>   printf ("#define gen_rtx_fmt_%s(c, m", format);
>>   for (p = format, i = 0; *p != 0; p++)
>>     if (*p != '0')
>> -      printf (", p%i",i++);
>> -  printf (")\\\n        gen_rtx_fmt_%s_stat (c, m", format);
>> +      printf (", arg%d", i++);
>> +  printf (") \\\n  gen_rtx_fmt_%s_stat ((c), (m)", format);
>>   for (p = format, i = 0; *p != 0; p++)
>>     if (*p != '0')
>> -      printf (", p%i",i++);
>> +      printf (", (arg%d)", i++);
>>   printf (" MEM_STAT_INFO)\n\n");
>> +
>> +  /* Write the definition of alloca macro.  */
>> +
>> +  printf ("#define alloca_rtx_fmt_%s(rt, c, m", format);
>> +  for (p = format, i = 0; *p != 0; p++)
>> +    if (*p != '0')
>> +      printf (", arg%d", i++);
>> +  printf (") \\\n  rtx_alloca ((rt), (c)); \\\n");
>> +  printf ("  init_rtx_fmt_%s ((rt), (m)", format);
>> +  for (p = format, i = 0; *p != 0; p++)
>> +    if (*p != '0')
>> +      printf (", (arg%d)", i++);
>> +  printf (")\n\n");
>> }
>> 
>> /* Generate the documentation header for files we write.  */
>> diff --git a/gcc/rtl.h b/gcc/rtl.h
>> index efb9b3ce40d..44733d8a39e 100644
>> --- a/gcc/rtl.h
>> +++ b/gcc/rtl.h
>> @@ -2933,6 +2933,10 @@ extern HOST_WIDE_INT get_stack_check_protect (void);
>> 
>> /* In rtl.c */
>> extern rtx rtx_alloc (RTX_CODE CXX_MEM_STAT_INFO);
>> +#define rtx_alloca(rt, code) \
>> +  (rt) = (rtx) alloca (RTX_CODE_SIZE ((code))); \
>> +  memset ((rt), 0, RTX_HDR_SIZE); \
>> +  PUT_CODE ((rt), (code));
>> extern rtx rtx_alloc_stat_v (RTX_CODE MEM_STAT_DECL, int);
>> #define rtx_alloc_v(c, SZ) rtx_alloc_stat_v (c MEM_STAT_INFO, SZ)
>> #define const_wide_int_alloc(NWORDS)                           \
>> @@ -3797,7 +3801,11 @@ gen_rtx_INSN (machine_mode mode, rtx_insn *prev_insn, rtx_insn *next_insn,
>> extern rtx gen_rtx_CONST_INT (machine_mode, HOST_WIDE_INT);
>> extern rtx gen_rtx_CONST_VECTOR (machine_mode, rtvec);
>> extern void set_mode_and_regno (rtx, machine_mode, unsigned int);
>> +extern void init_raw_REG (rtx, machine_mode, unsigned int);
>> extern rtx gen_raw_REG (machine_mode, unsigned int);
>> +#define alloca_raw_REG(rt, mode, regno) \
>> +  rtx_alloca ((rt), REG); \
>> +  init_raw_REG ((rt), (mode), (regno))
>> extern rtx gen_rtx_REG (machine_mode, unsigned int);
>> extern rtx gen_rtx_SUBREG (machine_mode, rtx, poly_uint64);
>> extern rtx gen_rtx_MEM (machine_mode, rtx);
>> 
>> which now allows me to write:
>> 
>> rtx reg1, reg2, test;
>> alloca_raw_REG (reg1, cmp_op_mode, LAST_VIRTUAL_REGISTER + 1);
>> alloca_raw_REG (reg2, cmp_op_mode, LAST_VIRTUAL_REGISTER + 2);
>> alloca_rtx_fmt_ee (test, code, value_mode, reg1, reg2);
>> 
>> If that looks ok, I'll resend the series.
> 
> that looks OK to me - please leave Richard S. time to comment.  Also while
> I'd like to see
> 
> rtx reg1 = alloca_raw_REG (cmp_op_mode, LAST_VIRTUAL_REGISTER + 1);
> 
> I don't really see a way to write that portably (or at all), do you all agree?
> GCC doesn't seem to convert alloca() calls to __builtin_stack_save/restore
> nor place CLOBBERs to end their lifetime.  But is it guaranteed that the
> alloca result is valid until frame termination?

Hmm, the alloca man page says:

       The alloca() function allocates size bytes of space in the stack
       frame of the caller.  This temporary space is automatically freed
       when the function that called alloca() returns to its caller.
...
       The space allocated by alloca() is not automatically deallocated if
       the pointer that refers to it simply goes out of scope.

A quick experiment with gcc and clang confirms this.  I think this means
I can make alloca_raw_REG macro return the allocated pointer using the
return-from-block GNU extension.


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