Re: [PATCH 2/2] rs6000: Refine integer comparison handlings in rs6000_emit_vector_compare

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi Segher,

Thanks for the comments!

on 2022/11/17 02:58, Segher Boessenkool wrote:
> Hi!
> 
> On Wed, Nov 16, 2022 at 02:51:04PM +0800, Kewen.Lin wrote:
>> The current handlings in rs6000_emit_vector_compare is a bit
>> complicated to me, especially after we emit vector float
>> comparison insn with the given code directly.  This patch is
>> to refine the handlings for vector integer comparison operators,
>> it becomes not recursive, and we don't need the helper function
>> rs6000_emit_vector_compare_inner any more.
> 
> That sounds nice.
> 
>>    /* In vector.md, we support all kinds of vector float point
>>       comparison operators in a comparison rtl pattern, we can
>>       just emit the comparison rtx insn directly here.  Besides,
>>       we should have a centralized place to handle the possibility
>> -     of raising invalid exception.  */
>> -  if (GET_MODE_CLASS (dmode) == MODE_VECTOR_FLOAT)
>> +     of raising invalid exception.  Also emit directly for vector
>> +     integer comparison operators EQ/GT/GTU.  */
>> +  if (GET_MODE_CLASS (dmode) == MODE_VECTOR_FLOAT
>> +      || rcode == EQ
>> +      || rcode == GT
>> +      || rcode == GTU)
> 
> The comment still says it handles FP only.  That would be best to keep
> imo: add a separate block of code to handle the integer stuff you want
> to add.  You get the same or better generated code, the compiler is
> smart enough.  Code is for the user to read, and C is not a portable
> assembler language.

OK, I'll make two blocks for FP and integer respectively.  I struggled
a bit updating this hunk with comments for integer comparison
consideration, someone could argue that both can share the same handling
if updating the condition.

> 
> This whole series needs to be factored better, it does way too many
> things, and only marginally related things, at every step.  Or I don't
> see it anyway :-)

OK, I was thinking patch 1/2 is to unify the current vector float
comparison handlings, patch 2/2 is to refine the remaining handlings
for vector integer comparison.  I'm pleased to factor it better, any
suggestions on concrete code is highly appreciated.  :)

btw, I constructed one test case as below, there is no assembly change
before and after this patch.

#define GT(a, b) (((a) > (b)))
#define GE(a, b) (((a) >= (b)))
#define LT(a, b) (((a) < (b)))
#define LE(a, b) (((a) <= (b)))
#define EQ(a, b) (((a) == (b)))
#define NE(a, b) (((a) != (b)))

#define TEST_VECT(NAME, TYPE)                                                  \
  __attribute__ ((noipa)) void test_##NAME##_##TYPE (TYPE *x, TYPE *y,         \
                                                     int *res, int n)          \
  {                                                                            \
    for (int i = 0; i < n; i++)                                                \
      res[i] = NAME (x[i], y[i]);                                              \
  }

#include "stdint.h"

#define TEST(TYPE)                                                             \
  TEST_VECT (GT, TYPE)                                                         \
  TEST_VECT (GE, TYPE)                                                         \
  TEST_VECT (LT, TYPE)                                                         \
  TEST_VECT (LE, TYPE)                                                         \
  TEST_VECT (EQ, TYPE)                                                         \
  TEST_VECT (NE, TYPE)

TEST (int64_t)
TEST (uint64_t)
TEST (int32_t)
TEST (uint32_t)
TEST (int16_t)
TEST (uint16_t)
TEST (int8_t)
TEST (uint8_t)



BR,
Kewen