Re: [PATCH] Vectorizing abs(char/short/int) on x86.

[Richard Biener <richard dot guenther at gmail dot com>]

On Wed, Oct 23, 2013 at 5:11 AM,  <pinskia@gmail.com> wrote:
>
>
> Sent from my iPad
>
>> On Oct 22, 2013, at 7:23 PM, Cong Hou <congh@google.com> wrote:
>>
>> This patch aims at PR58762.
>>
>> Currently GCC could not vectorize abs() operation for integers on x86
>> with only SSE2 support. For int type, the reason is that the expand on
>> abs() is not defined for vector type. This patch defines such an
>> expand so that abs(int) will be vectorized with only SSE2.
>>
>> For abs(char/short), type conversions are needed as the current abs()
>> function/operation does not accept argument of char/short type.
>> Therefore when we want to get the absolute value of a char_val using
>> abs (char_val), it will be converted into abs ((int) char_val). It
>> then can be vectorized, but the generated code is not efficient as
>> lots of packings and unpackings are envolved. But if we convert
>> (char) abs ((int) char_val) to abs (char_val), the vectorizer will be
>> able to generate better code. Same for short.
>>
>> This conversion also enables vectorizing abs(char/short) operation
>> with PABSB and PABSW instructions in SSE3.
>>
>> With only SSE2 support, I developed three methods to expand
>> abs(char/short/int) seperately:
>>
>> 1. For 32 bit int value x, we can get abs (x) from (((signed) x >>
>> (W-1)) ^ x) - ((signed) x >> (W-1)). This is better than max (x, -x),
>> which needs bit masking.
>>
>> 2. For 16 bit int value x, we can get abs (x) from max (x, -x), as
>> SSE2 provides PMAXSW instruction.
>>
>> 3. For 8 bit int value x, we can get abs (x) from min ((unsigned char)
>> x, (unsigned char) (-x)), as SSE2 provides PMINUB instruction.
>>
>>
>> The patch is pasted below. Please point out any problem in my patch
>> and analysis.
>>
>>
>> thanks,
>> Cong
>>
>>
>>
>>
>> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
>> index 8a38316..e0f33ee 100644
>> --- a/gcc/ChangeLog
>> +++ b/gcc/ChangeLog
>> @@ -1,3 +1,13 @@
>> +2013-10-22  Cong Hou  <congh@google.com>
>> +
>> + PR target/58762
>> + * convert.c (convert_to_integer): Convert (char) abs ((int) char_val)
>> + into abs (char_val).  Also convert (short) abs ((int) short_val)
>> + into abs (short_val).
>
> I don't like this optimization in convert.  I think it should be submitted separately and should be done in tree-ssa-forwprop.
>
> Also I think you should have a generic (non x86) test case for the above optimization.

I agree.

Richard.

> Thanks,
> Andrew
>
>
>> + * config/i386/i386-protos.h (ix86_expand_sse2_absvxsi2): New function.
>> + * config/i386/i386.c (ix86_expand_sse2_absvxsi2): New function.
>> + * config/i386/sse.md: Add SSE2 support to abs (char/int/short).
>
>
>
>> +
>> 2013-10-14  David Malcolm  <dmalcolm@redhat.com>
>>
>>  * dumpfile.h (gcc::dump_manager): New class, to hold state
>> diff --git a/gcc/config/i386/i386-protos.h b/gcc/config/i386/i386-protos.h
>> index 3ab2f3a..e85f663 100644
>> --- a/gcc/config/i386/i386-protos.h
>> +++ b/gcc/config/i386/i386-protos.h
>> @@ -238,6 +238,7 @@ extern void ix86_expand_mul_widen_evenodd (rtx,
>> rtx, rtx, bool, bool);
>> extern void ix86_expand_mul_widen_hilo (rtx, rtx, rtx, bool, bool);
>> extern void ix86_expand_sse2_mulv4si3 (rtx, rtx, rtx);
>> extern void ix86_expand_sse2_mulvxdi3 (rtx, rtx, rtx);
>> +extern void ix86_expand_sse2_absvxsi2 (rtx, rtx);
>>
>> /* In i386-c.c  */
>> extern void ix86_target_macros (void);
>> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
>> index 02cbbbd..8050e02 100644
>> --- a/gcc/config/i386/i386.c
>> +++ b/gcc/config/i386/i386.c
>> @@ -41696,6 +41696,53 @@ ix86_expand_sse2_mulvxdi3 (rtx op0, rtx op1, rtx op2)
>>        gen_rtx_MULT (mode, op1, op2));
>> }
>>
>> +void
>> +ix86_expand_sse2_absvxsi2 (rtx op0, rtx op1)
>> +{
>> +  enum machine_mode mode = GET_MODE (op0);
>> +  rtx tmp0, tmp1;
>> +
>> +  switch (mode)
>> +    {
>> +      /* For 32-bit signed integer X, the best way to calculate the absolute
>> + value of X is (((signed) X >> (W-1)) ^ X) - ((signed) X >> (W-1)).  */
>> +      case V4SImode:
>> + tmp0 = expand_simple_binop (mode, ASHIFTRT, op1,
>> +    GEN_INT (GET_MODE_BITSIZE
>> + (GET_MODE_INNER (mode)) - 1),
>> +    NULL, 0, OPTAB_DIRECT);
>> + if (tmp0)
>> +  tmp1 = expand_simple_binop (mode, XOR, op1, tmp0,
>> +      NULL, 0, OPTAB_DIRECT);
>> + if (tmp0 && tmp1)
>> +  expand_simple_binop (mode, MINUS, tmp1, tmp0,
>> +       op0, 0, OPTAB_DIRECT);
>> + break;
>> +
>> +      /* For 16-bit signed integer X, the best way to calculate the absolute
>> + value of X is max (X, -X), as SSE2 provides the PMAXSW insn.  */
>> +      case V8HImode:
>> + tmp0 = expand_unop (mode, neg_optab, op1, NULL_RTX, 0);
>> + if (tmp0)
>> +  expand_simple_binop (mode, SMAX, op1, tmp0, op0, 0,
>> +       OPTAB_DIRECT);
>> + break;
>> +
>> +      /* For 8-bit signed integer X, the best way to calculate the absolute
>> + value of X is min ((unsigned char) X, (unsigned char) (-X)),
>> + as SSE2 provides the PMINUB insn.  */
>> +      case V16QImode:
>> + tmp0 = expand_unop (mode, neg_optab, op1, NULL_RTX, 0);
>> + if (tmp0)
>> +  expand_simple_binop (V16QImode, UMIN, op1, tmp0, op0, 0,
>> +       OPTAB_DIRECT);
>> + break;
>> +
>> +      default:
>> + break;
>> +    }
>> +}
>> +
>> /* Expand an insert into a vector register through pinsr insn.
>>    Return true if successful.  */
>>
>> diff --git a/gcc/config/i386/sse.md b/gcc/config/i386/sse.md
>> index c3f6c94..bd90f2d 100644
>> --- a/gcc/config/i386/sse.md
>> +++ b/gcc/config/i386/sse.md
>> @@ -8721,7 +8721,7 @@
>>    (set (attr "prefix_rex") (symbol_ref "x86_extended_reg_mentioned_p (insn)"))
>>    (set_attr "mode" "DI")])
>>
>> -(define_insn "abs<mode>2"
>> +(define_insn "*abs<mode>2"
>>   [(set (match_operand:VI124_AVX2_48_AVX512F 0 "register_operand" "=v")
>>  (abs:VI124_AVX2_48_AVX512F
>>   (match_operand:VI124_AVX2_48_AVX512F 1 "nonimmediate_operand" "vm")))]
>> @@ -8733,6 +8733,20 @@
>>    (set_attr "prefix" "maybe_vex")
>>    (set_attr "mode" "<sseinsnmode>")])
>>
>> +(define_expand "abs<mode>2"
>> +  [(set (match_operand:VI124_AVX2_48_AVX512F 0 "register_operand")
>> + (abs:VI124_AVX2_48_AVX512F
>> +  (match_operand:VI124_AVX2_48_AVX512F 1 "register_operand")))]
>> +  "TARGET_SSE2"
>> +{
>> +  if (TARGET_SSE2 && !TARGET_SSSE3)
>> +    ix86_expand_sse2_absvxsi2 (operands[0], operands[1]);
>> +  else if (TARGET_SSSE3)
>> +    emit_insn (gen_rtx_SET (VOIDmode, operands[0],
>> +    gen_rtx_ABS (<MODE>mode, operands[1])));
>> +  DONE;
>> +})
>> +
>> (define_insn "abs<mode>2"
>>   [(set (match_operand:MMXMODEI 0 "register_operand" "=y")
>>  (abs:MMXMODEI
>> diff --git a/gcc/convert.c b/gcc/convert.c
>> index b07f0ef..8c60038 100644
>> --- a/gcc/convert.c
>> +++ b/gcc/convert.c
>> @@ -798,6 +798,20 @@ convert_to_integer (tree type, tree expr)
>>       ? TREE_OPERAND (expr, 2)
>>       : convert (type, TREE_OPERAND (expr, 2)));
>>
>> + case ABS_EXPR:
>> +  {
>> +    /* Convert (char) abs ((int) char_val) into abs (char_val).
>> +       Convert (short) abs ((int) short_val) into abs (short_val).  */
>> +    tree op = TREE_OPERAND (expr, 0);
>> +    if (optimize && CONVERT_EXPR_P (op))
>> +      {
>> + tree op2 = TREE_OPERAND (op, 0);
>> + if (TREE_TYPE (op2) == type)
>> +  return build1 (TREE_CODE (expr), type, op2);
>> +      }
>> +    break;
>> +  }
>> +
>>  default:
>>   break;
>>  }
>> diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
>> index 075d071..cf5b942 100644
>> --- a/gcc/testsuite/ChangeLog
>> +++ b/gcc/testsuite/ChangeLog
>> @@ -1,3 +1,8 @@
>> +2013-10-22  Cong Hou  <congh@google.com>
>> +
>> + PR target/58762
>> + * gcc.dg/vect/pr58762.c: New test.
>> +
>> 2013-10-14  Tobias Burnus  <burnus@net-b.de>
>>
>>  PR fortran/58658
>> diff --git a/gcc/testsuite/gcc.dg/vect/pr58762.c
>> b/gcc/testsuite/gcc.dg/vect/pr58762.c
>> new file mode 100644
>> index 0000000..4e62de6
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/vect/pr58762.c
>> @@ -0,0 +1,27 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -ftree-vectorize" } */
>> +
>> +void test1 (char* a, char* b)
>> +{
>> +  int i;
>> +  for (i = 0; i < 10000; ++i)
>> +    a[i] = abs (b[i]);
>> +}
>> +
>> +void test2 (short* a, short* b)
>> +{
>> +  int i;
>> +  for (i = 0; i < 10000; ++i)
>> +    a[i] = abs (b[i]);
>> +}
>> +
>> +void test3 (int* a, int* b)
>> +{
>> +  int i;
>> +  for (i = 0; i < 10000; ++i)
>> +    a[i] = abs (b[i]);
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 3 "vect"
>> +       { target i?86-*-* x86_64-*-* ia64-*-* } } } */
>> +/* { dg-final { cleanup-tree-dump "vect" } } */
>> <patch-abs.txt>