Add RTX codes for BITREVERSE and COPYSIGN.

  An analysis of backend UNSPECs reveals that two of the most common UNSPECs
across target backends are for copysign and bit reversal.  This patch
adds RTX codes for these expressions to allow their representation to
be standardized, and them to optimized by the middle-end RTL optimizers.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-32} with
no new failures.  Ok for mainline?


2023-05-06  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        * doc/rtl.texi (bitreverse, copysign): Document new RTX codes.
        * rtl.def (BITREVERSE, COPYSIGN): Define new RTX codes.
        * simplify-rtx.cc (simplify_unary_operation_1): Optimize
        NOT (BITREVERSE x) as BITREVERSE (NOT x).
        Optimize POPCOUNT (BITREVERSE x) as POPCOUNT x.
        Optimize PARITY (BITREVERSE x) as PARITY x.
        Optimize BITREVERSE (BITREVERSE x) as x.
        (simplify_const_unary_operation) <case BITREVERSE>: Evaluate
        BITREVERSE of a constant integer at compile-time.
        (simplify_binary_operation_1) <case COPYSIGN>:  Optimize
        COPY_SIGN (x, x) as x.  Optimize COPYSIGN (x, C) as ABS x
        or NEG (ABS x) for constant C.  Optimize COPYSIGN (ABS x, y)
        and COPYSIGN (NEG x, y) as COPYSIGN (x, y).  Optimize
        COPYSIGN (x, ABS y) as ABS x.
        Optimize COPYSIGN (COPYSIGN (x, y), z) as COPYSIGN (x, z).
        Optimize COPYSIGN (x, COPYSIGN (y, z)) as COPYSIGN (x, z).
        (simplify_const_binary_operation): Evaluate COPYSIGN of constant
        arguments at compile-time.
        * wide-int.cc (wide_int_storage::bitreverse): Provide a
        wide_int implementation, based upon bswap implementation.
        * wide-int.g (wide_int_storage::bitreverse): Prototype here.


Thanks in advance,
Roger
--
  

On Sat, 6 May 2023, Roger Sayle wrote:

> An analysis of backend UNSPECs reveals that two of the most common UNSPECs
> across target backends are for copysign and bit reversal.  This patch
> adds RTX codes for these expressions to allow their representation to
> be standardized, and them to optimized by the middle-end RTL optimizers.

Note we have bug 50481 requesting (target-independent) built-in functions 
for bit reversal (so this patch could be useful as a basis for 
implementing such built-in functions, with appropriate lowering or libgcc 
implementation for targets without relevant instructions).
  

"Roger Sayle" <roger@nextmovesoftware.com> writes:
> An analysis of backend UNSPECs reveals that two of the most common UNSPECs
> across target backends are for copysign and bit reversal.  This patch
> adds RTX codes for these expressions to allow their representation to
> be standardized, and them to optimized by the middle-end RTL optimizers.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-32} with
> no new failures.  Ok for mainline?
>
>
> 2023-05-06  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         * doc/rtl.texi (bitreverse, copysign): Document new RTX codes.
>         * rtl.def (BITREVERSE, COPYSIGN): Define new RTX codes.
>         * simplify-rtx.cc (simplify_unary_operation_1): Optimize
>         NOT (BITREVERSE x) as BITREVERSE (NOT x).
>         Optimize POPCOUNT (BITREVERSE x) as POPCOUNT x.
>         Optimize PARITY (BITREVERSE x) as PARITY x.
>         Optimize BITREVERSE (BITREVERSE x) as x.
>         (simplify_const_unary_operation) <case BITREVERSE>: Evaluate
>         BITREVERSE of a constant integer at compile-time.
>         (simplify_binary_operation_1) <case COPYSIGN>:  Optimize
>         COPY_SIGN (x, x) as x.  Optimize COPYSIGN (x, C) as ABS x
>         or NEG (ABS x) for constant C.  Optimize COPYSIGN (ABS x, y)
>         and COPYSIGN (NEG x, y) as COPYSIGN (x, y).  Optimize
>         COPYSIGN (x, ABS y) as ABS x.
>         Optimize COPYSIGN (COPYSIGN (x, y), z) as COPYSIGN (x, z).
>         Optimize COPYSIGN (x, COPYSIGN (y, z)) as COPYSIGN (x, z).
>         (simplify_const_binary_operation): Evaluate COPYSIGN of constant
>         arguments at compile-time.
>         * wide-int.cc (wide_int_storage::bitreverse): Provide a
>         wide_int implementation, based upon bswap implementation.
>         * wide-int.g (wide_int_storage::bitreverse): Prototype here.
>
>
> Thanks in advance,
> Roger
> --
>
> diff --git a/gcc/doc/rtl.texi b/gcc/doc/rtl.texi
> index 1de2494..76aeafb 100644
> --- a/gcc/doc/rtl.texi
> +++ b/gcc/doc/rtl.texi
> @@ -2742,6 +2742,17 @@ integer of mode @var{m}.  The mode of @var{x} must be @var{m} or
>  Represents the value @var{x} with the order of bytes reversed, carried out
>  in mode @var{m}, which must be a fixed-point machine mode.
>  The mode of @var{x} must be @var{m} or @code{VOIDmode}.
> +
> +@findex bitreverse
> +@item (bitreverse:@var{m} @var{x})
> +Represents the value @var{x} with the order of bits reversed, carried out
> +in mode @var{m}, which must be a fixed-point machine mode.
> +The mode of @var{x} must be @var{m} or @code{VOIDmode}.
> +
> +@findex copysign
> +@item (copysign:@var{m} @var{x} @var{y})
> +Represents the value @var{x} with the sign of @var{y}.
> +Both @var{x} and @var{y} must have floating point machine mode @var{m}.
>  @end table
>  
>  @node Comparisons
> diff --git a/gcc/rtl.def b/gcc/rtl.def
> index 6ddbce3..88e2b19 100644
> --- a/gcc/rtl.def
> +++ b/gcc/rtl.def
> @@ -664,6 +664,9 @@ DEF_RTL_EXPR(POPCOUNT, "popcount", "e", RTX_UNARY)
>  /* Population parity (number of 1 bits modulo 2).  */
>  DEF_RTL_EXPR(PARITY, "parity", "e", RTX_UNARY)
>  
> +/* Reverse bits.  */
> +DEF_RTL_EXPR(BITREVERSE, "bitreverse", "e", RTX_UNARY)
> +
>  /* Reference to a signed bit-field of specified size and position.
>     Operand 0 is the memory unit (usually SImode or QImode) which
>     contains the field's first bit.  Operand 1 is the width, in bits.
> @@ -753,6 +756,9 @@ DEF_RTL_EXPR(US_TRUNCATE, "us_truncate", "e", RTX_UNARY)
>  /* Floating point multiply/add combined instruction.  */
>  DEF_RTL_EXPR(FMA, "fma", "eee", RTX_TERNARY)
>  
> +/* Floating point copysign.  Operand 0 with the sign of operand 1.  */
> +DEF_RTL_EXPR(COPYSIGN, "copysign", "ee", RTX_BIN_ARITH)
> +
>  /* Information about the variable and its location.  */
>  DEF_RTL_EXPR(VAR_LOCATION, "var_location", "te", RTX_EXTRA)
>  
> diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
> index d4aeebc..26fa2b9 100644
> --- a/gcc/simplify-rtx.cc
> +++ b/gcc/simplify-rtx.cc
> @@ -1040,10 +1040,10 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
>  	}
>  
>        /* (not (bswap x)) -> (bswap (not x)).  */
> -      if (GET_CODE (op) == BSWAP)
> +      if (GET_CODE (op) == BSWAP || GET_CODE (op) == BITREVERSE)
>  	{
>  	  rtx x = simplify_gen_unary (NOT, mode, XEXP (op, 0), mode);
> -	  return simplify_gen_unary (BSWAP, mode, x, mode);
> +	  return simplify_gen_unary (GET_CODE (op), mode, x, mode);
>  	}
>        break;
>  
> @@ -1419,6 +1419,7 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
>        switch (GET_CODE (op))
>  	{
>  	case BSWAP:
> +	case BITREVERSE:
>  	  /* (popcount (bswap <X>)) = (popcount <X>).  */
>  	  return simplify_gen_unary (POPCOUNT, mode, XEXP (op, 0),
>  				     GET_MODE (XEXP (op, 0)));
> @@ -1448,6 +1449,7 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
>  	{
>  	case NOT:
>  	case BSWAP:
> +	case BITREVERSE:
>  	  return simplify_gen_unary (PARITY, mode, XEXP (op, 0),
>  				     GET_MODE (XEXP (op, 0)));
>  
> @@ -1481,6 +1483,12 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
>  	return XEXP (op, 0);
>        break;
>  
> +    case BITREVERSE:
> +      /* (bitreverse (bitreverse x)) -> x.  */
> +      if (GET_CODE (op) == BITREVERSE)
> +	return XEXP (op, 0);
> +      break;
> +
>      case FLOAT:
>        /* (float (sign_extend <X>)) = (float <X>).  */
>        if (GET_CODE (op) == SIGN_EXTEND)
> @@ -2114,6 +2122,10 @@ simplify_const_unary_operation (enum rtx_code code, machine_mode mode,
>  	  result = wide_int (op0).bswap ();
>  	  break;
>  
> +	case BITREVERSE:
> +	  result = wide_int (op0).bitreverse ();
> +	  break;
> +
>  	case TRUNCATE:
>  	case ZERO_EXTEND:
>  	  result = wide_int::from (op0, width, UNSIGNED);
> @@ -4355,6 +4367,31 @@ simplify_ashift:
>  	return op0;
>        return 0;
>  
> +    case COPYSIGN:
> +      if (rtx_equal_p (trueop0, trueop1) && ! side_effects_p (op0))
> +	return op0;
> +      if (CONST_DOUBLE_AS_FLOAT_P (trueop1))
> +	{
> +	  REAL_VALUE_TYPE f1;
> +	  real_convert (&f1, mode, CONST_DOUBLE_REAL_VALUE (trueop1));
> +	  rtx tmp = simplify_gen_unary (ABS, mode, op0, mode);
> +	  if (REAL_VALUE_NEGATIVE (f1))
> +	    tmp = simplify_gen_unary (NEG, mode, op0, mode);
> +	  return tmp;
> +	}
> +      if (GET_CODE (op0) == NEG || GET_CODE (op0) == ABS)
> +	return simplify_gen_binary (COPYSIGN, mode, XEXP (op0, 0), op1);
> +      if (GET_CODE (op1) == ABS
> +	  && ! side_effects_p (op1))
> +	return simplify_gen_unary (ABS, mode, op0, mode);
> +      if (GET_CODE (op0) == COPYSIGN
> +	  && ! side_effects_p (XEXP (op0, 1)))
> +	return simplify_gen_binary (COPYSIGN, mode, XEXP (op0, 0), op1);
> +      if (GET_CODE (op1) == COPYSIGN
> +	  && ! side_effects_p (XEXP (op1, 0)))
> +	return simplify_gen_binary (COPYSIGN, mode, op0, XEXP (op1, 1));
> +      return 0;
> +
>      case VEC_SERIES:
>        if (op1 == CONST0_RTX (GET_MODE_INNER (mode)))
>  	return gen_vec_duplicate (mode, op0);
> @@ -4995,6 +5032,14 @@ simplify_const_binary_operation (enum rtx_code code, machine_mode mode,
>  	   real_from_target (&r, tmp0, mode);
>  	   return const_double_from_real_value (r, mode);
>  	}
> +      else if (code == COPYSIGN)
> +	{
> +	  REAL_VALUE_TYPE f0, f1;
> +	  real_convert (&f0, mode, CONST_DOUBLE_REAL_VALUE (op0));
> +	  real_convert (&f1, mode, CONST_DOUBLE_REAL_VALUE (op1));
> +	  real_copysign (&f0, &f1);
> +	  return const_double_from_real_value (f0, mode);
> +	}
>        else
>  	{
>  	  REAL_VALUE_TYPE f0, f1, value, result;
> diff --git a/gcc/wide-int.cc b/gcc/wide-int.cc
> index 8c81757..280348d 100644
> --- a/gcc/wide-int.cc
> +++ b/gcc/wide-int.cc
> @@ -770,6 +770,80 @@ wide_int_storage::bswap () const
>    return result;
>  }
>  
> +/* bitreverse THIS.  */
> +wide_int
> +wide_int_storage::bitreverse () const
> +{
> +  static const unsigned char bitreverse_byte_table[256] = {
> +    0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
> +    0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
> +    0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
> +    0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8,
> +    0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4,
> +    0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
> +    0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec,
> +    0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc,
> +    0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
> +    0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2,
> +    0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea,
> +    0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
> +    0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6,
> +    0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6,
> +    0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
> +    0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe,
> +    0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1,
> +    0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
> +    0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9,
> +    0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9,
> +    0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
> +    0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5,
> +    0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed,
> +    0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
> +    0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3,
> +    0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3,
> +    0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
> +    0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb,
> +    0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7,
> +    0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
> +    0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef,
> +    0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff
> +  };
> +
> +  wide_int result = wide_int::create (precision);
> +  unsigned int i, s;
> +  unsigned int len = BLOCKS_NEEDED (precision);
> +  unsigned int xlen = get_len ();
> +  const HOST_WIDE_INT *xval = get_val ();
> +  HOST_WIDE_INT *val = result.write_val ();
> +
> +  /* This is not a well defined operation if the precision is not a
> +     multiple of 8.  */
> +  gcc_assert ((precision & 0x7) == 0);

I don't see why though.  If we used a naive loop instead of the LUT,
I think we could handle all precisions naturally.  And I wouldn't
have expected this operation to be common enough that the optimisation
is important.

> +
> +  for (i = 0; i < len; i++)
> +    val[i] = 0;
> +
> +  /* Only swap the bits that are not the padding.  */
> +  for (s = 0; s < precision; s += 8)
> +    {
> +      unsigned int d = precision - s - 8;
> +      unsigned HOST_WIDE_INT byte;
> +
> +      unsigned int block = s / HOST_BITS_PER_WIDE_INT;
> +      unsigned int offset = s & (HOST_BITS_PER_WIDE_INT - 1);
> +
> +      byte = (safe_uhwi (xval, xlen, block) >> offset) & 0xff;
> +
> +      block = d / HOST_BITS_PER_WIDE_INT;
> +      offset = d & (HOST_BITS_PER_WIDE_INT - 1);
> +
> +      val[block] |= bitreverse_byte_table[byte << offset];
> +    }
> +
> +  result.set_len (canonize (val, len, precision));
> +  return result;
> +}
> +
>  /* Fill VAL with a mask where the lower WIDTH bits are ones and the bits
>     above that up to PREC are zeros.  The result is inverted if NEGATE
>     is true.  Return the number of blocks in VAL.  */
> diff --git a/gcc/wide-int.h b/gcc/wide-int.h
> index 6be343c..e78d83c 100644
> --- a/gcc/wide-int.h
> +++ b/gcc/wide-int.h
> @@ -1089,6 +1089,7 @@ public:
>  
>    /* FIXME: target-dependent, so should disappear.  */
>    wide_int bswap () const;
> +  wide_int bitreverse () const;

Would be worth adding a blank line here, since the FIXME doesn't apply
to the new routine.

But I think it would be better to define:

   wide_int wi::bitreverse (const wide_int_ref &);

in a similar way as other operations like wi::insert.  I can't remember
why bswap is different, but generally, the only member functions of
the wide_int_storage classes should be accessors.

Otherwise it looks good to me FWIW, but I'm a bit nervous about having
so much new code without any test coverage.

Thanks,
Richard