gcc/vec-perm-indices.c

/* A representation of vector permutation indices.
   Copyright (C) 2017-2020 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "vec-perm-indices.h"
#include "tree.h"
#include "fold-const.h"
#include "tree-vector-builder.h"
#include "backend.h"
#include "rtl.h"
#include "memmodel.h"
#include "emit-rtl.h"
#include "selftest.h"
#include "rtx-vector-builder.h"

/* Switch to a new permutation vector that selects between NINPUTS vector
   inputs that have NELTS_PER_INPUT elements each.  Take the elements of the
   new permutation vector from ELEMENTS, clamping each one to be in range.  */

void
vec_perm_indices::new_vector (const vec_perm_builder &elements,
			      unsigned int ninputs,
			      poly_uint64 nelts_per_input)
{
  m_ninputs = ninputs;
  m_nelts_per_input = nelts_per_input;
  /* If the vector has a constant number of elements, expand the
     encoding and clamp each element.  E.g. { 0, 2, 4, ... } might
     wrap halfway if there is only one vector input, and we want
     the wrapped form to be the canonical one.

     If the vector has a variable number of elements, just copy
     the encoding.  In that case the unwrapped form is canonical
     and there is no way of representing the wrapped form.  */
  poly_uint64 full_nelts = elements.full_nelts ();
  unsigned HOST_WIDE_INT copy_nelts;
  if (full_nelts.is_constant (&copy_nelts))
    m_encoding.new_vector (full_nelts, copy_nelts, 1);
  else
    {
      copy_nelts = elements.encoded_nelts ();
      m_encoding.new_vector (full_nelts, elements.npatterns (),
			     elements.nelts_per_pattern ());
    }
  unsigned int npatterns = m_encoding.npatterns ();
  for (unsigned int i = 0; i < npatterns; ++i)
    m_encoding.quick_push (clamp (elements.elt (i)));
  /* Use the fact that:

	(a + b) % c == ((a % c) + (b % c)) % c

     to simplify the clamping of variable-length vectors.  */
  for (unsigned int i = npatterns; i < copy_nelts; ++i)
    {
      element_type step = clamp (elements.elt (i)
				 - elements.elt (i - npatterns));
      m_encoding.quick_push (clamp (m_encoding[i - npatterns] + step));
    }
  m_encoding.finalize ();
}

/* Switch to a new permutation vector that selects the same input elements
   as ORIG, but with each element split into FACTOR pieces.  For example,
   if ORIG is { 1, 2, 0, 3 } and FACTOR is 2, the new permutation is
   { 2, 3, 4, 5, 0, 1, 6, 7 }.  */

void
vec_perm_indices::new_expanded_vector (const vec_perm_indices &orig,
				       unsigned int factor)
{
  m_ninputs = orig.m_ninputs;
  m_nelts_per_input = orig.m_nelts_per_input * factor;
  m_encoding.new_vector (orig.m_encoding.full_nelts () * factor,
			 orig.m_encoding.npatterns () * factor,
			 orig.m_encoding.nelts_per_pattern ());
  unsigned int encoded_nelts = orig.m_encoding.encoded_nelts ();
  for (unsigned int i = 0; i < encoded_nelts; ++i)
    {
      element_type base = orig.m_encoding[i] * factor;
      for (unsigned int j = 0; j < factor; ++j)
	m_encoding.quick_push (base + j);
    }
  m_encoding.finalize ();
}

/* Rotate the inputs of the permutation right by DELTA inputs.  This changes
   the values of the permutation vector but it doesn't change the way that
   the elements are encoded.  */

void
vec_perm_indices::rotate_inputs (int delta)
{
  element_type element_delta = delta * m_nelts_per_input;
  for (unsigned int i = 0; i < m_encoding.length (); ++i)
    m_encoding[i] = clamp (m_encoding[i] + element_delta);
}

/* Return true if index OUT_BASE + I * OUT_STEP selects input
   element IN_BASE + I * IN_STEP.  For example, the call to test
   whether a permute reverses a vector of N elements would be:

     series_p (0, 1, N - 1, -1)

   which would return true for { N - 1, N - 2, N - 3, ... }.
   The calls to test for an interleaving of elements starting
   at N1 and N2 would be:

     series_p (0, 2, N1, 1) && series_p (1, 2, N2, 1).

   which would return true for { N1, N2, N1 + 1, N2 + 1, ... }.  */

bool
vec_perm_indices::series_p (unsigned int out_base, unsigned int out_step,
			    element_type in_base, element_type in_step) const
{
  /* Check the base value.  */
  if (maybe_ne (clamp (m_encoding.elt (out_base)), clamp (in_base)))
    return false;

  element_type full_nelts = m_encoding.full_nelts ();
  unsigned int npatterns = m_encoding.npatterns ();

  /* Calculate which multiple of OUT_STEP elements we need to get
     back to the same pattern.  */
  unsigned int cycle_length = least_common_multiple (out_step, npatterns);

  /* Check the steps.  */
  in_step = clamp (in_step);
  out_base += out_step;
  unsigned int limit = 0;
  for (;;)
    {
      /* Succeed if we've checked all the elements in the vector.  */
      if (known_ge (out_base, full_nelts))
	return true;

      if (out_base >= npatterns)
	{
	  /* We've got to the end of the "foreground" values.  Check
	     2 elements from each pattern in the "background" values.  */
	  if (limit == 0)
	    limit = out_base + cycle_length * 2;
	  else if (out_base >= limit)
	    return true;
	}

      element_type v0 = m_encoding.elt (out_base - out_step);
      element_type v1 = m_encoding.elt (out_base);
      if (maybe_ne (clamp (v1 - v0), in_step))
	return false;

      out_base += out_step;
    }
  return true;
}

/* Return true if all elements of the permutation vector are in the range
   [START, START + SIZE).  */

bool
vec_perm_indices::all_in_range_p (element_type start, element_type size) const
{
  /* Check the first two elements of each pattern.  */
  unsigned int npatterns = m_encoding.npatterns ();
  unsigned int nelts_per_pattern = m_encoding.nelts_per_pattern ();
  unsigned int base_nelts = npatterns * MIN (nelts_per_pattern, 2);
  for (unsigned int i = 0; i < base_nelts; ++i)
    if (!known_in_range_p (m_encoding[i], start, size))
      return false;

  /* For stepped encodings, check the full range of the series.  */
  if (nelts_per_pattern == 3)
    {
      element_type limit = input_nelts ();

      /* The number of elements in each pattern beyond the first two
	 that we checked above.  */
      poly_int64 step_nelts = exact_div (m_encoding.full_nelts (),
					 npatterns) - 2;
      for (unsigned int i = 0; i < npatterns; ++i)
	{
	  /* BASE1 has been checked but BASE2 hasn't.   */
	  element_type base1 = m_encoding[i + npatterns];
	  element_type base2 = m_encoding[i + base_nelts];

	  /* The step to add to get from BASE1 to each subsequent value.  */
	  element_type step = clamp (base2 - base1);

	  /* STEP has no inherent sign, so a value near LIMIT can
	     act as a negative step.  The series is in range if it
	     is in range according to one of the two interpretations.

	     Since we're dealing with clamped values, ELEMENT_TYPE is
	     wide enough for overflow not to be a problem.  */
	  element_type headroom_down = base1 - start;
	  element_type headroom_up = size - headroom_down - 1;
	  HOST_WIDE_INT diff;
	  if ((!step.is_constant (&diff)
	       || maybe_lt (headroom_up, diff * step_nelts))
	      && (!(limit - step).is_constant (&diff)
		  || maybe_lt (headroom_down, diff * step_nelts)))
	    return false;
	}
    }
  return true;
}

/* Try to read the contents of VECTOR_CST CST as a constant permutation
   vector.  Return true and add the elements to BUILDER on success,
   otherwise return false without modifying BUILDER.  */

bool
tree_to_vec_perm_builder (vec_perm_builder *builder, tree cst)
{
  unsigned int encoded_nelts = vector_cst_encoded_nelts (cst);
  for (unsigned int i = 0; i < encoded_nelts; ++i)
    if (!tree_fits_poly_int64_p (VECTOR_CST_ENCODED_ELT (cst, i)))
      return false;

  builder->new_vector (TYPE_VECTOR_SUBPARTS (TREE_TYPE (cst)),
		       VECTOR_CST_NPATTERNS (cst),
		       VECTOR_CST_NELTS_PER_PATTERN (cst));
  for (unsigned int i = 0; i < encoded_nelts; ++i)
    builder->quick_push (tree_to_poly_int64 (VECTOR_CST_ENCODED_ELT (cst, i)));
  return true;
}

/* Return a VECTOR_CST of type TYPE for the permutation vector in INDICES.  */

tree
vec_perm_indices_to_tree (tree type, const vec_perm_indices &indices)
{
  gcc_assert (known_eq (TYPE_VECTOR_SUBPARTS (type), indices.length ()));
  tree_vector_builder sel (type, indices.encoding ().npatterns (),
			   indices.encoding ().nelts_per_pattern ());
  unsigned int encoded_nelts = sel.encoded_nelts ();
  for (unsigned int i = 0; i < encoded_nelts; i++)
    sel.quick_push (build_int_cst (TREE_TYPE (type), indices[i]));
  return sel.build ();
}

/* Return a CONST_VECTOR of mode MODE that contains the elements of
   INDICES.  */

rtx
vec_perm_indices_to_rtx (machine_mode mode, const vec_perm_indices &indices)
{
  gcc_assert (GET_MODE_CLASS (mode) == MODE_VECTOR_INT
	      && known_eq (GET_MODE_NUNITS (mode), indices.length ()));
  rtx_vector_builder sel (mode, indices.encoding ().npatterns (),
			  indices.encoding ().nelts_per_pattern ());
  unsigned int encoded_nelts = sel.encoded_nelts ();
  for (unsigned int i = 0; i < encoded_nelts; i++)
    sel.quick_push (gen_int_mode (indices[i], GET_MODE_INNER (mode)));
  return sel.build ();
}

#if CHECKING_P

namespace selftest {

/* Test a 12-element vector.  */

static void
test_vec_perm_12 (void)
{
  vec_perm_builder builder (12, 12, 1);
  for (unsigned int i = 0; i < 4; ++i)
    {
      builder.quick_push (i * 5);
      builder.quick_push (3 + i);
      builder.quick_push (2 + 3 * i);
    }
  vec_perm_indices indices (builder, 1, 12);
  ASSERT_TRUE (indices.series_p (0, 3, 0, 5));
  ASSERT_FALSE (indices.series_p (0, 3, 3, 5));
  ASSERT_FALSE (indices.series_p (0, 3, 0, 8));
  ASSERT_TRUE (indices.series_p (1, 3, 3, 1));
  ASSERT_TRUE (indices.series_p (2, 3, 2, 3));

  ASSERT_TRUE (indices.series_p (0, 4, 0, 4));
  ASSERT_FALSE (indices.series_p (1, 4, 3, 4));

  ASSERT_TRUE (indices.series_p (0, 6, 0, 10));
  ASSERT_FALSE (indices.series_p (0, 6, 0, 100));

  ASSERT_FALSE (indices.series_p (1, 10, 3, 7));
  ASSERT_TRUE (indices.series_p (1, 10, 3, 8));

  ASSERT_TRUE (indices.series_p (0, 12, 0, 10));
  ASSERT_TRUE (indices.series_p (0, 12, 0, 11));
  ASSERT_TRUE (indices.series_p (0, 12, 0, 100));
}

/* Run selftests for this file.  */

void
vec_perm_indices_c_tests ()
{
  test_vec_perm_12 ();
}

} // namespace selftest

#endif