2017-05-11 François Dumont <fdumont@gcc.gnu.org>

[official-gcc.git] / gcc / gimple-ssa-store-merging.c

/* GIMPLE store merging pass.
   Copyright (C) 2016-2017 Free Software Foundation, Inc.
   Contributed by ARM Ltd.

   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/>.  */

/* The purpose of this pass is to combine multiple memory stores of
   constant values to consecutive memory locations into fewer wider stores.
   For example, if we have a sequence peforming four byte stores to
   consecutive memory locations:
   [p     ] := imm1;
   [p + 1B] := imm2;
   [p + 2B] := imm3;
   [p + 3B] := imm4;
   we can transform this into a single 4-byte store if the target supports it:
  [p] := imm1:imm2:imm3:imm4 //concatenated immediates according to endianness.

   The algorithm is applied to each basic block in three phases:

   1) Scan through the basic block recording constant assignments to
   destinations that can be expressed as a store to memory of a certain size
   at a certain bit offset.  Record store chains to different bases in a
   hash_map (m_stores) and make sure to terminate such chains when appropriate
   (for example when when the stored values get used subsequently).
   These stores can be a result of structure element initializers, array stores
   etc.  A store_immediate_info object is recorded for every such store.
   Record as many such assignments to a single base as possible until a
   statement that interferes with the store sequence is encountered.

   2) Analyze the chain of stores recorded in phase 1) (i.e. the vector of
   store_immediate_info objects) and coalesce contiguous stores into
   merged_store_group objects.

   For example, given the stores:
   [p     ] := 0;
   [p + 1B] := 1;
   [p + 3B] := 0;
   [p + 4B] := 1;
   [p + 5B] := 0;
   [p + 6B] := 0;
   This phase would produce two merged_store_group objects, one recording the
   two bytes stored in the memory region [p : p + 1] and another
   recording the four bytes stored in the memory region [p + 3 : p + 6].

   3) The merged_store_group objects produced in phase 2) are processed
   to generate the sequence of wider stores that set the contiguous memory
   regions to the sequence of bytes that correspond to it.  This may emit
   multiple stores per store group to handle contiguous stores that are not
   of a size that is a power of 2.  For example it can try to emit a 40-bit
   store as a 32-bit store followed by an 8-bit store.
   We try to emit as wide stores as we can while respecting STRICT_ALIGNMENT or
   SLOW_UNALIGNED_ACCESS rules.

   Note on endianness and example:
   Consider 2 contiguous 16-bit stores followed by 2 contiguous 8-bit stores:
   [p     ] := 0x1234;
   [p + 2B] := 0x5678;
   [p + 4B] := 0xab;
   [p + 5B] := 0xcd;

   The memory layout for little-endian (LE) and big-endian (BE) must be:
  p |LE|BE|
  ---------
  0 |34|12|
  1 |12|34|
  2 |78|56|
  3 |56|78|
  4 |ab|ab|
  5 |cd|cd|

  To merge these into a single 48-bit merged value 'val' in phase 2)
  on little-endian we insert stores to higher (consecutive) bitpositions
  into the most significant bits of the merged value.
  The final merged value would be: 0xcdab56781234

  For big-endian we insert stores to higher bitpositions into the least
  significant bits of the merged value.
  The final merged value would be: 0x12345678abcd

  Then, in phase 3), we want to emit this 48-bit value as a 32-bit store
  followed by a 16-bit store.  Again, we must consider endianness when
  breaking down the 48-bit value 'val' computed above.
  For little endian we emit:
  [p]      (32-bit) := 0x56781234; // val & 0x0000ffffffff;
  [p + 4B] (16-bit) := 0xcdab;    // (val & 0xffff00000000) >> 32;

  Whereas for big-endian we emit:
  [p]      (32-bit) := 0x12345678; // (val & 0xffffffff0000) >> 16;
  [p + 4B] (16-bit) := 0xabcd;     //  val & 0x00000000ffff;  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "tree.h"
#include "gimple.h"
#include "builtins.h"
#include "fold-const.h"
#include "tree-pass.h"
#include "ssa.h"
#include "gimple-pretty-print.h"
#include "alias.h"
#include "fold-const.h"
#include "params.h"
#include "print-tree.h"
#include "tree-hash-traits.h"
#include "gimple-iterator.h"
#include "gimplify.h"
#include "stor-layout.h"
#include "timevar.h"
#include "tree-cfg.h"
#include "tree-eh.h"
#include "target.h"
#include "gimplify-me.h"
#include "selftest.h"

/* The maximum size (in bits) of the stores this pass should generate.  */
#define MAX_STORE_BITSIZE (BITS_PER_WORD)
#define MAX_STORE_BYTES (MAX_STORE_BITSIZE / BITS_PER_UNIT)

namespace {

/* Struct recording the information about a single store of an immediate
   to memory.  These are created in the first phase and coalesced into
   merged_store_group objects in the second phase.  */

struct store_immediate_info
{
  unsigned HOST_WIDE_INT bitsize;
  unsigned HOST_WIDE_INT bitpos;
  gimple *stmt;
  unsigned int order;
  store_immediate_info (unsigned HOST_WIDE_INT, unsigned HOST_WIDE_INT,
                        gimple *, unsigned int);
};

store_immediate_info::store_immediate_info (unsigned HOST_WIDE_INT bs,
                                            unsigned HOST_WIDE_INT bp,
                                            gimple *st,
                                            unsigned int ord)
  : bitsize (bs), bitpos (bp), stmt (st), order (ord)
{
}

/* Struct representing a group of stores to contiguous memory locations.
   These are produced by the second phase (coalescing) and consumed in the
   third phase that outputs the widened stores.  */

struct merged_store_group
{
  unsigned HOST_WIDE_INT start;
  unsigned HOST_WIDE_INT width;
  /* The size of the allocated memory for val.  */
  unsigned HOST_WIDE_INT buf_size;

  unsigned int align;
  unsigned int first_order;
  unsigned int last_order;

  auto_vec<struct store_immediate_info *> stores;
  /* We record the first and last original statements in the sequence because
     we'll need their vuse/vdef and replacement position.  It's easier to keep
     track of them separately as 'stores' is reordered by apply_stores.  */
  gimple *last_stmt;
  gimple *first_stmt;
  unsigned char *val;

  merged_store_group (store_immediate_info *);
  ~merged_store_group ();
  void merge_into (store_immediate_info *);
  void merge_overlapping (store_immediate_info *);
  bool apply_stores ();
};

/* Debug helper.  Dump LEN elements of byte array PTR to FD in hex.  */

static void
dump_char_array (FILE *fd, unsigned char *ptr, unsigned int len)
{
  if (!fd)
    return;

  for (unsigned int i = 0; i < len; i++)
    fprintf (fd, "%x ", ptr[i]);
  fprintf (fd, "\n");
}

/* Shift left the bytes in PTR of SZ elements by AMNT bits, carrying over the
   bits between adjacent elements.  AMNT should be within
   [0, BITS_PER_UNIT).
   Example, AMNT = 2:
   00011111|11100000 << 2 = 01111111|10000000
   PTR[1]  | PTR[0]         PTR[1]  | PTR[0].  */

static void
shift_bytes_in_array (unsigned char *ptr, unsigned int sz, unsigned int amnt)
{
  if (amnt == 0)
    return;

  unsigned char carry_over = 0U;
  unsigned char carry_mask = (~0U) << (unsigned char) (BITS_PER_UNIT - amnt);
  unsigned char clear_mask = (~0U) << amnt;

  for (unsigned int i = 0; i < sz; i++)
    {
      unsigned prev_carry_over = carry_over;
      carry_over = (ptr[i] & carry_mask) >> (BITS_PER_UNIT - amnt);

      ptr[i] <<= amnt;
      if (i != 0)
        {
          ptr[i] &= clear_mask;
          ptr[i] |= prev_carry_over;
        }
    }
}

/* Like shift_bytes_in_array but for big-endian.
   Shift right the bytes in PTR of SZ elements by AMNT bits, carrying over the
   bits between adjacent elements.  AMNT should be within
   [0, BITS_PER_UNIT).
   Example, AMNT = 2:
   00011111|11100000 >> 2 = 00000111|11111000
   PTR[0]  | PTR[1]         PTR[0]  | PTR[1].  */

static void
shift_bytes_in_array_right (unsigned char *ptr, unsigned int sz,
                            unsigned int amnt)
{
  if (amnt == 0)
    return;

  unsigned char carry_over = 0U;
  unsigned char carry_mask = ~(~0U << amnt);

  for (unsigned int i = 0; i < sz; i++)
    {
      unsigned prev_carry_over = carry_over;
      carry_over = ptr[i] & carry_mask;

      carry_over <<= (unsigned char) BITS_PER_UNIT - amnt;
      ptr[i] >>= amnt;
      ptr[i] |= prev_carry_over;
    }
}

/* Clear out LEN bits starting from bit START in the byte array
   PTR.  This clears the bits to the *right* from START.
   START must be within [0, BITS_PER_UNIT) and counts starting from
   the least significant bit.  */

static void
clear_bit_region_be (unsigned char *ptr, unsigned int start,
                     unsigned int len)
{
  if (len == 0)
    return;
  /* Clear len bits to the right of start.  */
  else if (len <= start + 1)
    {
      unsigned char mask = (~(~0U << len));
      mask = mask << (start + 1U - len);
      ptr[0] &= ~mask;
    }
  else if (start != BITS_PER_UNIT - 1)
    {
      clear_bit_region_be (ptr, start, (start % BITS_PER_UNIT) + 1);
      clear_bit_region_be (ptr + 1, BITS_PER_UNIT - 1,
                           len - (start % BITS_PER_UNIT) - 1);
    }
  else if (start == BITS_PER_UNIT - 1
           && len > BITS_PER_UNIT)
    {
      unsigned int nbytes = len / BITS_PER_UNIT;
      for (unsigned int i = 0; i < nbytes; i++)
        ptr[i] = 0U;
      if (len % BITS_PER_UNIT != 0)
        clear_bit_region_be (ptr + nbytes, BITS_PER_UNIT - 1,
                             len % BITS_PER_UNIT);
    }
  else
    gcc_unreachable ();
}

/* In the byte array PTR clear the bit region starting at bit
   START and is LEN bits wide.
   For regions spanning multiple bytes do this recursively until we reach
   zero LEN or a region contained within a single byte.  */

static void
clear_bit_region (unsigned char *ptr, unsigned int start,
                  unsigned int len)
{
  /* Degenerate base case.  */
  if (len == 0)
    return;
  else if (start >= BITS_PER_UNIT)
    clear_bit_region (ptr + 1, start - BITS_PER_UNIT, len);
  /* Second base case.  */
  else if ((start + len) <= BITS_PER_UNIT)
    {
      unsigned char mask = (~0U) << (unsigned char) (BITS_PER_UNIT - len);
      mask >>= BITS_PER_UNIT - (start + len);

      ptr[0] &= ~mask;

      return;
    }
  /* Clear most significant bits in a byte and proceed with the next byte.  */
  else if (start != 0)
    {
      clear_bit_region (ptr, start, BITS_PER_UNIT - start);
      clear_bit_region (ptr + 1, 0, len - (BITS_PER_UNIT - start));
    }
  /* Whole bytes need to be cleared.  */
  else if (start == 0 && len > BITS_PER_UNIT)
    {
      unsigned int nbytes = len / BITS_PER_UNIT;
      /* We could recurse on each byte but do the loop here to avoid
         recursing too deep.  */
      memset (ptr, '\0', nbytes);
      /* Clear the remaining sub-byte region if there is one.  */
      if (len % BITS_PER_UNIT != 0)
        clear_bit_region (ptr + nbytes, 0, len % BITS_PER_UNIT);
    }
  else
    gcc_unreachable ();
}

/* Write BITLEN bits of EXPR to the byte array PTR at
   bit position BITPOS.  PTR should contain TOTAL_BYTES elements.
   Return true if the operation succeeded.  */

static bool
encode_tree_to_bitpos (tree expr, unsigned char *ptr, int bitlen, int bitpos,
                       unsigned int total_bytes)
{
  unsigned int first_byte = bitpos / BITS_PER_UNIT;
  tree tmp_int = expr;
  bool sub_byte_op_p = ((bitlen % BITS_PER_UNIT)
                        || (bitpos % BITS_PER_UNIT)
                        || mode_for_size (bitlen, MODE_INT, 0) == BLKmode);

  if (!sub_byte_op_p)
    return (native_encode_expr (tmp_int, ptr + first_byte, total_bytes, 0)
            != 0);

  /* LITTLE-ENDIAN
     We are writing a non byte-sized quantity or at a position that is not
     at a byte boundary.
     |--------|--------|--------| ptr + first_byte
           ^              ^
           xxx xxxxxxxx xxx< bp>
           |______EXPR____|

     First native_encode_expr EXPR into a temporary buffer and shift each
     byte in the buffer by 'bp' (carrying the bits over as necessary).
     |00000000|00xxxxxx|xxxxxxxx| << bp = |000xxxxx|xxxxxxxx|xxx00000|
                                              <------bitlen---->< bp>
    Then we clear the destination bits:
    |---00000|00000000|000-----| ptr + first_byte
        <-------bitlen--->< bp>

    Finally we ORR the bytes of the shifted EXPR into the cleared region:
    |---xxxxx||xxxxxxxx||xxx-----| ptr + first_byte.

   BIG-ENDIAN
   We are writing a non byte-sized quantity or at a position that is not
   at a byte boundary.
     ptr + first_byte |--------|--------|--------|
                            ^              ^
                       <bp >xxx xxxxxxxx xxx
                            |_____EXPR_____|

     First native_encode_expr EXPR into a temporary buffer and shift each
     byte in the buffer to the right by (carrying the bits over as necessary).
     We shift by as much as needed to align the most significant bit of EXPR
     with bitpos:
     |00xxxxxx|xxxxxxxx| >> 3 = |00000xxx|xxxxxxxx|xxxxx000|
        <---bitlen---->          <bp ><-----bitlen----->
    Then we clear the destination bits:
    ptr + first_byte |-----000||00000000||00000---|
                      <bp ><-------bitlen----->

    Finally we ORR the bytes of the shifted EXPR into the cleared region:
    ptr + first_byte |---xxxxx||xxxxxxxx||xxx-----|.
    The awkwardness comes from the fact that bitpos is counted from the
    most significant bit of a byte.  */

  /* Allocate an extra byte so that we have space to shift into.  */
  unsigned int byte_size = GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (expr))) + 1;
  unsigned char *tmpbuf = XALLOCAVEC (unsigned char, byte_size);
  memset (tmpbuf, '\0', byte_size);
  /* The store detection code should only have allowed constants that are
     accepted by native_encode_expr.  */
  if (native_encode_expr (expr, tmpbuf, byte_size - 1, 0) == 0)
    gcc_unreachable ();

  /* The native_encode_expr machinery uses TYPE_MODE to determine how many
     bytes to write.  This means it can write more than
     ROUND_UP (bitlen, BITS_PER_UNIT) / BITS_PER_UNIT bytes (for example
     write 8 bytes for a bitlen of 40).  Skip the bytes that are not within
     bitlen and zero out the bits that are not relevant as well (that may
     contain a sign bit due to sign-extension).  */
  unsigned int padding
    = byte_size - ROUND_UP (bitlen, BITS_PER_UNIT) / BITS_PER_UNIT - 1;
  /* On big-endian the padding is at the 'front' so just skip the initial
     bytes.  */
  if (BYTES_BIG_ENDIAN)
    tmpbuf += padding;

  byte_size -= padding;

  if (bitlen % BITS_PER_UNIT != 0)
    {
      if (BYTES_BIG_ENDIAN)
        clear_bit_region_be (tmpbuf, BITS_PER_UNIT - 1,
                             BITS_PER_UNIT - (bitlen % BITS_PER_UNIT));
      else
        clear_bit_region (tmpbuf, bitlen,
                          byte_size * BITS_PER_UNIT - bitlen);
    }
  /* Left shifting relies on the last byte being clear if bitlen is
     a multiple of BITS_PER_UNIT, which might not be clear if
     there are padding bytes.  */
  else if (!BYTES_BIG_ENDIAN)
    tmpbuf[byte_size - 1] = '\0';

  /* Clear the bit region in PTR where the bits from TMPBUF will be
     inserted into.  */
  if (BYTES_BIG_ENDIAN)
    clear_bit_region_be (ptr + first_byte,
                         BITS_PER_UNIT - 1 - (bitpos % BITS_PER_UNIT), bitlen);
  else
    clear_bit_region (ptr + first_byte, bitpos % BITS_PER_UNIT, bitlen);

  int shift_amnt;
  int bitlen_mod = bitlen % BITS_PER_UNIT;
  int bitpos_mod = bitpos % BITS_PER_UNIT;

  bool skip_byte = false;
  if (BYTES_BIG_ENDIAN)
    {
      /* BITPOS and BITLEN are exactly aligned and no shifting
         is necessary.  */
      if (bitpos_mod + bitlen_mod == BITS_PER_UNIT
          || (bitpos_mod == 0 && bitlen_mod == 0))
        shift_amnt = 0;
      /* |. . . . . . . .|
          <bp >   <blen >.
         We always shift right for BYTES_BIG_ENDIAN so shift the beginning
         of the value until it aligns with 'bp' in the next byte over.  */
      else if (bitpos_mod + bitlen_mod < BITS_PER_UNIT)
        {
          shift_amnt = bitlen_mod + bitpos_mod;
          skip_byte = bitlen_mod != 0;
        }
      /* |. . . . . . . .|
          <----bp--->
            <---blen---->.
         Shift the value right within the same byte so it aligns with 'bp'.  */
      else
        shift_amnt = bitlen_mod + bitpos_mod - BITS_PER_UNIT;
    }
  else
    shift_amnt = bitpos % BITS_PER_UNIT;

  /* Create the shifted version of EXPR.  */
  if (!BYTES_BIG_ENDIAN)
    {
      shift_bytes_in_array (tmpbuf, byte_size, shift_amnt);
      if (shift_amnt == 0)
        byte_size--;
    }
  else
    {
      gcc_assert (BYTES_BIG_ENDIAN);
      shift_bytes_in_array_right (tmpbuf, byte_size, shift_amnt);
      /* If shifting right forced us to move into the next byte skip the now
         empty byte.  */
      if (skip_byte)
        {
          tmpbuf++;
          byte_size--;
        }
    }

  /* Insert the bits from TMPBUF.  */
  for (unsigned int i = 0; i < byte_size; i++)
    ptr[first_byte + i] |= tmpbuf[i];

  return true;
}

/* Sorting function for store_immediate_info objects.
   Sorts them by bitposition.  */

static int
sort_by_bitpos (const void *x, const void *y)
{
  store_immediate_info *const *tmp = (store_immediate_info * const *) x;
  store_immediate_info *const *tmp2 = (store_immediate_info * const *) y;

  if ((*tmp)->bitpos <= (*tmp2)->bitpos)
    return -1;
  else if ((*tmp)->bitpos > (*tmp2)->bitpos)
    return 1;

  gcc_unreachable ();
}

/* Sorting function for store_immediate_info objects.
   Sorts them by the order field.  */

static int
sort_by_order (const void *x, const void *y)
{
  store_immediate_info *const *tmp = (store_immediate_info * const *) x;
  store_immediate_info *const *tmp2 = (store_immediate_info * const *) y;

  if ((*tmp)->order < (*tmp2)->order)
    return -1;
  else if ((*tmp)->order > (*tmp2)->order)
    return 1;

  gcc_unreachable ();
}

/* Initialize a merged_store_group object from a store_immediate_info
   object.  */

merged_store_group::merged_store_group (store_immediate_info *info)
{
  start = info->bitpos;
  width = info->bitsize;
  /* VAL has memory allocated for it in apply_stores once the group
     width has been finalized.  */
  val = NULL;
  align = get_object_alignment (gimple_assign_lhs (info->stmt));
  stores.create (1);
  stores.safe_push (info);
  last_stmt = info->stmt;
  last_order = info->order;
  first_stmt = last_stmt;
  first_order = last_order;
  buf_size = 0;
}

merged_store_group::~merged_store_group ()
{
  if (val)
    XDELETEVEC (val);
}

/* Merge a store recorded by INFO into this merged store.
   The store is not overlapping with the existing recorded
   stores.  */

void
merged_store_group::merge_into (store_immediate_info *info)
{
  unsigned HOST_WIDE_INT wid = info->bitsize;
  /* Make sure we're inserting in the position we think we're inserting.  */
  gcc_assert (info->bitpos == start + width);

  width += wid;
  gimple *stmt = info->stmt;
  stores.safe_push (info);
  if (info->order > last_order)
    {
      last_order = info->order;
      last_stmt = stmt;
    }
  else if (info->order < first_order)
    {
      first_order = info->order;
      first_stmt = stmt;
    }
}

/* Merge a store described by INFO into this merged store.
   INFO overlaps in some way with the current store (i.e. it's not contiguous
   which is handled by merged_store_group::merge_into).  */

void
merged_store_group::merge_overlapping (store_immediate_info *info)
{
  gimple *stmt = info->stmt;
  stores.safe_push (info);

  /* If the store extends the size of the group, extend the width.  */
  if ((info->bitpos + info->bitsize) > (start + width))
    width += info->bitpos + info->bitsize - (start + width);

  if (info->order > last_order)
    {
      last_order = info->order;
      last_stmt = stmt;
    }
  else if (info->order < first_order)
    {
      first_order = info->order;
      first_stmt = stmt;
    }
}

/* Go through all the recorded stores in this group in program order and
   apply their values to the VAL byte array to create the final merged
   value.  Return true if the operation succeeded.  */

bool
merged_store_group::apply_stores ()
{
  /* The total width of the stores must add up to a whole number of bytes
     and start at a byte boundary.  We don't support emitting bitfield
     references for now.  Also, make sure we have more than one store
     in the group, otherwise we cannot merge anything.  */
  if (width % BITS_PER_UNIT != 0
      || start % BITS_PER_UNIT != 0
      || stores.length () == 1)
    return false;

  stores.qsort (sort_by_order);
  struct store_immediate_info *info;
  unsigned int i;
  /* Create a buffer of a size that is 2 times the number of bytes we're
     storing.  That way native_encode_expr can write power-of-2-sized
     chunks without overrunning.  */
  buf_size = 2 * (ROUND_UP (width, BITS_PER_UNIT) / BITS_PER_UNIT);
  val = XCNEWVEC (unsigned char, buf_size);

  FOR_EACH_VEC_ELT (stores, i, info)
    {
      unsigned int pos_in_buffer = info->bitpos - start;
      bool ret = encode_tree_to_bitpos (gimple_assign_rhs1 (info->stmt),
                                        val, info->bitsize,
                                        pos_in_buffer, buf_size);
      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          if (ret)
            {
              fprintf (dump_file, "After writing ");
              print_generic_expr (dump_file,
                                  gimple_assign_rhs1 (info->stmt), 0);
              fprintf (dump_file, " of size " HOST_WIDE_INT_PRINT_DEC
                        " at position %d the merged region contains:\n",
                        info->bitsize, pos_in_buffer);
              dump_char_array (dump_file, val, buf_size);
            }
          else
            fprintf (dump_file, "Failed to merge stores\n");
        }
      if (!ret)
        return false;
    }
  return true;
}

/* Structure describing the store chain.  */

struct imm_store_chain_info
{
  /* Doubly-linked list that imposes an order on chain processing.
     PNXP (prev's next pointer) points to the head of a list, or to
     the next field in the previous chain in the list.
     See pass_store_merging::m_stores_head for more rationale.  */
  imm_store_chain_info *next, **pnxp;
  tree base_addr;
  auto_vec<struct store_immediate_info *> m_store_info;
  auto_vec<merged_store_group *> m_merged_store_groups;

  imm_store_chain_info (imm_store_chain_info *&inspt, tree b_a)
  : next (inspt), pnxp (&inspt), base_addr (b_a)
  {
    inspt = this;
    if (next)
      {
        gcc_checking_assert (pnxp == next->pnxp);
        next->pnxp = &next;
      }
  }
  ~imm_store_chain_info ()
  {
    *pnxp = next;
    if (next)
      {
        gcc_checking_assert (&next == next->pnxp);
        next->pnxp = pnxp;
      }
  }
  bool terminate_and_process_chain ();
  bool coalesce_immediate_stores ();
  bool output_merged_store (merged_store_group *);
  bool output_merged_stores ();
};

const pass_data pass_data_tree_store_merging = {
  GIMPLE_PASS,     /* type */
  "store-merging", /* name */
  OPTGROUP_NONE,   /* optinfo_flags */
  TV_GIMPLE_STORE_MERGING,       /* tv_id */
  PROP_ssa,     /* properties_required */
  0,               /* properties_provided */
  0,               /* properties_destroyed */
  0,               /* todo_flags_start */
  TODO_update_ssa, /* todo_flags_finish */
};

class pass_store_merging : public gimple_opt_pass
{
public:
  pass_store_merging (gcc::context *ctxt)
    : gimple_opt_pass (pass_data_tree_store_merging, ctxt), m_stores_head ()
  {
  }

  /* Pass not supported for PDP-endianness.  */
  virtual bool
  gate (function *)
  {
    return flag_store_merging && (WORDS_BIG_ENDIAN == BYTES_BIG_ENDIAN);
  }

  virtual unsigned int execute (function *);

private:
  hash_map<tree_operand_hash, struct imm_store_chain_info *> m_stores;

  /* Form a doubly-linked stack of the elements of m_stores, so that
     we can iterate over them in a predictable way.  Using this order
     avoids extraneous differences in the compiler output just because
     of tree pointer variations (e.g. different chains end up in
     different positions of m_stores, so they are handled in different
     orders, so they allocate or release SSA names in different
     orders, and when they get reused, subsequent passes end up
     getting different SSA names, which may ultimately change
     decisions when going out of SSA).  */
  imm_store_chain_info *m_stores_head;

  bool terminate_and_process_all_chains ();
  bool terminate_all_aliasing_chains (imm_store_chain_info **,
                                      bool, gimple *);
  bool terminate_and_release_chain (imm_store_chain_info *);
}; // class pass_store_merging

/* Terminate and process all recorded chains.  Return true if any changes
   were made.  */

bool
pass_store_merging::terminate_and_process_all_chains ()
{
  bool ret = false;
  while (m_stores_head)
    ret |= terminate_and_release_chain (m_stores_head);
  gcc_assert (m_stores.elements () == 0);
  gcc_assert (m_stores_head == NULL);

  return ret;
}

/* Terminate all chains that are affected by the assignment to DEST, appearing
   in statement STMT and ultimately points to the object BASE.  Return true if
   at least one aliasing chain was terminated.  BASE and DEST are allowed to
   be NULL_TREE.  In that case the aliasing checks are performed on the whole
   statement rather than a particular operand in it.  VAR_OFFSET_P signifies
   whether STMT represents a store to BASE offset by a variable amount.
   If that is the case we have to terminate any chain anchored at BASE.  */

bool
pass_store_merging::terminate_all_aliasing_chains (imm_store_chain_info
                                                     **chain_info,
                                                   bool var_offset_p,
                                                   gimple *stmt)
{
  bool ret = false;

  /* If the statement doesn't touch memory it can't alias.  */
  if (!gimple_vuse (stmt))
    return false;

  /* Check if the assignment destination (BASE) is part of a store chain.
     This is to catch non-constant stores to destinations that may be part
     of a chain.  */
  if (chain_info)
    {
      /* We have a chain at BASE and we're writing to [BASE + <variable>].
         This can interfere with any of the stores so terminate
         the chain.  */
      if (var_offset_p)
        {
          terminate_and_release_chain (*chain_info);
          ret = true;
        }
      /* Otherwise go through every store in the chain to see if it
         aliases with any of them.  */
      else
        {
          struct store_immediate_info *info;
          unsigned int i;
          FOR_EACH_VEC_ELT ((*chain_info)->m_store_info, i, info)
            {
              if (ref_maybe_used_by_stmt_p (stmt,
                                            gimple_assign_lhs (info->stmt))
                  || stmt_may_clobber_ref_p (stmt,
                                             gimple_assign_lhs (info->stmt)))
                {
                  if (dump_file && (dump_flags & TDF_DETAILS))
                    {
                      fprintf (dump_file,
                               "stmt causes chain termination:\n");
                      print_gimple_stmt (dump_file, stmt, 0, 0);
                    }
                  terminate_and_release_chain (*chain_info);
                  ret = true;
                  break;
                }
            }
        }
    }

  /* Check for aliasing with all other store chains.  */
  for (imm_store_chain_info *next = m_stores_head, *cur = next; cur; cur = next)
    {
      next = cur->next;

      /* We already checked all the stores in chain_info and terminated the
         chain if necessary.  Skip it here.  */
      if (chain_info && (*chain_info) == cur)
        continue;

      /* We can't use the base object here as that does not reliably exist.
         Build a ao_ref from the base object address (if we know the
         minimum and maximum offset and the maximum size we could improve
         things here).  */
      ao_ref chain_ref;
      ao_ref_init_from_ptr_and_size (&chain_ref, cur->base_addr, NULL_TREE);
      if (ref_maybe_used_by_stmt_p (stmt, &chain_ref)
          || stmt_may_clobber_ref_p_1 (stmt, &chain_ref))
        {
          terminate_and_release_chain (cur);
          ret = true;
        }
    }

  return ret;
}

/* Helper function.  Terminate the recorded chain storing to base object
   BASE.  Return true if the merging and output was successful.  The m_stores
   entry is removed after the processing in any case.  */

bool
pass_store_merging::terminate_and_release_chain (imm_store_chain_info *chain_info)
{
  bool ret = chain_info->terminate_and_process_chain ();
  m_stores.remove (chain_info->base_addr);
  delete chain_info;
  return ret;
}

/* Go through the candidate stores recorded in m_store_info and merge them
   into merged_store_group objects recorded into m_merged_store_groups
   representing the widened stores.  Return true if coalescing was successful
   and the number of widened stores is fewer than the original number
   of stores.  */

bool
imm_store_chain_info::coalesce_immediate_stores ()
{
  /* Anything less can't be processed.  */
  if (m_store_info.length () < 2)
    return false;

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "Attempting to coalesce %u stores in chain.\n",
             m_store_info.length ());

  store_immediate_info *info;
  unsigned int i;

  /* Order the stores by the bitposition they write to.  */
  m_store_info.qsort (sort_by_bitpos);

  info = m_store_info[0];
  merged_store_group *merged_store = new merged_store_group (info);

  FOR_EACH_VEC_ELT (m_store_info, i, info)
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
        {
          fprintf (dump_file, "Store %u:\nbitsize:" HOST_WIDE_INT_PRINT_DEC
                              " bitpos:" HOST_WIDE_INT_PRINT_DEC " val:\n",
                   i, info->bitsize, info->bitpos);
          print_generic_expr (dump_file, gimple_assign_rhs1 (info->stmt), 0);
          fprintf (dump_file, "\n------------\n");
        }

      if (i == 0)
        continue;

      /* |---store 1---|
               |---store 2---|
       Overlapping stores.  */
      unsigned HOST_WIDE_INT start = info->bitpos;
      if (IN_RANGE (start, merged_store->start,
                    merged_store->start + merged_store->width - 1))
        {
          merged_store->merge_overlapping (info);
          continue;
        }

      /* |---store 1---| <gap> |---store 2---|.
         Gap between stores.  Start a new group.  */
      if (start != merged_store->start + merged_store->width)
        {
          /* Try to apply all the stores recorded for the group to determine
             the bitpattern they write and discard it if that fails.
             This will also reject single-store groups.  */
          if (!merged_store->apply_stores ())
            delete merged_store;
          else
            m_merged_store_groups.safe_push (merged_store);

          merged_store = new merged_store_group (info);

          continue;
        }

      /* |---store 1---||---store 2---|
         This store is consecutive to the previous one.
         Merge it into the current store group.  */
       merged_store->merge_into (info);
    }

    /* Record or discard the last store group.  */
    if (!merged_store->apply_stores ())
      delete merged_store;
    else
      m_merged_store_groups.safe_push (merged_store);

  gcc_assert (m_merged_store_groups.length () <= m_store_info.length ());
  bool success
    = !m_merged_store_groups.is_empty ()
      && m_merged_store_groups.length () < m_store_info.length ();

  if (success && dump_file)
    fprintf (dump_file, "Coalescing successful!\n"
                         "Merged into %u stores\n",
                m_merged_store_groups.length ());

  return success;
}

/* Return the type to use for the merged stores described by STMTS.
   This is needed to get the alias sets right.  */

static tree
get_alias_type_for_stmts (auto_vec<gimple *> &stmts)
{
  gimple *stmt;
  unsigned int i;
  tree lhs = gimple_assign_lhs (stmts[0]);
  tree type = reference_alias_ptr_type (lhs);

  FOR_EACH_VEC_ELT (stmts, i, stmt)
    {
      if (i == 0)
        continue;

      lhs = gimple_assign_lhs (stmt);
      tree type1 = reference_alias_ptr_type (lhs);
      if (!alias_ptr_types_compatible_p (type, type1))
        return ptr_type_node;
    }
  return type;
}

/* Return the location_t information we can find among the statements
   in STMTS.  */

static location_t
get_location_for_stmts (auto_vec<gimple *> &stmts)
{
  gimple *stmt;
  unsigned int i;

  FOR_EACH_VEC_ELT (stmts, i, stmt)
    if (gimple_has_location (stmt))
      return gimple_location (stmt);

  return UNKNOWN_LOCATION;
}

/* Used to decribe a store resulting from splitting a wide store in smaller
   regularly-sized stores in split_group.  */

struct split_store
{
  unsigned HOST_WIDE_INT bytepos;
  unsigned HOST_WIDE_INT size;
  unsigned HOST_WIDE_INT align;
  auto_vec<gimple *> orig_stmts;
  split_store (unsigned HOST_WIDE_INT, unsigned HOST_WIDE_INT,
               unsigned HOST_WIDE_INT);
};

/* Simple constructor.  */

split_store::split_store (unsigned HOST_WIDE_INT bp,
                          unsigned HOST_WIDE_INT sz,
                          unsigned HOST_WIDE_INT al)
                          : bytepos (bp), size (sz), align (al)
{
  orig_stmts.create (0);
}

/* Record all statements corresponding to stores in GROUP that write to
   the region starting at BITPOS and is of size BITSIZE.  Record such
   statements in STMTS.  The stores in GROUP must be sorted by
   bitposition.  */

static void
find_constituent_stmts (struct merged_store_group *group,
                         auto_vec<gimple *> &stmts,
                         unsigned HOST_WIDE_INT bitpos,
                         unsigned HOST_WIDE_INT bitsize)
{
  struct store_immediate_info *info;
  unsigned int i;
  unsigned HOST_WIDE_INT end = bitpos + bitsize;
  FOR_EACH_VEC_ELT (group->stores, i, info)
    {
      unsigned HOST_WIDE_INT stmt_start = info->bitpos;
      unsigned HOST_WIDE_INT stmt_end = stmt_start + info->bitsize;
      if (stmt_end < bitpos)
        continue;
      /* The stores in GROUP are ordered by bitposition so if we're past
          the region for this group return early.  */
      if (stmt_start > end)
        return;

      if (IN_RANGE (stmt_start, bitpos, bitpos + bitsize)
          || IN_RANGE (stmt_end, bitpos, end)
          /* The statement writes a region that completely encloses the region
             that this group writes.  Unlikely to occur but let's
             handle it.  */
          || IN_RANGE (bitpos, stmt_start, stmt_end))
        stmts.safe_push (info->stmt);
    }
}

/* Split a merged store described by GROUP by populating the SPLIT_STORES
   vector with split_store structs describing the byte offset (from the base),
   the bit size and alignment of each store as well as the original statements
   involved in each such split group.
   This is to separate the splitting strategy from the statement
   building/emission/linking done in output_merged_store.
   At the moment just start with the widest possible size and keep emitting
   the widest we can until we have emitted all the bytes, halving the size
   when appropriate.  */

static bool
split_group (merged_store_group *group,
             auto_vec<struct split_store *> &split_stores)
{
  unsigned HOST_WIDE_INT pos = group->start;
  unsigned HOST_WIDE_INT size = group->width;
  unsigned HOST_WIDE_INT bytepos = pos / BITS_PER_UNIT;
  unsigned HOST_WIDE_INT align = group->align;

  /* We don't handle partial bitfields for now.  We shouldn't have
     reached this far.  */
  gcc_assert ((size % BITS_PER_UNIT == 0) && (pos % BITS_PER_UNIT == 0));

  bool allow_unaligned
    = !STRICT_ALIGNMENT && PARAM_VALUE (PARAM_STORE_MERGING_ALLOW_UNALIGNED);

  unsigned int try_size = MAX_STORE_BITSIZE;
  while (try_size > size
         || (!allow_unaligned
             && try_size > align))
    {
      try_size /= 2;
      if (try_size < BITS_PER_UNIT)
        return false;
    }

  unsigned HOST_WIDE_INT try_pos = bytepos;
  group->stores.qsort (sort_by_bitpos);

  while (size > 0)
    {
      struct split_store *store = new split_store (try_pos, try_size, align);
      unsigned HOST_WIDE_INT try_bitpos = try_pos * BITS_PER_UNIT;
      find_constituent_stmts (group, store->orig_stmts, try_bitpos, try_size);
      split_stores.safe_push (store);

      try_pos += try_size / BITS_PER_UNIT;

      size -= try_size;
      align = try_size;
      while (size < try_size)
        try_size /= 2;
    }
  return true;
}

/* Given a merged store group GROUP output the widened version of it.
   The store chain is against the base object BASE.
   Try store sizes of at most MAX_STORE_BITSIZE bits wide and don't output
   unaligned stores for STRICT_ALIGNMENT targets or if it's too expensive.
   Make sure that the number of statements output is less than the number of
   original statements.  If a better sequence is possible emit it and
   return true.  */

bool
imm_store_chain_info::output_merged_store (merged_store_group *group)
{
  unsigned HOST_WIDE_INT start_byte_pos = group->start / BITS_PER_UNIT;

  unsigned int orig_num_stmts = group->stores.length ();
  if (orig_num_stmts < 2)
    return false;

  auto_vec<struct split_store *> split_stores;
  split_stores.create (0);
  if (!split_group (group, split_stores))
    return false;

  gimple_stmt_iterator last_gsi = gsi_for_stmt (group->last_stmt);
  gimple_seq seq = NULL;
  unsigned int num_stmts = 0;
  tree last_vdef, new_vuse;
  last_vdef = gimple_vdef (group->last_stmt);
  new_vuse = gimple_vuse (group->last_stmt);

  gimple *stmt = NULL;
  /* The new SSA names created.  Keep track of them so that we can free them
     if we decide to not use the new sequence.  */
  auto_vec<tree> new_ssa_names;
  split_store *split_store;
  unsigned int i;
  bool fail = false;

  tree addr = force_gimple_operand_1 (unshare_expr (base_addr), &seq,
                                      is_gimple_mem_ref_addr, NULL_TREE);
  FOR_EACH_VEC_ELT (split_stores, i, split_store)
    {
      unsigned HOST_WIDE_INT try_size = split_store->size;
      unsigned HOST_WIDE_INT try_pos = split_store->bytepos;
      unsigned HOST_WIDE_INT align = split_store->align;
      tree offset_type = get_alias_type_for_stmts (split_store->orig_stmts);
      location_t loc = get_location_for_stmts (split_store->orig_stmts);

      tree int_type = build_nonstandard_integer_type (try_size, UNSIGNED);
      int_type = build_aligned_type (int_type, align);
      tree dest = fold_build2 (MEM_REF, int_type, addr,
                               build_int_cst (offset_type, try_pos));

      tree src = native_interpret_expr (int_type,
                                        group->val + try_pos - start_byte_pos,
                                        group->buf_size);

      stmt = gimple_build_assign (dest, src);
      gimple_set_location (stmt, loc);
      gimple_set_vuse (stmt, new_vuse);
      gimple_seq_add_stmt_without_update (&seq, stmt);

      /* We didn't manage to reduce the number of statements.  Bail out.  */
      if (++num_stmts == orig_num_stmts)
        {
          if (dump_file && (dump_flags & TDF_DETAILS))
            {
              fprintf (dump_file, "Exceeded original number of stmts (%u)."
                                  "  Not profitable to emit new sequence.\n",
                       orig_num_stmts);
            }
          unsigned int ssa_count;
          tree ssa_name;
          /* Don't forget to cleanup the temporary SSA names.  */
          FOR_EACH_VEC_ELT (new_ssa_names, ssa_count, ssa_name)
            release_ssa_name (ssa_name);

          fail = true;
          break;
        }

      tree new_vdef;
      if (i < split_stores.length () - 1)
        {
          new_vdef = make_ssa_name (gimple_vop (cfun), stmt);
          new_ssa_names.safe_push (new_vdef);
        }
      else
        new_vdef = last_vdef;

      gimple_set_vdef (stmt, new_vdef);
      SSA_NAME_DEF_STMT (new_vdef) = stmt;
      new_vuse = new_vdef;
    }

  FOR_EACH_VEC_ELT (split_stores, i, split_store)
    delete split_store;

  if (fail)
    return false;

  gcc_assert (seq);
  if (dump_file)
    {
      fprintf (dump_file,
               "New sequence of %u stmts to replace old one of %u stmts\n",
               num_stmts, orig_num_stmts);
      if (dump_flags & TDF_DETAILS)
        print_gimple_seq (dump_file, seq, 0, TDF_VOPS | TDF_MEMSYMS);
    }
  gsi_insert_seq_after (&last_gsi, seq, GSI_SAME_STMT);

  return true;
}

/* Process the merged_store_group objects created in the coalescing phase.
   The stores are all against the base object BASE.
   Try to output the widened stores and delete the original statements if
   successful.  Return true iff any changes were made.  */

bool
imm_store_chain_info::output_merged_stores ()
{
  unsigned int i;
  merged_store_group *merged_store;
  bool ret = false;
  FOR_EACH_VEC_ELT (m_merged_store_groups, i, merged_store)
    {
      if (output_merged_store (merged_store))
        {
          unsigned int j;
          store_immediate_info *store;
          FOR_EACH_VEC_ELT (merged_store->stores, j, store)
            {
              gimple *stmt = store->stmt;
              gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
              gsi_remove (&gsi, true);
              if (stmt != merged_store->last_stmt)
                {
                  unlink_stmt_vdef (stmt);
                  release_defs (stmt);
                }
            }
          ret = true;
        }
    }
  if (ret && dump_file)
    fprintf (dump_file, "Merging successful!\n");

  return ret;
}

/* Coalesce the store_immediate_info objects recorded against the base object
   BASE in the first phase and output them.
   Delete the allocated structures.
   Return true if any changes were made.  */

bool
imm_store_chain_info::terminate_and_process_chain ()
{
  /* Process store chain.  */
  bool ret = false;
  if (m_store_info.length () > 1)
    {
      ret = coalesce_immediate_stores ();
      if (ret)
        ret = output_merged_stores ();
    }

  /* Delete all the entries we allocated ourselves.  */
  store_immediate_info *info;
  unsigned int i;
  FOR_EACH_VEC_ELT (m_store_info, i, info)
    delete info;

  merged_store_group *merged_info;
  FOR_EACH_VEC_ELT (m_merged_store_groups, i, merged_info)
    delete merged_info;

  return ret;
}

/* Return true iff LHS is a destination potentially interesting for
   store merging.  In practice these are the codes that get_inner_reference
   can process.  */

static bool
lhs_valid_for_store_merging_p (tree lhs)
{
  tree_code code = TREE_CODE (lhs);

  if (code == ARRAY_REF || code == ARRAY_RANGE_REF || code == MEM_REF
      || code == COMPONENT_REF || code == BIT_FIELD_REF)
    return true;

  return false;
}

/* Return true if the tree RHS is a constant we want to consider
   during store merging.  In practice accept all codes that
   native_encode_expr accepts.  */

static bool
rhs_valid_for_store_merging_p (tree rhs)
{
  tree type = TREE_TYPE (rhs);
  if (TREE_CODE_CLASS (TREE_CODE (rhs)) != tcc_constant
      || !can_native_encode_type_p (type))
    return false;

  return true;
}

/* Entry point for the pass.  Go over each basic block recording chains of
  immediate stores.  Upon encountering a terminating statement (as defined
  by stmt_terminates_chain_p) process the recorded stores and emit the widened
  variants.  */

unsigned int
pass_store_merging::execute (function *fun)
{
  basic_block bb;
  hash_set<gimple *> orig_stmts;

  FOR_EACH_BB_FN (bb, fun)
    {
      gimple_stmt_iterator gsi;
      unsigned HOST_WIDE_INT num_statements = 0;
      /* Record the original statements so that we can keep track of
         statements emitted in this pass and not re-process new
         statements.  */
      for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); gsi_next (&gsi))
        {
          if (is_gimple_debug (gsi_stmt (gsi)))
            continue;

          if (++num_statements > 2)
            break;
        }

      if (num_statements < 2)
        continue;

      if (dump_file && (dump_flags & TDF_DETAILS))
        fprintf (dump_file, "Processing basic block <%d>:\n", bb->index);

      for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); gsi_next (&gsi))
        {
          gimple *stmt = gsi_stmt (gsi);

          if (is_gimple_debug (stmt))
            continue;

          if (gimple_has_volatile_ops (stmt))
            {
              /* Terminate all chains.  */
              if (dump_file && (dump_flags & TDF_DETAILS))
                fprintf (dump_file, "Volatile access terminates "
                                    "all chains\n");
              terminate_and_process_all_chains ();
              continue;
            }

          if (gimple_assign_single_p (stmt) && gimple_vdef (stmt)
              && !stmt_can_throw_internal (stmt)
              && lhs_valid_for_store_merging_p (gimple_assign_lhs (stmt)))
            {
              tree lhs = gimple_assign_lhs (stmt);
              tree rhs = gimple_assign_rhs1 (stmt);

              HOST_WIDE_INT bitsize, bitpos;
              machine_mode mode;
              int unsignedp = 0, reversep = 0, volatilep = 0;
              tree offset, base_addr;
              base_addr
                = get_inner_reference (lhs, &bitsize, &bitpos, &offset, &mode,
                                       &unsignedp, &reversep, &volatilep);
              /* As a future enhancement we could handle stores with the same
                 base and offset.  */
              bool invalid = reversep
                             || ((bitsize > MAX_BITSIZE_MODE_ANY_INT)
                                  && (TREE_CODE (rhs) != INTEGER_CST))
                             || !rhs_valid_for_store_merging_p (rhs);

              /* We do not want to rewrite TARGET_MEM_REFs.  */
              if (TREE_CODE (base_addr) == TARGET_MEM_REF)
                invalid = true;
              /* In some cases get_inner_reference may return a
                 MEM_REF [ptr + byteoffset].  For the purposes of this pass
                 canonicalize the base_addr to MEM_REF [ptr] and take
                 byteoffset into account in the bitpos.  This occurs in
                 PR 23684 and this way we can catch more chains.  */
              else if (TREE_CODE (base_addr) == MEM_REF)
                {
                  offset_int bit_off, byte_off = mem_ref_offset (base_addr);
                  bit_off = byte_off << LOG2_BITS_PER_UNIT;
                  bit_off += bitpos;
                  if (!wi::neg_p (bit_off) && wi::fits_shwi_p (bit_off))
                    bitpos = bit_off.to_shwi ();
                  else
                    invalid = true;
                  base_addr = TREE_OPERAND (base_addr, 0);
                }
              /* get_inner_reference returns the base object, get at its
                 address now.  */
              else
                {
                  if (bitpos < 0)
                    invalid = true;
                  base_addr = build_fold_addr_expr (base_addr);
                }

              if (! invalid
                  && offset != NULL_TREE)
                {
                  /* If the access is variable offset then a base
                     decl has to be address-taken to be able to
                     emit pointer-based stores to it.
                     ???  We might be able to get away with
                     re-using the original base up to the first
                     variable part and then wrapping that inside
                     a BIT_FIELD_REF.  */
                  tree base = get_base_address (base_addr);
                  if (! base
                      || (DECL_P (base)
                          && ! TREE_ADDRESSABLE (base)))
                    invalid = true;
                  else
                    base_addr = build2 (POINTER_PLUS_EXPR,
                                        TREE_TYPE (base_addr),
                                        base_addr, offset);
                }

              struct imm_store_chain_info **chain_info
                = m_stores.get (base_addr);

              if (!invalid)
                {
                  store_immediate_info *info;
                  if (chain_info)
                    {
                      info = new store_immediate_info (
                        bitsize, bitpos, stmt,
                        (*chain_info)->m_store_info.length ());
                      if (dump_file && (dump_flags & TDF_DETAILS))
                        {
                          fprintf (dump_file,
                                   "Recording immediate store from stmt:\n");
                          print_gimple_stmt (dump_file, stmt, 0, 0);
                        }
                      (*chain_info)->m_store_info.safe_push (info);
                      /* If we reach the limit of stores to merge in a chain
                         terminate and process the chain now.  */
                      if ((*chain_info)->m_store_info.length ()
                           == (unsigned int)
                              PARAM_VALUE (PARAM_MAX_STORES_TO_MERGE))
                        {
                          if (dump_file && (dump_flags & TDF_DETAILS))
                            fprintf (dump_file,
                                 "Reached maximum number of statements"
                                 " to merge:\n");
                          terminate_and_release_chain (*chain_info);
                        }
                      continue;
                    }

                  /* Store aliases any existing chain?  */
                  terminate_all_aliasing_chains (chain_info, false, stmt);
                  /* Start a new chain.  */
                  struct imm_store_chain_info *new_chain
                    = new imm_store_chain_info (m_stores_head, base_addr);
                  info = new store_immediate_info (bitsize, bitpos,
                                                   stmt, 0);
                  new_chain->m_store_info.safe_push (info);
                  m_stores.put (base_addr, new_chain);
                  if (dump_file && (dump_flags & TDF_DETAILS))
                    {
                      fprintf (dump_file,
                               "Starting new chain with statement:\n");
                      print_gimple_stmt (dump_file, stmt, 0, 0);
                      fprintf (dump_file, "The base object is:\n");
                      print_generic_expr (dump_file, base_addr, 0);
                      fprintf (dump_file, "\n");
                    }
                }
              else
                terminate_all_aliasing_chains (chain_info,
                                               offset != NULL_TREE, stmt);

              continue;
            }

          terminate_all_aliasing_chains (NULL, false, stmt);
        }
      terminate_and_process_all_chains ();
    }
  return 0;
}

} // anon namespace

/* Construct and return a store merging pass object.  */

gimple_opt_pass *
make_pass_store_merging (gcc::context *ctxt)
{
  return new pass_store_merging (ctxt);
}

#if CHECKING_P

namespace selftest {

/* Selftests for store merging helpers.  */

/* Assert that all elements of the byte arrays X and Y, both of length N
   are equal.  */

static void
verify_array_eq (unsigned char *x, unsigned char *y, unsigned int n)
{
  for (unsigned int i = 0; i < n; i++)
    {
      if (x[i] != y[i])
        {
          fprintf (stderr, "Arrays do not match.  X:\n");
          dump_char_array (stderr, x, n);
          fprintf (stderr, "Y:\n");
          dump_char_array (stderr, y, n);
        }
      ASSERT_EQ (x[i], y[i]);
    }
}

/* Test shift_bytes_in_array and that it carries bits across between
   bytes correctly.  */

static void
verify_shift_bytes_in_array (void)
{
   /* byte 1   | byte 0
      00011111 | 11100000.  */
  unsigned char orig[2] = { 0xe0, 0x1f };
  unsigned char in[2];
  memcpy (in, orig, sizeof orig);

  unsigned char expected[2] = { 0x80, 0x7f };
  shift_bytes_in_array (in, sizeof (in), 2);
  verify_array_eq (in, expected, sizeof (in));

  memcpy (in, orig, sizeof orig);
  memcpy (expected, orig, sizeof orig);
  /* Check that shifting by zero doesn't change anything.  */
  shift_bytes_in_array (in, sizeof (in), 0);
  verify_array_eq (in, expected, sizeof (in));

}

/* Test shift_bytes_in_array_right and that it carries bits across between
   bytes correctly.  */

static void
verify_shift_bytes_in_array_right (void)
{
   /* byte 1   | byte 0
      00011111 | 11100000.  */
  unsigned char orig[2] = { 0x1f, 0xe0};
  unsigned char in[2];
  memcpy (in, orig, sizeof orig);
  unsigned char expected[2] = { 0x07, 0xf8};
  shift_bytes_in_array_right (in, sizeof (in), 2);
  verify_array_eq (in, expected, sizeof (in));

  memcpy (in, orig, sizeof orig);
  memcpy (expected, orig, sizeof orig);
  /* Check that shifting by zero doesn't change anything.  */
  shift_bytes_in_array_right (in, sizeof (in), 0);
  verify_array_eq (in, expected, sizeof (in));
}

/* Test clear_bit_region that it clears exactly the bits asked and
   nothing more.  */

static void
verify_clear_bit_region (void)
{
  /* Start with all bits set and test clearing various patterns in them.  */
  unsigned char orig[3] = { 0xff, 0xff, 0xff};
  unsigned char in[3];
  unsigned char expected[3];
  memcpy (in, orig, sizeof in);

  /* Check zeroing out all the bits.  */
  clear_bit_region (in, 0, 3 * BITS_PER_UNIT);
  expected[0] = expected[1] = expected[2] = 0;
  verify_array_eq (in, expected, sizeof in);

  memcpy (in, orig, sizeof in);
  /* Leave the first and last bits intact.  */
  clear_bit_region (in, 1, 3 * BITS_PER_UNIT - 2);
  expected[0] = 0x1;
  expected[1] = 0;
  expected[2] = 0x80;
  verify_array_eq (in, expected, sizeof in);
}

/* Test verify_clear_bit_region_be that it clears exactly the bits asked and
   nothing more.  */

static void
verify_clear_bit_region_be (void)
{
  /* Start with all bits set and test clearing various patterns in them.  */
  unsigned char orig[3] = { 0xff, 0xff, 0xff};
  unsigned char in[3];
  unsigned char expected[3];
  memcpy (in, orig, sizeof in);

  /* Check zeroing out all the bits.  */
  clear_bit_region_be (in, BITS_PER_UNIT - 1, 3 * BITS_PER_UNIT);
  expected[0] = expected[1] = expected[2] = 0;
  verify_array_eq (in, expected, sizeof in);

  memcpy (in, orig, sizeof in);
  /* Leave the first and last bits intact.  */
  clear_bit_region_be (in, BITS_PER_UNIT - 2, 3 * BITS_PER_UNIT - 2);
  expected[0] = 0x80;
  expected[1] = 0;
  expected[2] = 0x1;
  verify_array_eq (in, expected, sizeof in);
}


/* Run all of the selftests within this file.  */

void
store_merging_c_tests (void)
{
  verify_shift_bytes_in_array ();
  verify_shift_bytes_in_array_right ();
  verify_clear_bit_region ();
  verify_clear_bit_region_be ();
}

} // namespace selftest
#endif /* CHECKING_P.  */