re PR middle-end/31150 (Not promoting an whole array to be static const)

	PR middle-end/31150
	* dse.c (struct store_info): Add const_rhs field.
	(clear_rhs_from_active_local_stores): Clear also const_rhs.
	(record_store): Try also cselib_expand_value_rtx to get a constant.
	(find_shift_sequence, get_stored_val): Use const_rhs instead of
	rhs if worthwhile.
	* cselib.c (cselib_record_sets): If !cselib_record_memory and
	there is just one set from read-only MEM, look at REG_EQUAL or
	REG_EQUIV note.

	* dse.c (struct store_info): Add redundant_reason field.
	(record_store): When storing the same constant as has been
	stored by an earlier store, set redundant_reason field
	to the earlier store's insn_info_t.  Don't delete cannot_delete
	insns.
	(find_shift_sequence): Remove read_info argument, add read_mode
	and require_cst arguments.  Return early if require_cst and
	constant wouldn't be returned.
	(get_stored_val): New function.
	(replace_read): Use it.
	(scan_insn): Put even cannot_delete insns with exactly 1 store
	into active_local_stores.
	(dse_step1): Don't delete cannot_delete insns.  Remove redundant
	constant stores if contains_cselib_groups and earlier store storing
	the same value hasn't been eliminated.
	(dse_step6): Renamed to dse_step7.  New function.
	(dse_step7): Renamed from dse_step6.
	(rest_of_handle_dse): Call dse_step6 and dse_step7 at the end.
	* cselib.c (cselib_expand_value_rtx): Don't wrap CONST_INTs
	into CONST unless really necessary.  Handle SUBREG, unary,
	ternary, bitfield and compares specially, to be able to simplify
	operations on constants.
	(expand_loc): Try to optimize LO_SUM.

	* dse.c (get_call_args): New function.
	(scan_insn): Don't handle BUILT_IN_BZERO.  For memset, attempt
	to get call arguments and if successful and both len and val are
	constants, handle the call as (mem:BLK) (const_int) store.

	* dse.c (struct store_info): Add is_large bool field, change
	positions_needed into a union of a bitmask and bitmap + count.
	(free_store_info): Free bitmap if is_large.
	(set_usage_bits): Don't look at stores where
	offset + width >= MAX_OFFSET.
	(set_position_unneeded, set_all_positions_unneeded,
	any_positions_needed_p, all_positions_needed_p): New static inline
	functions.
	(record_store): Handle BLKmode stores of CONST_INT, if
	MEM_SIZE is set on the MEM.  Use the new positions_needed
	accessor inlines.
	(replace_read): Handle reads from BLKmode CONST_INT stores.
	(check_mem_read_rtx): Use all_positions_needed_p function.
	(dse_step1): Free large positions_needed bitmaps and clear is_large.

	* dse.c (struct store_info): Change begin and end types to
	HOST_WIDE_INT.

	* dse.c (record_store): Fix check for unused store.

	* expr.c (block_clear_fn): No longer static.
	* expr.h (block_clear_fn): Declare.
	* dse.c (scan_insn): Memset and bzero can just read their
	arguments.

	* gcc.c-torture/execute/20081218-1.c: New test.

From-SVN: r142892

1 files changed, 553 insertions, 111 deletions

diff --git a/gcc/dse.c b/gcc/dse.c
index 3269c7a..95a351b 100644
--- a/gcc/dse.c
+++ b/gcc/dse.c
@@ -91,7 +91,10 @@ along with GCC; see the file COPYING3.  If not see
    5) Delete the insns that the global analysis has indicated are
    unnecessary.
 
-   6) Cleanup.
+   6) Delete insns that store the same value as preceeding store
+   where the earlier store couldn't be eliminated.
+
+   7) Cleanup.
 
    This step uses cselib and canon_rtx to build the largest expression
    possible for each address.  This pass is a forwards pass through
@@ -205,6 +208,9 @@ struct store_info
   /* False means this is a clobber.  */
   bool is_set;
 
+  /* False if a single HOST_WIDE_INT bitmap is used for positions_needed.  */
+  bool is_large;
+
   /* The id of the mem group of the base address.  If rtx_varies_p is
      true, this is -1.  Otherwise, it is the index into the group
      table.  */
@@ -224,12 +230,26 @@ struct store_info
 
   /* The offset of the first and byte before the last byte associated
      with the operation.  */
-  int begin, end;
+  HOST_WIDE_INT begin, end;
+
+  union
+    {
+      /* A bitmask as wide as the number of bytes in the word that
+	 contains a 1 if the byte may be needed.  The store is unused if
+	 all of the bits are 0.  This is used if IS_LARGE is false.  */
+      unsigned HOST_WIDE_INT small_bitmask;
+
+      struct
+	{
+	  /* A bitmap with one bit per byte.  Cleared bit means the position
+	     is needed.  Used if IS_LARGE is false.  */
+	  bitmap bitmap;
 
-  /* An bitmask as wide as the number of bytes in the word that
-     contains a 1 if the byte may be needed.  The store is unused if
-     all of the bits are 0.  */
-  unsigned HOST_WIDE_INT positions_needed;
+	  /* Number of set bits (i.e. unneeded bytes) in BITMAP.  If it is
+	     equal to END - BEGIN, the whole store is unused.  */
+	  int count;
+	} large;
+    } positions_needed;
 
   /* The next store info for this insn.  */
   struct store_info *next;
@@ -237,7 +257,16 @@ struct store_info
   /* The right hand side of the store.  This is used if there is a
      subsequent reload of the mems address somewhere later in the
      basic block.  */
-  rtx rhs;  
+  rtx rhs;
+
+  /* If rhs is or holds a constant, this contains that constant,
+     otherwise NULL.  */
+  rtx const_rhs;
+
+  /* Set if this store stores the same constant value as REDUNDANT_REASON
+     insn stored.  These aren't eliminated early, because doing that
+     might prevent the earlier larger store to be eliminated.  */
+  struct insn_info *redundant_reason;
 };
 
 /* Return a bitmask with the first N low bits set.  */
@@ -760,6 +789,8 @@ free_store_info (insn_info_t insn_info)
   while (store_info)
     {
       store_info_t next = store_info->next;
+      if (store_info->is_large)
+	BITMAP_FREE (store_info->positions_needed.large.bitmap);
       if (store_info->cse_base)
 	pool_free (cse_store_info_pool, store_info);
       else
@@ -911,7 +942,7 @@ set_usage_bits (group_info_t group, HOST_WIDE_INT offset, HOST_WIDE_INT width)
 {
   HOST_WIDE_INT i;
 
-  if ((offset > -MAX_OFFSET) && (offset < MAX_OFFSET))
+  if (offset > -MAX_OFFSET && offset + width < MAX_OFFSET)
     for (i=offset; i<offset+width; i++)
       {
 	bitmap store1;
@@ -1167,12 +1198,86 @@ clear_rhs_from_active_local_stores (void)
 	store_info = store_info->next;
 
       store_info->rhs = NULL;
+      store_info->const_rhs = NULL;
 
       ptr = ptr->next_local_store;
     }
 }
 
 
+/* Mark byte POS bytes from the beginning of store S_INFO as unneeded.  */
+
+static inline void
+set_position_unneeded (store_info_t s_info, int pos)
+{
+  if (__builtin_expect (s_info->is_large, false))
+    {
+      if (!bitmap_bit_p (s_info->positions_needed.large.bitmap, pos))
+	{
+	  s_info->positions_needed.large.count++;
+	  bitmap_set_bit (s_info->positions_needed.large.bitmap, pos);
+	}
+    }
+  else
+    s_info->positions_needed.small_bitmask
+      &= ~(((unsigned HOST_WIDE_INT) 1) << pos);
+}
+
+/* Mark the whole store S_INFO as unneeded.  */
+
+static inline void
+set_all_positions_unneeded (store_info_t s_info)
+{
+  if (__builtin_expect (s_info->is_large, false))
+    {
+      int pos, end = s_info->end - s_info->begin;
+      for (pos = 0; pos < end; pos++)
+	bitmap_set_bit (s_info->positions_needed.large.bitmap, pos);
+      s_info->positions_needed.large.count = end;
+    }
+  else
+    s_info->positions_needed.small_bitmask = (unsigned HOST_WIDE_INT) 0;
+}
+
+/* Return TRUE if any bytes from S_INFO store are needed.  */
+
+static inline bool
+any_positions_needed_p (store_info_t s_info)
+{
+  if (__builtin_expect (s_info->is_large, false))
+    return (s_info->positions_needed.large.count
+	    < s_info->end - s_info->begin);
+  else
+    return (s_info->positions_needed.small_bitmask
+	    != (unsigned HOST_WIDE_INT) 0);
+}
+
+/* Return TRUE if all bytes START through START+WIDTH-1 from S_INFO
+   store are needed.  */
+
+static inline bool
+all_positions_needed_p (store_info_t s_info, int start, int width)
+{
+  if (__builtin_expect (s_info->is_large, false))
+    {
+      int end = start + width;
+      while (start < end)
+	if (bitmap_bit_p (s_info->positions_needed.large.bitmap, start++))
+	  return false;
+      return true;
+    }
+  else
+    {
+      unsigned HOST_WIDE_INT mask = lowpart_bitmask (width) << start;
+      return (s_info->positions_needed.small_bitmask & mask) == mask;
+    }
+}
+
+
+static rtx get_stored_val (store_info_t, enum machine_mode, HOST_WIDE_INT,
+			   HOST_WIDE_INT, basic_block, bool);
+
+
 /* BODY is an instruction pattern that belongs to INSN.  Return 1 if
    there is a candidate store, after adding it to the appropriate
    local store group if so.  */
@@ -1180,7 +1285,7 @@ clear_rhs_from_active_local_stores (void)
 static int
 record_store (rtx body, bb_info_t bb_info)
 {
-  rtx mem;
+  rtx mem, rhs, const_rhs;
   HOST_WIDE_INT offset = 0;
   HOST_WIDE_INT width = 0;
   alias_set_type spill_alias_set;
@@ -1188,20 +1293,21 @@ record_store (rtx body, bb_info_t bb_info)
   store_info_t store_info = NULL;
   int group_id;
   cselib_val *base = NULL;
-  insn_info_t ptr, last;
+  insn_info_t ptr, last, redundant_reason;
   bool store_is_unused;
 
   if (GET_CODE (body) != SET && GET_CODE (body) != CLOBBER)
     return 0;
 
+  mem = SET_DEST (body);
+
   /* If this is not used, then this cannot be used to keep the insn
      from being deleted.  On the other hand, it does provide something
      that can be used to prove that another store is dead.  */
   store_is_unused
-    = (find_reg_note (insn_info->insn, REG_UNUSED, body) != NULL);
+    = (find_reg_note (insn_info->insn, REG_UNUSED, mem) != NULL);
 
   /* Check whether that value is a suitable memory location.  */
-  mem = SET_DEST (body);
   if (!MEM_P (mem))
     {
       /* If the set or clobber is unused, then it does not effect our
@@ -1220,20 +1326,31 @@ record_store (rtx body, bb_info_t bb_info)
 	    fprintf (dump_file, " adding wild read for (clobber (mem:BLK (scratch))\n");
 	  add_wild_read (bb_info);
 	  insn_info->cannot_delete = true;
+	  return 0;
 	}
-      else if (!store_is_unused)
+      /* Handle (set (mem:BLK (addr) [... S36 ...]) (const_int 0))
+	 as memset (addr, 0, 36);  */
+      else if (!MEM_SIZE (mem)
+	       || !CONST_INT_P (MEM_SIZE (mem))
+	       || GET_CODE (body) != SET
+	       || INTVAL (MEM_SIZE (mem)) <= 0
+	       || INTVAL (MEM_SIZE (mem)) > MAX_OFFSET
+	       || !CONST_INT_P (SET_SRC (body)))
 	{
-	  /* If the set or clobber is unused, then it does not effect our
-	     ability to get rid of the entire insn.  */
-	  insn_info->cannot_delete = true;
-	  clear_rhs_from_active_local_stores ();
+	  if (!store_is_unused)
+	    {
+	      /* If the set or clobber is unused, then it does not effect our
+		 ability to get rid of the entire insn.  */
+	      insn_info->cannot_delete = true;
+	      clear_rhs_from_active_local_stores ();
+	    }
+	  return 0;
 	}
-      return 0;
     }
 
   /* We can still process a volatile mem, we just cannot delete it.  */
   if (MEM_VOLATILE_P (mem))
-      insn_info->cannot_delete = true;
+    insn_info->cannot_delete = true;
 
   if (!canon_address (mem, &spill_alias_set, &group_id, &offset, &base))
     {
@@ -1241,12 +1358,20 @@ record_store (rtx body, bb_info_t bb_info)
       return 0;
     }
 
-  width = GET_MODE_SIZE (GET_MODE (mem));
+  if (GET_MODE (mem) == BLKmode)
+    width = INTVAL (MEM_SIZE (mem));
+  else
+    {
+      width = GET_MODE_SIZE (GET_MODE (mem));
+      gcc_assert ((unsigned) width <= HOST_BITS_PER_WIDE_INT);
+    }
 
   if (spill_alias_set)
     {
       bitmap store1 = clear_alias_group->store1_p;
       bitmap store2 = clear_alias_group->store2_p;
+
+      gcc_assert (GET_MODE (mem) != BLKmode);
       
       if (bitmap_bit_p (store1, spill_alias_set))
 	bitmap_set_bit (store2, spill_alias_set);
@@ -1295,10 +1420,41 @@ record_store (rtx body, bb_info_t bb_info)
 		 (int)offset, (int)(offset+width));
     }
 
+  const_rhs = rhs = NULL_RTX;
+  if (GET_CODE (body) == SET
+      /* No place to keep the value after ra.  */
+      && !reload_completed
+      && (REG_P (SET_SRC (body))
+	  || GET_CODE (SET_SRC (body)) == SUBREG
+	  || CONSTANT_P (SET_SRC (body)))
+      && !MEM_VOLATILE_P (mem)
+      /* Sometimes the store and reload is used for truncation and
+	 rounding.  */
+      && !(FLOAT_MODE_P (GET_MODE (mem)) && (flag_float_store)))
+    {
+      rhs = SET_SRC (body);
+      if (CONSTANT_P (rhs))
+	const_rhs = rhs;
+      else if (body == PATTERN (insn_info->insn))
+	{
+	  rtx tem = find_reg_note (insn_info->insn, REG_EQUAL, NULL_RTX);
+	  if (tem && CONSTANT_P (XEXP (tem, 0)))
+	    const_rhs = XEXP (tem, 0);
+	}
+      if (const_rhs == NULL_RTX && REG_P (rhs))
+	{
+	  rtx tem = cselib_expand_value_rtx (rhs, scratch, 5);
+
+	  if (tem && CONSTANT_P (tem))
+	    const_rhs = tem;
+	}
+    }
+
   /* Check to see if this stores causes some other stores to be
      dead.  */
   ptr = active_local_stores;
   last = NULL;
+  redundant_reason = NULL;
 
   while (ptr)
     {
@@ -1327,7 +1483,7 @@ record_store (rtx body, bb_info_t bb_info)
 	      && (GET_MODE (mem) == entry->mode))
 	    {
 	      del = true;
-	      s_info->positions_needed = (unsigned HOST_WIDE_INT) 0;
+	      set_all_positions_unneeded (s_info);
 	    }
 	  if (dump_file)
 	    fprintf (dump_file, "    trying spill store in insn=%d alias_set=%d\n",
@@ -1341,10 +1497,46 @@ record_store (rtx body, bb_info_t bb_info)
 	    fprintf (dump_file, "    trying store in insn=%d gid=%d[%d..%d)\n",
 		     INSN_UID (ptr->insn), s_info->group_id, 
 		     (int)s_info->begin, (int)s_info->end);
-	  for (i = offset; i < offset+width; i++)
-	    if (i >= s_info->begin && i < s_info->end)
-	      s_info->positions_needed
-		&= ~(((unsigned HOST_WIDE_INT) 1) << (i - s_info->begin));
+
+	  /* Even if PTR won't be eliminated as unneeded, if both
+	     PTR and this insn store the same constant value, we might
+	     eliminate this insn instead.  */
+	  if (s_info->const_rhs
+	      && const_rhs
+	      && offset >= s_info->begin
+	      && offset + width <= s_info->end
+	      && all_positions_needed_p (s_info, offset - s_info->begin,
+					 width))
+	    {
+	      if (GET_MODE (mem) == BLKmode)
+		{
+		  if (GET_MODE (s_info->mem) == BLKmode
+		      && s_info->const_rhs == const_rhs)
+		    redundant_reason = ptr;
+		}
+	      else if (s_info->const_rhs == const0_rtx
+		       && const_rhs == const0_rtx)
+		redundant_reason = ptr;
+	      else
+		{
+		  rtx val;
+		  start_sequence ();
+		  val = get_stored_val (s_info, GET_MODE (mem),
+					offset, offset + width,
+					BLOCK_FOR_INSN (insn_info->insn),
+					true);
+		  if (get_insns () != NULL)
+		    val = NULL_RTX;
+		  end_sequence ();
+		  if (val && rtx_equal_p (val, const_rhs))
+		    redundant_reason = ptr;
+		}
+	    }
+
+	  for (i = MAX (offset, s_info->begin);
+	       i < offset + width && i < s_info->end;
+	       i++)
+	    set_position_unneeded (s_info, i - s_info->begin);
 	}
       else if (s_info->rhs)
 	/* Need to see if it is possible for this store to overwrite
@@ -1355,14 +1547,18 @@ record_store (rtx body, bb_info_t bb_info)
 				     GET_MODE (s_info->mem),
 				     s_info->mem_addr,
 				     mem, rtx_varies_p))
-	    s_info->rhs = NULL;
+	    {
+	      s_info->rhs = NULL;
+	      s_info->const_rhs = NULL;
+	    }
 	}
       
       /* An insn can be deleted if every position of every one of
 	 its s_infos is zero.  */
-      if (s_info->positions_needed != (unsigned HOST_WIDE_INT) 0)
+      if (any_positions_needed_p (s_info)
+	  || ptr->cannot_delete)
 	del = false;
-      
+
       if (del)
 	{
 	  insn_info_t insn_to_delete = ptr;
@@ -1380,8 +1576,6 @@ record_store (rtx body, bb_info_t bb_info)
       ptr = next;
     }
   
-  gcc_assert ((unsigned) width <= HOST_BITS_PER_WIDE_INT);
-  
   /* Finish filling in the store_info.  */
   store_info->next = insn_info->store_rec;
   insn_info->store_rec = store_info;
@@ -1389,25 +1583,25 @@ record_store (rtx body, bb_info_t bb_info)
   store_info->alias_set = spill_alias_set;
   store_info->mem_addr = get_addr (XEXP (mem, 0));
   store_info->cse_base = base;
-  store_info->positions_needed = lowpart_bitmask (width);
+  if (width > HOST_BITS_PER_WIDE_INT)
+    {
+      store_info->is_large = true;
+      store_info->positions_needed.large.count = 0;
+      store_info->positions_needed.large.bitmap = BITMAP_ALLOC (NULL);
+    }
+  else
+    {
+      store_info->is_large = false;
+      store_info->positions_needed.small_bitmask = lowpart_bitmask (width);
+    }
   store_info->group_id = group_id;
   store_info->begin = offset;
   store_info->end = offset + width;
   store_info->is_set = GET_CODE (body) == SET;
+  store_info->rhs = rhs;
+  store_info->const_rhs = const_rhs;
+  store_info->redundant_reason = redundant_reason;
 
-  if (store_info->is_set 
-      /* No place to keep the value after ra.  */
-      && !reload_completed
-      && (REG_P (SET_SRC (body))
-	  || GET_CODE (SET_SRC (body)) == SUBREG
-	  || CONSTANT_P (SET_SRC (body)))
-      /* Sometimes the store and reload is used for truncation and
-	 rounding.  */
-      && !(FLOAT_MODE_P (GET_MODE (mem)) && (flag_float_store)))
-    store_info->rhs = SET_SRC (body);
-  else
-    store_info->rhs = NULL;
-  
   /* If this is a clobber, we return 0.  We will only be able to
      delete this insn if there is only one store USED store, but we
      can use the clobber to delete other stores earlier.  */
@@ -1435,12 +1629,10 @@ dump_insn_info (const char * start, insn_info_t insn_info)
 static rtx
 find_shift_sequence (int access_size,
 		     store_info_t store_info,
-		     read_info_t read_info,
-		     int shift,
-		     bool speed)
+		     enum machine_mode read_mode,
+		     int shift, bool speed, bool require_cst)
 {
   enum machine_mode store_mode = GET_MODE (store_info->mem);
-  enum machine_mode read_mode = GET_MODE (read_info->mem);
   enum machine_mode new_mode;
   rtx read_reg = NULL;
 
@@ -1462,11 +1654,11 @@ find_shift_sequence (int access_size,
       /* If a constant was stored into memory, try to simplify it here,
 	 otherwise the cost of the shift might preclude this optimization
 	 e.g. at -Os, even when no actual shift will be needed.  */
-      if (CONSTANT_P (store_info->rhs))
+      if (store_info->const_rhs)
 	{
 	  unsigned int byte = subreg_lowpart_offset (new_mode, store_mode);
-	  rtx ret = simplify_subreg (new_mode, store_info->rhs, store_mode,
-				     byte);
+	  rtx ret = simplify_subreg (new_mode, store_info->const_rhs,
+				     store_mode, byte);
 	  if (ret && CONSTANT_P (ret))
 	    {
 	      ret = simplify_const_binary_operation (LSHIFTRT, new_mode,
@@ -1482,6 +1674,9 @@ find_shift_sequence (int access_size,
 	    }
 	}
 
+      if (require_cst)
+	return NULL_RTX;
+
       /* Try a wider mode if truncating the store mode to NEW_MODE
 	 requires a real instruction.  */
       if (GET_MODE_BITSIZE (new_mode) < GET_MODE_BITSIZE (store_mode)
@@ -1563,6 +1758,79 @@ look_for_hardregs (rtx x, const_rtx pat ATTRIBUTE_UNUSED, void *data)
     }
 }
 
+/* Helper function for replace_read and record_store.
+   Attempt to return a value stored in STORE_INFO, from READ_BEGIN
+   to one before READ_END bytes read in READ_MODE.  Return NULL
+   if not successful.  If REQUIRE_CST is true, return always constant.  */
+
+static rtx
+get_stored_val (store_info_t store_info, enum machine_mode read_mode,
+		HOST_WIDE_INT read_begin, HOST_WIDE_INT read_end,
+		basic_block bb, bool require_cst)
+{
+  enum machine_mode store_mode = GET_MODE (store_info->mem);
+  int shift;
+  int access_size; /* In bytes.  */
+  rtx read_reg;
+
+  /* To get here the read is within the boundaries of the write so
+     shift will never be negative.  Start out with the shift being in
+     bytes.  */
+  if (store_mode == BLKmode)
+    shift = 0;
+  else if (BYTES_BIG_ENDIAN)
+    shift = store_info->end - read_end;
+  else
+    shift = read_begin - store_info->begin;
+
+  access_size = shift + GET_MODE_SIZE (read_mode);
+
+  /* From now on it is bits.  */
+  shift *= BITS_PER_UNIT;
+
+  if (shift)
+    read_reg = find_shift_sequence (access_size, store_info, read_mode, shift,
+    				    optimize_bb_for_speed_p (bb),
+				    require_cst);
+  else if (store_mode == BLKmode)
+    {
+      /* The store is a memset (addr, const_val, const_size).  */
+      gcc_assert (CONST_INT_P (store_info->rhs));
+      store_mode = int_mode_for_mode (read_mode);
+      if (store_mode == BLKmode)
+	read_reg = NULL_RTX;
+      else if (store_info->rhs == const0_rtx)
+	read_reg = extract_low_bits (read_mode, store_mode, const0_rtx);
+      else if (GET_MODE_BITSIZE (store_mode) > HOST_BITS_PER_WIDE_INT
+	       || BITS_PER_UNIT >= HOST_BITS_PER_WIDE_INT)
+	read_reg = NULL_RTX;
+      else
+	{
+	  unsigned HOST_WIDE_INT c
+	    = INTVAL (store_info->rhs)
+	      & (((HOST_WIDE_INT) 1 << BITS_PER_UNIT) - 1);
+	  int shift = BITS_PER_UNIT;
+	  while (shift < HOST_BITS_PER_WIDE_INT)
+	    {
+	      c |= (c << shift);
+	      shift <<= 1;
+	    }
+	  read_reg = GEN_INT (trunc_int_for_mode (c, store_mode));
+	  read_reg = extract_low_bits (read_mode, store_mode, read_reg);
+	}
+    }
+  else if (store_info->const_rhs
+	   && (require_cst
+	       || GET_MODE_CLASS (read_mode) != GET_MODE_CLASS (store_mode)))
+    read_reg = extract_low_bits (read_mode, store_mode,
+				 copy_rtx (store_info->const_rhs));
+  else
+    read_reg = extract_low_bits (read_mode, store_mode,
+				 copy_rtx (store_info->rhs));
+  if (require_cst && read_reg && !CONSTANT_P (read_reg))
+    read_reg = NULL_RTX;
+  return read_reg;
+}
 
 /* Take a sequence of:
      A <- r1
@@ -1597,30 +1865,17 @@ look_for_hardregs (rtx x, const_rtx pat ATTRIBUTE_UNUSED, void *data)
 
 static bool
 replace_read (store_info_t store_info, insn_info_t store_insn, 
-	      read_info_t read_info, insn_info_t read_insn, rtx *loc, bitmap regs_live)
+	      read_info_t read_info, insn_info_t read_insn, rtx *loc,
+	      bitmap regs_live)
 {
   enum machine_mode store_mode = GET_MODE (store_info->mem);
   enum machine_mode read_mode = GET_MODE (read_info->mem);
-  int shift;
-  int access_size; /* In bytes.  */
   rtx insns, this_insn, read_reg;
+  basic_block bb;
 
   if (!dbg_cnt (dse))
     return false;
 
-  /* To get here the read is within the boundaries of the write so
-     shift will never be negative.  Start out with the shift being in
-     bytes.  */
-  if (BYTES_BIG_ENDIAN)
-    shift = store_info->end - read_info->end;
-  else
-    shift = read_info->begin - store_info->begin;
-
-  access_size = shift + GET_MODE_SIZE (read_mode);
-
-  /* From now on it is bits.  */
-  shift *= BITS_PER_UNIT;
-
   /* Create a sequence of instructions to set up the read register.
      This sequence goes immediately before the store and its result
      is read by the load.
@@ -1636,12 +1891,10 @@ replace_read (store_info_t store_info, insn_info_t store_insn,
 	     GET_MODE_NAME (read_mode), INSN_UID (read_insn->insn),
 	     GET_MODE_NAME (store_mode), INSN_UID (store_insn->insn));
   start_sequence ();
-  if (shift)
-    read_reg = find_shift_sequence (access_size, store_info, read_info, shift,
-    				    optimize_bb_for_speed_p (BLOCK_FOR_INSN (read_insn->insn)));
-  else
-    read_reg = extract_low_bits (read_mode, store_mode,
-				 copy_rtx (store_info->rhs));
+  bb = BLOCK_FOR_INSN (read_insn->insn);
+  read_reg = get_stored_val (store_info,
+			     read_mode, read_info->begin, read_info->end,
+			     bb, false);
   if (read_reg == NULL_RTX)
     {
       end_sequence ();
@@ -1892,18 +2145,15 @@ check_mem_read_rtx (rtx *loc, void *data)
 	      else 
 		{
 		  if (store_info->rhs
-		      && (offset >= store_info->begin)
-		      && (offset + width <= store_info->end))
-		    {
-		      unsigned HOST_WIDE_INT mask
-			= (lowpart_bitmask (width)
-			   << (offset - store_info->begin));
-
-		      if ((store_info->positions_needed & mask) == mask
-			  && replace_read (store_info, i_ptr, 
-					   read_info, insn_info, loc, bb_info->regs_live))
-			return 0;
-		    }
+		      && offset >= store_info->begin
+		      && offset + width <= store_info->end
+		      && all_positions_needed_p (store_info,
+						 offset - store_info->begin,
+						 width)
+		      && replace_read (store_info, i_ptr, read_info,
+				       insn_info, loc, bb_info->regs_live))
+		    return 0;
+
 		  /* The bases are the same, just see if the offsets
 		     overlap.  */
 		  if ((offset < store_info->end) 
@@ -1961,18 +2211,13 @@ check_mem_read_rtx (rtx *loc, void *data)
 	  if (store_info->rhs
 	      && store_info->group_id == -1
 	      && store_info->cse_base == base
-	      && (offset >= store_info->begin)
-	      && (offset + width <= store_info->end))
-	    {
-	      unsigned HOST_WIDE_INT mask
-		= (lowpart_bitmask (width)
-		   << (offset - store_info->begin));
-
-	      if ((store_info->positions_needed & mask) == mask
-		  && replace_read (store_info, i_ptr, 
-				   read_info, insn_info, loc, bb_info->regs_live))
-		return 0;
-	    }
+	      && offset >= store_info->begin
+	      && offset + width <= store_info->end
+	      && all_positions_needed_p (store_info,
+					 offset - store_info->begin, width)
+	      && replace_read (store_info, i_ptr,  read_info, insn_info, loc,
+			       bb_info->regs_live))
+	    return 0;
 
 	  if (!store_info->alias_set)
 	    remove = canon_true_dependence (store_info->mem, 
@@ -2008,6 +2253,67 @@ check_mem_read_use (rtx *loc, void *data)
   for_each_rtx (loc, check_mem_read_rtx, data);
 }
 
+
+/* Get arguments passed to CALL_INSN.  Return TRUE if successful.
+   So far it only handles arguments passed in registers.  */
+
+static bool
+get_call_args (rtx call_insn, tree fn, rtx *args, int nargs)
+{
+  CUMULATIVE_ARGS args_so_far;
+  tree arg;
+  int idx;
+
+  INIT_CUMULATIVE_ARGS (args_so_far, TREE_TYPE (fn), NULL_RTX, 0, 3);
+
+  arg = TYPE_ARG_TYPES (TREE_TYPE (fn));
+  for (idx = 0;
+       arg != void_list_node && idx < nargs;
+       arg = TREE_CHAIN (arg), idx++)
+    {
+      enum machine_mode mode = TYPE_MODE (TREE_VALUE (arg));
+      rtx reg = FUNCTION_ARG (args_so_far, mode, NULL_TREE, 1), link, tmp;
+      if (!reg || !REG_P (reg) || GET_MODE (reg) != mode
+	  || GET_MODE_CLASS (mode) != MODE_INT)
+	return false;
+
+      for (link = CALL_INSN_FUNCTION_USAGE (call_insn);
+	   link;
+	   link = XEXP (link, 1))
+	if (GET_CODE (XEXP (link, 0)) == USE)
+	  {
+	    args[idx] = XEXP (XEXP (link, 0), 0);
+	    if (REG_P (args[idx])
+		&& REGNO (args[idx]) == REGNO (reg)
+		&& (GET_MODE (args[idx]) == mode
+		    || (GET_MODE_CLASS (GET_MODE (args[idx])) == MODE_INT
+			&& (GET_MODE_SIZE (GET_MODE (args[idx]))
+			    <= UNITS_PER_WORD)
+			&& (GET_MODE_SIZE (GET_MODE (args[idx]))
+			    > GET_MODE_SIZE (mode)))))
+	      break;
+	  }
+      if (!link)
+	return false;
+
+      tmp = cselib_expand_value_rtx (args[idx], scratch, 5);
+      if (GET_MODE (args[idx]) != mode)
+	{
+	  if (!tmp || !CONST_INT_P (tmp))
+	    return false;
+	  tmp = GEN_INT (trunc_int_for_mode (INTVAL (tmp), mode));
+	}
+      if (tmp)
+	args[idx] = tmp;
+
+      FUNCTION_ARG_ADVANCE (args_so_far, mode, NULL_TREE, 1);
+    }
+  if (arg != void_list_node || idx != nargs)
+    return false;
+  return true;
+}
+
+
 /* Apply record_store to all candidate stores in INSN.  Mark INSN
    if some part of it is not a candidate store and assigns to a
    non-register target.  */
@@ -2045,18 +2351,48 @@ scan_insn (bb_info_t bb_info, rtx insn)
 
   if (CALL_P (insn))
     {
+      bool const_call;
+      tree memset_call = NULL_TREE;
+
       insn_info->cannot_delete = true;
 
       /* Const functions cannot do anything bad i.e. read memory,
 	 however, they can read their parameters which may have
-	 been pushed onto the stack.  */
-      if (RTL_CONST_CALL_P (insn))
+	 been pushed onto the stack.
+	 memset and bzero don't read memory either.  */
+      const_call = RTL_CONST_CALL_P (insn);
+      if (!const_call)
+	{
+	  rtx call = PATTERN (insn);
+	  if (GET_CODE (call) == PARALLEL)
+	    call = XVECEXP (call, 0, 0);
+	  if (GET_CODE (call) == SET)
+	    call = SET_SRC (call);
+	  if (GET_CODE (call) == CALL
+	      && MEM_P (XEXP (call, 0))
+	      && GET_CODE (XEXP (XEXP (call, 0), 0)) == SYMBOL_REF)
+	    {
+	      rtx symbol = XEXP (XEXP (call, 0), 0);
+	      if (SYMBOL_REF_DECL (symbol)
+		  && TREE_CODE (SYMBOL_REF_DECL (symbol)) == FUNCTION_DECL)
+		{
+		  if ((DECL_BUILT_IN_CLASS (SYMBOL_REF_DECL (symbol))
+		       == BUILT_IN_NORMAL
+		       && (DECL_FUNCTION_CODE (SYMBOL_REF_DECL (symbol))
+			   == BUILT_IN_MEMSET))
+		      || SYMBOL_REF_DECL (symbol) == block_clear_fn)
+		    memset_call = SYMBOL_REF_DECL (symbol);
+		}
+	    }
+	}
+      if (const_call || memset_call)
 	{
 	  insn_info_t i_ptr = active_local_stores;
 	  insn_info_t last = NULL;
 
 	  if (dump_file)
-	    fprintf (dump_file, "const call %d\n", INSN_UID (insn));
+	    fprintf (dump_file, "%s call %d\n",
+		     const_call ? "const" : "memset", INSN_UID (insn));
 
 	  /* See the head comment of the frame_read field.  */
 	  if (reload_completed)
@@ -2102,6 +2438,28 @@ scan_insn (bb_info_t bb_info, rtx insn)
 
 	      i_ptr = i_ptr->next_local_store;
 	    }
+
+	  if (memset_call)
+	    {
+	      rtx args[3];
+	      if (get_call_args (insn, memset_call, args, 3)
+		  && CONST_INT_P (args[1])
+		  && CONST_INT_P (args[2])
+		  && INTVAL (args[2]) > 0)
+		{
+		  rtx mem = gen_rtx_MEM (BLKmode, args[0]);
+		  set_mem_size (mem, args[2]);
+		  body = gen_rtx_SET (VOIDmode, mem, args[1]);
+		  mems_found += record_store (body, bb_info);
+		  if (dump_file)
+		    fprintf (dump_file, "handling memset as BLKmode store\n");
+		  if (mems_found == 1)
+		    {
+		      insn_info->next_local_store = active_local_stores;
+		      active_local_stores = insn_info;
+		    }
+		}
+	    }
 	}
 
       else
@@ -2134,11 +2492,11 @@ scan_insn (bb_info_t bb_info, rtx insn)
     fprintf (dump_file, "mems_found = %d, cannot_delete = %s\n", 
 	     mems_found, insn_info->cannot_delete ? "true" : "false");
 
-  /* If we found some sets of mems, and the insn has not been marked
-     cannot delete, add it into the active_local_stores so that it can
-     be locally deleted if found dead.  Otherwise mark it as cannot
-     delete.  This simplifies the processing later.  */ 
-  if (mems_found == 1 && !insn_info->cannot_delete)
+  /* If we found some sets of mems, add it into the active_local_stores so
+     that it can be locally deleted if found dead or used for
+     replace_read and redundant constant store elimination.  Otherwise mark
+     it as cannot delete.  This simplifies the processing later.  */
+  if (mems_found == 1)
     {
       insn_info->next_local_store = active_local_stores;
       active_local_stores = insn_info;
@@ -2263,14 +2621,14 @@ dse_step1 (void)
 		  /* Skip the clobbers.  */
 		  while (!store_info->is_set)
 		    store_info = store_info->next;
-		  if (store_info->alias_set)
+		  if (store_info->alias_set && !i_ptr->cannot_delete)
 		    delete_dead_store_insn (i_ptr);
 		  else 
 		    if (store_info->group_id >= 0)
 		      {
 			group_info_t group 
 			  = VEC_index (group_info_t, rtx_group_vec, store_info->group_id);
-			if (group->frame_related)
+			if (group->frame_related && !i_ptr->cannot_delete)
 			  delete_dead_store_insn (i_ptr);
 		      }
 
@@ -2298,7 +2656,40 @@ dse_step1 (void)
 	  while (ptr)
 	    {
 	      if (ptr->contains_cselib_groups)
-		free_store_info (ptr);
+		{
+		  store_info_t s_info = ptr->store_rec;
+		  while (s_info && !s_info->is_set)
+		    s_info = s_info->next;
+		  if (s_info
+		      && s_info->redundant_reason
+		      && s_info->redundant_reason->insn
+		      && !ptr->cannot_delete)
+		    {
+		      if (dump_file)
+			fprintf (dump_file, "Locally deleting insn %d "
+					    "because insn %d stores the "
+					    "same value and couldn't be "
+					    "eliminated\n",
+				 INSN_UID (ptr->insn),
+				 INSN_UID (s_info->redundant_reason->insn));
+		      delete_dead_store_insn (ptr);
+		    }
+		  if (s_info)
+		    s_info->redundant_reason = NULL;
+		  free_store_info (ptr);
+		}
+	      else
+		{
+		  store_info_t s_info;
+
+		  /* Free at least positions_needed bitmaps.  */
+		  for (s_info = ptr->store_rec; s_info; s_info = s_info->next)
+		    if (s_info->is_large)
+		      {
+			BITMAP_FREE (s_info->positions_needed.large.bitmap);
+			s_info->is_large = false;
+		      }
+		}
 	      ptr = ptr->prev_insn;
 	    }
 
@@ -3236,11 +3627,61 @@ dse_step5_spill (void)
 /*----------------------------------------------------------------------------
    Sixth step.
 
+   Delete stores made redundant by earlier stores (which store the same
+   value) that couldn't be eliminated.
+----------------------------------------------------------------------------*/
+
+static void
+dse_step6 (void)
+{
+  basic_block bb;
+
+  FOR_ALL_BB (bb)
+    {
+      bb_info_t bb_info = bb_table[bb->index];
+      insn_info_t insn_info = bb_info->last_insn;
+
+      while (insn_info)
+	{
+	  /* There may have been code deleted by the dce pass run before
+	     this phase.  */
+	  if (insn_info->insn
+	      && INSN_P (insn_info->insn)
+	      && !insn_info->cannot_delete)
+	    {
+	      store_info_t s_info = insn_info->store_rec;
+
+	      while (s_info && !s_info->is_set)
+		s_info = s_info->next;
+	      if (s_info
+		  && s_info->redundant_reason
+		  && s_info->redundant_reason->insn
+		  && INSN_P (s_info->redundant_reason->insn))
+		{
+		  rtx rinsn = s_info->redundant_reason->insn;
+		  if (dump_file)
+		    fprintf (dump_file, "Locally deleting insn %d "
+					"because insn %d stores the "
+					"same value and couldn't be "
+					"eliminated\n",
+					INSN_UID (insn_info->insn),
+					INSN_UID (rinsn));
+		  delete_dead_store_insn (insn_info);
+		}
+	    }
+	  insn_info = insn_info->prev_insn;
+	}
+    }
+}
+
+/*----------------------------------------------------------------------------
+   Seventh step.
+
    Destroy everything left standing. 
 ----------------------------------------------------------------------------*/
 
 static void 
-dse_step6 (bool global_done)
+dse_step7 (bool global_done)
 {
   unsigned int i;
   group_info_t group;
@@ -3346,8 +3787,9 @@ rest_of_handle_dse (void)
       dse_step4 ();
       dse_step5_spill ();
     }
-  
-  dse_step6 (did_global);
+
+  dse_step6 ();
+  dse_step7 (did_global);
 
   if (dump_file)
     fprintf (dump_file, "dse: local deletions = %d, global deletions = %d, spill deletions = %d\n",