--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/lower-subreg.c	Fri Jul 17 14:47:48 2009 +0900
@@ -0,0 +1,1365 @@
+/* Decompose multiword subregs.
+   Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
+   Contributed by Richard Henderson <rth@redhat.com>
+		  Ian Lance Taylor <iant@google.com>
+
+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 "machmode.h"
+#include "tm.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "timevar.h"
+#include "flags.h"
+#include "insn-config.h"
+#include "obstack.h"
+#include "basic-block.h"
+#include "recog.h"
+#include "bitmap.h"
+#include "expr.h"
+#include "except.h"
+#include "regs.h"
+#include "tree-pass.h"
+#include "df.h"
+
+#ifdef STACK_GROWS_DOWNWARD
+# undef STACK_GROWS_DOWNWARD
+# define STACK_GROWS_DOWNWARD 1
+#else
+# define STACK_GROWS_DOWNWARD 0
+#endif
+
+DEF_VEC_P (bitmap);
+DEF_VEC_ALLOC_P (bitmap,heap);
+
+/* Decompose multi-word pseudo-registers into individual
+   pseudo-registers when possible.  This is possible when all the uses
+   of a multi-word register are via SUBREG, or are copies of the
+   register to another location.  Breaking apart the register permits
+   more CSE and permits better register allocation.  */
+
+/* Bit N in this bitmap is set if regno N is used in a context in
+   which we can decompose it.  */
+static bitmap decomposable_context;
+
+/* Bit N in this bitmap is set if regno N is used in a context in
+   which it can not be decomposed.  */
+static bitmap non_decomposable_context;
+
+/* Bit N in the bitmap in element M of this array is set if there is a
+   copy from reg M to reg N.  */
+static VEC(bitmap,heap) *reg_copy_graph;
+
+/* Return whether X is a simple object which we can take a word_mode
+   subreg of.  */
+
+static bool
+simple_move_operand (rtx x)
+{
+  if (GET_CODE (x) == SUBREG)
+    x = SUBREG_REG (x);
+
+  if (!OBJECT_P (x))
+    return false;
+
+  if (GET_CODE (x) == LABEL_REF
+      || GET_CODE (x) == SYMBOL_REF
+      || GET_CODE (x) == HIGH
+      || GET_CODE (x) == CONST)
+    return false;
+
+  if (MEM_P (x)
+      && (MEM_VOLATILE_P (x)
+	  || mode_dependent_address_p (XEXP (x, 0))))
+    return false;
+
+  return true;
+}
+
+/* If INSN is a single set between two objects, return the single set.
+   Such an insn can always be decomposed.  INSN should have been
+   passed to recog and extract_insn before this is called.  */
+
+static rtx
+simple_move (rtx insn)
+{
+  rtx x;
+  rtx set;
+  enum machine_mode mode;
+
+  if (recog_data.n_operands != 2)
+    return NULL_RTX;
+
+  set = single_set (insn);
+  if (!set)
+    return NULL_RTX;
+
+  x = SET_DEST (set);
+  if (x != recog_data.operand[0] && x != recog_data.operand[1])
+    return NULL_RTX;
+  if (!simple_move_operand (x))
+    return NULL_RTX;
+
+  x = SET_SRC (set);
+  if (x != recog_data.operand[0] && x != recog_data.operand[1])
+    return NULL_RTX;
+  /* For the src we can handle ASM_OPERANDS, and it is beneficial for
+     things like x86 rdtsc which returns a DImode value.  */
+  if (GET_CODE (x) != ASM_OPERANDS
+      && !simple_move_operand (x))
+    return NULL_RTX;
+
+  /* We try to decompose in integer modes, to avoid generating
+     inefficient code copying between integer and floating point
+     registers.  That means that we can't decompose if this is a
+     non-integer mode for which there is no integer mode of the same
+     size.  */
+  mode = GET_MODE (SET_SRC (set));
+  if (!SCALAR_INT_MODE_P (mode)
+      && (mode_for_size (GET_MODE_SIZE (mode) * BITS_PER_UNIT, MODE_INT, 0)
+	  == BLKmode))
+    return NULL_RTX;
+
+  /* Reject PARTIAL_INT modes.  They are used for processor specific
+     purposes and it's probably best not to tamper with them.  */
+  if (GET_MODE_CLASS (mode) == MODE_PARTIAL_INT)
+    return NULL_RTX;
+
+  return set;
+}
+
+/* If SET is a copy from one multi-word pseudo-register to another,
+   record that in reg_copy_graph.  Return whether it is such a
+   copy.  */
+
+static bool
+find_pseudo_copy (rtx set)
+{
+  rtx dest = SET_DEST (set);
+  rtx src = SET_SRC (set);
+  unsigned int rd, rs;
+  bitmap b;
+
+  if (!REG_P (dest) || !REG_P (src))
+    return false;
+
+  rd = REGNO (dest);
+  rs = REGNO (src);
+  if (HARD_REGISTER_NUM_P (rd) || HARD_REGISTER_NUM_P (rs))
+    return false;
+
+  if (GET_MODE_SIZE (GET_MODE (dest)) <= UNITS_PER_WORD)
+    return false;
+
+  b = VEC_index (bitmap, reg_copy_graph, rs);
+  if (b == NULL)
+    {
+      b = BITMAP_ALLOC (NULL);
+      VEC_replace (bitmap, reg_copy_graph, rs, b);
+    }
+
+  bitmap_set_bit (b, rd);
+
+  return true;
+}
+
+/* Look through the registers in DECOMPOSABLE_CONTEXT.  For each case
+   where they are copied to another register, add the register to
+   which they are copied to DECOMPOSABLE_CONTEXT.  Use
+   NON_DECOMPOSABLE_CONTEXT to limit this--we don't bother to track
+   copies of registers which are in NON_DECOMPOSABLE_CONTEXT.  */
+
+static void
+propagate_pseudo_copies (void)
+{
+  bitmap queue, propagate;
+
+  queue = BITMAP_ALLOC (NULL);
+  propagate = BITMAP_ALLOC (NULL);
+
+  bitmap_copy (queue, decomposable_context);
+  do
+    {
+      bitmap_iterator iter;
+      unsigned int i;
+
+      bitmap_clear (propagate);
+
+      EXECUTE_IF_SET_IN_BITMAP (queue, 0, i, iter)
+	{
+	  bitmap b = VEC_index (bitmap, reg_copy_graph, i);
+	  if (b)
+	    bitmap_ior_and_compl_into (propagate, b, non_decomposable_context);
+	}
+
+      bitmap_and_compl (queue, propagate, decomposable_context);
+      bitmap_ior_into (decomposable_context, propagate);
+    }
+  while (!bitmap_empty_p (queue));
+
+  BITMAP_FREE (queue);
+  BITMAP_FREE (propagate);
+}
+
+/* A pointer to one of these values is passed to
+   find_decomposable_subregs via for_each_rtx.  */
+
+enum classify_move_insn
+{
+  /* Not a simple move from one location to another.  */
+  NOT_SIMPLE_MOVE,
+  /* A simple move from one pseudo-register to another.  */
+  SIMPLE_PSEUDO_REG_MOVE,
+  /* A simple move involving a non-pseudo-register.  */
+  SIMPLE_MOVE
+};
+
+/* This is called via for_each_rtx.  If we find a SUBREG which we
+   could use to decompose a pseudo-register, set a bit in
+   DECOMPOSABLE_CONTEXT.  If we find an unadorned register which is
+   not a simple pseudo-register copy, DATA will point at the type of
+   move, and we set a bit in DECOMPOSABLE_CONTEXT or
+   NON_DECOMPOSABLE_CONTEXT as appropriate.  */
+
+static int
+find_decomposable_subregs (rtx *px, void *data)
+{
+  enum classify_move_insn *pcmi = (enum classify_move_insn *) data;
+  rtx x = *px;
+
+  if (x == NULL_RTX)
+    return 0;
+
+  if (GET_CODE (x) == SUBREG)
+    {
+      rtx inner = SUBREG_REG (x);
+      unsigned int regno, outer_size, inner_size, outer_words, inner_words;
+
+      if (!REG_P (inner))
+	return 0;
+
+      regno = REGNO (inner);
+      if (HARD_REGISTER_NUM_P (regno))
+	return -1;
+
+      outer_size = GET_MODE_SIZE (GET_MODE (x));
+      inner_size = GET_MODE_SIZE (GET_MODE (inner));
+      outer_words = (outer_size + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
+      inner_words = (inner_size + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
+
+      /* We only try to decompose single word subregs of multi-word
+	 registers.  When we find one, we return -1 to avoid iterating
+	 over the inner register.
+
+	 ??? This doesn't allow, e.g., DImode subregs of TImode values
+	 on 32-bit targets.  We would need to record the way the
+	 pseudo-register was used, and only decompose if all the uses
+	 were the same number and size of pieces.  Hopefully this
+	 doesn't happen much.  */
+
+      if (outer_words == 1 && inner_words > 1)
+	{
+	  bitmap_set_bit (decomposable_context, regno);
+	  return -1;
+	}
+
+      /* If this is a cast from one mode to another, where the modes
+	 have the same size, and they are not tieable, then mark this
+	 register as non-decomposable.  If we decompose it we are
+	 likely to mess up whatever the backend is trying to do.  */
+      if (outer_words > 1
+	  && outer_size == inner_size
+	  && !MODES_TIEABLE_P (GET_MODE (x), GET_MODE (inner)))
+	{
+	  bitmap_set_bit (non_decomposable_context, regno);
+	  return -1;
+	}
+    }
+  else if (REG_P (x))
+    {
+      unsigned int regno;
+
+      /* We will see an outer SUBREG before we see the inner REG, so
+	 when we see a plain REG here it means a direct reference to
+	 the register.
+
+	 If this is not a simple copy from one location to another,
+	 then we can not decompose this register.  If this is a simple
+	 copy from one pseudo-register to another, and the mode is right
+	 then we mark the register as decomposable.
+	 Otherwise we don't say anything about this register --
+	 it could be decomposed, but whether that would be
+	 profitable depends upon how it is used elsewhere.
+
+	 We only set bits in the bitmap for multi-word
+	 pseudo-registers, since those are the only ones we care about
+	 and it keeps the size of the bitmaps down.  */
+
+      regno = REGNO (x);
+      if (!HARD_REGISTER_NUM_P (regno)
+	  && GET_MODE_SIZE (GET_MODE (x)) > UNITS_PER_WORD)
+	{
+	  switch (*pcmi)
+	    {
+	    case NOT_SIMPLE_MOVE:
+	      bitmap_set_bit (non_decomposable_context, regno);
+	      break;
+	    case SIMPLE_PSEUDO_REG_MOVE:
+	      if (MODES_TIEABLE_P (GET_MODE (x), word_mode))
+		bitmap_set_bit (decomposable_context, regno);
+	      break;
+	    case SIMPLE_MOVE:
+	      break;
+	    default:
+	      gcc_unreachable ();
+	    }
+	}
+    }
+  else if (MEM_P (x))
+    {
+      enum classify_move_insn cmi_mem = NOT_SIMPLE_MOVE;
+
+      /* Any registers used in a MEM do not participate in a
+	 SIMPLE_MOVE or SIMPLE_PSEUDO_REG_MOVE.  Do our own recursion
+	 here, and return -1 to block the parent's recursion.  */
+      for_each_rtx (&XEXP (x, 0), find_decomposable_subregs, &cmi_mem);
+      return -1;
+    }
+
+  return 0;
+}
+
+/* Decompose REGNO into word-sized components.  We smash the REG node
+   in place.  This ensures that (1) something goes wrong quickly if we
+   fail to make some replacement, and (2) the debug information inside
+   the symbol table is automatically kept up to date.  */
+
+static void
+decompose_register (unsigned int regno)
+{
+  rtx reg;
+  unsigned int words, i;
+  rtvec v;
+
+  reg = regno_reg_rtx[regno];
+
+  regno_reg_rtx[regno] = NULL_RTX;
+
+  words = GET_MODE_SIZE (GET_MODE (reg));
+  words = (words + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
+
+  v = rtvec_alloc (words);
+  for (i = 0; i < words; ++i)
+    RTVEC_ELT (v, i) = gen_reg_rtx_offset (reg, word_mode, i * UNITS_PER_WORD);
+
+  PUT_CODE (reg, CONCATN);
+  XVEC (reg, 0) = v;
+
+  if (dump_file)
+    {
+      fprintf (dump_file, "; Splitting reg %u ->", regno);
+      for (i = 0; i < words; ++i)
+	fprintf (dump_file, " %u", REGNO (XVECEXP (reg, 0, i)));
+      fputc ('\n', dump_file);
+    }
+}
+
+/* Get a SUBREG of a CONCATN.  */
+
+static rtx
+simplify_subreg_concatn (enum machine_mode outermode, rtx op,
+			 unsigned int byte)
+{
+  unsigned int inner_size;
+  enum machine_mode innermode;
+  rtx part;
+  unsigned int final_offset;
+
+  gcc_assert (GET_CODE (op) == CONCATN);
+  gcc_assert (byte % GET_MODE_SIZE (outermode) == 0);
+
+  innermode = GET_MODE (op);
+  gcc_assert (byte < GET_MODE_SIZE (innermode));
+  gcc_assert (GET_MODE_SIZE (outermode) <= GET_MODE_SIZE (innermode));
+
+  inner_size = GET_MODE_SIZE (innermode) / XVECLEN (op, 0);
+  part = XVECEXP (op, 0, byte / inner_size);
+  final_offset = byte % inner_size;
+  if (final_offset + GET_MODE_SIZE (outermode) > inner_size)
+    return NULL_RTX;
+
+  return simplify_gen_subreg (outermode, part, GET_MODE (part), final_offset);
+}
+
+/* Wrapper around simplify_gen_subreg which handles CONCATN.  */
+
+static rtx
+simplify_gen_subreg_concatn (enum machine_mode outermode, rtx op,
+			     enum machine_mode innermode, unsigned int byte)
+{
+  rtx ret;
+
+  /* We have to handle generating a SUBREG of a SUBREG of a CONCATN.
+     If OP is a SUBREG of a CONCATN, then it must be a simple mode
+     change with the same size and offset 0, or it must extract a
+     part.  We shouldn't see anything else here.  */
+  if (GET_CODE (op) == SUBREG && GET_CODE (SUBREG_REG (op)) == CONCATN)
+    {
+      rtx op2;
+
+      if ((GET_MODE_SIZE (GET_MODE (op))
+	   == GET_MODE_SIZE (GET_MODE (SUBREG_REG (op))))
+	  && SUBREG_BYTE (op) == 0)
+	return simplify_gen_subreg_concatn (outermode, SUBREG_REG (op),
+					    GET_MODE (SUBREG_REG (op)), byte);
+
+      op2 = simplify_subreg_concatn (GET_MODE (op), SUBREG_REG (op),
+				     SUBREG_BYTE (op));
+      if (op2 == NULL_RTX)
+	{
+	  /* We don't handle paradoxical subregs here.  */
+	  gcc_assert (GET_MODE_SIZE (outermode)
+		      <= GET_MODE_SIZE (GET_MODE (op)));
+	  gcc_assert (GET_MODE_SIZE (GET_MODE (op))
+		      <= GET_MODE_SIZE (GET_MODE (SUBREG_REG (op))));
+	  op2 = simplify_subreg_concatn (outermode, SUBREG_REG (op),
+					 byte + SUBREG_BYTE (op));
+	  gcc_assert (op2 != NULL_RTX);
+	  return op2;
+	}
+
+      op = op2;
+      gcc_assert (op != NULL_RTX);
+      gcc_assert (innermode == GET_MODE (op));
+    }
+
+  if (GET_CODE (op) == CONCATN)
+    return simplify_subreg_concatn (outermode, op, byte);
+
+  ret = simplify_gen_subreg (outermode, op, innermode, byte);
+
+  /* If we see an insn like (set (reg:DI) (subreg:DI (reg:SI) 0)) then
+     resolve_simple_move will ask for the high part of the paradoxical
+     subreg, which does not have a value.  Just return a zero.  */
+  if (ret == NULL_RTX
+      && GET_CODE (op) == SUBREG
+      && SUBREG_BYTE (op) == 0
+      && (GET_MODE_SIZE (innermode)
+	  > GET_MODE_SIZE (GET_MODE (SUBREG_REG (op)))))
+    return CONST0_RTX (outermode);
+
+  gcc_assert (ret != NULL_RTX);
+  return ret;
+}
+
+/* Return whether we should resolve X into the registers into which it
+   was decomposed.  */
+
+static bool
+resolve_reg_p (rtx x)
+{
+  return GET_CODE (x) == CONCATN;
+}
+
+/* Return whether X is a SUBREG of a register which we need to
+   resolve.  */
+
+static bool
+resolve_subreg_p (rtx x)
+{
+  if (GET_CODE (x) != SUBREG)
+    return false;
+  return resolve_reg_p (SUBREG_REG (x));
+}
+
+/* This is called via for_each_rtx.  Look for SUBREGs which need to be
+   decomposed.  */
+
+static int
+resolve_subreg_use (rtx *px, void *data)
+{
+  rtx insn = (rtx) data;
+  rtx x = *px;
+
+  if (x == NULL_RTX)
+    return 0;
+
+  if (resolve_subreg_p (x))
+    {
+      x = simplify_subreg_concatn (GET_MODE (x), SUBREG_REG (x),
+				   SUBREG_BYTE (x));
+
+      /* It is possible for a note to contain a reference which we can
+	 decompose.  In this case, return 1 to the caller to indicate
+	 that the note must be removed.  */
+      if (!x)
+	{
+	  gcc_assert (!insn);
+	  return 1;
+	}
+
+      validate_change (insn, px, x, 1);
+      return -1;
+    }
+
+  if (resolve_reg_p (x))
+    {
+      /* Return 1 to the caller to indicate that we found a direct
+	 reference to a register which is being decomposed.  This can
+	 happen inside notes, multiword shift or zero-extend
+	 instructions.  */
+      return 1;
+    }
+
+  return 0;
+}
+
+/* We are deleting INSN.  Move any EH_REGION notes to INSNS.  */
+
+static void
+move_eh_region_note (rtx insn, rtx insns)
+{
+  rtx note, p;
+
+  note = find_reg_note (insn, REG_EH_REGION, NULL_RTX);
+  if (note == NULL_RTX)
+    return;
+
+  gcc_assert (CALL_P (insn)
+	      || (flag_non_call_exceptions && may_trap_p (PATTERN (insn))));
+
+  for (p = insns; p != NULL_RTX; p = NEXT_INSN (p))
+    {
+      if (CALL_P (p)
+	  || (flag_non_call_exceptions
+	      && INSN_P (p)
+	      && may_trap_p (PATTERN (p))))
+	add_reg_note (p, REG_EH_REGION, XEXP (note, 0));
+    }
+}
+
+/* Resolve any decomposed registers which appear in register notes on
+   INSN.  */
+
+static void
+resolve_reg_notes (rtx insn)
+{
+  rtx *pnote, note;
+
+  note = find_reg_equal_equiv_note (insn);
+  if (note)
+    {
+      int old_count = num_validated_changes ();
+      if (for_each_rtx (&XEXP (note, 0), resolve_subreg_use, NULL))
+	remove_note (insn, note);
+      else
+	if (old_count != num_validated_changes ())
+	  df_notes_rescan (insn);
+    }
+
+  pnote = &REG_NOTES (insn);
+  while (*pnote != NULL_RTX)
+    {
+      bool del = false;
+
+      note = *pnote;
+      switch (REG_NOTE_KIND (note))
+	{
+	case REG_DEAD:
+	case REG_UNUSED:
+	  if (resolve_reg_p (XEXP (note, 0)))
+	    del = true;
+	  break;
+
+	default:
+	  break;
+	}
+
+      if (del)
+	*pnote = XEXP (note, 1);
+      else
+	pnote = &XEXP (note, 1);
+    }
+}
+
+/* Return whether X can be decomposed into subwords.  */
+
+static bool
+can_decompose_p (rtx x)
+{
+  if (REG_P (x))
+    {
+      unsigned int regno = REGNO (x);
+
+      if (HARD_REGISTER_NUM_P (regno))
+	return (validate_subreg (word_mode, GET_MODE (x), x, UNITS_PER_WORD)
+		&& HARD_REGNO_MODE_OK (regno, word_mode));
+      else
+	return !bitmap_bit_p (non_decomposable_context, regno);
+    }
+
+  return true;
+}
+
+/* Decompose the registers used in a simple move SET within INSN.  If
+   we don't change anything, return INSN, otherwise return the start
+   of the sequence of moves.  */
+
+static rtx
+resolve_simple_move (rtx set, rtx insn)
+{
+  rtx src, dest, real_dest, insns;
+  enum machine_mode orig_mode, dest_mode;
+  unsigned int words;
+  bool pushing;
+
+  src = SET_SRC (set);
+  dest = SET_DEST (set);
+  orig_mode = GET_MODE (dest);
+
+  words = (GET_MODE_SIZE (orig_mode) + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
+  if (words <= 1)
+    return insn;
+
+  start_sequence ();
+
+  /* We have to handle copying from a SUBREG of a decomposed reg where
+     the SUBREG is larger than word size.  Rather than assume that we
+     can take a word_mode SUBREG of the destination, we copy to a new
+     register and then copy that to the destination.  */
+
+  real_dest = NULL_RTX;
+
+  if (GET_CODE (src) == SUBREG
+      && resolve_reg_p (SUBREG_REG (src))
+      && (SUBREG_BYTE (src) != 0
+	  || (GET_MODE_SIZE (orig_mode)
+	      != GET_MODE_SIZE (GET_MODE (SUBREG_REG (src))))))
+    {
+      real_dest = dest;
+      dest = gen_reg_rtx (orig_mode);
+      if (REG_P (real_dest))
+	REG_ATTRS (dest) = REG_ATTRS (real_dest);
+    }
+
+  /* Similarly if we are copying to a SUBREG of a decomposed reg where
+     the SUBREG is larger than word size.  */
+
+  if (GET_CODE (dest) == SUBREG
+      && resolve_reg_p (SUBREG_REG (dest))
+      && (SUBREG_BYTE (dest) != 0
+	  || (GET_MODE_SIZE (orig_mode)
+	      != GET_MODE_SIZE (GET_MODE (SUBREG_REG (dest))))))
+    {
+      rtx reg, minsn, smove;
+
+      reg = gen_reg_rtx (orig_mode);
+      minsn = emit_move_insn (reg, src);
+      smove = single_set (minsn);
+      gcc_assert (smove != NULL_RTX);
+      resolve_simple_move (smove, minsn);
+      src = reg;
+    }
+
+  /* If we didn't have any big SUBREGS of decomposed registers, and
+     neither side of the move is a register we are decomposing, then
+     we don't have to do anything here.  */
+
+  if (src == SET_SRC (set)
+      && dest == SET_DEST (set)
+      && !resolve_reg_p (src)
+      && !resolve_subreg_p (src)
+      && !resolve_reg_p (dest)
+      && !resolve_subreg_p (dest))
+    {
+      end_sequence ();
+      return insn;
+    }
+
+  /* It's possible for the code to use a subreg of a decomposed
+     register while forming an address.  We need to handle that before
+     passing the address to emit_move_insn.  We pass NULL_RTX as the
+     insn parameter to resolve_subreg_use because we can not validate
+     the insn yet.  */
+  if (MEM_P (src) || MEM_P (dest))
+    {
+      int acg;
+
+      if (MEM_P (src))
+	for_each_rtx (&XEXP (src, 0), resolve_subreg_use, NULL_RTX);
+      if (MEM_P (dest))
+	for_each_rtx (&XEXP (dest, 0), resolve_subreg_use, NULL_RTX);
+      acg = apply_change_group ();
+      gcc_assert (acg);
+    }
+
+  /* If SRC is a register which we can't decompose, or has side
+     effects, we need to move via a temporary register.  */
+
+  if (!can_decompose_p (src)
+      || side_effects_p (src)
+      || GET_CODE (src) == ASM_OPERANDS)
+    {
+      rtx reg;
+
+      reg = gen_reg_rtx (orig_mode);
+      emit_move_insn (reg, src);
+      src = reg;
+    }
+
+  /* If DEST is a register which we can't decompose, or has side
+     effects, we need to first move to a temporary register.  We
+     handle the common case of pushing an operand directly.  We also
+     go through a temporary register if it holds a floating point
+     value.  This gives us better code on systems which can't move
+     data easily between integer and floating point registers.  */
+
+  dest_mode = orig_mode;
+  pushing = push_operand (dest, dest_mode);
+  if (!can_decompose_p (dest)
+      || (side_effects_p (dest) && !pushing)
+      || (!SCALAR_INT_MODE_P (dest_mode)
+	  && !resolve_reg_p (dest)
+	  && !resolve_subreg_p (dest)))
+    {
+      if (real_dest == NULL_RTX)
+	real_dest = dest;
+      if (!SCALAR_INT_MODE_P (dest_mode))
+	{
+	  dest_mode = mode_for_size (GET_MODE_SIZE (dest_mode) * BITS_PER_UNIT,
+				     MODE_INT, 0);
+	  gcc_assert (dest_mode != BLKmode);
+	}
+      dest = gen_reg_rtx (dest_mode);
+      if (REG_P (real_dest))
+	REG_ATTRS (dest) = REG_ATTRS (real_dest);
+    }
+
+  if (pushing)
+    {
+      unsigned int i, j, jinc;
+
+      gcc_assert (GET_MODE_SIZE (orig_mode) % UNITS_PER_WORD == 0);
+      gcc_assert (GET_CODE (XEXP (dest, 0)) != PRE_MODIFY);
+      gcc_assert (GET_CODE (XEXP (dest, 0)) != POST_MODIFY);
+
+      if (WORDS_BIG_ENDIAN == STACK_GROWS_DOWNWARD)
+	{
+	  j = 0;
+	  jinc = 1;
+	}
+      else
+	{
+	  j = words - 1;
+	  jinc = -1;
+	}
+
+      for (i = 0; i < words; ++i, j += jinc)
+	{
+	  rtx temp;
+
+	  temp = copy_rtx (XEXP (dest, 0));
+	  temp = adjust_automodify_address_nv (dest, word_mode, temp,
+					       j * UNITS_PER_WORD);
+	  emit_move_insn (temp,
+			  simplify_gen_subreg_concatn (word_mode, src,
+						       orig_mode,
+						       j * UNITS_PER_WORD));
+	}
+    }
+  else
+    {
+      unsigned int i;
+
+      if (REG_P (dest) && !HARD_REGISTER_NUM_P (REGNO (dest)))
+	emit_clobber (dest);
+
+      for (i = 0; i < words; ++i)
+	emit_move_insn (simplify_gen_subreg_concatn (word_mode, dest,
+						     dest_mode,
+						     i * UNITS_PER_WORD),
+			simplify_gen_subreg_concatn (word_mode, src,
+						     orig_mode,
+						     i * UNITS_PER_WORD));
+    }
+
+  if (real_dest != NULL_RTX)
+    {
+      rtx mdest, minsn, smove;
+
+      if (dest_mode == orig_mode)
+	mdest = dest;
+      else
+	mdest = simplify_gen_subreg (orig_mode, dest, GET_MODE (dest), 0);
+      minsn = emit_move_insn (real_dest, mdest);
+
+      smove = single_set (minsn);
+      gcc_assert (smove != NULL_RTX);
+
+      resolve_simple_move (smove, minsn);
+    }
+
+  insns = get_insns ();
+  end_sequence ();
+
+  move_eh_region_note (insn, insns);
+
+  emit_insn_before (insns, insn);
+
+  delete_insn (insn);
+
+  return insns;
+}
+
+/* Change a CLOBBER of a decomposed register into a CLOBBER of the
+   component registers.  Return whether we changed something.  */
+
+static bool
+resolve_clobber (rtx pat, rtx insn)
+{
+  rtx reg;
+  enum machine_mode orig_mode;
+  unsigned int words, i;
+  int ret;
+
+  reg = XEXP (pat, 0);
+  if (!resolve_reg_p (reg) && !resolve_subreg_p (reg))
+    return false;
+
+  orig_mode = GET_MODE (reg);
+  words = GET_MODE_SIZE (orig_mode);
+  words = (words + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
+
+  ret = validate_change (NULL_RTX, &XEXP (pat, 0),
+			 simplify_gen_subreg_concatn (word_mode, reg,
+						      orig_mode, 0),
+			 0);
+  df_insn_rescan (insn);
+  gcc_assert (ret != 0);
+
+  for (i = words - 1; i > 0; --i)
+    {
+      rtx x;
+
+      x = simplify_gen_subreg_concatn (word_mode, reg, orig_mode,
+				       i * UNITS_PER_WORD);
+      x = gen_rtx_CLOBBER (VOIDmode, x);
+      emit_insn_after (x, insn);
+    }
+
+  resolve_reg_notes (insn);
+
+  return true;
+}
+
+/* A USE of a decomposed register is no longer meaningful.  Return
+   whether we changed something.  */
+
+static bool
+resolve_use (rtx pat, rtx insn)
+{
+  if (resolve_reg_p (XEXP (pat, 0)) || resolve_subreg_p (XEXP (pat, 0)))
+    {
+      delete_insn (insn);
+      return true;
+    }
+
+  resolve_reg_notes (insn);
+
+  return false;
+}
+
+/* Checks if INSN is a decomposable multiword-shift or zero-extend and
+   sets the decomposable_context bitmap accordingly.  A non-zero value
+   is returned if a decomposable insn has been found.  */
+
+static int
+find_decomposable_shift_zext (rtx insn)
+{
+  rtx set;
+  rtx op;
+  rtx op_operand;
+
+  set = single_set (insn);
+  if (!set)
+    return 0;
+
+  op = SET_SRC (set);
+  if (GET_CODE (op) != ASHIFT
+      && GET_CODE (op) != LSHIFTRT
+      && GET_CODE (op) != ZERO_EXTEND)
+    return 0;
+
+  op_operand = XEXP (op, 0);
+  if (!REG_P (SET_DEST (set)) || !REG_P (op_operand)
+      || HARD_REGISTER_NUM_P (REGNO (SET_DEST (set)))
+      || HARD_REGISTER_NUM_P (REGNO (op_operand))
+      || !SCALAR_INT_MODE_P (GET_MODE (op)))
+    return 0;
+
+  if (GET_CODE (op) == ZERO_EXTEND)
+    {
+      if (GET_MODE (op_operand) != word_mode
+	  || GET_MODE_BITSIZE (GET_MODE (op)) != 2 * BITS_PER_WORD)
+	return 0;
+    }
+  else /* left or right shift */
+    {
+      if (GET_CODE (XEXP (op, 1)) != CONST_INT
+	  || INTVAL (XEXP (op, 1)) < BITS_PER_WORD
+	  || GET_MODE_BITSIZE (GET_MODE (op_operand)) != 2 * BITS_PER_WORD)
+	return 0;
+    }
+
+  bitmap_set_bit (decomposable_context, REGNO (SET_DEST (set)));
+
+  if (GET_CODE (op) != ZERO_EXTEND)
+    bitmap_set_bit (decomposable_context, REGNO (op_operand));
+
+  return 1;
+}
+
+/* Decompose a more than word wide shift (in INSN) of a multiword
+   pseudo or a multiword zero-extend of a wordmode pseudo into a move
+   and 'set to zero' insn.  Return a pointer to the new insn when a
+   replacement was done.  */
+
+static rtx
+resolve_shift_zext (rtx insn)
+{
+  rtx set;
+  rtx op;
+  rtx op_operand;
+  rtx insns;
+  rtx src_reg, dest_reg, dest_zero;
+  int src_reg_num, dest_reg_num, offset1, offset2, src_offset;
+
+  set = single_set (insn);
+  if (!set)
+    return NULL_RTX;
+
+  op = SET_SRC (set);
+  if (GET_CODE (op) != ASHIFT
+      && GET_CODE (op) != LSHIFTRT
+      && GET_CODE (op) != ZERO_EXTEND)
+    return NULL_RTX;
+
+  op_operand = XEXP (op, 0);
+
+  if (!resolve_reg_p (SET_DEST (set)) && !resolve_reg_p (op_operand))
+    return NULL_RTX;
+
+  /* src_reg_num is the number of the word mode register which we
+     are operating on.  For a left shift and a zero_extend on little
+     endian machines this is register 0.  */
+  src_reg_num = GET_CODE (op) == LSHIFTRT ? 1 : 0;
+
+  if (WORDS_BIG_ENDIAN
+      && GET_MODE_SIZE (GET_MODE (op_operand)) > UNITS_PER_WORD)
+    src_reg_num = 1 - src_reg_num;
+
+  if (GET_CODE (op) == ZERO_EXTEND)
+    dest_reg_num = WORDS_BIG_ENDIAN ? 1 : 0;
+  else
+    dest_reg_num = 1 - src_reg_num;
+
+  offset1 = UNITS_PER_WORD * dest_reg_num;
+  offset2 = UNITS_PER_WORD * (1 - dest_reg_num);
+  src_offset = UNITS_PER_WORD * src_reg_num;
+
+  if (WORDS_BIG_ENDIAN != BYTES_BIG_ENDIAN)
+    {
+      offset1 += UNITS_PER_WORD - 1;
+      offset2 += UNITS_PER_WORD - 1;
+      src_offset += UNITS_PER_WORD - 1;
+    }
+
+  start_sequence ();
+
+  dest_reg = simplify_gen_subreg_concatn (word_mode, SET_DEST (set),
+                                          GET_MODE (SET_DEST (set)),
+                                          offset1);
+  dest_zero = simplify_gen_subreg_concatn (word_mode, SET_DEST (set),
+                                           GET_MODE (SET_DEST (set)),
+                                           offset2);
+  src_reg = simplify_gen_subreg_concatn (word_mode, op_operand,
+                                         GET_MODE (op_operand),
+                                         src_offset);
+  if (GET_CODE (op) != ZERO_EXTEND)
+    {
+      int shift_count = INTVAL (XEXP (op, 1));
+      if (shift_count > BITS_PER_WORD)
+	src_reg = expand_shift (GET_CODE (op) == ASHIFT ?
+				LSHIFT_EXPR : RSHIFT_EXPR,
+				word_mode, src_reg,
+				build_int_cst (NULL_TREE,
+					       shift_count - BITS_PER_WORD),
+				dest_reg, 1);
+    }
+
+  if (dest_reg != src_reg)
+    emit_move_insn (dest_reg, src_reg);
+  emit_move_insn (dest_zero, CONST0_RTX (word_mode));
+  insns = get_insns ();
+
+  end_sequence ();
+
+  emit_insn_before (insns, insn);
+
+  if (dump_file)
+    {
+      rtx in;
+      fprintf (dump_file, "; Replacing insn: %d with insns: ", INSN_UID (insn));
+      for (in = insns; in != insn; in = NEXT_INSN (in))
+	fprintf (dump_file, "%d ", INSN_UID (in));
+      fprintf (dump_file, "\n");
+    }
+
+  delete_insn (insn);
+  return insns;
+}
+
+/* Look for registers which are always accessed via word-sized SUBREGs
+   or via copies.  Decompose these registers into several word-sized
+   pseudo-registers.  */
+
+static void
+decompose_multiword_subregs (void)
+{
+  unsigned int max;
+  basic_block bb;
+
+  if (df)
+    df_set_flags (DF_DEFER_INSN_RESCAN);
+
+  max = max_reg_num ();
+
+  /* First see if there are any multi-word pseudo-registers.  If there
+     aren't, there is nothing we can do.  This should speed up this
+     pass in the normal case, since it should be faster than scanning
+     all the insns.  */
+  {
+    unsigned int i;
+
+    for (i = FIRST_PSEUDO_REGISTER; i < max; ++i)
+      {
+	if (regno_reg_rtx[i] != NULL
+	    && GET_MODE_SIZE (GET_MODE (regno_reg_rtx[i])) > UNITS_PER_WORD)
+	  break;
+      }
+    if (i == max)
+      return;
+  }
+
+  /* FIXME: When the dataflow branch is merged, we can change this
+     code to look for each multi-word pseudo-register and to find each
+     insn which sets or uses that register.  That should be faster
+     than scanning all the insns.  */
+
+  decomposable_context = BITMAP_ALLOC (NULL);
+  non_decomposable_context = BITMAP_ALLOC (NULL);
+
+  reg_copy_graph = VEC_alloc (bitmap, heap, max);
+  VEC_safe_grow (bitmap, heap, reg_copy_graph, max);
+  memset (VEC_address (bitmap, reg_copy_graph), 0, sizeof (bitmap) * max);
+
+  FOR_EACH_BB (bb)
+    {
+      rtx insn;
+
+      FOR_BB_INSNS (bb, insn)
+	{
+	  rtx set;
+	  enum classify_move_insn cmi;
+	  int i, n;
+
+	  if (!INSN_P (insn)
+	      || GET_CODE (PATTERN (insn)) == CLOBBER
+	      || GET_CODE (PATTERN (insn)) == USE)
+	    continue;
+
+	  if (find_decomposable_shift_zext (insn))
+	    continue;
+
+	  recog_memoized (insn);
+	  extract_insn (insn);
+
+	  set = simple_move (insn);
+
+	  if (!set)
+	    cmi = NOT_SIMPLE_MOVE;
+	  else
+	    {
+	      if (find_pseudo_copy (set))
+		cmi = SIMPLE_PSEUDO_REG_MOVE;
+	      else
+		cmi = SIMPLE_MOVE;
+	    }
+
+	  n = recog_data.n_operands;
+	  for (i = 0; i < n; ++i)
+	    {
+	      for_each_rtx (&recog_data.operand[i],
+			    find_decomposable_subregs,
+			    &cmi);
+
+	      /* We handle ASM_OPERANDS as a special case to support
+		 things like x86 rdtsc which returns a DImode value.
+		 We can decompose the output, which will certainly be
+		 operand 0, but not the inputs.  */
+
+	      if (cmi == SIMPLE_MOVE
+		  && GET_CODE (SET_SRC (set)) == ASM_OPERANDS)
+		{
+		  gcc_assert (i == 0);
+		  cmi = NOT_SIMPLE_MOVE;
+		}
+	    }
+	}
+    }
+
+  bitmap_and_compl_into (decomposable_context, non_decomposable_context);
+  if (!bitmap_empty_p (decomposable_context))
+    {
+      sbitmap sub_blocks;
+      unsigned int i;
+      sbitmap_iterator sbi;
+      bitmap_iterator iter;
+      unsigned int regno;
+
+      propagate_pseudo_copies ();
+
+      sub_blocks = sbitmap_alloc (last_basic_block);
+      sbitmap_zero (sub_blocks);
+
+      EXECUTE_IF_SET_IN_BITMAP (decomposable_context, 0, regno, iter)
+	decompose_register (regno);
+
+      FOR_EACH_BB (bb)
+	{
+	  rtx insn;
+
+	  FOR_BB_INSNS (bb, insn)
+	    {
+	      rtx next, pat;
+
+	      if (!INSN_P (insn))
+		continue;
+
+	      next = NEXT_INSN (insn);
+
+	      pat = PATTERN (insn);
+	      if (GET_CODE (pat) == CLOBBER)
+		resolve_clobber (pat, insn);
+	      else if (GET_CODE (pat) == USE)
+		resolve_use (pat, insn);
+	      else
+		{
+		  rtx set;
+		  int i;
+
+		  recog_memoized (insn);
+		  extract_insn (insn);
+
+		  set = simple_move (insn);
+		  if (set)
+		    {
+		      rtx orig_insn = insn;
+		      bool cfi = control_flow_insn_p (insn);
+
+		      /* We can end up splitting loads to multi-word pseudos
+			 into separate loads to machine word size pseudos.
+			 When this happens, we first had one load that can
+			 throw, and after resolve_simple_move we'll have a
+			 bunch of loads (at least two).  All those loads may
+			 trap if we can have non-call exceptions, so they
+			 all will end the current basic block.  We split the
+			 block after the outer loop over all insns, but we
+			 make sure here that we will be able to split the
+			 basic block and still produce the correct control
+			 flow graph for it.  */
+		      gcc_assert (!cfi
+				  || (flag_non_call_exceptions
+				      && can_throw_internal (insn)));
+
+		      insn = resolve_simple_move (set, insn);
+		      if (insn != orig_insn)
+			{
+			  recog_memoized (insn);
+			  extract_insn (insn);
+
+			  if (cfi)
+			    SET_BIT (sub_blocks, bb->index);
+			}
+		    }
+		  else
+		    {
+		      rtx decomposed_shift;
+
+		      decomposed_shift = resolve_shift_zext (insn);
+		      if (decomposed_shift != NULL_RTX)
+			{
+			  insn = decomposed_shift;
+			  recog_memoized (insn);
+			  extract_insn (insn);
+			}
+		    }
+
+		  for (i = recog_data.n_operands - 1; i >= 0; --i)
+		    for_each_rtx (recog_data.operand_loc[i],
+				  resolve_subreg_use,
+				  insn);
+
+		  resolve_reg_notes (insn);
+
+		  if (num_validated_changes () > 0)
+		    {
+		      for (i = recog_data.n_dups - 1; i >= 0; --i)
+			{
+			  rtx *pl = recog_data.dup_loc[i];
+			  int dup_num = recog_data.dup_num[i];
+			  rtx *px = recog_data.operand_loc[dup_num];
+
+			  validate_unshare_change (insn, pl, *px, 1);
+			}
+
+		      i = apply_change_group ();
+		      gcc_assert (i);
+		    }
+		}
+	    }
+	}
+
+      /* If we had insns to split that caused control flow insns in the middle
+	 of a basic block, split those blocks now.  Note that we only handle
+	 the case where splitting a load has caused multiple possibly trapping
+	 loads to appear.  */
+      EXECUTE_IF_SET_IN_SBITMAP (sub_blocks, 0, i, sbi)
+	{
+	  rtx insn, end;
+	  edge fallthru;
+
+	  bb = BASIC_BLOCK (i);
+	  insn = BB_HEAD (bb);
+	  end = BB_END (bb);
+
+	  while (insn != end)
+	    {
+	      if (control_flow_insn_p (insn))
+		{
+		  /* Split the block after insn.  There will be a fallthru
+		     edge, which is OK so we keep it.  We have to create the
+		     exception edges ourselves.  */
+		  fallthru = split_block (bb, insn);
+		  rtl_make_eh_edge (NULL, bb, BB_END (bb));
+		  bb = fallthru->dest;
+		  insn = BB_HEAD (bb);
+		}
+	      else
+	        insn = NEXT_INSN (insn);
+	    }
+	}
+
+      sbitmap_free (sub_blocks);
+    }
+
+  {
+    unsigned int i;
+    bitmap b;
+
+    for (i = 0; VEC_iterate (bitmap, reg_copy_graph, i, b); ++i)
+      if (b)
+	BITMAP_FREE (b);
+  }
+
+  VEC_free (bitmap, heap, reg_copy_graph);  
+
+  BITMAP_FREE (decomposable_context);
+  BITMAP_FREE (non_decomposable_context);
+}
+
+/* Gate function for lower subreg pass.  */
+
+static bool
+gate_handle_lower_subreg (void)
+{
+  return flag_split_wide_types != 0;
+}
+
+/* Implement first lower subreg pass.  */
+
+static unsigned int
+rest_of_handle_lower_subreg (void)
+{
+  decompose_multiword_subregs ();
+  return 0;
+}
+
+/* Implement second lower subreg pass.  */
+
+static unsigned int
+rest_of_handle_lower_subreg2 (void)
+{
+  decompose_multiword_subregs ();
+  return 0;
+}
+
+struct rtl_opt_pass pass_lower_subreg =
+{
+ {
+  RTL_PASS,
+  "subreg1",	                        /* name */
+  gate_handle_lower_subreg,             /* gate */
+  rest_of_handle_lower_subreg,          /* execute */
+  NULL,                                 /* sub */
+  NULL,                                 /* next */
+  0,                                    /* static_pass_number */
+  TV_LOWER_SUBREG,                      /* tv_id */
+  0,                                    /* properties_required */
+  0,                                    /* properties_provided */
+  0,                                    /* properties_destroyed */
+  0,                                    /* todo_flags_start */
+  TODO_dump_func |
+  TODO_ggc_collect |
+  TODO_verify_flow                      /* todo_flags_finish */
+ }
+};
+
+struct rtl_opt_pass pass_lower_subreg2 =
+{
+ {
+  RTL_PASS,
+  "subreg2",	                        /* name */
+  gate_handle_lower_subreg,             /* gate */
+  rest_of_handle_lower_subreg2,          /* execute */
+  NULL,                                 /* sub */
+  NULL,                                 /* next */
+  0,                                    /* static_pass_number */
+  TV_LOWER_SUBREG,                      /* tv_id */
+  0,                                    /* properties_required */
+  0,                                    /* properties_provided */
+  0,                                    /* properties_destroyed */
+  0,                                    /* todo_flags_start */
+  TODO_df_finish | TODO_verify_rtl_sharing |
+  TODO_dump_func |
+  TODO_ggc_collect |
+  TODO_verify_flow                      /* todo_flags_finish */
+ }
+};