FSF GCC version 2.7.2

1 files changed, 770 insertions, 0 deletions

diff --git a/gnu/usr.bin/gcc/caller-save.c b/gnu/usr.bin/gcc/caller-save.c
new file mode 100644
index 00000000000..6dc90189ee6
--- /dev/null
+++ b/gnu/usr.bin/gcc/caller-save.c
@@ -0,0 +1,770 @@
+/* Save and restore call-clobbered registers which are live across a call.
+   Copyright (C) 1989, 1992, 1994, 1995 Free Software Foundation, Inc.
+
+This file is part of GNU CC.
+
+GNU CC 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 2, or (at your option)
+any later version.
+
+GNU CC 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 GNU CC; see the file COPYING.  If not, write to
+the Free Software Foundation, 59 Temple Place - Suite 330,
+Boston, MA 02111-1307, USA.  */
+
+#include "config.h"
+#include "rtl.h"
+#include "insn-config.h"
+#include "flags.h"
+#include "regs.h"
+#include "hard-reg-set.h"
+#include "recog.h"
+#include "basic-block.h"
+#include "reload.h"
+#include "expr.h"
+
+#ifndef MAX_MOVE_MAX
+#define MAX_MOVE_MAX MOVE_MAX
+#endif
+
+#ifndef MIN_UNITS_PER_WORD
+#define MIN_UNITS_PER_WORD UNITS_PER_WORD
+#endif
+
+/* Modes for each hard register that we can save.  The smallest mode is wide
+   enough to save the entire contents of the register.  When saving the
+   register because it is live we first try to save in multi-register modes.
+   If that is not possible the save is done one register at a time.  */
+
+static enum machine_mode 
+  regno_save_mode[FIRST_PSEUDO_REGISTER][MAX_MOVE_MAX / MIN_UNITS_PER_WORD + 1];
+
+/* For each hard register, a place on the stack where it can be saved,
+   if needed.  */
+
+static rtx 
+  regno_save_mem[FIRST_PSEUDO_REGISTER][MAX_MOVE_MAX / MIN_UNITS_PER_WORD + 1];
+
+/* We will only make a register eligible for caller-save if it can be
+   saved in its widest mode with a simple SET insn as long as the memory
+   address is valid.  We record the INSN_CODE is those insns here since
+   when we emit them, the addresses might not be valid, so they might not
+   be recognized.  */
+
+static enum insn_code 
+  reg_save_code[FIRST_PSEUDO_REGISTER][MAX_MOVE_MAX / MIN_UNITS_PER_WORD + 1];
+static enum insn_code 
+  reg_restore_code[FIRST_PSEUDO_REGISTER][MAX_MOVE_MAX / MIN_UNITS_PER_WORD + 1];
+
+/* Set of hard regs currently live (during scan of all insns).  */
+
+static HARD_REG_SET hard_regs_live;
+
+/* Set of hard regs currently residing in save area (during insn scan).  */
+
+static HARD_REG_SET hard_regs_saved;
+
+/* Set of hard regs which need to be restored before referenced.  */
+
+static HARD_REG_SET hard_regs_need_restore;
+
+/* Number of registers currently in hard_regs_saved.  */
+
+int n_regs_saved;
+
+static void set_reg_live		PROTO((rtx, rtx));
+static void clear_reg_live		PROTO((rtx));
+static void restore_referenced_regs	PROTO((rtx, rtx, enum machine_mode));
+static int insert_save_restore		PROTO((rtx, int, int,
+					       enum machine_mode, int));
+
+/* Initialize for caller-save.
+
+   Look at all the hard registers that are used by a call and for which
+   regclass.c has not already excluded from being used across a call.
+
+   Ensure that we can find a mode to save the register and that there is a 
+   simple insn to save and restore the register.  This latter check avoids
+   problems that would occur if we tried to save the MQ register of some
+   machines directly into memory.  */
+
+void
+init_caller_save ()
+{
+  char *first_obj = (char *) oballoc (0);
+  rtx addr_reg;
+  int offset;
+  rtx address;
+  int i, j;
+
+  /* First find all the registers that we need to deal with and all
+     the modes that they can have.  If we can't find a mode to use,
+     we can't have the register live over calls.  */
+
+  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+    {
+      if (call_used_regs[i] && ! call_fixed_regs[i])
+	{
+	  for (j = 1; j <= MOVE_MAX / UNITS_PER_WORD; j++)
+	    {
+	      regno_save_mode[i][j] = choose_hard_reg_mode (i, j);
+	      if (regno_save_mode[i][j] == VOIDmode && j == 1)
+		{
+		  call_fixed_regs[i] = 1;
+		  SET_HARD_REG_BIT (call_fixed_reg_set, i);
+		}
+	    }
+	}
+      else
+	regno_save_mode[i][1] = VOIDmode;
+    }
+
+  /* The following code tries to approximate the conditions under which
+     we can easily save and restore a register without scratch registers or
+     other complexities.  It will usually work, except under conditions where
+     the validity of an insn operand is dependent on the address offset.
+     No such cases are currently known.
+
+     We first find a typical offset from some BASE_REG_CLASS register.
+     This address is chosen by finding the first register in the class
+     and by finding the smallest power of two that is a valid offset from
+     that register in every mode we will use to save registers.  */
+
+  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+    if (TEST_HARD_REG_BIT (reg_class_contents[(int) BASE_REG_CLASS], i))
+      break;
+
+  if (i == FIRST_PSEUDO_REGISTER)
+    abort ();
+
+  addr_reg = gen_rtx (REG, Pmode, i);
+
+  for (offset = 1 << (HOST_BITS_PER_INT / 2); offset; offset >>= 1)
+    {
+      address = gen_rtx (PLUS, Pmode, addr_reg, GEN_INT (offset));
+
+      for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+	if (regno_save_mode[i][1] != VOIDmode
+	  && ! strict_memory_address_p (regno_save_mode[i][1], address))
+	  break;
+
+      if (i == FIRST_PSEUDO_REGISTER)
+	break;
+    }
+
+  /* If we didn't find a valid address, we must use register indirect.  */
+  if (offset == 0)
+    address = addr_reg;
+
+  /* Next we try to form an insn to save and restore the register.  We
+     see if such an insn is recognized and meets its constraints.  */
+
+  start_sequence ();
+
+  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+    for (j = 1; j <= MOVE_MAX / UNITS_PER_WORD; j++)
+      if (regno_save_mode[i][j] != VOIDmode)
+        {
+	  rtx mem = gen_rtx (MEM, regno_save_mode[i][j], address);
+	  rtx reg = gen_rtx (REG, regno_save_mode[i][j], i);
+	  rtx savepat = gen_rtx (SET, VOIDmode, mem, reg);
+	  rtx restpat = gen_rtx (SET, VOIDmode, reg, mem);
+	  rtx saveinsn = emit_insn (savepat);
+	  rtx restinsn = emit_insn (restpat);
+	  int ok;
+
+	  reg_save_code[i][j] = recog_memoized (saveinsn);
+	  reg_restore_code[i][j] = recog_memoized (restinsn);
+
+	  /* Now extract both insns and see if we can meet their constraints. */
+	  ok = (reg_save_code[i][j] != -1 && reg_restore_code[i][j] != -1);
+	  if (ok)
+	    {
+	      insn_extract (saveinsn);
+	      ok = constrain_operands (reg_save_code[i][j], 1);
+	      insn_extract (restinsn);
+	      ok &= constrain_operands (reg_restore_code[i][j], 1);
+	    }
+
+	  if (! ok)
+	    {
+	      regno_save_mode[i][j] = VOIDmode;
+	      if (j == 1)
+		{
+		  call_fixed_regs[i] = 1;
+		  SET_HARD_REG_BIT (call_fixed_reg_set, i);
+		}
+	    }
+      }
+
+  end_sequence ();
+
+  obfree (first_obj);
+}
+
+/* Initialize save areas by showing that we haven't allocated any yet.  */
+
+void
+init_save_areas ()
+{
+  int i, j;
+
+  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+    for (j = 1; j <= MOVE_MAX / UNITS_PER_WORD; j++)
+      regno_save_mem[i][j] = 0;
+}
+
+/* Allocate save areas for any hard registers that might need saving.
+   We take a conservative approach here and look for call-clobbered hard
+   registers that are assigned to pseudos that cross calls.  This may
+   overestimate slightly (especially if some of these registers are later
+   used as spill registers), but it should not be significant.
+
+   Then perform register elimination in the addresses of the save area
+   locations; return 1 if all eliminated addresses are strictly valid.
+   We assume that our caller has set up the elimination table to the
+   worst (largest) possible offsets.
+
+   Set *PCHANGED to 1 if we had to allocate some memory for the save area.  
+
+   Future work:
+
+     In the fallback case we should iterate backwards across all possible
+     modes for the save, choosing the largest available one instead of 
+     falling back to the smallest mode immediately.  (eg TF -> DF -> SF).
+
+     We do not try to use "move multiple" instructions that exist
+     on some machines (such as the 68k moveml).  It could be a win to try 
+     and use them when possible.  The hard part is doing it in a way that is
+     machine independent since they might be saving non-consecutive 
+     registers. (imagine caller-saving d0,d1,a0,a1 on the 68k) */
+
+int
+setup_save_areas (pchanged)
+     int *pchanged;
+{
+  int i, j, k;
+  HARD_REG_SET hard_regs_used;
+  int ok = 1;
+
+
+  /* Allocate space in the save area for the largest multi-register
+     pseudos first, then work backwards to single register
+     pseudos.  */
+
+  /* Find and record all call-used hard-registers in this function.  */
+  CLEAR_HARD_REG_SET (hard_regs_used);
+  for (i = FIRST_PSEUDO_REGISTER; i < max_regno; i++)
+    if (reg_renumber[i] >= 0 && reg_n_calls_crossed[i] > 0)
+      {
+	int regno = reg_renumber[i];
+	int endregno 
+	  = regno + HARD_REGNO_NREGS (regno, GET_MODE (regno_reg_rtx[i]));
+	int nregs = endregno - regno;
+
+	for (j = 0; j < nregs; j++)
+	  {
+	    if (call_used_regs[regno+j]) 
+	      SET_HARD_REG_BIT (hard_regs_used, regno+j);
+	  }
+      }
+
+  /* Now run through all the call-used hard-registers and allocate
+     space for them in the caller-save area.  Try to allocate space
+     in a manner which allows multi-register saves/restores to be done.  */
+
+  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+    for (j = MOVE_MAX / UNITS_PER_WORD; j > 0; j--)
+      {
+	int ok = 1;
+	int do_save;
+
+	/* If no mode exists for this size, try another.  Also break out
+	   if we have already saved this hard register.  */
+	if (regno_save_mode[i][j] == VOIDmode || regno_save_mem[i][1] != 0)
+	  continue;
+
+	/* See if any register in this group has been saved.  */
+	do_save = 1;
+	for (k = 0; k < j; k++)
+	  if (regno_save_mem[i + k][1])
+	    {
+	      do_save = 0;
+	      break;
+	    }
+	if (! do_save)
+	  continue;
+
+	for (k = 0; k < j; k++)
+	    {
+	      int regno = i + k;
+	      ok &= (TEST_HARD_REG_BIT (hard_regs_used, regno) != 0);
+	    }
+
+	/* We have found an acceptable mode to store in. */
+	if (ok)
+	  {
+
+	    regno_save_mem[i][j]
+	      = assign_stack_local (regno_save_mode[i][j],
+				    GET_MODE_SIZE (regno_save_mode[i][j]), 0);
+
+	    /* Setup single word save area just in case... */
+	    for (k = 0; k < j; k++)
+	      {
+		/* This should not depend on WORDS_BIG_ENDIAN.
+		   The order of words in regs is the same as in memory.  */
+		rtx temp = gen_rtx (MEM, regno_save_mode[i+k][1], 
+				    XEXP (regno_save_mem[i][j], 0));
+
+		regno_save_mem[i+k][1] 
+		  = adj_offsettable_operand (temp, k * UNITS_PER_WORD);
+	      }
+	    *pchanged = 1;
+	  }
+      }
+
+  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
+    for (j = 1; j <= MOVE_MAX / UNITS_PER_WORD; j++)
+      if (regno_save_mem[i][j] != 0)
+	ok &= strict_memory_address_p (GET_MODE (regno_save_mem[i][j]),
+				       XEXP (eliminate_regs (regno_save_mem[i][j], 0, NULL_RTX), 0));
+
+  return ok;
+}
+
+/* Find the places where hard regs are live across calls and save them.
+
+   INSN_MODE is the mode to assign to any insns that we add.  This is used
+   by reload to determine whether or not reloads or register eliminations
+   need be done on these insns.  */
+
+void
+save_call_clobbered_regs (insn_mode)
+     enum machine_mode insn_mode;
+{
+  rtx insn;
+  int b;
+
+  for (b = 0; b < n_basic_blocks; b++)
+    {
+      regset regs_live = basic_block_live_at_start[b];
+      rtx prev_block_last = PREV_INSN (basic_block_head[b]);
+      REGSET_ELT_TYPE bit;
+      int offset, i, j;
+      int regno;
+
+      /* Compute hard regs live at start of block -- this is the
+	 real hard regs marked live, plus live pseudo regs that
+	 have been renumbered to hard regs.  No registers have yet been
+	 saved because we restore all of them before the end of the basic
+	 block.  */
+
+#ifdef HARD_REG_SET
+      hard_regs_live = *regs_live;
+#else
+      COPY_HARD_REG_SET (hard_regs_live, regs_live);
+#endif
+
+      CLEAR_HARD_REG_SET (hard_regs_saved);
+      CLEAR_HARD_REG_SET (hard_regs_need_restore);
+      n_regs_saved = 0;
+
+      for (offset = 0, i = 0; offset < regset_size; offset++)
+	{
+	  if (regs_live[offset] == 0)
+	    i += REGSET_ELT_BITS;
+	  else
+	    for (bit = 1; bit && i < max_regno; bit <<= 1, i++)
+	      if ((regs_live[offset] & bit)
+		  && (regno = reg_renumber[i]) >= 0)
+		for (j = regno;
+		     j < regno + HARD_REGNO_NREGS (regno,
+						   PSEUDO_REGNO_MODE (i));
+		     j++)
+		  SET_HARD_REG_BIT (hard_regs_live, j);
+
+	}
+
+      /* Now scan the insns in the block, keeping track of what hard
+	 regs are live as we go.  When we see a call, save the live
+	 call-clobbered hard regs.  */
+
+      for (insn = basic_block_head[b]; ; insn = NEXT_INSN (insn))
+	{
+	  RTX_CODE code = GET_CODE (insn);
+
+	  if (GET_RTX_CLASS (code) == 'i')
+	    {
+	      rtx link;
+
+	      /* If some registers have been saved, see if INSN references
+		 any of them.  We must restore them before the insn if so.  */
+
+	      if (n_regs_saved)
+		restore_referenced_regs (PATTERN (insn), insn, insn_mode);
+
+	      /* NB: the normal procedure is to first enliven any
+		 registers set by insn, then deaden any registers that
+		 had their last use at insn.  This is incorrect now,
+		 since multiple pseudos may have been mapped to the
+		 same hard reg, and the death notes are ambiguous.  So
+		 it must be done in the other, safe, order.  */
+
+	      for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
+		if (REG_NOTE_KIND (link) == REG_DEAD)
+		  clear_reg_live (XEXP (link, 0));
+
+	      /* When we reach a call, we need to save all registers that are
+		 live, call-used, not fixed, and not already saved.  We must
+		 test at this point because registers that die in a CALL_INSN
+		 are not live across the call and likewise for registers that
+		 are born in the CALL_INSN.
+		 
+		 If registers are filled with parameters for this function,
+		 and some of these are also being set by this function, then
+		 they will not appear to die (no REG_DEAD note for them),
+		 to check if in fact they do, collect the set registers in
+		 hard_regs_live first.  */
+
+	      if (code == CALL_INSN)
+		{
+		  HARD_REG_SET this_call_sets;
+		  {
+		    HARD_REG_SET old_hard_regs_live;
+
+		    /* Save the hard_regs_live information.  */
+		    COPY_HARD_REG_SET (old_hard_regs_live, hard_regs_live);
+
+		    /* Now calculate hard_regs_live for this CALL_INSN
+		       only.  */
+		    CLEAR_HARD_REG_SET (hard_regs_live);
+		    note_stores (PATTERN (insn), set_reg_live);
+		    COPY_HARD_REG_SET (this_call_sets, hard_regs_live);
+
+		    /* Restore the hard_regs_live information.  */
+		    COPY_HARD_REG_SET (hard_regs_live, old_hard_regs_live);
+		  }
+
+		  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
+		    if (call_used_regs[regno] && ! call_fixed_regs[regno]
+		        && TEST_HARD_REG_BIT (hard_regs_live, regno)
+			/* It must not be set by this instruction.  */
+		        && ! TEST_HARD_REG_BIT (this_call_sets, regno)
+		        && ! TEST_HARD_REG_BIT (hard_regs_saved, regno))
+		      regno += insert_save_restore (insn, 1, regno, 
+						    insn_mode, 0);
+
+		  /* Put the information for this CALL_INSN on top of what
+		     we already had.  */
+		  IOR_HARD_REG_SET (hard_regs_live, this_call_sets);
+		  COPY_HARD_REG_SET (hard_regs_need_restore, hard_regs_saved);
+
+		  /* Must recompute n_regs_saved.  */
+		  n_regs_saved = 0;
+		  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
+		    if (TEST_HARD_REG_BIT (hard_regs_saved, regno))
+		      n_regs_saved++;
+		}
+	      else
+		{
+		  note_stores (PATTERN (insn), set_reg_live);
+#ifdef AUTO_INC_DEC
+		  for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
+		    if (REG_NOTE_KIND (link) == REG_INC)
+		      set_reg_live (XEXP (link, 0), NULL_RTX);
+#endif
+		}
+
+	      for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
+		if (REG_NOTE_KIND (link) == REG_UNUSED)
+		  clear_reg_live (XEXP (link, 0));
+	    }
+
+	  if (insn == basic_block_end[b])
+	    break;
+	}
+
+      /* At the end of the basic block, we must restore any registers that
+	 remain saved.  If the last insn in the block is a JUMP_INSN, put
+	 the restore before the insn, otherwise, put it after the insn.  */
+
+      if (n_regs_saved)
+	for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
+	  if (TEST_HARD_REG_BIT (hard_regs_need_restore, regno))
+	    regno += insert_save_restore ((GET_CODE (insn) == JUMP_INSN
+				  ? insn : NEXT_INSN (insn)), 0,
+				  regno, insn_mode, MOVE_MAX / UNITS_PER_WORD);
+
+      /* If we added any insns at the start of the block, update the start
+	 of the block to point at those insns.  */
+      basic_block_head[b] = NEXT_INSN (prev_block_last);
+    }
+}
+
+/* Here from note_stores when an insn stores a value in a register.
+   Set the proper bit or bits in hard_regs_live.  All pseudos that have
+   been assigned hard regs have had their register number changed already,
+   so we can ignore pseudos.  */
+
+static void
+set_reg_live (reg, setter)
+     rtx reg, setter;
+{
+  register int regno, endregno, i;
+  enum machine_mode mode = GET_MODE (reg);
+  int word = 0;
+
+  if (GET_CODE (reg) == SUBREG)
+    {
+      word = SUBREG_WORD (reg);
+      reg = SUBREG_REG (reg);
+    }
+
+  if (GET_CODE (reg) != REG || REGNO (reg) >= FIRST_PSEUDO_REGISTER)
+    return;
+
+  regno = REGNO (reg) + word;
+  endregno = regno + HARD_REGNO_NREGS (regno, mode);
+
+  for (i = regno; i < endregno; i++)
+    {
+      SET_HARD_REG_BIT (hard_regs_live, i);
+      CLEAR_HARD_REG_BIT (hard_regs_saved, i);
+      CLEAR_HARD_REG_BIT (hard_regs_need_restore, i);
+    }
+}
+
+/* Here when a REG_DEAD note records the last use of a reg.  Clear
+   the appropriate bit or bits in hard_regs_live.  Again we can ignore
+   pseudos.  */
+
+static void
+clear_reg_live (reg)
+     rtx reg;
+{
+  register int regno, endregno, i;
+
+  if (GET_CODE (reg) != REG || REGNO (reg) >= FIRST_PSEUDO_REGISTER)
+    return;
+
+  regno = REGNO (reg);
+  endregno= regno + HARD_REGNO_NREGS (regno, GET_MODE (reg));
+
+  for (i = regno; i < endregno; i++)
+    {
+      CLEAR_HARD_REG_BIT (hard_regs_live, i);
+      CLEAR_HARD_REG_BIT (hard_regs_need_restore, i);
+      CLEAR_HARD_REG_BIT (hard_regs_saved, i);
+    }
+}      
+
+/* If any register currently residing in the save area is referenced in X,
+   which is part of INSN, emit code to restore the register in front of INSN.
+   INSN_MODE is the mode to assign to any insns that we add.  */
+
+static void
+restore_referenced_regs (x, insn, insn_mode)
+     rtx x;
+     rtx insn;
+     enum machine_mode insn_mode;
+{
+  enum rtx_code code = GET_CODE (x);
+  char *fmt;
+  int i, j;
+
+  if (code == CLOBBER)
+    return;
+
+  if (code == REG)
+    {
+      int regno = REGNO (x);
+
+      /* If this is a pseudo, scan its memory location, since it might
+	 involve the use of another register, which might be saved.  */
+
+      if (regno >= FIRST_PSEUDO_REGISTER
+	  && reg_equiv_mem[regno] != 0)
+	restore_referenced_regs (XEXP (reg_equiv_mem[regno], 0),
+				 insn, insn_mode);
+      else if (regno >= FIRST_PSEUDO_REGISTER
+	       && reg_equiv_address[regno] != 0)
+	restore_referenced_regs (reg_equiv_address[regno],
+				 insn, insn_mode);
+
+      /* Otherwise if this is a hard register, restore any piece of it that
+	 is currently saved.  */
+
+      else if (regno < FIRST_PSEUDO_REGISTER)
+	{
+	  int numregs = HARD_REGNO_NREGS (regno, GET_MODE (x));
+	  /* Save at most SAVEREGS at a time.  This can not be larger than
+	     MOVE_MAX, because that causes insert_save_restore to fail.  */
+	  int saveregs = MIN (numregs, MOVE_MAX / UNITS_PER_WORD);
+	  int endregno = regno + numregs;
+
+	  for (i = regno; i < endregno; i++)
+	    if (TEST_HARD_REG_BIT (hard_regs_need_restore, i))
+	      i += insert_save_restore (insn, 0, i, insn_mode, saveregs);
+	}
+
+      return;
+    }
+	  
+  fmt = GET_RTX_FORMAT (code);
+  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
+    {
+      if (fmt[i] == 'e')
+	restore_referenced_regs (XEXP (x, i), insn, insn_mode);
+      else if (fmt[i] == 'E')
+	for (j = XVECLEN (x, i) - 1; j >= 0; j--)
+	  restore_referenced_regs (XVECEXP (x, i, j), insn, insn_mode);
+    }
+}
+
+/* Insert a sequence of insns to save or restore, SAVE_P says which,
+   REGNO.  Place these insns in front of INSN.  INSN_MODE is the mode
+   to assign to these insns.   MAXRESTORE is the maximum number of registers
+   which should be restored during this call (when SAVE_P == 0).  It should
+   never be less than 1 since we only work with entire registers.
+
+   Note that we have verified in init_caller_save that we can do this
+   with a simple SET, so use it.  Set INSN_CODE to what we save there
+   since the address might not be valid so the insn might not be recognized.
+   These insns will be reloaded and have register elimination done by
+   find_reload, so we need not worry about that here.
+
+   Return the extra number of registers saved.  */
+
+static int
+insert_save_restore (insn, save_p, regno, insn_mode, maxrestore)
+     rtx insn;
+     int save_p;
+     int regno;
+     enum machine_mode insn_mode;
+     int maxrestore;
+{
+  rtx pat;
+  enum insn_code code;
+  int i, numregs;
+
+  /* A common failure mode if register status is not correct in the RTL
+     is for this routine to be called with a REGNO we didn't expect to
+     save.  That will cause us to write an insn with a (nil) SET_DEST
+     or SET_SRC.  Instead of doing so and causing a crash later, check
+     for this common case and abort here instead.  This will remove one
+     step in debugging such problems.  */
+
+  if (regno_save_mem[regno][1] == 0)
+    abort ();
+
+#ifdef HAVE_cc0
+  /* If INSN references CC0, put our insns in front of the insn that sets
+     CC0.  This is always safe, since the only way we could be passed an
+     insn that references CC0 is for a restore, and doing a restore earlier
+     isn't a problem.  We do, however, assume here that CALL_INSNs don't
+     reference CC0.  Guard against non-INSN's like CODE_LABEL.  */
+
+  if ((GET_CODE (insn) == INSN || GET_CODE (insn) == JUMP_INSN)
+      && reg_referenced_p (cc0_rtx, PATTERN (insn)))
+    insn = prev_nonnote_insn (insn);
+#endif
+
+  /* Get the pattern to emit and update our status.  */
+  if (save_p)
+    {
+      int i, j, k;
+      int ok;
+
+      /* See if we can save several registers with a single instruction.  
+	 Work backwards to the single register case.  */
+      for (i = MOVE_MAX / UNITS_PER_WORD; i > 0; i--)
+	{
+	  ok = 1;
+	  if (regno_save_mem[regno][i] != 0)
+	    for (j = 0; j < i; j++)
+	      {
+		if (! call_used_regs[regno + j] || call_fixed_regs[regno + j]
+		    || ! TEST_HARD_REG_BIT (hard_regs_live, regno + j)
+		    || TEST_HARD_REG_BIT (hard_regs_saved, regno + j))
+		  ok = 0;
+	      }
+	  else 
+	    continue;
+
+	  /* Must do this one save at a time */
+	  if (! ok)
+	    continue;
+
+          pat = gen_rtx (SET, VOIDmode, regno_save_mem[regno][i],
+		     gen_rtx (REG, GET_MODE (regno_save_mem[regno][i]), regno));
+          code = reg_save_code[regno][i];
+
+	  /* Set hard_regs_saved for all the registers we saved.  */
+	  for (k = 0; k < i; k++)
+	    {
+	      SET_HARD_REG_BIT (hard_regs_saved, regno + k);
+	      SET_HARD_REG_BIT (hard_regs_need_restore, regno + k);
+	      n_regs_saved++;
+	    }
+
+	  numregs = i;
+	  break;
+        }
+    }
+  else
+    {
+      int i, j, k;
+      int ok;
+
+      /* See if we can restore `maxrestore' registers at once.  Work
+	 backwards to the single register case.  */
+      for (i = maxrestore; i > 0; i--)
+	{
+	  ok = 1;
+	  if (regno_save_mem[regno][i])
+	    for (j = 0; j < i; j++)
+	      {
+	  	if (! TEST_HARD_REG_BIT (hard_regs_need_restore, regno + j))
+		  ok = 0;
+	      }
+	  else
+	    continue;
+
+	  /* Must do this one restore at a time */
+	  if (! ok)
+	    continue;
+	    
+          pat = gen_rtx (SET, VOIDmode,
+		         gen_rtx (REG, GET_MODE (regno_save_mem[regno][i]), 
+				  regno), 
+			 regno_save_mem[regno][i]);
+          code = reg_restore_code[regno][i];
+
+
+	  /* Clear status for all registers we restored.  */
+	  for (k = 0; k < i; k++)
+	    {
+	      CLEAR_HARD_REG_BIT (hard_regs_need_restore, regno + k);
+	      n_regs_saved--;
+	    }
+
+	  numregs = i;
+	  break;
+        }
+    }
+  /* Emit the insn and set the code and mode.  */
+
+  insn = emit_insn_before (pat, insn);
+  PUT_MODE (insn, insn_mode);
+  INSN_CODE (insn) = code;
+
+  /* Tell our callers how many extra registers we saved/restored */
+  return numregs - 1;
+}