path: root/gnu/usr.bin/gcc/alias.c

/* Alias analysis for GNU C, by John Carr (jfc@mit.edu).
   Derived in part from sched.c  */
#include "config.h"
#include "rtl.h"
#include "expr.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"

static rtx canon_rtx			PROTO((rtx));
static int rtx_equal_for_memref_p	PROTO((rtx, rtx));
static rtx find_symbolic_term		PROTO((rtx));
static int memrefs_conflict_p		PROTO((int, rtx, int, rtx,
					       HOST_WIDE_INT));

/* Set up all info needed to perform alias analysis on memory references.  */

#define SIZE_FOR_MODE(X) (GET_MODE_SIZE (GET_MODE (X)))

/* reg_base_value[N] gives an address to which register N is related.
   If all sets after the first add or subtract to the current value
   or otherwise modify it so it does not point to a different top level
   object, reg_base_value[N] is equal to the address part of the source
   of the first set.  The value will be a SYMBOL_REF, a LABEL_REF, or
   (address (reg)) to indicate that the address is derived from an
   argument or fixed register.  */
rtx *reg_base_value;
unsigned int reg_base_value_size;	/* size of reg_base_value array */
#define REG_BASE_VALUE(X) \
	(REGNO (X) < reg_base_value_size ? reg_base_value[REGNO (X)] : 0)

/* Vector indexed by N giving the initial (unchanging) value known
   for pseudo-register N.  */
rtx *reg_known_value;

/* Indicates number of valid entries in reg_known_value.  */
static int reg_known_value_size;

/* Vector recording for each reg_known_value whether it is due to a
   REG_EQUIV note.  Future passes (viz., reload) may replace the
   pseudo with the equivalent expression and so we account for the
   dependences that would be introduced if that happens. */
/* ??? This is a problem only on the Convex.  The REG_EQUIV notes created in
   assign_parms mention the arg pointer, and there are explicit insns in the
   RTL that modify the arg pointer.  Thus we must ensure that such insns don't
   get scheduled across each other because that would invalidate the REG_EQUIV
   notes.  One could argue that the REG_EQUIV notes are wrong, but solving
   the problem in the scheduler will likely give better code, so we do it
   here.  */
char *reg_known_equiv_p;

/* Inside SRC, the source of a SET, find a base address.  */

/* When copying arguments into pseudo-registers, record the (ADDRESS)
   expression for the argument directly so that even if the argument
   register is changed later (e.g. for a function call) the original
   value is noted.  */
static int copying_arguments;

static rtx
find_base_value (src)
     register rtx src;
{
  switch (GET_CODE (src))
    {
    case SYMBOL_REF:
    case LABEL_REF:
      return src;

    case REG:
      if (copying_arguments && REGNO (src) < FIRST_PSEUDO_REGISTER)
	return reg_base_value[REGNO (src)];
      return src;

    case MEM:
      /* Check for an argument passed in memory.  Only record in the
	 copying-arguments block; it is too hard to track changes
	 otherwise.  */
      if (copying_arguments
	  && (XEXP (src, 0) == arg_pointer_rtx
	      || (GET_CODE (XEXP (src, 0)) == PLUS
		  && XEXP (XEXP (src, 0), 0) == arg_pointer_rtx)))
	return gen_rtx (ADDRESS, VOIDmode, src);
      return 0;

    case CONST:
      src = XEXP (src, 0);
      if (GET_CODE (src) != PLUS && GET_CODE (src) != MINUS)
	break;
      /* fall through */
    case PLUS:
    case MINUS:
      /* Guess which operand to set the register equivalent to.  */
      /* If the first operand is a symbol or the second operand is
	 an integer, the first operand is the base address.  */
      if (GET_CODE (XEXP (src, 0)) == SYMBOL_REF
	  || GET_CODE (XEXP (src, 0)) == LABEL_REF
	  || GET_CODE (XEXP (src, 1)) == CONST_INT)
	return XEXP (src, 0);
      /* If an operand is a register marked as a pointer, it is the base.  */
      if (GET_CODE (XEXP (src, 0)) == REG
	  && REGNO_POINTER_FLAG (REGNO (XEXP (src, 0))))
	src = XEXP (src, 0);
      else if (GET_CODE (XEXP (src, 1)) == REG
	  && REGNO_POINTER_FLAG (REGNO (XEXP (src, 1))))
	src = XEXP (src, 1);
      else
	return 0;
      if (copying_arguments && REGNO (src) < FIRST_PSEUDO_REGISTER)
	return reg_base_value[REGNO (src)];
      return src;

    case AND:
      /* If the second operand is constant set the base
	 address to the first operand. */
      if (GET_CODE (XEXP (src, 1)) == CONST_INT
	  && GET_CODE (XEXP (src, 0)) == REG)
	{
	  src = XEXP (src, 0);
	  if (copying_arguments && REGNO (src) < FIRST_PSEUDO_REGISTER)
	    return reg_base_value[REGNO (src)];
	  return src;
	}
      return 0;

    case HIGH:
      return XEXP (src, 0);
    }

  return 0;
}

/* Called from init_alias_analysis indirectly through note_stores.  */

/* while scanning insns to find base values, reg_seen[N] is nonzero if
   register N has been set in this function.  */
static char *reg_seen;

static
void record_set (dest, set)
     rtx dest, set;
{
  register int regno;
  rtx src;

  if (GET_CODE (dest) != REG)
    return;

  regno = REGNO (dest);

  if (set)
    {
      /* A CLOBBER wipes out any old value but does not prevent a previously
	 unset register from acquiring a base address (i.e. reg_seen is not
	 set).  */
      if (GET_CODE (set) == CLOBBER)
	{
	  reg_base_value[regno] = 0;
	  return;
	}
      src = SET_SRC (set);
    }
  else
    {
      static int unique_id;
      if (reg_seen[regno])
	{
	  reg_base_value[regno] = 0;
	  return;
	}
      reg_seen[regno] = 1;
      reg_base_value[regno] = gen_rtx (ADDRESS, Pmode,
				       GEN_INT (unique_id++));
      return;
    }

  /* This is not the first set.  If the new value is not related to the
     old value, forget the base value. Note that the following code is
     not detected:
     extern int x, y;  int *p = &x; p += (&y-&x);
     ANSI C does not allow computing the difference of addresses
     of distinct top level objects.  */
  if (reg_base_value[regno])
    switch (GET_CODE (src))
      {
      case PLUS:
      case MINUS:
	if (XEXP (src, 0) != dest && XEXP (src, 1) != dest)
	  reg_base_value[regno] = 0;
	break;
      case AND:
	if (XEXP (src, 0) != dest || GET_CODE (XEXP (src, 1)) != CONST_INT)
	  reg_base_value[regno] = 0;
	break;
      case LO_SUM:
	if (XEXP (src, 0) != dest)
	  reg_base_value[regno] = 0;
	break;
      default:
	reg_base_value[regno] = 0;
	break;
      }
  /* If this is the first set of a register, record the value.  */
  else if ((regno >= FIRST_PSEUDO_REGISTER || ! fixed_regs[regno])
	   && ! reg_seen[regno] && reg_base_value[regno] == 0)
    reg_base_value[regno] = find_base_value (src);

  reg_seen[regno] = 1;
}

/* Called from loop optimization when a new pseudo-register is created.  */
void
record_base_value (regno, val)
     int regno;
     rtx val;
{
  if (!flag_alias_check || regno >= reg_base_value_size)
    return;
  if (GET_CODE (val) == REG)
    {
      if (REGNO (val) < reg_base_value_size)
	reg_base_value[regno] = reg_base_value[REGNO (val)];
      return;
    }
  reg_base_value[regno] = find_base_value (val);
}

static rtx
canon_rtx (x)
     rtx x;
{
  /* Recursively look for equivalences.  */
  if (GET_CODE (x) == REG && REGNO (x) >= FIRST_PSEUDO_REGISTER
      && REGNO (x) < reg_known_value_size)
    return reg_known_value[REGNO (x)] == x
      ? x : canon_rtx (reg_known_value[REGNO (x)]);
  else if (GET_CODE (x) == PLUS)
    {
      rtx x0 = canon_rtx (XEXP (x, 0));
      rtx x1 = canon_rtx (XEXP (x, 1));

      if (x0 != XEXP (x, 0) || x1 != XEXP (x, 1))
	{
	  /* We can tolerate LO_SUMs being offset here; these
	     rtl are used for nothing other than comparisons.  */
	  if (GET_CODE (x0) == CONST_INT)
	    return plus_constant_for_output (x1, INTVAL (x0));
	  else if (GET_CODE (x1) == CONST_INT)
	    return plus_constant_for_output (x0, INTVAL (x1));
	  return gen_rtx (PLUS, GET_MODE (x), x0, x1);
	}
    }
  /* This gives us much better alias analysis when called from
     the loop optimizer.   Note we want to leave the original
     MEM alone, but need to return the canonicalized MEM with
     all the flags with their original values.  */
  else if (GET_CODE (x) == MEM)
    {
      rtx addr = canon_rtx (XEXP (x, 0));
      if (addr != XEXP (x, 0))
	{
	  rtx new = gen_rtx (MEM, GET_MODE (x), addr);
	  MEM_VOLATILE_P (new) = MEM_VOLATILE_P (x);
	  RTX_UNCHANGING_P (new) = RTX_UNCHANGING_P (x);
	  MEM_IN_STRUCT_P (new) = MEM_IN_STRUCT_P (x);
	  x = new;
	}
    }
  return x;
}

/* Return 1 if X and Y are identical-looking rtx's.

   We use the data in reg_known_value above to see if two registers with
   different numbers are, in fact, equivalent.  */

static int
rtx_equal_for_memref_p (x, y)
     rtx x, y;
{
  register int i;
  register int j;
  register enum rtx_code code;
  register char *fmt;

  if (x == 0 && y == 0)
    return 1;
  if (x == 0 || y == 0)
    return 0;
  x = canon_rtx (x);
  y = canon_rtx (y);

  if (x == y)
    return 1;

  code = GET_CODE (x);
  /* Rtx's of different codes cannot be equal.  */
  if (code != GET_CODE (y))
    return 0;

  /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
     (REG:SI x) and (REG:HI x) are NOT equivalent.  */

  if (GET_MODE (x) != GET_MODE (y))
    return 0;

  /* REG, LABEL_REF, and SYMBOL_REF can be compared nonrecursively.  */

  if (code == REG)
    return REGNO (x) == REGNO (y);
  if (code == LABEL_REF)
    return XEXP (x, 0) == XEXP (y, 0);
  if (code == SYMBOL_REF)
    return XSTR (x, 0) == XSTR (y, 0);

  /* For commutative operations, the RTX match if the operand match in any
     order.  Also handle the simple binary and unary cases without a loop.  */
  if (code == EQ || code == NE || GET_RTX_CLASS (code) == 'c')
    return ((rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0))
	     && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1)))
	    || (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 1))
		&& rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 0))));
  else if (GET_RTX_CLASS (code) == '<' || GET_RTX_CLASS (code) == '2')
    return (rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0))
	    && rtx_equal_for_memref_p (XEXP (x, 1), XEXP (y, 1)));
  else if (GET_RTX_CLASS (code) == '1')
    return rtx_equal_for_memref_p (XEXP (x, 0), XEXP (y, 0));

  /* Compare the elements.  If any pair of corresponding elements
     fail to match, return 0 for the whole things.  */

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      switch (fmt[i])
	{
	case 'w':
	  if (XWINT (x, i) != XWINT (y, i))
	    return 0;
	  break;

	case 'n':
	case 'i':
	  if (XINT (x, i) != XINT (y, i))
	    return 0;
	  break;

	case 'V':
	case 'E':
	  /* Two vectors must have the same length.  */
	  if (XVECLEN (x, i) != XVECLEN (y, i))
	    return 0;

	  /* And the corresponding elements must match.  */
	  for (j = 0; j < XVECLEN (x, i); j++)
	    if (rtx_equal_for_memref_p (XVECEXP (x, i, j), XVECEXP (y, i, j)) == 0)
	      return 0;
	  break;

	case 'e':
	  if (rtx_equal_for_memref_p (XEXP (x, i), XEXP (y, i)) == 0)
	    return 0;
	  break;

	case 'S':
	case 's':
	  if (strcmp (XSTR (x, i), XSTR (y, i)))
	    return 0;
	  break;

	case 'u':
	  /* These are just backpointers, so they don't matter.  */
	  break;

	case '0':
	  break;

	  /* It is believed that rtx's at this level will never
	     contain anything but integers and other rtx's,
	     except for within LABEL_REFs and SYMBOL_REFs.  */
	default:
	  abort ();
	}
    }
  return 1;
}

/* Given an rtx X, find a SYMBOL_REF or LABEL_REF within
   X and return it, or return 0 if none found.  */

static rtx
find_symbolic_term (x)
     rtx x;
{
  register int i;
  register enum rtx_code code;
  register char *fmt;

  code = GET_CODE (x);
  if (code == SYMBOL_REF || code == LABEL_REF)
    return x;
  if (GET_RTX_CLASS (code) == 'o')
    return 0;

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      rtx t;

      if (fmt[i] == 'e')
	{
	  t = find_symbolic_term (XEXP (x, i));
	  if (t != 0)
	    return t;
	}
      else if (fmt[i] == 'E')
	break;
    }
  return 0;
}

static rtx
find_base_term (x)
     rtx x;
{
  switch (GET_CODE (x))
    {
    case REG:
      return REG_BASE_VALUE (x);

    case HIGH:
      return find_base_value (XEXP (x, 0));

    case CONST:
      x = XEXP (x, 0);
      if (GET_CODE (x) != PLUS && GET_CODE (x) != MINUS)
	return 0;
      /* fall through */
    case LO_SUM:
    case PLUS:
    case MINUS:
      {
	rtx tmp = find_base_term (XEXP (x, 0));
	if (tmp)
	  return tmp;
	return find_base_term (XEXP (x, 1));
      }

    case AND:
      if (GET_CODE (XEXP (x, 0)) == REG && GET_CODE (XEXP (x, 1)) == CONST_INT)
	return REG_BASE_VALUE (XEXP (x, 0));
      return 0;

    case SYMBOL_REF:
    case LABEL_REF:
      return x;

    default:
      return 0;
    }
}

/* Return 0 if the addresses X and Y are known to point to different
   objects, 1 if they might be pointers to the same object.  */

static int
base_alias_check (x, y)
     rtx x, y;
{
  rtx x_base = find_base_term (x);
  rtx y_base = find_base_term (y);

  /* If either base address is unknown or the base addresses are equal,
     nothing is known about aliasing.  */
  if (x_base == 0 || y_base == 0 || rtx_equal_p (x_base, y_base))
    return 1;

  /* The base addresses of the read and write are different
     expressions.  If they are both symbols there is no
     conflict.  */
  if (GET_CODE (x_base) != ADDRESS && GET_CODE (y_base) != ADDRESS)
    return 0;

  /* If one address is a stack reference there can be no alias:
     stack references using different base registers do not alias,
     a stack reference can not alias a parameter, and a stack reference
     can not alias a global.  */
  if ((GET_CODE (x_base) == ADDRESS && GET_MODE (x_base) == Pmode)
      || (GET_CODE (y_base) == ADDRESS && GET_MODE (y_base) == Pmode))
    return 0;

  if (! flag_argument_noalias)
    return 1;

  if (flag_argument_noalias > 1)
    return 0;

  /* Weak noalias assertion (arguments are distinct, but may match globals). */
  return ! (GET_MODE (x_base) == VOIDmode && GET_MODE (y_base) == VOIDmode);
}

/* Return nonzero if X and Y (memory addresses) could reference the
   same location in memory.  C is an offset accumulator.  When
   C is nonzero, we are testing aliases between X and Y + C.
   XSIZE is the size in bytes of the X reference,
   similarly YSIZE is the size in bytes for Y.

   If XSIZE or YSIZE is zero, we do not know the amount of memory being
   referenced (the reference was BLKmode), so make the most pessimistic
   assumptions.

   We recognize the following cases of non-conflicting memory:

	(1) addresses involving the frame pointer cannot conflict
	    with addresses involving static variables.
	(2) static variables with different addresses cannot conflict.

   Nice to notice that varying addresses cannot conflict with fp if no
   local variables had their addresses taken, but that's too hard now.  */


static int
memrefs_conflict_p (xsize, x, ysize, y, c)
     register rtx x, y;
     int xsize, ysize;
     HOST_WIDE_INT c;
{
  if (GET_CODE (x) == HIGH)
    x = XEXP (x, 0);
  else if (GET_CODE (x) == LO_SUM)
    x = XEXP (x, 1);
  else
    x = canon_rtx (x);
  if (GET_CODE (y) == HIGH)
    y = XEXP (y, 0);
  else if (GET_CODE (y) == LO_SUM)
    y = XEXP (y, 1);
  else
    y = canon_rtx (y);

  if (rtx_equal_for_memref_p (x, y))
    {
      if (xsize == 0 || ysize == 0)
	return 1;
      if (c >= 0 && xsize > c)
	return 1;
      if (c < 0 && ysize+c > 0)
	return 1;
      return 0;
    }

  if (y == frame_pointer_rtx || y == hard_frame_pointer_rtx
      || y == stack_pointer_rtx)
    {
      rtx t = y;
      int tsize = ysize;
      y = x; ysize = xsize;
      x = t; xsize = tsize;
    }

  if (x == frame_pointer_rtx || x == hard_frame_pointer_rtx
      || x == stack_pointer_rtx)
    {
      rtx y1;

      if (CONSTANT_P (y))
	return 0;

      if (GET_CODE (y) == PLUS
	  && canon_rtx (XEXP (y, 0)) == x
	  && (y1 = canon_rtx (XEXP (y, 1)))
	  && GET_CODE (y1) == CONST_INT)
	{
	  c += INTVAL (y1);
	  return (xsize == 0 || ysize == 0
		  || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
	}

      if (GET_CODE (y) == PLUS
	  && (y1 = canon_rtx (XEXP (y, 0)))
	  && CONSTANT_P (y1))
	return 0;

      return 1;
    }

  if (GET_CODE (x) == PLUS)
    {
      /* The fact that X is canonicalized means that this
	 PLUS rtx is canonicalized.  */
      rtx x0 = XEXP (x, 0);
      rtx x1 = XEXP (x, 1);

      if (GET_CODE (y) == PLUS)
	{
	  /* The fact that Y is canonicalized means that this
	     PLUS rtx is canonicalized.  */
	  rtx y0 = XEXP (y, 0);
	  rtx y1 = XEXP (y, 1);

	  if (rtx_equal_for_memref_p (x1, y1))
	    return memrefs_conflict_p (xsize, x0, ysize, y0, c);
	  if (rtx_equal_for_memref_p (x0, y0))
	    return memrefs_conflict_p (xsize, x1, ysize, y1, c);
	  if (GET_CODE (x1) == CONST_INT)
	    if (GET_CODE (y1) == CONST_INT)
	      return memrefs_conflict_p (xsize, x0, ysize, y0,
					 c - INTVAL (x1) + INTVAL (y1));
	    else
	      return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1));
	  else if (GET_CODE (y1) == CONST_INT)
	    return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1));

	  /* Handle case where we cannot understand iteration operators,
	     but we notice that the base addresses are distinct objects.  */
	  /* ??? Is this still necessary? */
	  x = find_symbolic_term (x);
	  if (x == 0)
	    return 1;
	  y = find_symbolic_term (y);
	  if (y == 0)
	    return 1;
	  return rtx_equal_for_memref_p (x, y);
	}
      else if (GET_CODE (x1) == CONST_INT)
	return memrefs_conflict_p (xsize, x0, ysize, y, c - INTVAL (x1));
    }
  else if (GET_CODE (y) == PLUS)
    {
      /* The fact that Y is canonicalized means that this
	 PLUS rtx is canonicalized.  */
      rtx y0 = XEXP (y, 0);
      rtx y1 = XEXP (y, 1);

      if (GET_CODE (y1) == CONST_INT)
	return memrefs_conflict_p (xsize, x, ysize, y0, c + INTVAL (y1));
      else
	return 1;
    }

  if (GET_CODE (x) == GET_CODE (y))
    switch (GET_CODE (x))
      {
      case MULT:
	{
	  /* Handle cases where we expect the second operands to be the
	     same, and check only whether the first operand would conflict
	     or not.  */
	  rtx x0, y0;
	  rtx x1 = canon_rtx (XEXP (x, 1));
	  rtx y1 = canon_rtx (XEXP (y, 1));
	  if (! rtx_equal_for_memref_p (x1, y1))
	    return 1;
	  x0 = canon_rtx (XEXP (x, 0));
	  y0 = canon_rtx (XEXP (y, 0));
	  if (rtx_equal_for_memref_p (x0, y0))
	    return (xsize == 0 || ysize == 0
		    || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));

	  /* Can't properly adjust our sizes.  */
	  if (GET_CODE (x1) != CONST_INT)
	    return 1;
	  xsize /= INTVAL (x1);
	  ysize /= INTVAL (x1);
	  c /= INTVAL (x1);
	  return memrefs_conflict_p (xsize, x0, ysize, y0, c);
	}
      }

  /* Treat an access through an AND (e.g. a subword access on an Alpha)
     as an access with indeterminate size.  */
  if (GET_CODE (x) == AND && GET_CODE (XEXP (x, 1)) == CONST_INT)
    return memrefs_conflict_p (0, XEXP (x, 0), ysize, y, c);
  if (GET_CODE (y) == AND && GET_CODE (XEXP (y, 1)) == CONST_INT)
    return memrefs_conflict_p (xsize, x, 0, XEXP (y, 0), c);

  if (CONSTANT_P (x))
    {
      if (GET_CODE (x) == CONST_INT && GET_CODE (y) == CONST_INT)
	{
	  c += (INTVAL (y) - INTVAL (x));
	  return (xsize == 0 || ysize == 0
		  || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0));
	}

      if (GET_CODE (x) == CONST)
	{
	  if (GET_CODE (y) == CONST)
	    return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)),
				       ysize, canon_rtx (XEXP (y, 0)), c);
	  else
	    return memrefs_conflict_p (xsize, canon_rtx (XEXP (x, 0)),
				       ysize, y, c);
	}
      if (GET_CODE (y) == CONST)
	return memrefs_conflict_p (xsize, x, ysize,
				   canon_rtx (XEXP (y, 0)), c);

      if (CONSTANT_P (y))
	return (rtx_equal_for_memref_p (x, y)
		&& (xsize == 0 || ysize == 0
		    || (c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)));

      return 1;
    }
  return 1;
}

/* Functions to compute memory dependencies.

   Since we process the insns in execution order, we can build tables
   to keep track of what registers are fixed (and not aliased), what registers
   are varying in known ways, and what registers are varying in unknown
   ways.

   If both memory references are volatile, then there must always be a
   dependence between the two references, since their order can not be
   changed.  A volatile and non-volatile reference can be interchanged
   though. 

   A MEM_IN_STRUCT reference at a non-QImode varying address can never
   conflict with a non-MEM_IN_STRUCT reference at a fixed address.   We must
   allow QImode aliasing because the ANSI C standard allows character
   pointers to alias anything.  We are assuming that characters are
   always QImode here.  */

/* Read dependence: X is read after read in MEM takes place.  There can
   only be a dependence here if both reads are volatile.  */

int
read_dependence (mem, x)
     rtx mem;
     rtx x;
{
  return MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem);
}

/* True dependence: X is read after store in MEM takes place.  */

int
true_dependence (mem, mem_mode, x, varies)
     rtx mem;
     enum machine_mode mem_mode;
     rtx x;
     int (*varies)();
{
  rtx x_addr, mem_addr;

  if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
    return 1;

  x_addr = XEXP (x, 0);
  mem_addr = XEXP (mem, 0);

  if (flag_alias_check && ! base_alias_check (x_addr, mem_addr))
    return 0;

  /* If X is an unchanging read, then it can't possibly conflict with any
     non-unchanging store.  It may conflict with an unchanging write though,
     because there may be a single store to this address to initialize it.
     Just fall through to the code below to resolve the case where we have
     both an unchanging read and an unchanging write.  This won't handle all
     cases optimally, but the possible performance loss should be
     negligible.  */
  if (RTX_UNCHANGING_P (x) && ! RTX_UNCHANGING_P (mem))
    return 0;

  x_addr = canon_rtx (x_addr);
  mem_addr = canon_rtx (mem_addr);
  if (mem_mode == VOIDmode)
    mem_mode = GET_MODE (mem);

  if (! memrefs_conflict_p (mem_mode, mem_addr, SIZE_FOR_MODE (x), x_addr, 0))
    return 0;

  /* If both references are struct references, or both are not, nothing
     is known about aliasing.

     If either reference is QImode or BLKmode, ANSI C permits aliasing.

     If both addresses are constant, or both are not, nothing is known
     about aliasing.  */
  if (MEM_IN_STRUCT_P (x) == MEM_IN_STRUCT_P (mem)
      || mem_mode == QImode || mem_mode == BLKmode
      || GET_MODE (x) == QImode || GET_MODE (mem) == BLKmode
      || varies (x_addr) == varies (mem_addr))
    return 1;

  /* One memory reference is to a constant address, one is not.
     One is to a structure, the other is not.

     If either memory reference is a variable structure the other is a
     fixed scalar and there is no aliasing.  */
  if ((MEM_IN_STRUCT_P (mem) && varies (mem_addr))
      || (MEM_IN_STRUCT_P (x) && varies (x)))
    return 0;

  return 1;
}

/* Anti dependence: X is written after read in MEM takes place.  */

int
anti_dependence (mem, x)
     rtx mem;
     rtx x;
{
  if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
    return 1;

  if (flag_alias_check && ! base_alias_check (XEXP (x, 0), XEXP (mem, 0)))
    return 0;

  /* If MEM is an unchanging read, then it can't possibly conflict with
     the store to X, because there is at most one store to MEM, and it must
     have occurred somewhere before MEM.  */
  x = canon_rtx (x);
  mem = canon_rtx (mem);
  if (RTX_UNCHANGING_P (mem))
    return 0;

  return (memrefs_conflict_p (SIZE_FOR_MODE (mem), XEXP (mem, 0),
			      SIZE_FOR_MODE (x), XEXP (x, 0), 0)
	  && ! (MEM_IN_STRUCT_P (mem) && rtx_addr_varies_p (mem)
		&& GET_MODE (mem) != QImode
		&& ! MEM_IN_STRUCT_P (x) && ! rtx_addr_varies_p (x))
	  && ! (MEM_IN_STRUCT_P (x) && rtx_addr_varies_p (x)
		&& GET_MODE (x) != QImode
		&& ! MEM_IN_STRUCT_P (mem) && ! rtx_addr_varies_p (mem)));
}

/* Output dependence: X is written after store in MEM takes place.  */

int
output_dependence (mem, x)
     register rtx mem;
     register rtx x;
{
  if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
    return 1;

  if (flag_alias_check && !base_alias_check (XEXP (x, 0), XEXP (mem, 0)))
    return 0;

  x = canon_rtx (x);
  mem = canon_rtx (mem);
  return (memrefs_conflict_p (SIZE_FOR_MODE (mem), XEXP (mem, 0),
			      SIZE_FOR_MODE (x), XEXP (x, 0), 0)
	  && ! (MEM_IN_STRUCT_P (mem) && rtx_addr_varies_p (mem)
		&& GET_MODE (mem) != QImode
		&& ! MEM_IN_STRUCT_P (x) && ! rtx_addr_varies_p (x))
	  && ! (MEM_IN_STRUCT_P (x) && rtx_addr_varies_p (x)
		&& GET_MODE (x) != QImode
		&& ! MEM_IN_STRUCT_P (mem) && ! rtx_addr_varies_p (mem)));
}

void
init_alias_analysis ()
{
  int maxreg = max_reg_num ();
  register int i;
  register rtx insn;
  rtx note;
  rtx set;
  int changed;

  reg_known_value_size = maxreg;

  reg_known_value
    = (rtx *) oballoc ((maxreg - FIRST_PSEUDO_REGISTER) * sizeof (rtx))
    - FIRST_PSEUDO_REGISTER;
  reg_known_equiv_p =
    oballoc (maxreg - FIRST_PSEUDO_REGISTER) - FIRST_PSEUDO_REGISTER;
  bzero ((char *) (reg_known_value + FIRST_PSEUDO_REGISTER),
	 (maxreg-FIRST_PSEUDO_REGISTER) * sizeof (rtx));
  bzero (reg_known_equiv_p + FIRST_PSEUDO_REGISTER,
	 (maxreg - FIRST_PSEUDO_REGISTER) * sizeof (char));

  if (flag_alias_check)
    {
      /* Overallocate reg_base_value to allow some growth during loop
	 optimization.  Loop unrolling can create a large number of
	 registers.  */
      reg_base_value_size = maxreg * 2;
      reg_base_value = (rtx *)oballoc (reg_base_value_size * sizeof (rtx));
      reg_seen = (char *)alloca (reg_base_value_size);
      bzero (reg_base_value, reg_base_value_size * sizeof (rtx));
      bzero (reg_seen, reg_base_value_size);

      /* Mark all hard registers which may contain an address.
	 The stack, frame and argument pointers may contain an address.
	 An argument register which can hold a Pmode value may contain
	 an address even if it is not in BASE_REGS.

	 The address expression is VOIDmode for an argument and
	 Pmode for other registers.  */
      for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
	if (FUNCTION_ARG_REGNO_P (i) && HARD_REGNO_MODE_OK (i, Pmode))
	  reg_base_value[i] = gen_rtx (ADDRESS, VOIDmode,
				       gen_rtx (REG, Pmode, i));

      reg_base_value[STACK_POINTER_REGNUM]
	= gen_rtx (ADDRESS, Pmode, stack_pointer_rtx);
      reg_base_value[ARG_POINTER_REGNUM]
	= gen_rtx (ADDRESS, Pmode, arg_pointer_rtx);
      reg_base_value[FRAME_POINTER_REGNUM]
	= gen_rtx (ADDRESS, Pmode, frame_pointer_rtx);
      reg_base_value[HARD_FRAME_POINTER_REGNUM]
	= gen_rtx (ADDRESS, Pmode, hard_frame_pointer_rtx);
    }

  copying_arguments = 1;
  /* Fill in the entries with known constant values.  */
  for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
    {
      if (flag_alias_check && GET_RTX_CLASS (GET_CODE (insn)) == 'i')
	{
	  /* If this insn has a noalias note, process it,  Otherwise,
	     scan for sets.  A simple set will have no side effects
	     which could change the base value of any other register. */
	  rtx noalias_note;
	  if (GET_CODE (PATTERN (insn)) == SET
	      && (noalias_note = find_reg_note (insn, REG_NOALIAS, NULL_RTX)))
	      record_set(SET_DEST (PATTERN (insn)), 0);
	  else
	    note_stores (PATTERN (insn), record_set);
	}
      else if (GET_CODE (insn) == NOTE
	       && NOTE_LINE_NUMBER (insn) == NOTE_INSN_FUNCTION_BEG)
	copying_arguments = 0;

      if ((set = single_set (insn)) != 0
	  && GET_CODE (SET_DEST (set)) == REG
	  && REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER
	  && (((note = find_reg_note (insn, REG_EQUAL, 0)) != 0
	       && reg_n_sets[REGNO (SET_DEST (set))] == 1)
	      || (note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) != 0)
	  && GET_CODE (XEXP (note, 0)) != EXPR_LIST)
	{
	  int regno = REGNO (SET_DEST (set));
	  reg_known_value[regno] = XEXP (note, 0);
	  reg_known_equiv_p[regno] = REG_NOTE_KIND (note) == REG_EQUIV;
	}
    }

  /* Fill in the remaining entries.  */
  for (i = FIRST_PSEUDO_REGISTER; i < maxreg; i++)
    if (reg_known_value[i] == 0)
      reg_known_value[i] = regno_reg_rtx[i];

  if (! flag_alias_check)
    return;

  /* Simplify the reg_base_value array so that no register refers to
     another register, except to special registers indirectly through
     ADDRESS expressions.

     In theory this loop can take as long as O(registers^2), but unless
     there are very long dependency chains it will run in close to linear
     time.  */
  do
    {
      changed = 0;
      for (i = FIRST_PSEUDO_REGISTER; i < reg_base_value_size; i++)
	{
	  rtx base = reg_base_value[i];
	  if (base && GET_CODE (base) == REG)
	    {
	      int base_regno = REGNO (base);
	      if (base_regno == i)		/* register set from itself */
		reg_base_value[i] = 0;
	      else
		reg_base_value[i] = reg_base_value[base_regno];
	      changed = 1;
	    }
	}
    }
  while (changed);

  reg_seen = 0;
}

void
end_alias_analysis ()
{
  reg_known_value = 0;
  reg_base_value = 0;
  reg_base_value_size = 0;
}