explow.c

gcc库的原代码,对编程有很大帮助.

/* Subroutines for manipulating rtx's in semantically interesting ways.
   Copyright (C) 1987, 1991, 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 "tree.h"
#include "flags.h"
#include "expr.h"
#include "hard-reg-set.h"
#include "insn-config.h"
#include "recog.h"
#include "insn-flags.h"
#include "insn-codes.h"

static rtx break_out_memory_refs	PROTO((rtx));

/* Return an rtx for the sum of X and the integer C.

   This function should be used via the `plus_constant' macro.  */

rtx
plus_constant_wide (x, c)
     register rtx x;
     register HOST_WIDE_INT c;
{
  register RTX_CODE code;
  register enum machine_mode mode;
  register rtx tem;
  int all_constant = 0;

  if (c == 0)
    return x;

 restart:

  code = GET_CODE (x);
  mode = GET_MODE (x);
  switch (code)
    {
    case CONST_INT:
      return GEN_INT (INTVAL (x) + c);

    case CONST_DOUBLE:
      {
	HOST_WIDE_INT l1 = CONST_DOUBLE_LOW (x);
	HOST_WIDE_INT h1 = CONST_DOUBLE_HIGH (x);
	HOST_WIDE_INT l2 = c;
	HOST_WIDE_INT h2 = c < 0 ? ~0 : 0;
	HOST_WIDE_INT lv, hv;

	add_double (l1, h1, l2, h2, &lv, &hv);

	return immed_double_const (lv, hv, VOIDmode);
      }

    case MEM:
      /* If this is a reference to the constant pool, try replacing it with
	 a reference to a new constant.  If the resulting address isn't
	 valid, don't return it because we have no way to validize it.  */
      if (GET_CODE (XEXP (x, 0)) == SYMBOL_REF
	  && CONSTANT_POOL_ADDRESS_P (XEXP (x, 0)))
	{
	  tem
	    = force_const_mem (GET_MODE (x),
			       plus_constant (get_pool_constant (XEXP (x, 0)),
					      c));
	  if (memory_address_p (GET_MODE (tem), XEXP (tem, 0)))
	    return tem;
	}
      break;

    case CONST:
      /* If adding to something entirely constant, set a flag
	 so that we can add a CONST around the result.  */
      x = XEXP (x, 0);
      all_constant = 1;
      goto restart;

    case SYMBOL_REF:
    case LABEL_REF:
      all_constant = 1;
      break;

    case PLUS:
      /* The interesting case is adding the integer to a sum.
	 Look for constant term in the sum and combine
	 with C.  For an integer constant term, we make a combined
	 integer.  For a constant term that is not an explicit integer,
	 we cannot really combine, but group them together anyway.  

	 Use a recursive call in case the remaining operand is something
	 that we handle specially, such as a SYMBOL_REF.  */

      if (GET_CODE (XEXP (x, 1)) == CONST_INT)
	return plus_constant (XEXP (x, 0), c + INTVAL (XEXP (x, 1)));
      else if (CONSTANT_P (XEXP (x, 0)))
	return gen_rtx (PLUS, mode,
			plus_constant (XEXP (x, 0), c),
			XEXP (x, 1));
      else if (CONSTANT_P (XEXP (x, 1)))
	return gen_rtx (PLUS, mode,
			XEXP (x, 0),
			plus_constant (XEXP (x, 1), c));
    }

  if (c != 0)
    x = gen_rtx (PLUS, mode, x, GEN_INT (c));

  if (GET_CODE (x) == SYMBOL_REF || GET_CODE (x) == LABEL_REF)
    return x;
  else if (all_constant)
    return gen_rtx (CONST, mode, x);
  else
    return x;
}

/* This is the same as `plus_constant', except that it handles LO_SUM.

   This function should be used via the `plus_constant_for_output' macro.  */

rtx
plus_constant_for_output_wide (x, c)
     register rtx x;
     register HOST_WIDE_INT c;
{
  register RTX_CODE code = GET_CODE (x);
  register enum machine_mode mode = GET_MODE (x);
  int all_constant = 0;

  if (GET_CODE (x) == LO_SUM)
    return gen_rtx (LO_SUM, mode, XEXP (x, 0),
		    plus_constant_for_output (XEXP (x, 1), c));

  else
    return plus_constant (x, c);
}

/* If X is a sum, return a new sum like X but lacking any constant terms.
   Add all the removed constant terms into *CONSTPTR.
   X itself is not altered.  The result != X if and only if
   it is not isomorphic to X.  */

rtx
eliminate_constant_term (x, constptr)
     rtx x;
     rtx *constptr;
{
  register rtx x0, x1;
  rtx tem;

  if (GET_CODE (x) != PLUS)
    return x;

  /* First handle constants appearing at this level explicitly.  */
  if (GET_CODE (XEXP (x, 1)) == CONST_INT
      && 0 != (tem = simplify_binary_operation (PLUS, GET_MODE (x), *constptr,
						XEXP (x, 1)))
      && GET_CODE (tem) == CONST_INT)
    {
      *constptr = tem;
      return eliminate_constant_term (XEXP (x, 0), constptr);
    }

  tem = const0_rtx;
  x0 = eliminate_constant_term (XEXP (x, 0), &tem);
  x1 = eliminate_constant_term (XEXP (x, 1), &tem);
  if ((x1 != XEXP (x, 1) || x0 != XEXP (x, 0))
      && 0 != (tem = simplify_binary_operation (PLUS, GET_MODE (x),
						*constptr, tem))
      && GET_CODE (tem) == CONST_INT)
    {
      *constptr = tem;
      return gen_rtx (PLUS, GET_MODE (x), x0, x1);
    }

  return x;
}

/* Returns the insn that next references REG after INSN, or 0
   if REG is clobbered before next referenced or we cannot find
   an insn that references REG in a straight-line piece of code.  */

rtx
find_next_ref (reg, insn)
     rtx reg;
     rtx insn;
{
  rtx next;

  for (insn = NEXT_INSN (insn); insn; insn = next)
    {
      next = NEXT_INSN (insn);
      if (GET_CODE (insn) == NOTE)
	continue;
      if (GET_CODE (insn) == CODE_LABEL
	  || GET_CODE (insn) == BARRIER)
	return 0;
      if (GET_CODE (insn) == INSN
	  || GET_CODE (insn) == JUMP_INSN
	  || GET_CODE (insn) == CALL_INSN)
	{
	  if (reg_set_p (reg, insn))
	    return 0;
	  if (reg_mentioned_p (reg, PATTERN (insn)))
	    return insn;
	  if (GET_CODE (insn) == JUMP_INSN)
	    {
	      if (simplejump_p (insn))
		next = JUMP_LABEL (insn);
	      else
		return 0;
	    }
	  if (GET_CODE (insn) == CALL_INSN
	      && REGNO (reg) < FIRST_PSEUDO_REGISTER
	      && call_used_regs[REGNO (reg)])
	    return 0;
	}
      else
	abort ();
    }
  return 0;
}

/* Return an rtx for the size in bytes of the value of EXP.  */

rtx
expr_size (exp)
     tree exp;
{
  tree size = size_in_bytes (TREE_TYPE (exp));

  if (TREE_CODE (size) != INTEGER_CST
      && contains_placeholder_p (size))
    size = build (WITH_RECORD_EXPR, sizetype, size, exp);

  return expand_expr (size, NULL_RTX, TYPE_MODE (sizetype), 0);
}

/* Return a copy of X in which all memory references
   and all constants that involve symbol refs
   have been replaced with new temporary registers.
   Also emit code to load the memory locations and constants
   into those registers.

   If X contains no such constants or memory references,
   X itself (not a copy) is returned.

   If a constant is found in the address that is not a legitimate constant
   in an insn, it is left alone in the hope that it might be valid in the
   address.

   X may contain no arithmetic except addition, subtraction and multiplication.
   Values returned by expand_expr with 1 for sum_ok fit this constraint.  */

static rtx
break_out_memory_refs (x)
     register rtx x;
{
  if (GET_CODE (x) == MEM
      || (CONSTANT_P (x) && CONSTANT_ADDRESS_P (x)
	  && GET_MODE (x) != VOIDmode))
    x = force_reg (GET_MODE (x), x);
  else if (GET_CODE (x) == PLUS || GET_CODE (x) == MINUS
	   || GET_CODE (x) == MULT)
    {
      register rtx op0 = break_out_memory_refs (XEXP (x, 0));
      register rtx op1 = break_out_memory_refs (XEXP (x, 1));

      if (op0 != XEXP (x, 0) || op1 != XEXP (x, 1))
	x = gen_rtx (GET_CODE (x), Pmode, op0, op1);
    }

  return x;
}

#ifdef POINTERS_EXTEND_UNSIGNED

/* Given X, a memory address in ptr_mode, convert it to an address
   in Pmode, or vice versa (TO_MODE says which way).  We take advantage of
   the fact that pointers are not allowed to overflow by commuting arithmetic
   operations over conversions so that address arithmetic insns can be
   used.  */

rtx
convert_memory_address (to_mode, x)
     enum machine_mode to_mode;
     rtx x;
{
  rtx temp;

  switch (GET_CODE (x))
    {
    case CONST_INT:
    case CONST_DOUBLE:
      return x;

    case LABEL_REF:
      return gen_rtx (LABEL_REF, to_mode, XEXP (x, 0));

    case SYMBOL_REF:
      temp = gen_rtx (SYMBOL_REF, to_mode, XSTR (x, 0));
      SYMBOL_REF_FLAG (temp) = SYMBOL_REF_FLAG (x);
      return temp;

    case PLUS:
    case MULT:
      return gen_rtx (GET_CODE (x), to_mode, 
		      convert_memory_address (to_mode, XEXP (x, 0)),
		      convert_memory_address (to_mode, XEXP (x, 1)));

    case CONST:
      return gen_rtx (CONST, to_mode, 
		      convert_memory_address (to_mode, XEXP (x, 0)));

    default:
      return convert_modes (to_mode,
			    to_mode == ptr_mode ? Pmode : ptr_mode,
			    x, POINTERS_EXTEND_UNSIGNED);
    }
}
#endif

/* Given a memory address or facsimile X, construct a new address,
   currently equivalent, that is stable: future stores won't change it.

   X must be composed of constants, register and memory references
   combined with addition, subtraction and multiplication:
   in other words, just what you can get from expand_expr if sum_ok is 1.

   Works by making copies of all regs and memory locations used
   by X and combining them the same way X does.
   You could also stabilize the reference to this address
   by copying the address to a register with copy_to_reg;
   but then you wouldn't get indexed addressing in the reference.  */

rtx
copy_all_regs (x)
     register rtx x;
{
  if (GET_CODE (x) == REG)
    {
      if (REGNO (x) != FRAME_POINTER_REGNUM
#if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
	  && REGNO (x) != HARD_FRAME_POINTER_REGNUM
#endif
	  )
	x = copy_to_reg (x);
    }
  else if (GET_CODE (x) == MEM)
    x = copy_to_reg (x);
  else if (GET_CODE (x) == PLUS || GET_CODE (x) == MINUS
	   || GET_CODE (x) == MULT)
    {
      register rtx op0 = copy_all_regs (XEXP (x, 0));
      register rtx op1 = copy_all_regs (XEXP (x, 1));
      if (op0 != XEXP (x, 0) || op1 != XEXP (x, 1))
	x = gen_rtx (GET_CODE (x), Pmode, op0, op1);
    }
  return x;
}

/* Return something equivalent to X but valid as a memory address
   for something of mode MODE.  When X is not itself valid, this
   works by copying X or subexpressions of it into registers.  */

rtx
memory_address (mode, x)
     enum machine_mode mode;
     register rtx x;
{
  register rtx oldx = x;

#ifdef POINTERS_EXTEND_UNSIGNED
  if (GET_MODE (x) == ptr_mode)
    x = convert_memory_address (Pmode, x);
#endif

  /* By passing constant addresses thru registers
     we get a chance to cse them.  */
  if (! cse_not_expected && CONSTANT_P (x) && CONSTANT_ADDRESS_P (x))
    x = force_reg (Pmode, x);

  /* Accept a QUEUED that refers to a REG
     even though that isn't a valid address.
     On attempting to put this in an insn we will call protect_from_queue
     which will turn it into a REG, which is valid.  */
  else if (GET_CODE (x) == QUEUED
      && GET_CODE (QUEUED_VAR (x)) == REG)
    ;