explow.c

这是完整的gcc源代码

/* Subroutines for manipulating rtx's in semantically interesting ways.
   Copyright (C) 1987 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 1, 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, 675 Mass Ave, Cambridge, MA 02139, USA.  */


#include "config.h"
#include "rtl.h"
#include "tree.h"
#include "flags.h"
#include "expr.h"

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

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

  if (c == 0)
    return x;

  if (code == CONST_INT)
    return gen_rtx (CONST_INT, VOIDmode, (INTVAL (x) + c));

  /* If adding to something entirely constant, set a flag
     so that we can add a CONST around the result.  */
  if (code == CONST)
    {
      x = XEXP (x, 0);
      all_constant = 1;
    }
  else if (code == SYMBOL_REF || code == LABEL_REF)
    all_constant = 1;

  /* 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.  */

  if (GET_CODE (x) == PLUS)
    {
      if (GET_CODE (XEXP (x, 0)) == CONST_INT)
	{
	  c += INTVAL (XEXP (x, 0));
	  x = XEXP (x, 1);
	}
      else if (GET_CODE (XEXP (x, 1)) == CONST_INT)
	{
	  c += INTVAL (XEXP (x, 1));
	  x = XEXP (x, 0);
	}
      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));
	}
#ifdef OLD_INDEXING
      /* Detect adding a constant to an indexed address
	 of the form (PLUS (MULT (REG) (CONST)) regs-and-constants).
	 Keep the (MULT ...) at the top level of addition so that
	 the result is still suitable for indexing and constants
	 are combined.  */
      else if (GET_CODE (XEXP (x, 0)) == MULT)
	{
	  return gen_rtx (PLUS, mode, XEXP (x, 0),
			  plus_constant (XEXP (x, 1), c));
	}
      else if (GET_CODE (XEXP (x, 1)) == MULT)
	{
	  return gen_rtx (PLUS, mode, plus_constant (XEXP (x, 0), c),
			  XEXP (x, 1));
	}
#endif
    }
  if (c != 0)
    x = gen_rtx (PLUS, mode, x, gen_rtx (CONST_INT, VOIDmode, 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;
}

/* 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;
     int *constptr;
{
  int c;
  register rtx x0, x1;

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

  /* First handle constants appearing at this level explicitly.  */
  if (GET_CODE (XEXP (x, 0)) == CONST_INT)
    {
      *constptr += INTVAL (XEXP (x, 0));
      return eliminate_constant_term (XEXP (x, 1), constptr);
    }

  if (GET_CODE (XEXP (x, 1)) == CONST_INT)
    {
      *constptr += INTVAL (XEXP (x, 1));
      return eliminate_constant_term (XEXP (x, 0), constptr);
    }

  c = 0;
  x0 = eliminate_constant_term (XEXP (x, 0), &c);
  x1 = eliminate_constant_term (XEXP (x, 1), &c);
  if (x1 != XEXP (x, 1) || x0 != XEXP (x, 0))
    {
      *constptr += c;
      return gen_rtx (PLUS, GET_MODE (x), x0, x1);
    }
  return x;
}

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

rtx
expr_size (exp)
     tree exp;
{
  return expand_expr (size_in_bytes (TREE_TYPE (exp)), 0, SImode, 0);
}

/* Not yet really written since C does not need it.  */

rtx
lookup_static_chain (context)
     rtx context;
{
  abort ();
}

/* 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.

   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 || GET_CODE (x) == CONST
      || GET_CODE (x) == SYMBOL_REF)
    {
      register rtx temp = force_reg (Pmode, x);
      mark_reg_pointer (temp);
      x = temp;
    }
  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;
}

/* 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)
	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;

  /* By passing constant addresses thru registers
     we get a chance to cse them.  */
  if (! cse_not_expected && CONSTANT_P (x))
    return 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.  */
  if (GET_CODE (x) == QUEUED
      && GET_CODE (QUEUED_VAR (x)) == REG)
    return x;

  /* We get better cse by rejecting indirect addressing at this stage.
     Let the combiner create indirect addresses where appropriate.
     For now, generate the code so that the subexpressions useful to share
     are visible.  But not if cse won't be done!  */
  oldx = x;
  if (! cse_not_expected && GET_CODE (x) != REG)
    x = break_out_memory_refs (x);

  /* At this point, any valid address is accepted.  */
  GO_IF_LEGITIMATE_ADDRESS (mode, x, win);

  /* If it was valid before but breaking out memory refs invalidated it,
     use it the old way.  */
  if (memory_address_p (mode, oldx))
    goto win2;

  /* Perform machine-dependent transformations on X
     in certain cases.  This is not necessary since the code
     below can handle all possible cases, but machine-dependent
     transformations can make better code.  */
  LEGITIMIZE_ADDRESS (x, oldx, mode, win);

  /* PLUS and MULT can appear in special ways
     as the result of attempts to make an address usable for indexing.
     Usually they are dealt with by calling force_operand, below.