reload.c

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/* Search an insn for pseudo regs that must be in hard regs and are not.
   Copyright (C) 1987, 88, 89, 92, 93, 94, 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.  */


/* This file contains subroutines used only from the file reload1.c.
   It knows how to scan one insn for operands and values
   that need to be copied into registers to make valid code.
   It also finds other operands and values which are valid
   but for which equivalent values in registers exist and
   ought to be used instead.

   Before processing the first insn of the function, call `init_reload'.

   To scan an insn, call `find_reloads'.  This does two things:
   1. sets up tables describing which values must be reloaded
   for this insn, and what kind of hard regs they must be reloaded into;
   2. optionally record the locations where those values appear in
   the data, so they can be replaced properly later.
   This is done only if the second arg to `find_reloads' is nonzero.

   The third arg to `find_reloads' specifies the number of levels
   of indirect addressing supported by the machine.  If it is zero,
   indirect addressing is not valid.  If it is one, (MEM (REG n))
   is valid even if (REG n) did not get a hard register; if it is two,
   (MEM (MEM (REG n))) is also valid even if (REG n) did not get a
   hard register, and similarly for higher values.

   Then you must choose the hard regs to reload those pseudo regs into,
   and generate appropriate load insns before this insn and perhaps
   also store insns after this insn.  Set up the array `reload_reg_rtx'
   to contain the REG rtx's for the registers you used.  In some
   cases `find_reloads' will return a nonzero value in `reload_reg_rtx'
   for certain reloads.  Then that tells you which register to use,
   so you do not need to allocate one.  But you still do need to add extra
   instructions to copy the value into and out of that register.

   Finally you must call `subst_reloads' to substitute the reload reg rtx's
   into the locations already recorded.

NOTE SIDE EFFECTS:

   find_reloads can alter the operands of the instruction it is called on.

   1. Two operands of any sort may be interchanged, if they are in a
   commutative instruction.
   This happens only if find_reloads thinks the instruction will compile
   better that way.

   2. Pseudo-registers that are equivalent to constants are replaced
   with those constants if they are not in hard registers.

1 happens every time find_reloads is called.
2 happens only when REPLACE is 1, which is only when
actually doing the reloads, not when just counting them.


Using a reload register for several reloads in one insn:

When an insn has reloads, it is considered as having three parts:
the input reloads, the insn itself after reloading, and the output reloads.
Reloads of values used in memory addresses are often needed for only one part.

When this is so, reload_when_needed records which part needs the reload.
Two reloads for different parts of the insn can share the same reload
register.

When a reload is used for addresses in multiple parts, or when it is
an ordinary operand, it is classified as RELOAD_OTHER, and cannot share
a register with any other reload.  */

#define REG_OK_STRICT

#include <stdio.h>
#include "config.h"
#include "rtl.h"
#include "insn-config.h"
#include "insn-codes.h"
#include "recog.h"
#include "reload.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"
#include "real.h"
#include "output.h"

#ifndef REGISTER_MOVE_COST
#define REGISTER_MOVE_COST(x, y) 2
#endif

/* The variables set up by `find_reloads' are:

   n_reloads		  number of distinct reloads needed; max reload # + 1
       tables indexed by reload number
   reload_in		  rtx for value to reload from
   reload_out		  rtx for where to store reload-reg afterward if nec
			   (often the same as reload_in)
   reload_reg_class	  enum reg_class, saying what regs to reload into
   reload_inmode	  enum machine_mode; mode this operand should have
			   when reloaded, on input.
   reload_outmode	  enum machine_mode; mode this operand should have
			   when reloaded, on output.
   reload_optional	  char, nonzero for an optional reload.
			   Optional reloads are ignored unless the
			   value is already sitting in a register.
   reload_inc		  int, positive amount to increment or decrement by if
			   reload_in is a PRE_DEC, PRE_INC, POST_DEC, POST_INC.
			   Ignored otherwise (don't assume it is zero).
   reload_in_reg	  rtx.  A reg for which reload_in is the equivalent.
			   If reload_in is a symbol_ref which came from
			   reg_equiv_constant, then this is the pseudo
			   which has that symbol_ref as equivalent.
   reload_reg_rtx	  rtx.  This is the register to reload into.
			   If it is zero when `find_reloads' returns,
			   you must find a suitable register in the class
			   specified by reload_reg_class, and store here
			   an rtx for that register with mode from
			   reload_inmode or reload_outmode.
   reload_nocombine	  char, nonzero if this reload shouldn't be
			   combined with another reload.
   reload_opnum		  int, operand number being reloaded.  This is
			   used to group related reloads and need not always
			   be equal to the actual operand number in the insn,
			   though it current will be; for in-out operands, it
			   is one of the two operand numbers.
   reload_when_needed    enum, classifies reload as needed either for
			   addressing an input reload, addressing an output,
			   for addressing a non-reloaded mem ref,
			   or for unspecified purposes (i.e., more than one
			   of the above).
   reload_secondary_p	  int, 1 if this is a secondary register for one
			   or more reloads.
   reload_secondary_in_reload
   reload_secondary_out_reload
   			  int, gives the reload number of a secondary
			   reload, when needed; otherwise -1
   reload_secondary_in_icode
   reload_secondary_out_icode
			  enum insn_code, if a secondary reload is required,
			   gives the INSN_CODE that uses the secondary
			   reload as a scratch register, or CODE_FOR_nothing
			   if the secondary reload register is to be an
			   intermediate register.  */
int n_reloads;

rtx reload_in[MAX_RELOADS];
rtx reload_out[MAX_RELOADS];
enum reg_class reload_reg_class[MAX_RELOADS];
enum machine_mode reload_inmode[MAX_RELOADS];
enum machine_mode reload_outmode[MAX_RELOADS];
rtx reload_reg_rtx[MAX_RELOADS];
char reload_optional[MAX_RELOADS];
int reload_inc[MAX_RELOADS];
rtx reload_in_reg[MAX_RELOADS];
char reload_nocombine[MAX_RELOADS];
int reload_opnum[MAX_RELOADS];
enum reload_type reload_when_needed[MAX_RELOADS];
int reload_secondary_p[MAX_RELOADS];
int reload_secondary_in_reload[MAX_RELOADS];
int reload_secondary_out_reload[MAX_RELOADS];
enum insn_code reload_secondary_in_icode[MAX_RELOADS];
enum insn_code reload_secondary_out_icode[MAX_RELOADS];

/* All the "earlyclobber" operands of the current insn
   are recorded here.  */
int n_earlyclobbers;
rtx reload_earlyclobbers[MAX_RECOG_OPERANDS];

int reload_n_operands;

/* Replacing reloads.

   If `replace_reloads' is nonzero, then as each reload is recorded
   an entry is made for it in the table `replacements'.
   Then later `subst_reloads' can look through that table and
   perform all the replacements needed.  */

/* Nonzero means record the places to replace.  */
static int replace_reloads;

/* Each replacement is recorded with a structure like this.  */
struct replacement
{
  rtx *where;			/* Location to store in */
  rtx *subreg_loc;		/* Location of SUBREG if WHERE is inside
				   a SUBREG; 0 otherwise.  */
  int what;			/* which reload this is for */
  enum machine_mode mode;	/* mode it must have */
};

static struct replacement replacements[MAX_RECOG_OPERANDS * ((MAX_REGS_PER_ADDRESS * 2) + 1)];

/* Number of replacements currently recorded.  */
static int n_replacements;

/* Used to track what is modified by an operand.  */
struct decomposition
{
  int reg_flag;		/* Nonzero if referencing a register. */
  int safe;		/* Nonzero if this can't conflict with anything. */
  rtx base;		/* Base address for MEM. */
  HOST_WIDE_INT start;	/* Starting offset or register number. */
  HOST_WIDE_INT end;	/* Ending offset or register number.  */
};

/* MEM-rtx's created for pseudo-regs in stack slots not directly addressable;
   (see reg_equiv_address).  */
static rtx memlocs[MAX_RECOG_OPERANDS * ((MAX_REGS_PER_ADDRESS * 2) + 1)];
static int n_memlocs;

#ifdef SECONDARY_MEMORY_NEEDED

/* Save MEMs needed to copy from one class of registers to another.  One MEM
   is used per mode, but normally only one or two modes are ever used.  

   We keep two versions, before and after register elimination.  The one 
   after register elimination is record separately for each operand.  This
   is done in case the address is not valid to be sure that we separately
   reload each.  */

static rtx secondary_memlocs[NUM_MACHINE_MODES];
static rtx secondary_memlocs_elim[NUM_MACHINE_MODES][MAX_RECOG_OPERANDS];
#endif

/* The instruction we are doing reloads for;
   so we can test whether a register dies in it.  */
static rtx this_insn;

/* Nonzero if this instruction is a user-specified asm with operands.  */
static int this_insn_is_asm;

/* If hard_regs_live_known is nonzero,
   we can tell which hard regs are currently live,
   at least enough to succeed in choosing dummy reloads.  */
static int hard_regs_live_known;

/* Indexed by hard reg number,
   element is nonegative if hard reg has been spilled.
   This vector is passed to `find_reloads' as an argument
   and is not changed here.  */
static short *static_reload_reg_p;

/* Set to 1 in subst_reg_equivs if it changes anything.  */
static int subst_reg_equivs_changed;

/* On return from push_reload, holds the reload-number for the OUT
   operand, which can be different for that from the input operand.  */
static int output_reloadnum;

  /* Compare two RTX's.  */
#define MATCHES(x, y) \
 (x == y || (x != 0 && (GET_CODE (x) == REG				\
			? GET_CODE (y) == REG && REGNO (x) == REGNO (y)	\
			: rtx_equal_p (x, y) && ! side_effects_p (x))))

  /* Indicates if two reloads purposes are for similar enough things that we
     can merge their reloads.  */
#define MERGABLE_RELOADS(when1, when2, op1, op2) \
  ((when1) == RELOAD_OTHER || (when2) == RELOAD_OTHER	\
   || ((when1) == (when2) && (op1) == (op2))		\
   || ((when1) == RELOAD_FOR_INPUT && (when2) == RELOAD_FOR_INPUT) \
   || ((when1) == RELOAD_FOR_OPERAND_ADDRESS		\
       && (when2) == RELOAD_FOR_OPERAND_ADDRESS)	\
   || ((when1) == RELOAD_FOR_OTHER_ADDRESS		\
       && (when2) == RELOAD_FOR_OTHER_ADDRESS))

  /* Nonzero if these two reload purposes produce RELOAD_OTHER when merged.  */
#define MERGE_TO_OTHER(when1, when2, op1, op2) \
  ((when1) != (when2)					\
   || ! ((op1) == (op2)					\
	 || (when1) == RELOAD_FOR_INPUT			\
	 || (when1) == RELOAD_FOR_OPERAND_ADDRESS	\
	 || (when1) == RELOAD_FOR_OTHER_ADDRESS))

static int push_secondary_reload PROTO((int, rtx, int, int, enum reg_class,
					enum machine_mode, enum reload_type,
					enum insn_code *));
static int push_reload		PROTO((rtx, rtx, rtx *, rtx *, enum reg_class,
				       enum machine_mode, enum machine_mode,
				       int, int, int, enum reload_type));
static void push_replacement	PROTO((rtx *, int, enum machine_mode));
static void combine_reloads	PROTO((void));
static rtx find_dummy_reload	PROTO((rtx, rtx, rtx *, rtx *,
				       enum machine_mode, enum machine_mode,
				       enum reg_class, int));
static int earlyclobber_operand_p PROTO((rtx));
static int hard_reg_set_here_p	PROTO((int, int, rtx));
static struct decomposition decompose PROTO((rtx));
static int immune_p		PROTO((rtx, rtx, struct decomposition));
static int alternative_allows_memconst PROTO((char *, int));
static rtx find_reloads_toplev	PROTO((rtx, int, enum reload_type, int, int));
static rtx make_memloc		PROTO((rtx, int));
static int find_reloads_address	PROTO((enum machine_mode, rtx *, rtx, rtx *,
				       int, enum reload_type, int));
static rtx subst_reg_equivs	PROTO((rtx));
static rtx subst_indexed_address PROTO((rtx));
static int find_reloads_address_1 PROTO((rtx, int, rtx *, int,
					 enum reload_type,int));
static void find_reloads_address_part PROTO((rtx, rtx *, enum reg_class,
					     enum machine_mode, int,
					     enum reload_type, int));
static int find_inc_amount	PROTO((rtx, rtx));

#ifdef HAVE_SECONDARY_RELOADS

/* Determine if any secondary reloads are needed for loading (if IN_P is
   non-zero) or storing (if IN_P is zero) X to or from a reload register of
   register class RELOAD_CLASS in mode RELOAD_MODE.  If secondary reloads
   are needed, push them.

   Return the reload number of the secondary reload we made, or -1 if
   we didn't need one.  *PICODE is set to the insn_code to use if we do
   need a secondary reload.  */

static int
push_secondary_reload (in_p, x, opnum, optional, reload_class, reload_mode,
		       type, picode)
     int in_p;
     rtx x;
     int opnum;
     int optional;
     enum reg_class reload_class;
     enum machine_mode reload_mode;
     enum reload_type type;
     enum insn_code *picode;
{
  enum reg_class class = NO_REGS;
  enum machine_mode mode = reload_mode;
  enum insn_code icode = CODE_FOR_nothing;
  enum reg_class t_class = NO_REGS;
  enum machine_mode t_mode = VOIDmode;
  enum insn_code t_icode = CODE_FOR_nothing;
  enum reload_type secondary_type;
  int i;
  int s_reload, t_reload = -1;

  if (type == RELOAD_FOR_INPUT_ADDRESS || type == RELOAD_FOR_OUTPUT_ADDRESS)