flow.c

早期freebsd实现

/* If X is the pattern of the last insn in a libcall, and assuming X is dead,
   return 1 if the entire library call is dead.
   This is true if X copies a register (hard or pseudo)
   and if the hard return  reg of the call insn is dead.
   (The caller should have tested the destination of X already for death.)

   If this insn doesn't just copy a register, then we don't
   have an ordinary libcall.  In that case, cse could not have
   managed to substitute the source for the dest later on,
   so we can assume the libcall is dead.

   NEEDED is the bit vector of pseudoregs live before this insn.
   NOTE is the REG_RETVAL note of the insn.  INSN is the insn itself.  */

static int
libcall_dead_p (x, needed, note, insn)
     rtx x;
     regset needed;
     rtx note;
     rtx insn;
{
  register RTX_CODE code = GET_CODE (x);

  if (code == SET)
    {
      register rtx r = SET_SRC (x);
      if (GET_CODE (r) == REG)
	{
	  rtx call = XEXP (note, 0);
	  register int i;

	  /* Find the call insn.  */
	  while (call != insn && GET_CODE (call) != CALL_INSN)
	    call = NEXT_INSN (call);

	  /* If there is none, do nothing special,
	     since ordinary death handling can understand these insns.  */
	  if (call == insn)
	    return 0;

	  /* See if the hard reg holding the value is dead.
	     If this is a PARALLEL, find the call within it.  */
	  call = PATTERN (call);
	  if (GET_CODE (call) == PARALLEL)
	    {
	      for (i = XVECLEN (call, 0) - 1; i >= 0; i--)
		if (GET_CODE (XVECEXP (call, 0, i)) == SET
		    && GET_CODE (SET_SRC (XVECEXP (call, 0, i))) == CALL)
		  break;

	      if (i < 0)
		abort ();

	      call = XVECEXP (call, 0, i);
	    }

	  return insn_dead_p (call, needed, 1);
	}
    }
  return 1;
}

/* Return 1 if register REGNO was used before it was set.
   In other words, if it is live at function entry.
   Don't count global regster variables, though.  */

int
regno_uninitialized (regno)
     int regno;
{
  if (n_basic_blocks == 0 || global_regs[regno])
    return 0;

  return (basic_block_live_at_start[0][regno / REGSET_ELT_BITS]
	  & ((REGSET_ELT_TYPE) 1 << (regno % REGSET_ELT_BITS)));
}

/* 1 if register REGNO was alive at a place where `setjmp' was called
   and was set more than once or is an argument.
   Such regs may be clobbered by `longjmp'.  */

int
regno_clobbered_at_setjmp (regno)
     int regno;
{
  if (n_basic_blocks == 0)
    return 0;

  return ((reg_n_sets[regno] > 1
	   || (basic_block_live_at_start[0][regno / REGSET_ELT_BITS]
	       & ((REGSET_ELT_TYPE) 1 << (regno % REGSET_ELT_BITS))))
	  && (regs_live_at_setjmp[regno / REGSET_ELT_BITS]
	      & ((REGSET_ELT_TYPE) 1 << (regno % REGSET_ELT_BITS))));
}

/* Process the registers that are set within X.
   Their bits are set to 1 in the regset DEAD,
   because they are dead prior to this insn.

   If INSN is nonzero, it is the insn being processed
   and the fact that it is nonzero implies this is the FINAL pass
   in propagate_block.  In this case, various info about register
   usage is stored, LOG_LINKS fields of insns are set up.  */

static void mark_set_1 ();

static void
mark_set_regs (needed, dead, x, insn, significant)
     regset needed;
     regset dead;
     rtx x;
     rtx insn;
     regset significant;
{
  register RTX_CODE code = GET_CODE (x);

  if (code == SET || code == CLOBBER)
    mark_set_1 (needed, dead, x, insn, significant);
  else if (code == PARALLEL)
    {
      register int i;
      for (i = XVECLEN (x, 0) - 1; i >= 0; i--)
	{
	  code = GET_CODE (XVECEXP (x, 0, i));
	  if (code == SET || code == CLOBBER)
	    mark_set_1 (needed, dead, XVECEXP (x, 0, i), insn, significant);
	}
    }
}

/* Process a single SET rtx, X.  */

static void
mark_set_1 (needed, dead, x, insn, significant)
     regset needed;
     regset dead;
     rtx x;
     rtx insn;
     regset significant;
{
  register int regno;
  register rtx reg = SET_DEST (x);

  /* Modifying just one hardware register of a multi-reg value
     or just a byte field of a register
     does not mean the value from before this insn is now dead.
     But it does mean liveness of that register at the end of the block
     is significant.

     Within mark_set_1, however, we treat it as if the register is
     indeed modified.  mark_used_regs will, however, also treat this
     register as being used.  Thus, we treat these insns as setting a
     new value for the register as a function of its old value.  This
     cases LOG_LINKS to be made appropriately and this will help combine.  */

  while (GET_CODE (reg) == SUBREG || GET_CODE (reg) == ZERO_EXTRACT
	 || GET_CODE (reg) == SIGN_EXTRACT
	 || GET_CODE (reg) == STRICT_LOW_PART)
    reg = XEXP (reg, 0);

  /* If we are writing into memory or into a register mentioned in the
     address of the last thing stored into memory, show we don't know
     what the last store was.  If we are writing memory, save the address
     unless it is volatile.  */
  if (GET_CODE (reg) == MEM
      || (GET_CODE (reg) == REG
	  && last_mem_set != 0 && reg_overlap_mentioned_p (reg, last_mem_set)))
    last_mem_set = 0;
    
  if (GET_CODE (reg) == MEM && ! side_effects_p (reg)
      /* There are no REG_INC notes for SP, so we can't assume we'll see 
	 everything that invalidates it.  To be safe, don't eliminate any
	 stores though SP; none of them should be redundant anyway.  */
      && ! reg_mentioned_p (stack_pointer_rtx, reg))
    last_mem_set = reg;

  if (GET_CODE (reg) == REG
      && (regno = REGNO (reg), regno != FRAME_POINTER_REGNUM)
#if FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
      && ! (regno == ARG_POINTER_REGNUM && fixed_regs[regno])
#endif
      && ! (regno < FIRST_PSEUDO_REGISTER && global_regs[regno]))
    /* && regno != STACK_POINTER_REGNUM) -- let's try without this.  */
    {
      register int offset = regno / REGSET_ELT_BITS;
      register REGSET_ELT_TYPE bit
	= (REGSET_ELT_TYPE) 1 << (regno % REGSET_ELT_BITS);
      REGSET_ELT_TYPE all_needed = (needed[offset] & bit);
      REGSET_ELT_TYPE some_needed = (needed[offset] & bit);

      /* Mark it as a significant register for this basic block.  */
      if (significant)
	significant[offset] |= bit;

      /* Mark it as as dead before this insn.  */
      dead[offset] |= bit;

      /* A hard reg in a wide mode may really be multiple registers.
	 If so, mark all of them just like the first.  */
      if (regno < FIRST_PSEUDO_REGISTER)
	{
	  int n;

	  /* Nothing below is needed for the stack pointer; get out asap.
	     Eg, log links aren't needed, since combine won't use them.  */
	  if (regno == STACK_POINTER_REGNUM)
	    return;

	  n = HARD_REGNO_NREGS (regno, GET_MODE (reg));
	  while (--n > 0)
	    {
	      if (significant)
		significant[(regno + n) / REGSET_ELT_BITS]
		  |= (REGSET_ELT_TYPE) 1 << ((regno + n) % REGSET_ELT_BITS);
	      dead[(regno + n) / REGSET_ELT_BITS]
		|= (REGSET_ELT_TYPE) 1 << ((regno + n) % REGSET_ELT_BITS);
	      some_needed
		|= (needed[(regno + n) / REGSET_ELT_BITS]
		    & (REGSET_ELT_TYPE) 1 << ((regno + n) % REGSET_ELT_BITS));
	      all_needed
		&= (needed[(regno + n) / REGSET_ELT_BITS]
		    & (REGSET_ELT_TYPE) 1 << ((regno + n) % REGSET_ELT_BITS));
	    }
	}
      /* Additional data to record if this is the final pass.  */
      if (insn)
	{
	  register rtx y = reg_next_use[regno];
	  register int blocknum = BLOCK_NUM (insn);

	  /* If this is a hard reg, record this function uses the reg.  */

	  if (regno < FIRST_PSEUDO_REGISTER)
	    {
	      register int i;
	      int endregno = regno + HARD_REGNO_NREGS (regno, GET_MODE (reg));

	      for (i = regno; i < endregno; i++)
		{
		  regs_ever_live[i] = 1;
		  reg_n_sets[i]++;
		}
	    }
	  else
	    {
	      /* Keep track of which basic blocks each reg appears in.  */

	      if (reg_basic_block[regno] == REG_BLOCK_UNKNOWN)
		reg_basic_block[regno] = blocknum;
	      else if (reg_basic_block[regno] != blocknum)
		reg_basic_block[regno] = REG_BLOCK_GLOBAL;

	      /* Count (weighted) references, stores, etc.  This counts a
		 register twice if it is modified, but that is correct.  */
	      reg_n_sets[regno]++;

	      reg_n_refs[regno] += loop_depth;
		  
	      /* The insns where a reg is live are normally counted
		 elsewhere, but we want the count to include the insn
		 where the reg is set, and the normal counting mechanism
		 would not count it.  */
	      reg_live_length[regno]++;
	    }

	  /* The next use is no longer "next", since a store intervenes.  */
	  reg_next_use[regno] = 0;

	  if (all_needed)
	    {
	      /* Make a logical link from the next following insn
		 that uses this register, back to this insn.
		 The following insns have already been processed.

		 We don't build a LOG_LINK for hard registers containing
		 in ASM_OPERANDs.  If these registers get replaced,
		 we might wind up changing the semantics of the insn,
		 even if reload can make what appear to be valid assignments
		 later.  */
	      if (y && (BLOCK_NUM (y) == blocknum)
		  && (regno >= FIRST_PSEUDO_REGISTER
		      || asm_noperands (PATTERN (y)) < 0))
		LOG_LINKS (y)
		  = gen_rtx (INSN_LIST, VOIDmode, insn, LOG_LINKS (y));
	    }
	  else if (! some_needed)
	    {
	      /* Note that dead stores have already been deleted when possible
		 If we get here, we have found a dead store that cannot
		 be eliminated (because the same insn does something useful).
		 Indicate this by marking the reg being set as dying here.  */
	      REG_NOTES (insn)
		= gen_rtx (EXPR_LIST, REG_UNUSED, reg, REG_NOTES (insn));
	      reg_n_deaths[REGNO (reg)]++;
	    }
	  else
	    {
	      /* This is a case where we have a multi-word hard register
		 and some, but not all, of the words of the register are
		 needed in subsequent insns.  Write REG_UNUSED notes
		 for those parts that were not needed.  This case should
		 be rare.  */

	      int i;

	      for (i = HARD_REGNO_NREGS (regno, GET_MODE (reg)) - 1;
		   i >= 0; i--)
		if ((needed[(regno + i) / REGSET_ELT_BITS]
		     & ((REGSET_ELT_TYPE) 1
			<< ((regno + i) % REGSET_ELT_BITS))) == 0)
		  REG_NOTES (insn)
		    = gen_rtx (EXPR_LIST, REG_UNUSED,
			       gen_rtx (REG, word_mode, regno + i),
			       REG_NOTES (insn));
	    }
	}
    }

  /* If this is the last pass and this is a SCRATCH, show it will be dying
     here and count it.  */
  else if (GET_CODE (reg) == SCRATCH && insn != 0)
    {
      REG_NOTES (insn)
	= gen_rtx (EXPR_LIST, REG_UNUSED, reg, REG_NOTES (insn));
      num_scratch++;
    }
}

#ifdef AUTO_INC_DEC

/* X is a MEM found in INSN.  See if we can convert it into an auto-increment
   reference.  */

static void
find_auto_inc (needed, x, insn)
     regset needed;
     rtx x;
     rtx insn;
{
  rtx addr = XEXP (x, 0);
  int offset = 0;

  /* Here we detect use of an index register which might be good for
     postincrement, postdecrement, preincrement, or predecrement.  */

  if (GET_CODE (addr) == PLUS && GET_CODE (XEXP (addr, 1)) == CONST_INT)
    offset = INTVAL (XEXP (addr, 1)), addr = XEXP (addr, 0);

  if (GET_CODE (addr) == REG)
    {
      register rtx y;
      register int size = GET_MODE_SIZE (GET_MODE (x));
      rtx use;
      rtx incr;
      int regno = REGNO (addr);

      /* Is the next use an increment that might make auto-increment? */
      incr = reg_next_use[regno];
      if (incr && GET_CODE (PATTERN (incr)) == SET
	  && BLOCK_NUM (incr) == BLOCK_NUM (insn)
	  /* Can't add side effects to jumps; if reg is spilled and
	     reloaded, there's no way to store back the altered value.  */
	  && GET_CODE (insn) != JUMP_INSN
	  && (y = SET_SRC (PATTERN (incr)), GET_CODE (y) == PLUS)
	  && XEXP (y, 0) == addr
	  && GET_CODE (XEXP (y, 1)) == CONST_INT
	  && (0
#ifdef HAVE_POST_INCREMENT
	      || (INTVAL (XEXP (y, 1)) == size && offset == 0)
#endif
#ifdef HAVE_POST_DECREMENT
	      || (INTVAL (XEXP (y, 1)) == - size && offset == 0)
#endif
#ifdef HAVE_PRE_INCREMENT
	      || (INTVAL (XEXP (y, 1)) == size && offset == size)
#endif
#ifdef HAVE_PRE_DECREMENT
	      || (INTVAL (XEXP (y, 1)) == - size && offset == - size)
#endif
	      )
	  /* Make sure this reg appears only once in this insn.  */
	  && (use = find_use_as_address (PATTERN (insn), addr, offset),
	      use != 0 && use != (rtx) 1))
	{
	  int win = 0;
	  rtx q = SET_DEST (PATTERN (incr));

	  if (dead_or_set_p (incr, addr))
	    win = 1;
	  else if (GET_CODE (q) == REG && ! reg_used_between_p (q, insn, incr))
	    {
	      /* We have *p followed by q = p+size.
		 Both p and q must be live afterward,
		 and q must be dead before.
		 Change it to q = p, ...*q..., q = q+size.
		 Then fall into the usual case.  */