final.c

gcc库的原代码,对编程有很大帮助.

	  ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, "LPBX", 5);
	  for ((ptr = bb_head), (i = 0); ptr != 0; (ptr = ptr->next), i++)
	    assemble_integer (GEN_INT (ptr->line_num), UNITS_PER_WORD, 1);

	  for ( ; i < count_basic_blocks; i++)
	    assemble_integer (const0_rtx, UNITS_PER_WORD, 1);

	  /* Output the table of file names.  */
	  ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, "LPBX", 6);
	  for ((ptr = bb_head), (i = 0); ptr != 0; (ptr = ptr->next), i++)
	    {
	      if (ptr->file_label_num >= 0)
		{
		  ASM_GENERATE_INTERNAL_LABEL (name, "LPBC", ptr->file_label_num);
		  assemble_integer (gen_rtx (SYMBOL_REF, Pmode, name),
				    UNITS_PER_WORD, 1);
		}
	      else
		assemble_integer (const0_rtx, UNITS_PER_WORD, 1);
	    }

	  for ( ; i < count_basic_blocks; i++)
	    assemble_integer (const0_rtx, UNITS_PER_WORD, 1);
	}

      /* End with the address of the table of addresses,
	 so we can find it easily, as the last word in the file's text.  */
      ASM_GENERATE_INTERNAL_LABEL (name, "LPBX", 3);
      assemble_integer (gen_rtx (SYMBOL_REF, Pmode, name), UNITS_PER_WORD, 1);
    }
}

/* Enable APP processing of subsequent output.
   Used before the output from an `asm' statement.  */

void
app_enable ()
{
  if (! app_on)
    {
      fprintf (asm_out_file, ASM_APP_ON);
      app_on = 1;
    }
}

/* Disable APP processing of subsequent output.
   Called from varasm.c before most kinds of output.  */

void
app_disable ()
{
  if (app_on)
    {
      fprintf (asm_out_file, ASM_APP_OFF);
      app_on = 0;
    }
}

/* Return the number of slots filled in the current 
   delayed branch sequence (we don't count the insn needing the
   delay slot).   Zero if not in a delayed branch sequence.  */

#ifdef DELAY_SLOTS
int
dbr_sequence_length ()
{
  if (final_sequence != 0)
    return XVECLEN (final_sequence, 0) - 1;
  else
    return 0;
}
#endif

/* The next two pages contain routines used to compute the length of an insn
   and to shorten branches.  */

/* Arrays for insn lengths, and addresses.  The latter is referenced by
   `insn_current_length'.  */

static short *insn_lengths;
int *insn_addresses;

/* Address of insn being processed.  Used by `insn_current_length'.  */
int insn_current_address;

/* Indicate that branch shortening hasn't yet been done.  */

void
init_insn_lengths ()
{
  insn_lengths = 0;
}

/* Obtain the current length of an insn.  If branch shortening has been done,
   get its actual length.  Otherwise, get its maximum length.  */

int
get_attr_length (insn)
     rtx insn;
{
#ifdef HAVE_ATTR_length
  rtx body;
  int i;
  int length = 0;

  if (insn_lengths)
    return insn_lengths[INSN_UID (insn)];
  else
    switch (GET_CODE (insn))
      {
      case NOTE:
      case BARRIER:
      case CODE_LABEL:
	return 0;

      case CALL_INSN:
	length = insn_default_length (insn);
	break;

      case JUMP_INSN:
	body = PATTERN (insn);
        if (GET_CODE (body) == ADDR_VEC || GET_CODE (body) == ADDR_DIFF_VEC)
	  {
	    /* This only takes room if jump tables go into the text section.  */
#if !defined(READONLY_DATA_SECTION) || defined(JUMP_TABLES_IN_TEXT_SECTION)
	    length = (XVECLEN (body, GET_CODE (body) == ADDR_DIFF_VEC)
		      * GET_MODE_SIZE (GET_MODE (body)));

	    /* Be pessimistic and assume worst-case alignment.  */
	    length += (GET_MODE_SIZE (GET_MODE (body)) - 1);
#else
	    return 0;
#endif
	  }
	else
	  length = insn_default_length (insn);
	break;

      case INSN:
	body = PATTERN (insn);
	if (GET_CODE (body) == USE || GET_CODE (body) == CLOBBER)
	  return 0;

	else if (GET_CODE (body) == ASM_INPUT || asm_noperands (body) >= 0)
	  length = asm_insn_count (body) * insn_default_length (insn);
	else if (GET_CODE (body) == SEQUENCE)
	  for (i = 0; i < XVECLEN (body, 0); i++)
	    length += get_attr_length (XVECEXP (body, 0, i));
	else
	  length = insn_default_length (insn);
      }

#ifdef ADJUST_INSN_LENGTH
  ADJUST_INSN_LENGTH (insn, length);
#endif
  return length;
#else /* not HAVE_ATTR_length */
  return 0;
#endif /* not HAVE_ATTR_length */
}

/* Make a pass over all insns and compute their actual lengths by shortening
   any branches of variable length if possible.  */

/* Give a default value for the lowest address in a function.  */

#ifndef FIRST_INSN_ADDRESS
#define FIRST_INSN_ADDRESS 0
#endif

void
shorten_branches (first)
     rtx first;
{
#ifdef HAVE_ATTR_length
  rtx insn;
  int something_changed = 1;
  int max_uid = 0;
  char *varying_length;
  rtx body;
  int uid;

  /* Compute maximum UID and allocate arrays.  */
  for (insn = first; insn; insn = NEXT_INSN (insn))
    if (INSN_UID (insn) > max_uid)
      max_uid = INSN_UID (insn);

  max_uid++;
  insn_lengths = (short *) oballoc (max_uid * sizeof (short));
  insn_addresses = (int *) oballoc (max_uid * sizeof (int));
  varying_length = (char *) oballoc (max_uid * sizeof (char));

  /* Compute initial lengths, addresses, and varying flags for each insn.  */
  for (insn_current_address = FIRST_INSN_ADDRESS, insn = first;
       insn != 0;
       insn_current_address += insn_lengths[uid], insn = NEXT_INSN (insn))
    {
      uid = INSN_UID (insn);
      insn_addresses[uid] = insn_current_address;
      insn_lengths[uid] = 0;
      varying_length[uid] = 0;
      
      if (GET_CODE (insn) == NOTE || GET_CODE (insn) == BARRIER
	  || GET_CODE (insn) == CODE_LABEL)
	continue;

      body = PATTERN (insn);
      if (GET_CODE (body) == ADDR_VEC || GET_CODE (body) == ADDR_DIFF_VEC)
	{
	  /* This only takes room if read-only data goes into the text
	     section.  */
#if !defined(READONLY_DATA_SECTION) || defined(JUMP_TABLES_IN_TEXT_SECTION)
	  int unitsize = GET_MODE_SIZE (GET_MODE (body));

	  insn_lengths[uid] = (XVECLEN (body, GET_CODE (body) == ADDR_DIFF_VEC)
			       * GET_MODE_SIZE (GET_MODE (body)));

	  /* Account for possible alignment.  */
	  insn_lengths[uid]
	    += unitsize - (insn_current_address & (unitsize - 1));
#else
	  ;
#endif
	}
      else if (asm_noperands (body) >= 0)
	insn_lengths[uid] = asm_insn_count (body) * insn_default_length (insn);
      else if (GET_CODE (body) == SEQUENCE)
	{
	  int i;
	  int const_delay_slots;
#ifdef DELAY_SLOTS
	  const_delay_slots = const_num_delay_slots (XVECEXP (body, 0, 0));
#else
	  const_delay_slots = 0;
#endif
	  /* Inside a delay slot sequence, we do not do any branch shortening
	     if the shortening could change the number of delay slots
	     of the branch. */
	  for (i = 0; i < XVECLEN (body, 0); i++)
	    {
	      rtx inner_insn = XVECEXP (body, 0, i);
	      int inner_uid = INSN_UID (inner_insn);
	      int inner_length;

	      if (asm_noperands (PATTERN (XVECEXP (body, 0, i))) >= 0)
		inner_length = (asm_insn_count (PATTERN (inner_insn))
				* insn_default_length (inner_insn));
	      else
		inner_length = insn_default_length (inner_insn);
	      
	      insn_lengths[inner_uid] = inner_length;
	      if (const_delay_slots)
		{
		  if ((varying_length[inner_uid]
		       = insn_variable_length_p (inner_insn)) != 0)
		    varying_length[uid] = 1;
		  insn_addresses[inner_uid] = (insn_current_address +
					       insn_lengths[uid]);
		}
	      else
		varying_length[inner_uid] = 0;
	      insn_lengths[uid] += inner_length;
	    }
	}
      else if (GET_CODE (body) != USE && GET_CODE (body) != CLOBBER)
	{
	  insn_lengths[uid] = insn_default_length (insn);
	  varying_length[uid] = insn_variable_length_p (insn);
	}

      /* If needed, do any adjustment.  */
#ifdef ADJUST_INSN_LENGTH
      ADJUST_INSN_LENGTH (insn, insn_lengths[uid]);
#endif
    }

  /* Now loop over all the insns finding varying length insns.  For each,
     get the current insn length.  If it has changed, reflect the change.
     When nothing changes for a full pass, we are done.  */

  while (something_changed)
    {
      something_changed = 0;
      for (insn_current_address = FIRST_INSN_ADDRESS, insn = first;
	   insn != 0;
	   insn = NEXT_INSN (insn))
	{
	  int new_length;
	  int tmp_length;

	  uid = INSN_UID (insn);
	  insn_addresses[uid] = insn_current_address;
	  if (! varying_length[uid])
	    {
	      insn_current_address += insn_lengths[uid];
	      continue;
	    }
	  if (GET_CODE (insn) == INSN && GET_CODE (PATTERN (insn)) == SEQUENCE)
	    {
	      int i;
	      
	      body = PATTERN (insn);
	      new_length = 0;
	      for (i = 0; i < XVECLEN (body, 0); i++)
		{
		  rtx inner_insn = XVECEXP (body, 0, i);
		  int inner_uid = INSN_UID (inner_insn);
		  int inner_length;

		  insn_addresses[inner_uid] = insn_current_address;

		  /* insn_current_length returns 0 for insns with a
		     non-varying length.  */
		  if (! varying_length[inner_uid])
		    inner_length = insn_lengths[inner_uid];
		  else
		    inner_length = insn_current_length (inner_insn);

		  if (inner_length != insn_lengths[inner_uid])
		    {
		      insn_lengths[inner_uid] = inner_length;
		      something_changed = 1;
		    }
		  insn_current_address += insn_lengths[inner_uid];
		  new_length += inner_length;
		}
	    }
	  else
	    {
	      new_length = insn_current_length (insn);
	      insn_current_address += new_length;
	    }

#ifdef SHORTEN_WITH_ADJUST_INSN_LENGTH
#ifdef ADJUST_INSN_LENGTH
	  /* If needed, do any adjustment.  */
	  tmp_length = new_length;
	  ADJUST_INSN_LENGTH (insn, new_length);
	  insn_current_address += (new_length - tmp_length);
#endif
#endif

	  if (new_length != insn_lengths[uid])
	    {
	      insn_lengths[uid] = new_length;
	      something_changed = 1;
	    }
	}
      /* For a non-optimizing compile, do only a single pass.  */
      if (!optimize)
	break;
    }
#endif /* HAVE_ATTR_length */
}

#ifdef HAVE_ATTR_length
/* Given the body of an INSN known to be generated by an ASM statement, return
   the number of machine instructions likely to be generated for this insn.
   This is used to compute its length.  */

static int
asm_insn_count (body)
     rtx body;
{
  char *template;
  int count = 1;

  if (GET_CODE (body) == ASM_INPUT)
    template = XSTR (body, 0);
  else
    template = decode_asm_operands (body, NULL_PTR, NULL_PTR,
				    NULL_PTR, NULL_PTR);

  for ( ; *template; template++)
    if (IS_ASM_LOGICAL_LINE_SEPARATOR(*template) || *template == '\n')
      count++;

  return count;
}
#endif

/* Output assembler code for the start of a function,
   and initialize some of the variables in this file
   for the new function.  The label for the function and associated
   assembler pseudo-ops have already been output in `assemble_start_function'.

   FIRST is the first insn of the rtl for the function being compiled.
   FILE is the file to write assembler code to.
   OPTIMIZE is nonzero if we should eliminate redundant
     test and compare insns.  */

void
final_start_function (first, file, optimize)
     rtx first;
     FILE *file;
     int optimize;
{
  block_depth = 0;

  this_is_asm_operands = 0;

#ifdef NON_SAVING_SETJMP
  /* A function that calls setjmp should save and restore all the
     call-saved registers on a system where longjmp clobbers them.  */
  if (NON_SAVING_SETJMP && current_function_calls_setjmp)
    {
      int i;

      for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
	if (!call_used_regs[i] && !call_fixed_regs[i])
	  regs_ever_live[i] = 1;
    }
#endif
  
  /* Initial line number is supposed to be output
     before the function's prologue and label
     so that the function's address will not appear to be
     in the last statement of the preceding function.  */
  if (NOTE_LINE_NUMBER (first) != NOTE_INSN_DELETED)
    last_linenum = high_block_linenum = high_function_linenum
      = NOTE_LINE_NUMBER (first);

  /* For SDB and XCOFF, the function beginning must be marked between
     the function label and the prologue.  We always need this, even when
     -g1 was used.  Defer on MIPS systems so that parameter descriptions
     follow function entry. */
#if defined(SDB_DEBUGGING_INFO) && !defined(MIPS_DEBUGGING_INFO)
  if (write_symbols == SDB_DEBUG)
    sdbout_begin_function (last_linenum);
  else
#endif
#ifdef XCOFF_DEBUGGING_INFO
    if (write_symbols == XCOFF_DEBUG)
      xcoffout_begin_function (file, last_linenum);
    else
#endif	  
      /* But only output line number for other debug info types if -g2
	 or better.  */
      if (NOTE_LINE_NUMBER (first) != NOTE_INSN_DELETED)
	output_source_line (file, first);

#ifdef LEAF_REG_REMAP
  if (leaf_function)
    leaf_renumber_regs (first);
#endif

  /* The Sun386i and perhaps other machines don't work right
     if the profiling code comes after the prologue.  */
#ifdef PROFILE_BEFORE_PROLOGUE
  if (profile_flag)
    profile_function (file);
#endif /* PROFILE_BEFORE_PROLOGUE */

#ifdef FUNCTION_PROLOGUE
  /* First output the function prologue: code to set up the stack frame.  */
  FUNCTION_PROLOGUE (file, get_frame_size ());
#endif

#if defined (SDB_DEBUGGING_INFO) || defined (XCOFF_DEBUGGING_INFO)
  if (write_symbols == SDB_DEBUG || write_symbols == XCOFF_DEBUG)
    next_block_index = 1;
#endif

  /* If the machine represents the prologue as RTL, the profiling code must
     be emitted when NOTE_INSN_PROLOGUE_END is scanned.  */
#ifdef HAVE_prologue
  if (! HAVE_prologue)
#endif
    profile_after_prologue (file);