i370.c

linux下的gcc编译器

int
i370_short_branch (insn)
     rtx insn;
{
  int base_offset;

  base_offset = i370_branch_length(insn);
  if (0 > base_offset) 
    {
      base_offset += mvs_page_code;
    } 
  else 
    {
      /* avoid bumping into lit pool; use 2x to estimate max possible lits */
      base_offset *= 2;
      base_offset += mvs_page_code + mvs_page_lit;
    }
  
  /* make a conservative estimate of room left on page */
  if ((4060 >base_offset) && ( 0 < base_offset)) return 1;
  return 0;
}

/* The i370_label_scan() routine is supposed to loop over
   all labels and label references in a compilation unit,
   and determine whether all label refs appear on the same 
   code page as the label. If they do, then we can avoid 
   a reload of the base register for that label.
  
   Note that the instruction addresses used here are only 
   approximate, and make the sizes of the jumps appear
   farther apart then they will actually be.  This makes 
   this code far more conservative than it needs to be.
 */

#define I370_RECORD_LABEL_REF(label,addr) {				\
	label_node_t *lp;						\
	int labelno = CODE_LABEL_NUMBER (label);			\
	lp = mvs_get_label (labelno);					\
	if (addr < lp -> label_first_ref) lp->label_first_ref = addr;	\
	if (addr > lp -> label_last_ref) lp->label_last_ref = addr;	\
}

static void 
i370_label_scan () 
{
   rtx insn;
   label_node_t *lp;
   int tablejump_offset = 0;

   for (insn = get_insns(); insn; insn = NEXT_INSN(insn))
     {
       int here = INSN_ADDRESSES (INSN_UID (insn));
       enum rtx_code code = GET_CODE(insn);

       /* ??? adjust for tables embedded in the .text section that
        * the compiler didn't take into account */
       here += tablejump_offset;
       INSN_ADDRESSES (INSN_UID (insn)) = here;

       /* check to see if this insn is a label ...  */
       if (CODE_LABEL == code)
         {
           int labelno = CODE_LABEL_NUMBER (insn);

           lp = mvs_get_label (labelno);
           lp -> label_addr = here;
#if 0
           /* Supposedly, labels are supposed to have circular
              lists of label-refs that reference them, 
              setup in flow.c, but this does not appear to be the case.  */
           rtx labelref = LABEL_REFS (insn);
           rtx ref = labelref;
           do 
             {
               rtx linsn = CONTAINING_INSN(ref);
               ref =  LABEL_NEXTREF(ref);
             } while (ref && (ref != labelref));
#endif
         }
       else
       if (JUMP_INSN == code)
         {
           rtx label = JUMP_LABEL (insn);

           /* If there is no label for this jump, then this
              had better be a ADDR_VEC or an ADDR_DIFF_VEC
              and there had better be a vector of labels.  */
           if (!label) 
             {
               int j;
               rtx body = PATTERN (insn);
               if (ADDR_VEC == GET_CODE(body)) 
                 {
                    for (j=0; j < XVECLEN (body, 0); j++)
                      {
                         rtx lref = XVECEXP (body, 0, j);
                         if (LABEL_REF != GET_CODE (lref)) abort ();
                         label = XEXP (lref,0);
                         if (CODE_LABEL != GET_CODE (label)) abort ();
                         tablejump_offset += 4;
                         here += 4;
                         I370_RECORD_LABEL_REF(label,here);
                      }
                    /* finished with the vector go do next insn */
                    continue;
                 }
               else
               if (ADDR_DIFF_VEC == GET_CODE(body))
                 {
/* XXX hack alert.
   Right now, we leave this as a no-op, but strictly speaking,
   this is incorrect.  It is possible that a table-jump
   driven off of a relative address could take us off-page,
   to a place where we need to reload the base reg.  So really,
   we need to examing both labels, and compare thier values
   to the current basereg value.
  
   More generally, this brings up a troubling issue overall:
   what happens if a tablejump is split across two pages? I do 
   not beleive that this case is handled correctly at all, and
   can only lead to horrible results if this were to occur.
  
   However, the current situation is not any worse than it was 
   last week, and so we punt for now.  */

                    debug_rtx (insn);
                    for (j=0; j < XVECLEN (body, 0); j++)
                      {
                      }
                    /* finished with the vector go do next insn */
                    continue;
                 }
               else 
                 {
/* XXX hack alert.
   Compiling the exception handling (L_eh) in libgcc2.a will trip
   up right here, with something that looks like
   (set (pc) (mem:SI (plus:SI (reg/v:SI 1 r1) (const_int 4))))
      {indirect_jump} 
   I'm not sure of what leads up to this, but it looks like
   the makings of a long jump which will surely get us into trouble
   because the base & page registers don't get reloaded.  For now
   I'm not sure of what to do ... again we punt ... we are not worse
   off than yesterday.  */

                    /* print_rtl_single (stdout, insn); */
                    debug_rtx (insn);
                    /* abort(); */
                    continue;
                 }
            }
          else
            {
              /* At this point, this jump_insn had better be a plain-old
                 ordinary one, grap the label id and go */
              if (CODE_LABEL != GET_CODE (label)) abort ();
              I370_RECORD_LABEL_REF(label,here);
            }
        }

      /* Sometimes, we take addresses of labels and use them
         as instruction operands ... these show up as REG_NOTES */
      else
      if (INSN == code)
       {
         if ('i' == GET_RTX_CLASS (code)) 
           {
              rtx note;
              for (note = REG_NOTES (insn); note;  note = XEXP(note,1))
                {
                   if (REG_LABEL == REG_NOTE_KIND(note))
                     {
                        rtx label = XEXP (note,0);
                        if (!label || CODE_LABEL != GET_CODE (label)) abort ();

                        I370_RECORD_LABEL_REF(label,here);
                     }
                }
           }
       }
   }
}

/* ===================================================== */

/* Emit reload of base register if indicated.  This is to eliminate multiple
   reloads when several labels are generated pointing to the same place
   in the code.  

   The page table is written at the end of the function. 
   The entries in the page table look like
     .LPGT0:          // PGT0 EQU *
     .long .LPG0      // DC A(PG0)
     .long .LPG1      // DC A(PG1)
  while the prologue generates
      L       r4,=A(.LPGT0)

  Note that this paging scheme breaks down if a single subroutine 
  has more than about 10MB of code in it ... as long as humans write
  code, this shouldn't be a problem ...
 */

void
check_label_emit ()
{
  if (mvs_need_base_reload)
    {
      mvs_need_base_reload = 0;

      mvs_page_code += 4;
      fprintf (assembler_source, "\tL\t%d,%d(,%d)\n",
	  BASE_REGISTER, (mvs_page_num - function_base_page) * 4,
	  PAGE_REGISTER);
    }
}

/* Add the label to the current page label list.  If a free element is available
   it will be used for the new label.  Otherwise, a label element will be
   allocated from memory.
   ID is the label number of the label being added to the list.  */

static label_node_t *
mvs_get_label (id)
     int id;
{
  label_node_t *lp;

  /* first, lets see if we already go one, if so, use that.  */
  for (lp = label_anchor; lp; lp = lp->label_next)
    {
      if (lp->label_id == id) return lp;
    }

  /* not found, get a new one */
  if (free_anchor)
    {
      lp = free_anchor;
      free_anchor = lp->label_next;
    }
  else
    {
      lp = (label_node_t *) xmalloc (sizeof (label_node_t));
    }

  /* initialize for new label */
  lp->label_id = id;
  lp->label_page = -1;
  lp->label_next = label_anchor;
  lp->label_first_ref = 2000123123;
  lp->label_last_ref = -1;
  lp->label_addr = -1;
  lp->first_ref_page = -1;
  label_anchor = lp;

  return lp;
}

void
mvs_add_label (id)
     int id;
{
  label_node_t *lp;
  int fwd_distance;

  lp = mvs_get_label (id);
  lp->label_page = mvs_page_num;

  /* OK, we just saw the label.  Determine if this label
   * needs a reload of the base register */
  if ((-1 != lp->first_ref_page) && 
      (lp->first_ref_page != mvs_page_num)) 
    {
      /* Yep; the first label_ref was on a different page.  */
      mvs_need_base_reload ++;
      return;
    }

  /* Hmm.  Try to see if the estimated address of the last
     label_ref is on the current page.  If it is, then we
     don't need a base reg reload.  Note that this estimate
     is very conservatively handled; we'll tend to have 
     a good bit more reloads than actually needed.  Someday,
     we should tighten the estimates (which are driven by
     the (set_att "length") insn attibute.
    
     Currently, we estimate that number of page literals 
     same as number of insns, which is a vast overestimate,
     esp that the estimate of each insn size is its max size.  */

  /* if latest ref comes before label, we are clear */
  if (lp->label_last_ref < lp->label_addr) return;

  fwd_distance = lp->label_last_ref - lp->label_addr;

  if (mvs_page_code + 2 * fwd_distance + mvs_page_lit < 4060) return;

  mvs_need_base_reload ++;
}

/* Check to see if the label is in the list and in the current
   page.  If not found, we have to make worst case assumption 
   that label will be on a different page, and thus will have to
   generate a load and branch on register.  This is rather
   ugly for forward-jumps, but what can we do? For backward
   jumps on the same page we can branch directly to address.
   ID is the label number of the label being checked.  */

int
mvs_check_label (id)
     int id;
{
  label_node_t *lp;

  for (lp = label_anchor; lp; lp = lp->label_next)
    {
      if (lp->label_id == id) 
        {
          if (lp->label_page == mvs_page_num) 
            {
               return 1;
            } 
          else 
            {
	       return 0;
            } 
        }
    }
  return 0;
}

/* Get the page on which the label sits.  This will be used to 
   determine is a register reload is really needed.  */

#if 0
int
mvs_get_label_page(int id)
{
  label_node_t *lp;

  for (lp = label_anchor; lp; lp = lp->label_next)
    {
      if (lp->label_id == id)
	return lp->label_page;
    }
  return -1;
}
#endif

/* The label list for the current page freed by linking the list onto the free
   label element chain.  */

void
mvs_free_label_list ()
{

  if (label_anchor)
    {
      label_node_t *last_lp = label_anchor;
      while (last_lp->label_next) last_lp = last_lp->label_next;
      last_lp->label_next = free_anchor;
      free_anchor = label_anchor;
    }
  label_anchor = 0;
}

/* ====================================================================== */
/* If the page size limit is reached a new code page is started, and the base
   register is set to it.  This page break point is counted conservatively,
   most literals that have the same value are collapsed by the assembler.
   True is returned when a new page is started.
   FILE is the assembler output file descriptor.
   CODE is the length, in bytes, of the instruction to be emitted.
   LIT is the length of the literal to be emitted.  */

#ifdef TARGET_HLASM
int
mvs_check_page (file, code, lit)
     FILE *file;
     int code, lit;
{
  if (file)
    assembler_source = file;

  if (mvs_page_code + code + mvs_page_lit + lit > MAX_MVS_PAGE_LENGTH)
    {
      fprintf (assembler_source, "\tB\tPGE%d\n", mvs_page_num);
      fprintf (assembler_source, "\tDS\t0F\n");
      fprintf (assembler_source, "\tLTORG\n");
      fprintf (assembler_source, "\tDS\t0F\n");
      fprintf (assembler_source, "PGE%d\tEQU\t*\n", mvs_page_num);
      fprintf (assembler_source, "\tDROP\t%d\n", BASE_REGISTER);
      mvs_page_num++;
      /* Safe to use BASR not BALR, since we are
       * not switching addressing mode here ...  */
      fprintf (assembler_source, "\tBASR\t%d,0\n", BASE_REGISTER);
      fprintf (assembler_source, "PG%d\tEQU\t*\n", mvs_page_num);
      fprintf (assembler_source, "\tUSING\t*,%d\n", BASE_REGISTER);