conflicts.c

Bison 是替代yacc的语法解析器. Bison能生成可以分析文本文件结构的程序.

/* Find and resolve or report look-ahead conflicts for bison,
   Copyright (C) 1984, 1989 Free Software Foundation, Inc.

This file is part of Bison, the GNU Compiler Compiler.

Bison 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.

Bison 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 Bison; see the file COPYING.  If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

#ifdef _AIX
 #pragma alloca
#endif
#include <stdio.h>
#include "system.h"
#include "machine.h"
#include "new.h"
#include "files.h"
#include "gram.h"
#include "state.h"


#ifndef __GNUC__
#undef alloca
#define alloca __builtin_alloca
#else
#ifdef HAVE_ALLOCA_H
#include <alloca.h>
#else
#ifndef _AIX
extern char *alloca ();
#endif
#endif
#endif

extern char **tags;
extern int tokensetsize;
extern char *consistent;
extern short *accessing_symbol;
extern shifts **shift_table;
extern unsigned *LA;
extern short *LAruleno;
extern short *lookaheads;
extern int verboseflag;

void set_conflicts();
void resolve_sr_conflict();
void flush_shift();
void log_resolution();
void total_conflicts();
void count_sr_conflicts();
void count_rr_conflicts();

char any_conflicts;
char *conflicts;
errs **err_table;
int expected_conflicts;


static unsigned *shiftset;
static unsigned *lookaheadset;
static int src_total;
static int rrc_total;
static int src_count;
static int rrc_count;


void
initialize_conflicts()
{
  register int i;
/*  register errs *sp; JF unused */

  conflicts = NEW2(nstates, char);
  shiftset = NEW2(tokensetsize, unsigned);
  lookaheadset = NEW2(tokensetsize, unsigned);

  err_table = NEW2(nstates, errs *);

  any_conflicts = 0;

  for (i = 0; i < nstates; i++)
    set_conflicts(i);
}


void
set_conflicts(state)
int state;
{
  register int i;
  register int k;
  register shifts *shiftp;
  register unsigned *fp2;
  register unsigned *fp3;
  register unsigned *fp4;
  register unsigned *fp1;
  register int symbol;

  if (consistent[state]) return;

  for (i = 0; i < tokensetsize; i++)
    lookaheadset[i] = 0;

  shiftp = shift_table[state];
  if (shiftp)
    {
      k = shiftp->nshifts;
      for (i = 0; i < k; i++)
	{
	  symbol = accessing_symbol[shiftp->shifts[i]];
	  if (ISVAR(symbol)) break;
	  SETBIT(lookaheadset, symbol);
	}
    }

  k = lookaheads[state + 1];
  fp4 = lookaheadset + tokensetsize;

  /* loop over all rules which require lookahead in this state */
  /* first check for shift-reduce conflict, and try to resolve using precedence  */

  for (i = lookaheads[state]; i < k; i++)
    if (rprec[LAruleno[i]])
      {
	fp1 = LA + i * tokensetsize;
	fp2 = fp1;
	fp3 = lookaheadset;
  
	while (fp3 < fp4)
	  {
	    if (*fp2++ & *fp3++)
	      {
		resolve_sr_conflict(state, i);
		break;
	      }
	  }
      }

  /* loop over all rules which require lookahead in this state */
  /* Check for conflicts not resolved above.  */

  for (i = lookaheads[state]; i < k; i++)
    {
      fp1 = LA + i * tokensetsize;
      fp2 = fp1;
      fp3 = lookaheadset;

      while (fp3 < fp4)
	{
	  if (*fp2++ & *fp3++)
	    {
	      conflicts[state] = 1;
	      any_conflicts = 1;
	    }
	}

      fp2 = fp1;
      fp3 = lookaheadset;

      while (fp3 < fp4)
	*fp3++ |= *fp2++;
    }
}



/* Attempt to resolve shift-reduce conflict for one rule
by means of precedence declarations.
It has already been checked that the rule has a precedence.
A conflict is resolved by modifying the shift or reduce tables
so that there is no longer a conflict.  */

void
resolve_sr_conflict(state, lookaheadnum)
int state;
int lookaheadnum;
{
  register int i;
  register int mask;
  register unsigned *fp1;
  register unsigned *fp2;
  register int redprec;
  /* Extra parens avoid errors on Ultrix 4.3.  */
  errs *errp = (errs *) alloca ((sizeof(errs) + ntokens * sizeof(short)));
  short *errtokens = errp->errs;

  /* find the rule to reduce by to get precedence of reduction  */
  redprec = rprec[LAruleno[lookaheadnum]];

  mask = 1;
  fp1 = LA + lookaheadnum * tokensetsize;
  fp2 = lookaheadset;
  for (i = 0; i < ntokens; i++)
    {
      if ((mask & *fp2 & *fp1) && sprec[i])
	/* Shift-reduce conflict occurs for token number i
	   and it has a precedence.
	   The precedence of shifting is that of token i.  */
	{
	  if (sprec[i] < redprec)
	    {
	      if (verboseflag) log_resolution(state, lookaheadnum, i, "reduce");
	      *fp2 &= ~mask;  /* flush the shift for this token */
	      flush_shift(state, i);
	    }
	  else if (sprec[i] > redprec)
	    {
	      if (verboseflag) log_resolution(state, lookaheadnum, i, "shift");
	      *fp1 &= ~mask;  /* flush the reduce for this token */
	    }
	  else
	    {
	      /* Matching precedence levels.
		 For left association, keep only the reduction.
		 For right association, keep only the shift.
		 For nonassociation, keep neither.  */

	      switch (sassoc[i])
		{

		case RIGHT_ASSOC:
	          if (verboseflag) log_resolution(state, lookaheadnum, i, "shift");
		  break;

		case LEFT_ASSOC:
	          if (verboseflag) log_resolution(state, lookaheadnum, i, "reduce");
		  break;

		case NON_ASSOC:
	          if (verboseflag) log_resolution(state, lookaheadnum, i, "an error");
		  break;
		}

	      if (sassoc[i] != RIGHT_ASSOC)
		{
		  *fp2 &= ~mask;  /* flush the shift for this token */
		  flush_shift(state, i);
		}
	      if (sassoc[i] != LEFT_ASSOC)
	        {
		  *fp1 &= ~mask;  /* flush the reduce for this token */
		}
	      if (sassoc[i] == NON_ASSOC)
		{
		  /* Record an explicit error for this token.  */
		  *errtokens++ = i;
		}
	    }
	}

      mask <<= 1;
      if (mask == 0)
	{
	  mask = 1;
	  fp2++;  fp1++;
	}
    }
  errp->nerrs = errtokens - errp->errs;
  if (errp->nerrs)
    {
      /* Some tokens have been explicitly made errors.  Allocate
	 a permanent errs structure for this state, to record them.  */
      i = (char *) errtokens - (char *) errp;
      err_table[state] = (errs *) xmalloc ((unsigned int)i);
      bcopy (errp, err_table[state], i);
    }
  else
    err_table[state] = 0;
}



/* turn off the shift recorded for the specified token in the specified state.
Used when we resolve a shift-reduce conflict in favor of the reduction.  */

void
flush_shift(state, token)
int state;
int token;
{
  register shifts *shiftp;
  register int k, i;
/*  register unsigned symbol; JF unused */

  shiftp = shift_table[state];

  if (shiftp)
    {
      k = shiftp->nshifts;
      for (i = 0; i < k; i++)
	{
	  if (shiftp->shifts[i] && token == accessing_symbol[shiftp->shifts[i]])
	    (shiftp->shifts[i]) = 0;
	}
    }
}


void
log_resolution(state, LAno, token, resolution)
int state, LAno, token;
char *resolution;
{
  fprintf(foutput,
	  "Conflict in state %d between rule %d and token %s resolved as %s.\n",
	  state, LAruleno[LAno], tags[token], resolution);
}


void
conflict_log()
{
  register int i;

  src_total = 0;
  rrc_total = 0;

  for (i = 0; i < nstates; i++)
    {
      if (conflicts[i])
	{
	  count_sr_conflicts(i);
	  count_rr_conflicts(i);
	  src_total += src_count;
	  rrc_total += rrc_count;
	}
    }

  total_conflicts();
}
  

void
verbose_conflict_log()
{
  register int i;

  src_total = 0;
  rrc_total = 0;

  for (i = 0; i < nstates; i++)
    {
      if (conflicts[i])
	{
	  count_sr_conflicts(i);
	  count_rr_conflicts(i);
	  src_total += src_count;
	  rrc_total += rrc_count;

	  fprintf(foutput, "State %d contains", i);

	  if (src_count == 1)
	    fprintf(foutput, " 1 shift/reduce conflict");
	  else if (src_count > 1)
	    fprintf(foutput, " %d shift/reduce conflicts", src_count);

	  if (src_count > 0 && rrc_count > 0)
	    fprintf(foutput, " and");

	  if (rrc_count == 1)
	    fprintf(foutput, " 1 reduce/reduce conflict");
	  else if (rrc_count > 1)
	    fprintf(foutput, " %d reduce/reduce conflicts", rrc_count);

	  putc('.', foutput);
	  putc('\n', foutput);
	}
    }

  total_conflicts();
}


void
total_conflicts()