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Overview
Comment:Lemon enhancement: avoid unnecessary reduce actions that convert one non-terminal into another but have no side effects.
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SHA1:a86e782ad1aa6f5a8b2c54f9dcf0fa61960843f3
User & Date: drh 2016-05-23 16:15:02
Context
2016-05-23
16:16
Improve the error messages generated by the rtree module when a constraint fails. check-in: 3ad2531e user: dan tags: trunk
16:15
Lemon enhancement: avoid unnecessary reduce actions that convert one non-terminal into another but have no side effects. check-in: a86e782a user: drh tags: trunk
14:24
Fix comment typos and improve clarity of presention in Lemon. The output should be identical. check-in: b91a5b82 user: drh tags: trunk
Changes
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Changes to tool/lemon.c.

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struct action {
  struct symbol *sp;       /* The look-ahead symbol */
  enum e_action type;
  union {
    struct state *stp;     /* The new state, if a shift */
    struct rule *rp;       /* The rule, if a reduce */
  } x;

  struct action *next;     /* Next action for this state */
  struct action *collide;  /* Next action with the same hash */
};

/* Each state of the generated parser's finite state machine
** is encoded as an instance of the following structure. */
struct state {
................................................................................
){
  struct action *newaction;
  newaction = Action_new();
  newaction->next = *app;
  *app = newaction;
  newaction->type = type;
  newaction->sp = sp;

  if( type==SHIFT ){
    newaction->x.stp = (struct state *)arg;
  }else{
    newaction->x.rp = (struct rule *)arg;
  }
}
/********************** New code to implement the "acttab" module ***********/
................................................................................
        result = 0;
      }
      break;
    case NOT_USED:
      result = 0;
      break;
  }



  return result;
}

/* Generate the "*.out" log file */
void ReportOutput(struct lemon *lemp)
{
  int i;
................................................................................
** In this version, we take the most frequent REDUCE action and make
** it the default.  Except, there is no default if the wildcard token
** is a possible look-ahead.
*/
void CompressTables(struct lemon *lemp)
{
  struct state *stp;
  struct action *ap, *ap2;
  struct rule *rp, *rp2, *rbest;
  int nbest, n;
  int i;
  int usesWildcard;

  for(i=0; i<lemp->nstate; i++){
    stp = lemp->sorted[i];
................................................................................
      pNextState = ap->x.stp;
      if( pNextState->autoReduce && pNextState->pDfltReduce!=0 ){
        ap->type = SHIFTREDUCE;
        ap->x.rp = pNextState->pDfltReduce;
      }
    }
  }






























}


/*
** Compare two states for sorting purposes.  The smaller state is the
** one with the most non-terminal actions.  If they have the same number
** of non-terminal actions, then the smaller is the one with the most







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struct action {
  struct symbol *sp;       /* The look-ahead symbol */
  enum e_action type;
  union {
    struct state *stp;     /* The new state, if a shift */
    struct rule *rp;       /* The rule, if a reduce */
  } x;
  struct symbol *spOpt;    /* SHIFTREDUCE optimization to this symbol */
  struct action *next;     /* Next action for this state */
  struct action *collide;  /* Next action with the same hash */
};

/* Each state of the generated parser's finite state machine
** is encoded as an instance of the following structure. */
struct state {
................................................................................
){
  struct action *newaction;
  newaction = Action_new();
  newaction->next = *app;
  *app = newaction;
  newaction->type = type;
  newaction->sp = sp;
  newaction->spOpt = 0;
  if( type==SHIFT ){
    newaction->x.stp = (struct state *)arg;
  }else{
    newaction->x.rp = (struct rule *)arg;
  }
}
/********************** New code to implement the "acttab" module ***********/
................................................................................
        result = 0;
      }
      break;
    case NOT_USED:
      result = 0;
      break;
  }
  if( result && ap->spOpt ){
    fprintf(fp,"  /* because %s==%s */", ap->sp->name, ap->spOpt->name);
  }
  return result;
}

/* Generate the "*.out" log file */
void ReportOutput(struct lemon *lemp)
{
  int i;
................................................................................
** In this version, we take the most frequent REDUCE action and make
** it the default.  Except, there is no default if the wildcard token
** is a possible look-ahead.
*/
void CompressTables(struct lemon *lemp)
{
  struct state *stp;
  struct action *ap, *ap2, *nextap;
  struct rule *rp, *rp2, *rbest;
  int nbest, n;
  int i;
  int usesWildcard;

  for(i=0; i<lemp->nstate; i++){
    stp = lemp->sorted[i];
................................................................................
      pNextState = ap->x.stp;
      if( pNextState->autoReduce && pNextState->pDfltReduce!=0 ){
        ap->type = SHIFTREDUCE;
        ap->x.rp = pNextState->pDfltReduce;
      }
    }
  }

  /* If a SHIFTREDUCE action specifies a rule that has a single RHS term
  ** (meaning that the SHIFTREDUCE will land back in the state where it
  ** started) and if there is no C-code associated with the reduce action,
  ** then we can go ahead and convert the action to be the same as the
  ** action for the RHS of the rule.
  */
  for(i=0; i<lemp->nstate; i++){
    stp = lemp->sorted[i];
    for(ap=stp->ap; ap; ap=nextap){
      nextap = ap->next;
      if( ap->type!=SHIFTREDUCE ) continue;
      rp = ap->x.rp;
      if( rp->noCode==0 ) continue;
      if( rp->nrhs!=1 ) continue;
#if 1
      /* Only apply this optimization to non-terminals.  It would be OK to
      ** apply it to terminal symbols too, but that makes the parser tables
      ** larger. */
      if( ap->sp->index<lemp->nterminal ) continue;
#endif
      /* If we reach this point, it means the optimization can be applied */
      nextap = ap;
      for(ap2=stp->ap; ap2 && (ap2==ap || ap2->sp!=rp->lhs); ap2=ap2->next){}
      assert( ap2!=0 );
      ap->spOpt = ap2->sp;
      ap->type = ap2->type;
      ap->x = ap2->x;
    }
  }
}


/*
** Compare two states for sorting purposes.  The smaller state is the
** one with the most non-terminal actions.  If they have the same number
** of non-terminal actions, then the smaller is the one with the most