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Overview
Comment:In the lemon-generated parser, automatically promote SHIFTREDUCE actions on nonterminal systems to pure REDUCE actions, for a performance enhancement.
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SHA3-256: c46d94a8cde816ca383e771721ebd4900de77950cba700e35a26f70fd5b794a4
User & Date: drh 2017-06-28 11:56:18.525
Context
2017-06-28
13:47
In the lemon-generated parser, store the number of symbols on the RHS of each rule as a negative number and add it to the stack pointer, rather than storing the value as a positive and subtracting it. This makes the parser faster. (check-in: b362f0d8ed user: drh tags: trunk)
11:56
In the lemon-generated parser, automatically promote SHIFTREDUCE actions on nonterminal systems to pure REDUCE actions, for a performance enhancement. (check-in: c46d94a8cd user: drh tags: trunk)
01:21
Simplify error handling logic in sqlite3_exec() to save about 40 bytes. (check-in: 6480916c72 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to tool/lemon.c.
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** Return negative if no action should be generated.
*/
PRIVATE int compute_action(struct lemon *lemp, struct action *ap)
{
  int act;
  switch( ap->type ){
    case SHIFT:  act = ap->x.stp->statenum;                        break;

    case SHIFTREDUCE: act = ap->x.rp->iRule + lemp->nstate;        break;






    case REDUCE: act = ap->x.rp->iRule + lemp->nstate+lemp->nrule; break;
    case ERROR:  act = lemp->nstate + lemp->nrule*2;               break;
    case ACCEPT: act = lemp->nstate + lemp->nrule*2 + 1;           break;
    default:     act = -1; break;
  }
  return act;
}








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** Return negative if no action should be generated.
*/
PRIVATE int compute_action(struct lemon *lemp, struct action *ap)
{
  int act;
  switch( ap->type ){
    case SHIFT:  act = ap->x.stp->statenum;                        break;
    case SHIFTREDUCE: {
      act = ap->x.rp->iRule + lemp->nstate;
      /* Since a SHIFT is inherient after a prior REDUCE, convert any
      ** SHIFTREDUCE action with a nonterminal on the LHS into a simple
      ** REDUCE action: */
      if( ap->sp->index>=lemp->nterminal ) act += lemp->nrule;
      break;
    }
    case REDUCE: act = ap->x.rp->iRule + lemp->nstate+lemp->nrule; break;
    case ERROR:  act = lemp->nstate + lemp->nrule*2;               break;
    case ACCEPT: act = lemp->nstate + lemp->nrule*2 + 1;           break;
    default:     act = -1; break;
  }
  return act;
}
︙︙
Changes to tool/lempar.c.
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%%
/********** End reduce actions ************************************************/
  };
  assert( yyruleno<sizeof(yyRuleInfo)/sizeof(yyRuleInfo[0]) );
  yygoto = yyRuleInfo[yyruleno].lhs;
  yysize = yyRuleInfo[yyruleno].nrhs;
  yyact = yy_find_reduce_action(yymsp[-yysize].stateno,(YYCODETYPE)yygoto);
  if( yyact <= YY_MAX_SHIFTREDUCE ){


    if( yyact>YY_MAX_SHIFT ){
      yyact += YY_MIN_REDUCE - YY_MIN_SHIFTREDUCE;


    }




    yymsp -= yysize-1;
    yypParser->yytos = yymsp;
    yymsp->stateno = (YYACTIONTYPE)yyact;
    yymsp->major = (YYCODETYPE)yygoto;
    yyTraceShift(yypParser, yyact);
  }else{
    assert( yyact == YY_ACCEPT_ACTION );
    yypParser->yytos -= yysize;
    yy_accept(yypParser);
  }
}

/*
** The following code executes when the parse fails
*/
#ifndef YYNOERRORRECOVERY








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%%
/********** End reduce actions ************************************************/
  };
  assert( yyruleno<sizeof(yyRuleInfo)/sizeof(yyRuleInfo[0]) );
  yygoto = yyRuleInfo[yyruleno].lhs;
  yysize = yyRuleInfo[yyruleno].nrhs;
  yyact = yy_find_reduce_action(yymsp[-yysize].stateno,(YYCODETYPE)yygoto);

  /* There are no SHIFTREDUCE actions on nonterminals because the table
  ** generator has simplified them to pure REDUCE actions. */
  assert( !(yyact>YY_MAX_SHIFT && yyact<=YY_MAX_SHIFTREDUCE) );

  /* It is not possible for a REDUCE to be followed by an error */
  assert( yyact!=YY_ERROR_ACTION );

  if( yyact==YY_ACCEPT_ACTION ){
    yypParser->yytos -= yysize;
    yy_accept(yypParser);
  }else{
    yymsp -= yysize-1;
    yypParser->yytos = yymsp;
    yymsp->stateno = (YYACTIONTYPE)yyact;
    yymsp->major = (YYCODETYPE)yygoto;
    yyTraceShift(yypParser, yyact);




  }
}

/*
** The following code executes when the parse fails
*/
#ifndef YYNOERRORRECOVERY
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