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Overview
Comment:Be more aggressive in optimizing constant conditional expressions.
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SHA1: b7e39851a75b87ebca747b26a39989560fd6362b
User & Date: drh 2014-01-02 17:57:16.874
Context
2014-01-02
19:35
Avoid unnecessary affinity transformations when building indices using data from a table. (check-in: 10d851353c user: drh tags: trunk)
17:57
Be more aggressive in optimizing constant conditional expressions. (check-in: b7e39851a7 user: drh tags: trunk)
2014-01-01
15:18
Try to detect process ID changes due to fork() calls in os_unix.c and reset the PRNG when a process ID change is detected. (check-in: e1eba1fb09 user: drh tags: trunk)
Changes
Side-by-Side Diff Ignore Whitespace Patch
Changes to src/expr.c.
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  if( p ) {
    sqlite3ExprCheckHeight(pParse, p->nHeight);
  }
  return p;
}

/*
** If the expression is always either TRUE or FALSE (respectively),
** then return 1.  If one cannot determine the truth value of the
** Return 1 if an expression must be FALSE in all cases and 0 if the
** expression might be true.  This is an optimization.  If is OK to
** return 0 here even if the expression really is always false (a 
** false negative).  But it is a bug to return 1 if the expression
** might be true in some rare circumstances (a false positive.)
** expression at compile-time return 0.
**
** This is an optimization.  If is OK to return 0 here even if
** the expression really is always false or false (a false negative).
** But it is a bug to return 1 if the expression might have different
** boolean values in different circumstances (a false positive.)
**
** Note that if the expression is part of conditional for a
** LEFT JOIN, then we cannot determine at compile-time whether or not
** is it true or false, so always return 0.
*/
static int exprAlwaysTrue(Expr *p){
  int v = 0;
  if( ExprHasProperty(p, EP_FromJoin) ) return 0;
  if( !sqlite3ExprIsInteger(p, &v) ) return 0;
  return v!=0;
}
static int exprAlwaysFalse(Expr *p){
  int v = 0;
  if( ExprHasProperty(p, EP_FromJoin) ) return 0;
  if( !sqlite3ExprIsInteger(p, &v) ) return 0;
  return v==0;
}
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      sqlite3ExprCodeIN(pParse, pExpr, destIfFalse, destIfNull);
      sqlite3VdbeAddOp2(v, OP_Goto, 0, dest);
      sqlite3VdbeResolveLabel(v, destIfFalse);
      break;
    }
#endif
    default: {
      if( exprAlwaysTrue(pExpr) ){
        sqlite3VdbeAddOp2(v, OP_Goto, 0, dest);
      }else if( exprAlwaysFalse(pExpr) ){
        /* No-op */
      }else{
      r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
      sqlite3VdbeAddOp3(v, OP_If, r1, dest, jumpIfNull!=0);
      testcase( regFree1==0 );
      testcase( jumpIfNull==0 );
        r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
        sqlite3VdbeAddOp3(v, OP_If, r1, dest, jumpIfNull!=0);
        testcase( regFree1==0 );
        testcase( jumpIfNull==0 );
      }
      break;
    }
  }
  sqlite3ReleaseTempReg(pParse, regFree1);
  sqlite3ReleaseTempReg(pParse, regFree2);  
}
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        sqlite3ExprCodeIN(pParse, pExpr, dest, destIfNull);
        sqlite3VdbeResolveLabel(v, destIfNull);
      }
      break;
    }
#endif
    default: {
      if( exprAlwaysFalse(pExpr) ){
        sqlite3VdbeAddOp2(v, OP_Goto, 0, dest);
      }else if( exprAlwaysTrue(pExpr) ){
        /* no-op */
      }else{
      r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
      sqlite3VdbeAddOp3(v, OP_IfNot, r1, dest, jumpIfNull!=0);
      testcase( regFree1==0 );
      testcase( jumpIfNull==0 );
        r1 = sqlite3ExprCodeTemp(pParse, pExpr, &regFree1);
        sqlite3VdbeAddOp3(v, OP_IfNot, r1, dest, jumpIfNull!=0);
        testcase( regFree1==0 );
        testcase( jumpIfNull==0 );
      }
      break;
    }
  }
  sqlite3ReleaseTempReg(pParse, regFree1);
  sqlite3ReleaseTempReg(pParse, regFree2);
}
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