clauses.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 2,256 行 · 第 1/5 页

				}
				/* Else we still need a NOT node */
				return (Node *) make_notclause(lfirst(args));
			default:
				elog(ERROR, "unrecognized boolop: %d",
					 (int) expr->boolop);
				break;
		}
	}
	if (IsA(node, SubPlan))
	{
		/*
		 * Return a SubPlan unchanged --- too late to do anything with it.
		 *
		 * XXX should we ereport() here instead?  Probably this routine
		 * should never be invoked after SubPlan creation.
		 */
		return node;
	}
	if (IsA(node, RelabelType))
	{
		/*
		 * If we can simplify the input to a constant, then we don't need
		 * the RelabelType node anymore: just change the type field of the
		 * Const node.	Otherwise, must copy the RelabelType node.
		 */
		RelabelType *relabel = (RelabelType *) node;
		Node	   *arg;

		arg = eval_const_expressions_mutator((Node *) relabel->arg,
											 active_fns);

		/*
		 * If we find stacked RelabelTypes (eg, from foo :: int :: oid) we
		 * can discard all but the top one.
		 */
		while (arg && IsA(arg, RelabelType))
			arg = (Node *) ((RelabelType *) arg)->arg;

		if (arg && IsA(arg, Const))
		{
			Const	   *con = (Const *) arg;

			con->consttype = relabel->resulttype;

			/*
			 * relabel's resulttypmod is discarded, which is OK for now;
			 * if the type actually needs a runtime length coercion then
			 * there should be a function call to do it just above this
			 * node.
			 */
			return (Node *) con;
		}
		else
		{
			RelabelType *newrelabel = makeNode(RelabelType);

			newrelabel->arg = (Expr *) arg;
			newrelabel->resulttype = relabel->resulttype;
			newrelabel->resulttypmod = relabel->resulttypmod;
			return (Node *) newrelabel;
		}
	}
	if (IsA(node, CaseExpr))
	{

		/*----------
		 * CASE expressions can be simplified if there are constant
		 * condition clauses:
		 *		FALSE (or NULL): drop the alternative
		 *		TRUE: drop all remaining alternatives
		 * If the first non-FALSE alternative is a constant TRUE, we can
		 * simplify the entire CASE to that alternative's expression.
		 * If there are no non-FALSE alternatives, we simplify the entire
		 * CASE to the default result (ELSE result).
		 *----------
		 */
		CaseExpr   *caseexpr = (CaseExpr *) node;
		CaseExpr   *newcase;
		FastList	newargs;
		Node	   *defresult;
		Const	   *const_input;
		List	   *arg;

		FastListInit(&newargs);
		foreach(arg, caseexpr->args)
		{
			/* Simplify this alternative's condition and result */
			CaseWhen   *casewhen = (CaseWhen *)
			expression_tree_mutator((Node *) lfirst(arg),
									eval_const_expressions_mutator,
									(void *) active_fns);

			Assert(IsA(casewhen, CaseWhen));
			if (casewhen->expr == NULL ||
				!IsA(casewhen->expr, Const))
			{
				FastAppend(&newargs, casewhen);
				continue;
			}
			const_input = (Const *) casewhen->expr;
			if (const_input->constisnull ||
				!DatumGetBool(const_input->constvalue))
				continue;		/* drop alternative with FALSE condition */

			/*
			 * Found a TRUE condition.	If it's the first (un-dropped)
			 * alternative, the CASE reduces to just this alternative.
			 */
			if (FastListValue(&newargs) == NIL)
				return (Node *) casewhen->result;

			/*
			 * Otherwise, add it to the list, and drop all the rest.
			 */
			FastAppend(&newargs, casewhen);
			break;
		}

		/* Simplify the default result */
		defresult = eval_const_expressions_mutator((Node *) caseexpr->defresult,
												   active_fns);

		/*
		 * If no non-FALSE alternatives, CASE reduces to the default
		 * result
		 */
		if (FastListValue(&newargs) == NIL)
			return defresult;
		/* Otherwise we need a new CASE node */
		newcase = makeNode(CaseExpr);
		newcase->casetype = caseexpr->casetype;
		newcase->arg = NULL;
		newcase->args = FastListValue(&newargs);
		newcase->defresult = (Expr *) defresult;
		return (Node *) newcase;
	}
	if (IsA(node, ArrayExpr))
	{
		ArrayExpr  *arrayexpr = (ArrayExpr *) node;
		ArrayExpr  *newarray;
		bool		all_const = true;
		FastList	newelems;
		List	   *element;

		FastListInit(&newelems);
		foreach(element, arrayexpr->elements)
		{
			Node	   *e;

			e = eval_const_expressions_mutator((Node *) lfirst(element),
											   active_fns);
			if (!IsA(e, Const))
				all_const = false;
			FastAppend(&newelems, e);
		}

		newarray = makeNode(ArrayExpr);
		newarray->array_typeid = arrayexpr->array_typeid;
		newarray->element_typeid = arrayexpr->element_typeid;
		newarray->elements = FastListValue(&newelems);
		newarray->multidims = arrayexpr->multidims;

		if (all_const)
			return (Node *) evaluate_expr((Expr *) newarray,
										  newarray->array_typeid);

		return (Node *) newarray;
	}
	if (IsA(node, CoalesceExpr))
	{
		CoalesceExpr *coalesceexpr = (CoalesceExpr *) node;
		CoalesceExpr *newcoalesce;
		FastList	newargs;
		List	   *arg;

		FastListInit(&newargs);
		foreach(arg, coalesceexpr->args)
		{
			Node	   *e;

			e = eval_const_expressions_mutator((Node *) lfirst(arg),
											   active_fns);

			/*
			 * We can remove null constants from the list. For a non-null
			 * constant, if it has not been preceded by any other
			 * non-null-constant expressions then that is the result.
			 */
			if (IsA(e, Const))
			{
				if (((Const *) e)->constisnull)
					continue;	/* drop null constant */
				if (FastListValue(&newargs) == NIL)
					return e;	/* first expr */
			}
			FastAppend(&newargs, e);
		}

		newcoalesce = makeNode(CoalesceExpr);
		newcoalesce->coalescetype = coalesceexpr->coalescetype;
		newcoalesce->args = FastListValue(&newargs);
		return (Node *) newcoalesce;
	}
	if (IsA(node, FieldSelect))
	{
		/*
		 * We can optimize field selection from a whole-row Var into a
		 * simple Var.	(This case won't be generated directly by the
		 * parser, because ParseComplexProjection short-circuits it. But
		 * it can arise while simplifying functions.)  If the argument
		 * isn't a whole-row Var, just fall through to do generic
		 * processing.
		 */
		FieldSelect *fselect = (FieldSelect *) node;
		Var		   *argvar = (Var *) fselect->arg;

		if (argvar && IsA(argvar, Var) &&
			argvar->varattno == InvalidAttrNumber)
		{
			return (Node *) makeVar(argvar->varno,
									fselect->fieldnum,
									fselect->resulttype,
									fselect->resulttypmod,
									argvar->varlevelsup);
		}
	}

	/*
	 * For any node type not handled above, we recurse using
	 * expression_tree_mutator, which will copy the node unchanged but try
	 * to simplify its arguments (if any) using this routine. For example:
	 * we cannot eliminate an ArrayRef node, but we might be able to
	 * simplify constant expressions in its subscripts.
	 */
	return expression_tree_mutator(node, eval_const_expressions_mutator,
								   (void *) active_fns);
}

/*
 * Subroutine for eval_const_expressions: try to simplify a function call
 * (which might originally have been an operator; we don't care)
 *
 * Inputs are the function OID, actual result type OID (which is needed for
 * polymorphic functions), and the pre-simplified argument list;
 * also a list of already-active inline function expansions.
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function call.
 */
static Expr *
simplify_function(Oid funcid, Oid result_type, List *args,
				  bool allow_inline, List *active_fns)
{
	HeapTuple	func_tuple;
	Expr	   *newexpr;

	/*
	 * We have two strategies for simplification: either execute the
	 * function to deliver a constant result, or expand in-line the body
	 * of the function definition (which only works for simple
	 * SQL-language functions, but that is a common case).	In either case
	 * we need access to the function's pg_proc tuple, so fetch it just
	 * once to use in both attempts.
	 */
	func_tuple = SearchSysCache(PROCOID,
								ObjectIdGetDatum(funcid),
								0, 0, 0);
	if (!HeapTupleIsValid(func_tuple))
		elog(ERROR, "cache lookup failed for function %u", funcid);

	newexpr = evaluate_function(funcid, result_type, args, func_tuple);

	if (!newexpr && allow_inline)
		newexpr = inline_function(funcid, result_type, args,
								  func_tuple, active_fns);

	ReleaseSysCache(func_tuple);

	return newexpr;
}

/*
 * evaluate_function: try to pre-evaluate a function call
 *
 * We can do this if the function is strict and has any constant-null inputs
 * (just return a null constant), or if the function is immutable and has all
 * constant inputs (call it and return the result as a Const node).
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function.
 */
static Expr *
evaluate_function(Oid funcid, Oid result_type, List *args,
				  HeapTuple func_tuple)
{
	Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
	bool		has_nonconst_input = false;
	bool		has_null_input = false;
	List	   *arg;
	FuncExpr   *newexpr;
	char		result_typtype;

	/*
	 * Can't simplify if it returns a set.
	 */
	if (funcform->proretset)
		return NULL;

	/*
	 * Check for constant inputs and especially constant-NULL inputs.
	 */
	foreach(arg, args)
	{
		if (IsA(lfirst(arg), Const))
			has_null_input |= ((Const *) lfirst(arg))->constisnull;
		else
			has_nonconst_input = true;
	}

	/*
	 * If the function is strict and has a constant-NULL input, it will
	 * never be called at all, so we can replace the call by a NULL
	 * constant, even if there are other inputs that aren't constant, and
	 * even if the function is not otherwise immutable.
	 */
	if (funcform->proisstrict && has_null_input)
		return (Expr *) makeNullConst(result_type);

	/*
	 * Otherwise, can simplify only if the function is immutable and all
	 * inputs are constants. (For a non-strict function, constant NULL
	 * inputs are treated the same as constant non-NULL inputs.)
	 */
	if (funcform->provolatile != PROVOLATILE_IMMUTABLE ||
		has_nonconst_input)
		return NULL;

	/*
	 * Can't simplify functions returning composite types (mainly because
	 * datumCopy() doesn't cope; FIXME someday when we have a saner
	 * representation for whole-tuple results).
	 */
	result_typtype = get_typtype(funcform->prorettype);
	if (result_typtype == 'c')
		return NULL;

	/*
	 * OK, looks like we can simplify this operator/function.
	 *
	 * Build a new FuncExpr node containing the already-simplified arguments.
	 */
	newexpr = makeNode(FuncExpr);
	newexpr->funcid = funcid;
	newexpr->funcresulttype = result_type;
	newexpr->funcretset = false;
	newexpr->funcformat = COERCE_EXPLICIT_CALL; /* doesn't matter */
	newexpr->args = args;

	return evaluate_expr((Expr *) newexpr, result_type);
}

/*
 * inline_function: try to expand a function call inline
 *
 * If the function is a sufficiently simple SQL-language function
 * (just "SELECT expression"), then we can inline it and avoid the rather
 * high per-call overhead of SQL functions.  Furthermore, this can expose
 * opportunities for constant-folding within the function expression.
 *
 * We have to beware of some special cases however.  A directly or
 * indirectly recursive function would cause us to recurse forever,
 * so we keep track of which functions we are already expanding and
 * do not re-expand them.  Also, if a parameter is used more than once
 * in the SQL-function body, we require it not to contain any volatile
 * functions (volatiles might deliver inconsistent answers) nor to be
 * unreasonably expensive to evaluate.	The expensiveness check not only
 * prevents us from doing multiple evaluations of an expensive parameter
 * at runtime, but is a safety value to limit growth of an expression due
 * to repeated inlining.
 *
 * We must also beware of changing the volatility or strictness status of
 * functions by inlining them.
 *
 * Returns a simplified expression if successful, or NULL if cannot
 * simplify the function.
 */
static Expr *
inline_function(Oid funcid, Oid result_type, List *args,
				HeapTuple func_tuple, List *active_fns)
{
	Form_pg_proc funcform = (Form_pg_proc) GETSTRUCT(func_tuple);
	char		result_typtype;
	bool		polymorphic = false;
	Oid			argtypes[FUNC_MAX_ARGS];
	char	   *src;
	Datum		tmp;
	bool		isNull;
	MemoryContext oldcxt;
	MemoryContext mycxt;
	ErrorContextCallback sqlerrcontext;
	List	   *raw_parsetree_list;
	List	   *querytree_list;
	Query	   *querytree;
	Node	   *newexpr;
	int		   *usecounts;
	List	   *arg;
	int			i;

	/*
	 * Forget it if the function is not SQL-language or has other
	 * showstopper properties.	(The nargs check is just paranoia.)
	 */
	if (funcform->prolang != SQLlanguageId ||
		funcform->prosecdef ||
		funcform->proretset ||
		funcform->pronargs != length(args))
		return NULL;

	/*
	 * Forget it if declared return type is not base, domain, or
	 * polymorphic
	 */
	result_typtype = get_typtype(funcform->prorettype);
	if (result_typtype != 'b' &&
		result_typtype != 'd')
	{
		if (funcform->prorettype == ANYARRAYOID ||
			funcform->prorettype == ANYELEMENTOID)
			polymorphic = true;
		else
			return NULL;
	}

	/* Check for recursive function, and give up trying to expand if so */
	if (oidMember(funcid, active_fns))
		return NULL;

	/* Check permission to call function (fail later, if not) */
	if (pg_proc_aclcheck(funcid, GetUserId(), ACL_EXECUTE) != ACLCHECK_OK)
		return NULL;

	/* Check for polymorphic arguments, and substitute actual arg types */
	memcpy(argtypes, funcform->proargtypes, FUNC_MAX_ARGS * sizeof(Oid));
	for (i = 0; i < funcform->pronargs; i++)
	{
		if (argtypes[i] == ANYARRAYOID ||
			argtypes[i] == ANYELEMENTOID)
		{
			polymorphic = true;
			argtypes[i] = exprType((Node *) nth(i, args));
		}