Function exec_check_rw_parameter

src/pl/plpgsql/src/pl_exec.c:8111–8215

* exec_check_rw_parameter --- can we pass expanded object as read/write param? * * If we have an assignment like "x := array_append(x, foo)" in which the * top-level function is trusted not to corrupt its argument in case of an * error, then when x has an expanded object as value, it is safe to pass the * value as a read/write pointer and let the function modify the value * in-place. * * T

 * shakier in the general case.
 */
static void
exec_check_rw_parameter(PLpgSQL_expr *expr)
{
	int			target_dno;
	Oid			funcid;
	List	   *fargs;
	ListCell   *lc;

	/* Assume unsafe */
	expr->expr_rw_param = NULL;

	/* Done if expression isn't an assignment source */
	target_dno = expr->target_param;
	if (target_dno < 0)
		return;

	/*
	 * If target variable isn't referenced by expression, no need to look
	 * further.
	 */
	if (!bms_is_member(target_dno, expr->paramnos))
		return;

	/* Shouldn't be here for non-simple expression */
	Assert(expr->expr_simple_expr != NULL);

	/*
	 * Top level of expression must be a simple FuncExpr, OpExpr, or
	 * SubscriptingRef, else we can't optimize.
	 */
	if (IsA(expr->expr_simple_expr, FuncExpr))
	{
		FuncExpr   *fexpr = (FuncExpr *) expr->expr_simple_expr;

		funcid = fexpr->funcid;
		fargs = fexpr->args;
	}
	else if (IsA(expr->expr_simple_expr, OpExpr))
	{
		OpExpr	   *opexpr = (OpExpr *) expr->expr_simple_expr;

		funcid = opexpr->opfuncid;
		fargs = opexpr->args;
	}
	else if (IsA(expr->expr_simple_expr, SubscriptingRef))
	{
		SubscriptingRef *sbsref = (SubscriptingRef *) expr->expr_simple_expr;

		/* We only trust standard varlena arrays to be safe */
		if (get_typsubscript(sbsref->refcontainertype, NULL) !=
			F_ARRAY_SUBSCRIPT_HANDLER)
			return;

		/* We can optimize the refexpr if it's the target, otherwise not */
		if (sbsref->refexpr && IsA(sbsref->refexpr, Param))
		{
			Param	   *param = (Param *) sbsref->refexpr;