Re: [Boost-bugs] [Boost C++ Libraries] #5658: how to get rid of nasty compiler warning in boost/property_tree/detail/rapidxml.hpp

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5658: how to get rid of nasty compiler warning in boost/property_tree/detail/rapidxml.hpp
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-07-18 08:27:50

#5658: how to get  rid of nasty compiler warning in
boost/property_tree/detail/rapidxml.hpp
--------------------------------------------+---------------------------
  Reporter:  Dieter Stach <Dieter.Stach@…>  |      Owner:  cornedbee
      Type:  Tasks                          |     Status:  new
 Milestone:  To Be Determined               |  Component:  property_tree
   Version:  Boost 1.46.1                   |   Severity:  Optimization
Resolution:                                 |   Keywords:
--------------------------------------------+---------------------------
Changes (by mloskot):

 * cc: mateusz@… (added)


Old description:

> compiling e.g libs/graph/src/graphml.cpp warns ...
> -----
> /boost/property_tree/detail/rapidxml.hpp: In function `size_t
> boost::property_t
> ree::detail::rapidxml::internal::get_index(Ch) [with Ch = char]':
> ./boost/property_tree/detail/rapidxml.hpp:1413:   instantiated from
> `static unsi
> gned char
> boost::property_tree::detail::rapidxml::xml_document<Ch>::whitespace_p
> red::test(Ch) [with Ch = char]'
> ./boost/property_tree/detail/rapidxml.hpp:1542:   instantiated from
> `static void
>  boost::property_tree::detail::rapidxml::xml_document<Ch>::skip(Ch*&)
> [with Stop
> Pred =
> boost::property_tree::detail::rapidxml::xml_document<char>::whitespace_pr
> ed, int Flags = 3072, Ch = char]'
> ./boost/property_tree/detail/rapidxml.hpp:1377:   instantiated from `void
> boost:
> :property_tree::detail::rapidxml::xml_document<Ch>::parse(Ch*) [with int
> Flags =
>  3072, Ch = char]'
> ./boost/property_tree/detail/xml_parser_read_rapidxml.hpp:116:
> instantiated fr
> om `void
> boost::property_tree::xml_parser::read_xml_internal(std::basic_istream<
> typename Ptree::key_type::value_type, std::char_traits<typename
> Ptree::key_type:
> :value_type> >&, Ptree&, int, const std::string&) [with Ptree =
> boost::property_
> tree::basic_ptree<std::string, std::string, std::less<std::string> >]'
> ./boost/property_tree/xml_parser.hpp:52:   instantiated from `void
> boost::proper
> ty_tree::xml_parser::read_xml(std::basic_istream<typename
> Ptree::key_type::value
> _type, std::char_traits<typename Ptree::key_type::value_type> >&, Ptree&,
> int) [
> with Ptree = boost::property_tree::ptree]'
> libs/graph/src/graphml.cpp:49:   instantiated from here
> ./boost/property_tree/detail/rapidxml.hpp:317: warning: comparison is
> always fal
> se due to limited range of data type
> ---------
> Caused by the template:
> template<class Ch>
>         inline size_t get_index(const Ch c)
>         {
>             // If not ASCII char, its sematic is same as plain 'z'
>             if (c > 255)
>             {
>                 return 'z';
>             }
>             return c;
>         }
> ----------
> How to avoid ?
> Just specify additionally a user defined implementation
> of get_index for the "char" type :
>
>         inline size_t get_index(const char c)
>         {
>             return c;
>         }
>
>         template<class Ch>
>         inline size_t get_index(const Ch c)
>         {
>             // If not ASCII char, its sematic is same as plain 'z'
>             if (c > 255)
>             {
>                 return 'z';
>             }
>             return c;
>         }
> ---------
> I checked the code size (using gcc4.0) : same
> and the difference of the ASM code: "same"
>

> 14972c14972
> <       cmpq    (%r15), %rdi
> ---
> >       cmpq    %rdi, (%r15)
> 14974c14974
> <       jae     .L3637
> ---
> >       jbe     .L3637
> 15002c15002
> <       cmpq    -16(%rsi), %rdi
> ---
> >       cmpq    %rdi, -16(%rsi)
> 15004c15004
> <       jae     .L3643
> ---
> >       jbe     .L3643
> 15017c15017
> <       cmpq    -16(%rdx), %rdi
> ---
> >       cmpq    %rdi, -16(%rdx)
> 15019c15019
> <       jb      .L3796
> ---
> >       ja      .L3796
> 15487c15487
> ---

New description:

 compiling e.g libs/graph/src/graphml.cpp warns ...

 {{{
 /boost/property_tree/detail/rapidxml.hpp: In function `size_t
 boost::property_t
 ree::detail::rapidxml::internal::get_index(Ch) [with Ch = char]':
 ./boost/property_tree/detail/rapidxml.hpp:1413:   instantiated from
 `static unsi
 gned char
 boost::property_tree::detail::rapidxml::xml_document<Ch>::whitespace_p
 red::test(Ch) [with Ch = char]'
 ./boost/property_tree/detail/rapidxml.hpp:1542:   instantiated from
 `static void
  boost::property_tree::detail::rapidxml::xml_document<Ch>::skip(Ch*&)
 [with Stop
 Pred =
 boost::property_tree::detail::rapidxml::xml_document<char>::whitespace_pr
 ed, int Flags = 3072, Ch = char]'
 ./boost/property_tree/detail/rapidxml.hpp:1377:   instantiated from `void
 boost:
 :property_tree::detail::rapidxml::xml_document<Ch>::parse(Ch*) [with int
 Flags =
  3072, Ch = char]'
 ./boost/property_tree/detail/xml_parser_read_rapidxml.hpp:116:
 instantiated fr
 om `void
 boost::property_tree::xml_parser::read_xml_internal(std::basic_istream<
 typename Ptree::key_type::value_type, std::char_traits<typename
 Ptree::key_type:
 :value_type> >&, Ptree&, int, const std::string&) [with Ptree =
 boost::property_
 tree::basic_ptree<std::string, std::string, std::less<std::string> >]'
 ./boost/property_tree/xml_parser.hpp:52:   instantiated from `void
 boost::proper
 ty_tree::xml_parser::read_xml(std::basic_istream<typename
 Ptree::key_type::value
 _type, std::char_traits<typename Ptree::key_type::value_type> >&, Ptree&,
 int) [
 with Ptree = boost::property_tree::ptree]'
 libs/graph/src/graphml.cpp:49:   instantiated from here
 ./boost/property_tree/detail/rapidxml.hpp:317: warning: comparison is
 always fal
 se due to limited range of data type
 }}}

 Caused by the template:

 {{{
 template<class Ch>
         inline size_t get_index(const Ch c)
         {
             // If not ASCII char, its sematic is same as plain 'z'
             if (c > 255)
             {
                 return 'z';
             }
             return c;
         }
 }}}

 How to avoid ?
 Just specify additionally a user defined implementation
 of get_index for the "char" type :

 {{{
         inline size_t get_index(const char c)
         {
             return c;
         }

         template<class Ch>
         inline size_t get_index(const Ch c)
         {
             // If not ASCII char, its sematic is same as plain 'z'
             if (c > 255)
             {
                 return 'z';
             }
             return c;
         }
 }}}

 I checked the code size (using gcc4.0) : same
 and the difference of the ASM code: "same"

 {{{
 14972c14972
 <       cmpq    (%r15), %rdi
 ---
 >       cmpq    %rdi, (%r15)
 14974c14974
 <       jae     .L3637
 ---
 >       jbe     .L3637
 15002c15002
 <       cmpq    -16(%rsi), %rdi
 ---
 >       cmpq    %rdi, -16(%rsi)
 15004c15004
 <       jae     .L3643
 ---
 >       jbe     .L3643
 15017c15017
 <       cmpq    -16(%rdx), %rdi
 ---
 >       cmpq    %rdi, -16(%rdx)
 15019c15019
 <       jb      .L3796
 ---
 >       ja      .L3796
 15487c15487
 ---
 }}}

--
-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5658#comment:2>
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