[Bug c++/105749] New: Bogus maybe-unitialized when using std::optional, regex and sstream

[Bug c++/105749] New: Bogus maybe-unitialized when using std::optional, regex and sstream

[hi+gccbugs at yamlcoder dot me]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105749

            Bug ID: 105749
           Summary: Bogus maybe-unitialized when using std::optional,
                    regex and sstream
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hi+gccbugs at yamlcoder dot me
  Target Milestone: ---

Created attachment 53044
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53044&action=edit
t.ii reproducer

Compiling following with -Wall -Werror -Os produces bogus 
maybe-unitialized warning


/tmp/t.cpp: In function ‘void t(const string&)’:
/tmp/t.cpp:12:51: error: ‘*(int*)((char*)&port +
offsetof(std::optional<int>,std::optional<int>::<unnamed>.std::_Optional_base<int,
true, true>::<unnamed>))’ may be used uninitialized in this function
[-Werror=maybe-uninitialized]
   12 |         reqb << "Host: " << port.value_or(443) << "\r\n";



Attaching .ii (tar.gz due to attachment limit) file from 11.2.0, but it is also
reproducible on trunk in godbolt: https://godbolt.org/z/ha3vn61n9

Interesting that commenting unrelated parts or changing them slightly makes
warning go away.


#include <regex>
#include <optional>
#include <sstream>

void t(const std::string& i) {
        const std::regex re("^$"); //removing this works

        std::optional<int> port(i.length() > 0 ?
std::make_optional(std::strtol("99", nullptr, 10)) : std::nullopt);

        std::ostringstream reqb;
        reqb << "GET /" << i << " HTTP/1.1" << "\r\n"; //removing this works
        reqb << "Host: " << port.value_or(443) << "\r\n";
}

[Bug tree-optimization/105749] Bogus maybe-unitialized when using std::optional, regex and sstream

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105749

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
>Interesting that commenting unrelated parts or changing them slightly makes
warning go away.

Most likely inlining changes with those being there vs not being there.

[Bug tree-optimization/105749] Bogus maybe-unitialized when using std::optional, regex and sstream

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105749

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
<source>: In function 'void t(const std::string&)':
<source>:13:51: warning: '*(int*)((char*)&port +
offsetof(std::optional<int>,std::optional<int>::<unnamed>.std::_Optional_base<int,
true, true>::<unnamed>))' may be used uninitialized [-Wmaybe-uninitialized]
   13 |         reqb << "Host: " << port.value_or(443) << "\r\n";
      |                                                   ^~~~~~
<source>:9:28: note: '*(int*)((char*)&port +
offsetof(std::optional<int>,std::optional<int>::<unnamed>.std::_Optional_base<int,
true, true>::<unnamed>))' was declared here
    9 |         std::optional<int> port(i.length() > 0 ?
std::make_optional(std::strtol("99", nullptr, 10)) : std::nullopt);
      |                            ^~~~

[Bug tree-optimization/105749] Bogus maybe-unitialized when using std::optional, regex and sstream

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105749

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.3.0

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note in GCC 10.3.0 we got:
<source>: In function 'void t(const string&)':
<source>:13:51: warning: 'port' may be used uninitialized in this function
[-Wmaybe-uninitialized]
   13 |         reqb << "Host: " << port.value_or(443) << "\r\n";
      |                                                   ^~~~~~

[Bug tree-optimization/105749] Bogus maybe-unitialized when using std::optional, regex and sstream

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105749

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |12.2.1, 13.0
   Last reconfirmed|                            |2022-09-22
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed on the GCC 12 branch but on master the diagnostic only shows with -O1
now ...