https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103984
Bug ID: 103984
Summary: [12 regression] Possible maybe-uninitialized false
positive on shaderc-2021.0
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: slyfox at gcc dot gnu.org
Target Milestone: ---
Noticed new warning on shaderc-2021.0 which uses -Werror. Last week's gcc-12
snapshot did not flag it as a warning. Here is the extracted example:
// $ cat glslc/src/main.cc
#include <string>
#include <vector>
#include <cstring>
struct string_piece {
const char * begin_ = nullptr;
const char * end_ = nullptr;
std::string str() const { return std::string(begin_, end_); }
string_piece(const char* string) : begin_(string), end_(string) {
end_ += strlen(string);
}
string_piece(const string_piece& other) {
begin_ = other.begin_;
end_ = other.end_;
}
};
struct Z { std::string name; int stage; };
extern int to_stage(string_piece file_name);
int main(int argc, char** argv) {
std::vector<Z> input_files;
const std::string current_entry_point_name("main");
const string_piece arg = argv[0];
input_files.emplace_back(Z{
arg.str(), // what is the lifetime of this temporary?
to_stage(arg), // why does this constructor matter?
});
return 0;
}
$ g++-12.0.0 -O1 -Wall -Werror -std=c++11 -o main.cc.o -c glslc/src/main.cc
In file included from /<<NIX>>/gcc-12.0.0/include/c++/12.0.0/string:53,
from glslc/src/main.cc:1:
In member function 'std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::pointer std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_M_data()
const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]',
inlined from 'bool std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_M_is_local() const [with _CharT = char; _Traits =
std::char_traits<char>; _Alloc = std::allocator<char>]' at
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/bits/basic_string.h:275:23,
inlined from 'void std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_M_dispose() [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]' at
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/bits/basic_string.h:286:18,
inlined from 'std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::~basic_string() [with _CharT = char; _Traits = std::char_traits<char>;
_Alloc = std::allocator<char>]' at
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/bits/basic_string.h:793:19,
inlined from 'int main(int, char**)' at glslc/src/main.cc:35:1:
/<<NIX>>/gcc-12.0.0/include/c++/12.0.0/bits/basic_string.h:235:28: error:
'<unnamed>.Z::name.std::__cxx11::basic_string<char>::_M_dataplus.std::__cxx11::basic_string<char>::_Alloc_hider::_M_p'
may be used uninitialized [-Werror=maybe-uninitialized]
235 | { return _M_dataplus._M_p; }
| ^~~~
glslc/src/main.cc: In function 'int main(int, char**)':
glslc/src/main.cc:32:3: note: '<anonymous>' declared here
32 | });
| ^
cc1plus: all warnings being treated as errors
$ g++-12.0.0 -v
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-12.0.0/bin/g++
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-12.0.0/libexec/gcc/x86_64-unknown-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20220109 (experimental) (GCC)
