https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80935
Bug ID: 80935
Summary: [C++1z] incorrect error 'uninitialized variable in
constexpr function' when conditionally declaring
variable inside lambda inside template class
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vis...@royal-caliber.com
Target Milestone: ---
Created attachment 41445
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41445&action=edit
preprocessed file generated by g++ -std=c++1z -v -save-temps
The following code fails to compile with g++ 7.1.0 with flags -std=c++1z. It
compiles with -std=c++14 or -std=c++11. I believe expected behavior is to
compile cleanly. clang-4.0 also has no problem with this code.
struct S
{
int x;
int y;
};
template <class T>
struct Foo
{
void foo()
{
auto f = [](int x)
{
if (x)
{
S s;
s.x = 20;
s.y = 10;
(void) s;
}
};
f(10);
}
};
int main()
{
Foo<int> f;
f.foo();
}
When compiled with g++ -std=c++1z, the following error is raised:
test.cpp: In instantiation of ‘Foo<T>::foo()::<lambda(int)> [with T = int]’:
test.cpp:26:15: required from ‘struct Foo<T>::foo() [with T =
int]::<lambda(int)>’
test.cpp:26:10: required from ‘void Foo<T>::foo() [with T = int]’
test.cpp:45:9: required from here
test.cpp:30:11: error: uninitialized variable ‘s’ in ‘constexpr’ function
S s;
^
test.cpp:14:8: note: ‘struct S’ has no user-provided default constructor
struct S
^
test.cpp:16:7: note: and the implicitly-defined constructor does not initialize
‘int S::x’
int x;
The gcc build information is as follows:
Using built-in specs.
COLLECT_GCC=g++-7.1
COLLECT_LTO_WRAPPER=/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ./configure --prefix=/home/vishal/localbuild
--enable-languages=c,c++ --program-suffix=-7.1 --disable-multilib
Thread model: posix
gcc version 7.1.0 (GCC)
COLLECT_GCC_OPTIONS='-std=c++1z' '-Wall' '-Wextra' '-v' '-save-temps'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/home/vishal/localbuild/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/cc1plus
-fpreprocessed test.ii -quiet -dumpbase test.cpp -mtune=generic -march=x86-64
-auxbase test -Wall -Wextra -std=c++1z -version -o test.s
GNU C++14 (GCC) version 7.1.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 7.1.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++14 (GCC) version 7.1.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 7.1.0, GMP version 6.1.0, MPFR version
3.1.3-p4, MPC version 1.0.2, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
