llvm-cov: unused methods of template classes are not shown as uncovered

[def-]

Bugzilla Link	42110
Version	trunk
OS	Linux
CC	@dwblaikie

Extended Description

$ cat x.cpp template struct C { C(T x) : v(x) { }

void foo(T x)
{
    v = x;
}

T v;

};

int main() { C c(5); }

$ clang++ -fprofile-instr-generate -fcoverage-mapping x.cpp -o x $ ./x $ llvm-profdata merge -sparse default.profraw -o default.profdata $ llvm-cov show ./x -instr-profile=default.profdata 1| |template 2| |struct C 3| |{ 4| | C(T x) 5| | : v(x) 6| 1| { 7| 1| } 8| | 9| | void foo(T x) 10| | { 11| | v = x; 12| | } 13| | 14| | T v; 15| |}; 16| | 17| |int main() 18| 1|{ 19| 1| C c(5); 20| 1|}

I would expect foo to be considered uncovered, but since the method is inside of a template class it is apparently not generated when it's also not used. If the class is non-templated foo is shown correctly as being uncovered.

[def-]

My way of considering this is that these are lines of code that could be executed, but they are not. So if your target is to know how many percent code coverage your software has, this behavior distorts it.

[dwblaikie]

I'm guessing this is probably by design - member function templates that aren't called aren't instantiated & might not be valid instantiations (consider something like std::list::sort - not all Ts are sortable, so it's not necessarily reasonable to say "list::sort" is lacking coverage when it's not valid at all)