[cfe-dev] Invalid coverage results from Clang's Source-based Code Coverage

[Michał Pszona via cfe-dev]

Thanks a lot Alex!
regards,
Michał Pszona


On Fri, Feb 17, 2017 at 2:37 PM, Alex L <arphaman at gmail.com> wrote:
>
>
> On 17 February 2017 at 03:03, Michał Pszona via cfe-dev
> <cfe-dev at lists.llvm.org> wrote:
>>
>> I'm trying to get a reliable code coverage through Clang's
>> Source-based Code Coverage and am heading some false negatives on
>> virtual inheriting classes. In particular the inheriting class'
>> constructor is displayed as NOT covered.
>>
>> Given this code:
>>
>> #include <iostream>
>> class Foo
>> {
>> public:
>>     Foo()
>>     {
>>         std::cout << "in Foo()" << std::endl;
>>     }
>> };
>>
>> class Bar : virtual public Foo
>> {
>> public:
>>    Bar()
>>    {
>>         std::cout << "in Bar()" << std::endl;  // supposedly not covered
>>    };
>> };
>>
>> int main (int argc, char* argv[])
>> {
>>     Bar b;
>> }
>>
>> The output is, obviously:
>>
>> in Foo()
>> in Bar()
>>
>> but the Bar's constructor is reported as uncovered.
>>
>>
>> I'm folliwng the steps described on the above page ie.
>> 1. clang++ -fprofile-instr-generate -fcoverage-mapping main.cpp
>> 2. running the binary
>> 3. llvm-profdata merge default.profraw -o default.profdata
>> 4. llvm-cov-4.0 show a.out --instr-profile default.profdata
>>
>> Tried clang 4.0 and 5.0 (compiled from trunk) with same effect.
>>
>>
>> Could anyone help me with this issue?
>> Is there a way to workaround this issue?
>> How can I debug it to see what's causing it?
>
>
> Hi, this looks like a bug in the source-based PGO, which is used to get the
> coverage. The problem is that we only collect PGO data for the base
> constructors on platforms whose ABI supports constructor variants, which
> usually isn't a problem since complete constructors invoke them. However, in
> the code sample that you provided, clang will emit a C1 complete object
> constructor for Bar that doesn't invoke the C2 base constructor for Bar.
> This means that our assumptions about constructors are incorrect and should
> be fixed.
>
> I don't think there's a workaround for this issue unfortunately.
>
> I have filed the following bug to track this issue:
> http://bugs.llvm.org/show_bug.cgi?id=31992 .
>
>>
>>
>>
>> regards,
>> Michał Pszona
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>> cfe-dev at lists.llvm.org
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>
>