gcov function is not executed but lines are

Question

I have been using gcov to check code coverage. I now get a weird result, some functions are listed as not executed but the lines in the function is listed as executed.

lcov output:

  13           0 :     f<double>& operator*=(f<double>& lhs, const double& rhs)
  14             :     {
  15           9 :         // Some code...
  16           0 :         return lhs;
  17             :     }

gcov output:

#####:   13:    f<double>& operator*=(f<double>& lhs, const double& rhs)
    -:   14:    {
    9:   15:        // Some code...
#####:   16:        return lhs;
    -:   17:    }

How can the function be listed as NOT executed when the line(s) are? Is this possibly an artifact of GCC's optimization?

EDIT 1:

G++/gcov version: 4.9.2

lcov version: 1.11

EDIT 2:

Comping with -O2 yields the weird behavior. However, compiling with -O1 changes the #### to 9

Which version of gcc/gcov are you running? And what command line options do you use for gcov? — quamrana, Feb 01 '16 at 09:28
When I run gcov I get a different file format: `#####: 89: uint8_t index = dbSize - 1;` So it is `#####` which indicates not executed followed by the line number, then the text of the line. — quamrana, Feb 01 '16 at 09:35
@quamrana g++/gcov 4.9.2 and I used lgov to generate the output. — Jonas, Feb 01 '16 at 09:38
Can you run an experiment and define a whole function which is never called to see the difference to above? — quamrana, Feb 01 '16 at 09:39
@quamrana If a function is never called I believe the linker will remove it. And thus, the `x :`, where `x` is 0 or 9 in this case, would just not have an `x`. — Jonas, Feb 01 '16 at 09:44
Well, you can take the address of a function without calling it. That will keep the linker happy. — quamrana, Feb 01 '16 at 10:07

score 2 · Answer 1 · edited May 23 '17 at 12:18

The zero simply indicates that gcov had no data for the line of code. That could happen just because there's no convenient way for gcc to instrument — modify your program to add the counters (as in the entry to a function). For instance, if the optimizer removes or combines similar statements in nearby functions, there is nothing to count.

According to the manual:

The format is

 execution_count:line_number:source line text

Additional block information may succeed each line, when requested by command line option. The execution_count is ‘-’ for lines containing no code. Unexecuted lines are marked ‘#####’ or ‘====’, depending on whether they are reachable by non-exceptional paths or only exceptional paths such as C++ exception handlers, respectively.

gcov function is not executed but lines are

2 Answers2