I have this program:
#include <cstdio>
template<class T>
T add (T x, T y) {
if (x > y)
return x + y;
else
return x;
}
template<class T>
T sub (T x, T y) {
if (x > y)
return x - y;
else
return x;
}
int main() {
int i1 = 10;
int i2 = 12;
double d1 = 10.0;
double d2 = 12.0;
auto x = add(i1, i2);
auto y = add(d1, d2);
auto z = sub(i2, i1);
printf ("%d %f %d\n", x, y, z);
}
add() is instantiated for int, double, and sub() is only instantiated
for int.
$ gcc -v
gcc version 12.0.1 20220426 (experimental) (GCC)
$ gcc --coverage demo.cc -o demo && ./demo
$ gcov -mfb demo
Function 'int sub<int>(int, int)'
Lines executed:75.00% of 4
Function 'double add<double>(double, double)'
No executable lines
Function 'int add<int>(int, int)'
No executable lines
Function 'main'
Lines executed:100.00% of 10
File 'demo.cc'
Lines executed:88.89% of 18
Branches executed:100.00% of 2
Taken at least once:50.00% of 2
Calls executed:100.00% of 4
Creating 'demo.cc.gcov'
Lines executed:88.89% of 18
So it reports lines and branches accurately for templates with a single
instantiation, but nothing when there are multiple. When you look at the
.gcov file however the branches are reported for all the instantiations:
double add<double>(double, double):
function double add<double>(double, double) called 1 returned 100%
blocks executed 75%
1: 4:T add (T x, T y) {
1: 5: if (x > y)
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
#####: 6: return x + y;
-: 7: else
1: 8: return x;
-: 9:}
Skimming gcov.cc I found accumulate_line_info. By applying this patch
the file summary includes all instantiations:
diff --git a/gcc/gcov.cc b/gcc/gcov.cc
index 04bbc774eec..c0ee9d1cd3f 100644
--- a/gcc/gcov.cc
+++ b/gcc/gcov.cc
@@ -2952,7 +2952,7 @@ accumulate_line_counts (source_info *src)
it2 != fn->lines.end (); it2++)
{
line_info *line = &(*it2);
- accumulate_line_info (line, src, false);
+ accumulate_line_info (line, src, true);
}
}
File 'demo.cc'
Lines executed:84.62% of 26
Branches executed:100.00% of 6
Taken at least once:50.00% of 6
Calls executed:100.00% of 4
Creating 'demo.cc.gcov'
It doesn't fix the function summaries however:
Function 'int add<int>(int, int)'
No executable lines
Looking through the changelog it looks like this was introduced to work
with destructors/C++ clones
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48463
Is there a non-obvious downside to look into groups in order to have
templates count towards file- and function summaries? Any subtle
interactions at play? Is this a bug?
Thanks,
Jørgen
