http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45890
--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> 2011-10-04 09:14:42 UTC --- On Sat, 1 Oct 2011, singhai at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45890 > > --- Comment #2 from Sharad Singhai <singhai at gcc dot gnu.org> 2011-10-01 > 19:42:48 UTC --- > I don't know if it is related. But the coverage is imprecise in case of > attached source file foo.c. Build it with O2, as > > gcc --coverage -O2 foo.c > ./a.out > gcov -b foo.c > > Now the coverage data for the 'if' condition in 'sum' looks like this: > (in attached file foo.c.gcov) > > 8: 8: if (v[i]) total += 1; > branch 0 never executed > branch 1 never executed > branch 2 taken 75% (fallthrough) > branch 3 taken 25% > > Thus a simple two-way conditional looks like a four-way branch. It is due to > early inlining of 'sum' into 'main where a couple of bb's get > eliminated/merged > so that the branch coverage incorrectly gets attributed to the conditional. > Similarly the coverage data for the for-loop in 'sum' looks like this > > 9: 7: for (i = 0; i < N; ++i) { > branch 0 never executed > branch 1 never executed > branch 2 taken 89% > branch 3 taken 11% (fallthrough) > > After disabling early inlining, the coverage data looks saner. (Attached in > foo.c.gcov.no-early-inlining.) > > gcc --coverage -O2 -fno-early-inlining foo.c > ./a.out > gcov -b foo.c > > Adding the following patch mitigates the issue. That's surely not the way to go. Why do you want precise coverage with -O2? > 2011-09-30 Sharad Singhai <sing...@google.com> > > * gcc.c (cc1_options): Added -fno-early-inlining for coverage. > > Index: gcc.c > =================================================================== > --- gcc.c (revision 179402) > +++ gcc.c (working copy) > @@ -776,7 +776,7 @@ > %{!fsyntax-only:%{S:%W{o*}%{!o*:-o %b.s}}}\ > %{fsyntax-only:-o %j} %{-param*}\ > %{fmudflap|fmudflapth:-fno-builtin -fno-merge-constants}\ > - %{coverage:-fprofile-arcs -ftest-coverage}"; > + %{coverage:-fprofile-arcs -ftest-coverage -fno-early-inlining}"; > > /* If an assembler wrapper is used to invoke post-assembly tools > like MAO, --save-temps need to be passed to save the output of
