Hi, all I have some question about "branch probabilities". I think I don't quite understand how this works. - What is the purpose of calculating the branch probabilities? The propose is to use information about past executions (gcda files) to optimize better the program that is compiling? - "branch probabilities" is calculated by the compiler even when the parameters profile-arcs and ftest-coverage were not used? The source coverage.c has a method coverage_init which is called by toplev.c. The coverage_init calls the read_counts_file (in coverage.c), wich try to open a file gcda. If this method find the file gcda, load the file content in a hash (counts_hash) in memory ... Is that right? If I'm right, what is the purpose of loading the information from a GCDA in memory at compile time? This information is used by the compiler only for branch probabilities? Thanks, Harry 2011/4/6 Ian Lance Taylor <iant@xxxxxxxxxx> > > Harry Trinta <harrytpc@xxxxxxxxx> writes: > > > - The instrumentator uses any technique to reduce the amount of > > instrumentation points, for example, dominance? > > Yes. > > > - I know that the instrumentation is done at compile time. However, it > > is done in C code or in compiled code ? > > I'm not sure I understand this question. The compiler generates the > instrumentation code. It doesn't generate C code. It just adds > additional function calls as it compiles. So perhaps the answer is that > the instrumentation is done in compiled code. > > > - What commands runs when the probes are executed? The probes calls > > some function in lib? What? > > There are several different functions. They all have names start with > "__gcov_". > > > Now I'd want to know more about the sources that I have identified as > > part of gcov: > > > > - coverage.c: I do not know. > > Generates the .gcno file. If you don't know what that means, see > http://gcc.gnu.org/onlinedocs/gcc/Gcov-Data-Files.html . > > > - gcov: It is responsible for generating the file. gcov? > > Part of the gcov program which turns the .gcda files into a readable > form. > > > - profile: > > Branch probability coverage support. > > > - gcov-io: Responsible for reading and writing files. gcda and. gcno? > > Yes. Used by both gcov and the runtime library. > > > - libgcov: library that supports the execution of the instrumented program? > > Yes. > > > - tree-profile.c: insert the probes in code? > > Yes. > > > Which of these files are used during compile? And which of these files > > are used during program execution? > > All of the above are used at compile time except libgcov. gcov-io is > used at both compile time and runtime. > > Ian
