[llvm-dev] llvm-cov: Combined report for multiple executables

[Sadrul Chowdhury via llvm-dev]

Hi! I am trying to get a combined coverage report from multiple
executables. Looking at earlier discussions [1, 2], it looks like this
is supposed to work. I am having some difficulty getting this to work
as I would expect it to work, however. Following is a simple case to
explain:

////////// shared.h
#include <string>

void Print1(const std::string& msg);
void Print2(const std::string& msg);
////////// end

////////// shared.cc
#include <iostream>
#include <string>

void Print1(const std::string& msg) {
  std::cout << "1" << msg;
}

void Print2(const std::string& msg) {
  std::cout << "2" << msg;
}
////////// end

////////// first.cc
#include "shared.h"

int main() {
  Print1("First\n");
  return 0;
}
////////// end

////////// second.cc
#include "shared.h"

int main() {
  Print2("Second\n");
  return 0;
}
////////// end

I use the following commands to build 'first' and 'second' binaries:
  clang++ -O0 -c -fprofile-instr-generate -fcoverage-mapping shared.cc
-o ./out/shared.o
  clang++ -O0 -fprofile-instr-generate -fcoverage-mapping
./out/shared.o first.cc -o ./out/first
  clang++ -O0 -fprofile-instr-generate -fcoverage-mapping
./out/shared.o second.cc -o ./out/second

I then use the following to run the binaries:
  LLVM_PROFILE_FILE='./out/first.profraw' ./out/first
  LLVM_PROFILE_FILE='./out/second.profraw' ./out/second

I then use the following commands to show the report:
  llvm-profdata merge -sparse ./out/first.profraw ./out/second.profraw
-o ./out/all.profdata
  llvm-cov show ./out/second -object ./out/first -instr-profile
./out/all.profdata

But the output only contains:

second.cc:
    1|       |#include "shared.h"
    2|       |
    3|      2|int main() {
    4|      2|  Print2("Second\n");
    5|      2|  return 0;
    6|      2|}

shared.cc:
    1|       |#include <iostream>
    2|       |#include <string>
    3|       |
    4|      1|void Print1(const std::string& msg) {
    5|      1|  std::cout << "1" << msg;
    6|      1|}
    7|       |
    8|      1|void Print2(const std::string& msg) {
    9|      1|  std::cout << "2" << msg;
   10|      1|}

The output does not include anything for first.cc If I run the last
command with ./out/second and ./out/first swapped, then the output
only contains first.cc and shared.cc, but does not have second.cc

Is my expectation that the report should include both first.cc and
second.cc correct? If it is, then I am probably holding something
wrong? Any suggestions on what I should try?

[1] https://groups.google.com/forum/#!msg/llvm-dev/11mEQr1t2ys/9SOI39v-AAAJ;context-place=forum/llvm-dev
[2] https://reviews.llvm.org/D25086#change-SchnPUmKhFiN

Thank you!
Sadrul