[Bug gcov-profile/89469] New: [GCOV] wrong frequencies for the first statement in the for(;;) block

[yangyibiao at nju dot edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89469

            Bug ID: 89469
           Summary: [GCOV] wrong frequencies for the first statement in
                    the for(;;) block
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: gcov-profile
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yangyibiao at nju dot edu.cn
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
8.2.0-1ubuntu2~18.04' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr
--with-gcc-major-version-only --program-suffix=-8
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie
--with-system-zlib --with-target-system-zlib --enable-objc-gc=auto
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none --without-cuda-driver
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 8.2.0 (Ubuntu 8.2.0-1ubuntu2~18.04)

$ cat small.c
int main()
{
  int start = 0, mid = 3, limit = 3, lastMid = 6, r = 0;
  for (;;) {
      mid = (start + limit) / 2;
      if (lastMid == mid) {
        break;
      }

      r = mid == 1 ? 1 : 0;

      if (r > 0) {
        start = mid;
      } else {
        return 1;
      }
  }
  return 0;
}

$ gcc -O0 --coverage small.c -w; ./a.out; gcov small.c; cat small.c.gcov
File 'small.c'
Lines executed:80.00% of 10
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        1:    1:int main()
        -:    2:{
        1:    3:  int start = 0, mid = 3, limit = 3, lastMid = 6, r = 0;
        -:    4:  for (;;) {
        1:    5:      mid = (start + limit) / 2;
        2:    6:      if (lastMid == mid) {
    #####:    7:        break;
        -:    8:      }
        -:    9:
        2:   10:      r = mid == 1 ? 1 : 0;
        -:   11:
        2:   12:      if (r > 0) {
        1:   13:        start = mid;
        -:   14:      } else {
        1:   15:        return 1;
        -:   16:      }
        -:   17:  }
    #####:   18:  return 0;
        -:   19:}

Line #5 is wrongly marked as executed once which should be executed twice. 

When Line #7 is removed, the result is correct as:
$ gcc -O0 --coverage small.c -w; ./a.out; gcov small.c; cat small.c.gcov
File 'small.c'
Lines executed:100.00% of 7
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        1:    1:int main()
        -:    2:{
        1:    3:  int start = 0, mid = 3, limit = 3, lastMid = 6, r = 0;
        -:    4:  for (;;) {
        2:    5:      mid = (start + limit) / 2;
        -:    6:      if (lastMid == mid) {
        -:    7:        // break;
        -:    8:      }
        -:    9:
        2:   10:      r = mid == 1 ? 1 : 0;
        -:   11:
        2:   12:      if (r > 0) {
        1:   13:        start = mid;
        -:   14:      } else {
        1:   15:        return 1;
        -:   16:      }
        -:   17:  }
        -:   18:  return 0;
        -:   19:}