[Bug gcov-profile/85349] New: [GCOV] struct varaible definition in while(1) will cause incorrect coverage

["yangyibiao at nju dot edu.cn" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85349

            Bug ID: 85349
           Summary: [GCOV] struct varaible definition in while(1) will
                    cause incorrect coverage
           Product: gcc
           Version: 8.0
            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
8-20170923-1ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs
--enable-languages=c,c++,go,brig,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 --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
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 8.0.0 20170923 (experimental) [trunk revision 253118] (Ubuntu
8-20170923-1ubuntu2)

$ cat small.c
struct F {int x;};

int main()
{
  int x = 0;
  while (1) // first while
  {
    struct F f1 = {x};
    if (f1.x > 0)
      break;
    x++;
  }

  x = 0;
  while (1) // second while
  {
    if (x > 0)
      break;
    x++;
  }

  x = 0;
  while (x < 10) // third while
  {
    struct F f2 = {x};
    if (f2.x > 0)
      break;
    x++;
  }

  x = 0;
  while (x < 10)
  {
    if (x > 0)
      break;
    x++;
  }
  return 0;
}


$ gcc --coverage small.c; ./a.out; gcov-8 small.c; cat small.c.gcov
File 'small.c'
Lines executed:100.00% of 23
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:struct F {int x;};
        -:    2:
        1:    3:int main()
        -:    4:{
        1:    5:  int x = 0;
        -:    6:  while (1) // first while
        1:    7:  {
        2:    8:    struct F f1 = {x};
        2:    9:    if (f1.x > 0)
        1:   10:      break;
        1:   11:    x++;
        -:   12:  }
        -:   13:
        1:   14:  x = 0;
        -:   15:  while (1) // second while
        -:   16:  {
        2:   17:    if (x > 0)
        1:   18:      break;
        1:   19:    x++;
        -:   20:  }
        -:   21:
        1:   22:  x = 0;
        2:   23:  while (x < 10) // third while
        -:   24:  {
        2:   25:    struct F f2 = {x};
        2:   26:    if (f2.x > 0)
        1:   27:      break;
        1:   28:    x++;
        -:   29:  }
        -:   30:
        1:   31:  x = 0;
        2:   32:  while (x < 10)
        -:   33:  {
        2:   34:    if (x > 0)
        1:   35:      break;
        1:   36:    x++;
        -:   37:  }
        1:   38:  return 0;
        -:   39:}


Line #7 is wrongly marked as "1". 

Line #16 and Line #33 are also the first braces of while statement. While they
are marked as "-". 

By comparing these three while-statements, I think the inconsistency is caused
by the struct variable definition inside the while(1) statement.