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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug gcov-profile/96919] [GCOV] uncovered line of stack allocation
 while using virutal destructor
Date: Mon, 21 Sep 2020 11:05:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96919

--- Comment #2 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
Using latest GCC release you can see what happens:

$ g++ pr96919.cc --coverage && ./a.out && gcov a-pr96919.cc -t
hello
libgcov profiling
error:/home/marxin/Programming/testcases/a-pr96919.gcda:overwriting an exis=
ting
profile data with a different timestamp
        -:    0:Source:pr96919.cc
        -:    0:Graph:a-pr96919.gcno
        -:    0:Data:a-pr96919.gcda
        -:    0:Runs:1
        -:    1:class Base {
        -:    2:public:
        -:    3:  Base() =3D default;
       1*:    4:  virtual ~Base() =3D default;
------------------
_ZN4BaseD0Ev:
    #####:    4:  virtual ~Base() =3D default;
------------------
_ZN4BaseD2Ev:
        1:    4:  virtual ~Base() =3D default;
------------------
        -:    5:  virtual void foo() =3D 0;
        -:    6:};
        -:    7:class Hello : public Base {
        -:    8:public:
        -:    9:  Hello() =3D default;
       1*:   10:  ~Hello() =3D default;
------------------
_ZN5HelloD0Ev:
    #####:   10:  ~Hello() =3D default;
------------------
_ZN5HelloD2Ev:
        1:   10:  ~Hello() =3D default;
------------------
        -:   11:  void foo() override;
        -:   12:};
        -:   13:
        -:   14:#include <iostream>
        -:   15:
        -:   16:using namespace std;
        -:   17:
        1:   18:void Hello::foo() {
        1:   19:  cout << "hello" << endl;
        1:   20:}
        -:   21:
        1:   22:int main(int argc, char* argv[]) {
    #####:   23:  Hello hello;
        1:   24:  hello.foo();
        1:   25:  return 0;
        -:   26:}

So yes, it's a virtual destructor _ZN4BaseD0Ev that is not called.
And the not executed line:
    #####:    4:  Hello hello;

corresponds to a basic block=20

  <bb 5> :
<L3>:
  Hello::~Hello (&hello);
  resx 2

which would be executed when the Hellow constructor fails.=