[Bug c++/86176] New: Wnull-dereference warning disappears with a call to std::cout on the line after

[jg at jguk dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86176

            Bug ID: 86176
           Summary: Wnull-dereference warning disappears with a call to
                    std::cout on the line after
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jg at jguk dot org
  Target Milestone: ---

Hello

Some possible issues. Could you give your opinion please.

1. printf Wnull-dereference warning is only visible with -O2 (not -O0)
2. printf Wnull-dereference warning disappears if I uncomment the std::cout on
line after.

There is bug 86172 but I have not linked it.

note, I also tried g++8.1 x86-64, same results.


g++-8 --version
g++-8 (Ubuntu 8-20180414-1ubuntu2) 8.0.1 20180414 (experimental) [trunk
revision 259383]

jonny@asus:~/code$ g++-8 -O0 -Wall -Wextra -Wnull-dereference -Wpedantic -o
main.o -c main.cpp
jonny@asus:~/code$ g++-8 -O2 -Wall -Wextra -Wnull-dereference -Wpedantic -o
main.o -c main.cpp
main.cpp: In function ‘int main()’:
main.cpp:8:11: warning: null pointer dereference [-Wnull-dereference]
     printf("%d\n", *i);
     ~~~~~~^~~~~~~~~~~~
jonny@asus:~/code$ 



#include <stdio.h>
#include <iostream>

void f(const int *i)
{
    printf("%d\n", *i);
    //std::cout << *i;
}

int main () {
  f(nullptr);
  return 0;
}