gcc/testsuite/g++.dg/warn/pr8715.C

/* { dg-do compile } */
/* { dg-options "-Wsign-compare" } */

int foo()
{
  unsigned char b = '1';

  bool x = ~b; /* { dg-warning "promoted bitwise complement of an unsigned value is always nonzero" } */

  return 0;
}