[Bug c++/82741] New: Optimisations may cause noexcept specifier to be ignored

["pdziepak at quarnos dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82741

            Bug ID: 82741
           Summary: Optimisations may cause noexcept specifier to be
                    ignored
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pdziepak at quarnos dot org
  Target Milestone: ---

On x86_64:

  gcc version 7.2.1 20170915 (Red Hat 7.2.1-2) (GCC) 

The following code results in noexcept being ignored if optimisations are
enabled.

---<snip>---
volatile bool should_throw = false;

[[gnu::noinline]]
void foo() {
    if (should_throw) {
        throw 42;
    }
}

[[gnu::noinline]]
void bar() noexcept {
    should_throw = true;
    foo();
}

int main() {
    try {
        foo();
        bar();
        foo();
    } catch (...) { }
}
---<snip>---

When compiled with -O1 or higher exception thrown from bar() doesn't cause
std::terminate to be called.

bar() is compiled to:

0000000000400730 <bar()>:
  400730:       c6 05 2a 09 20 00 01    movb   $0x1,0x20092a(%rip)        #
601061 <should_throw>
  400737:       eb c7                   jmp    400700 <foo()>