[Bug tree-optimization/66163] [6 Regression] Not working Firefox built with LTO

["marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66163

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
According to -fsanitize=null, there are many places in Firefox that produce
undefined behavior in followin way:

https://bugzilla.mozilla.org/show_bug.cgi?id=1165904

One common example:

    static size_t offsetOfThis() {
        JitFrameLayout* base = nullptr;
        return reinterpret_cast<size_t>(&base->argv()[0]);
    }


Martin
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From: "dje at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/66192] New: C++ static initializer unnecessary __cxa_guard_acquire for TARGET_RELAXED_ORDERING
Date: Mon, 18 May 2015 14:28:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idf192

            Bug ID: 66192
           Summary: C++ static initializer unnecessary __cxa_guard_acquire
                    for TARGET_RELAXED_ORDERING
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dje at gcc dot gnu.org
  Target Milestone: ---

// static_init.cc

int* f(void) {
  static int* p = new int;
  return p;
}

$ g++ -O2 -S -fno-exceptions static_init.cc

generates an unnecessary call to __cxa_guard_acquire on what should be the fast
path for targets with TARGET_RELAXED_ORDERING defined.  The guard should be an
atomic variable accessed with the equivalent of __atomic_load(ACQUIRE) instead
of a heavy-weight __cxa_guard_acquire() call invoking heavier-weight
synchronization.