[Bug middle-end/111009] New: [12/13/14 regression] -fno-strict-overflow erroneously elides null pointer checks and causes SIGSEGV on perf from linux-6.4.10

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111009

            Bug ID: 111009
           Summary: [12/13/14 regression] -fno-strict-overflow erroneously
                    elides null pointer checks and causes SIGSEGV on perf
                    from linux-6.4.10
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Initially observed the failure as a perf SIGSEGV when running against
r14-3191-g614052dd4ea083.

I hope I did not break it too much when minimizing. Self-contained example:

// $ cat bug c.c
struct dso {
 struct dso * next;
 int maj;
};

__attribute__((noipa)) static void __dso_id__cmp_(void) {}

__attribute__((noipa))
static int bug(struct dso * d, struct dso *dso)
{
 struct dso **p = &d;
 struct dso *curr = 0;

 while (*p) {
  curr = *p;
  // prevent null deref below
  if (!dso) return 1;
  if (dso == curr) return 1;

  int *a = &dso->maj;
  // null deref
  if (!(a && *a)) __dso_id__cmp_();

  p = &curr->next;
 }
 return 0;
}

__attribute__((noipa))
int main(void) {
    struct dso d = { 0, 0, };
    bug(&d, 0);
}

Triggering the bug:

$ gcc -fno-strict-overflow -O3 bug.c.c -o bug3 && ./bug3
Segmentation fault (core dumped)

$ gcc -fno-strict-overflow -O2 bug.c.c -o bug2 && ./bug2
<ok>

$ gcc -v
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-14.0.0/bin/gcc
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-14.0.0/libexec/gcc/x86_64-unknown-linux-gnu/14.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../source/configure --prefix=/<<NIX>>/gcc-14.0.0
--with-gmp-include=/<<NIX>>/gmp-6.3.0-dev/include
--with-gmp-lib=/<<NIX>>/gmp-6.3.0/lib
--with-mpfr-include=/<<NIX>>/mpfr-4.2.0-12-dev/include
--with-mpfr-lib=/<<NIX>>/mpfr-4.2.0-12/lib --with-mpc=/<<NIX>>/libmpc-1.3.1
--with-native-system-header-dir=/<<NIX>>/glibc-2.38-dev/include
--with-build-sysroot=/ --program-prefix= --enable-lto --disable-libstdcxx-pch
--without-included-gettext --with-system-zlib --enable-checking=release
--enable-static --enable-languages=c,c++ --disable-multilib --enable-plugin
--disable-libcc1 --with-isl=/<<NIX>>/isl-0.20 --disable-bootstrap
--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu
--target=x86_64-unknown-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 99999999 (experimental) (GCC)