[Bug target/111048] New: [14 Regression] Wrong AVX2 code on highway-1.0.6 on -O2 and above

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111048

            Bug ID: 111048
           Summary: [14 Regression] Wrong AVX2 code on highway-1.0.6 on
                    -O2 and above
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Noticed wrong code with r14-3259-g24f7b20bbd87eb when running tests on
highway-1.0.6. Extracted example:

// $ cat bug.cc.cc
typedef unsigned char u8;

__attribute__((noipa))
static void check(const u8 * v) {
    if (*v != 15) __builtin_trap();
}

__attribute__((noipa))
static void bug(void) {
    u8 in_lanes[32];
    for (unsigned i = 0; i < 32; i += 2) {
      in_lanes[i + 0] = 0;
      in_lanes[i + 1] = ((u8)0xff) >> (i & 7);
    }

    check(&in_lanes[13]);
  }

int main() {
    bug();
}

Triggering:

$ g++ bug.cc.cc -mavx2 -O2 -o bug2 && ./bug2
Illegal

$ g++ bug.cc.cc -mavx2 -O1 -o bug1 && ./bug1
<ok>

$ g++ -v
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-14.0.0/bin/g++
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)