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From: "malat at debian dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/106322] tree-vectorize: Wrong code at O2
 level (-fno-tree-vectorize is working)
Date: Mon, 08 Aug 2022 10:00:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106322

--- Comment #18 from Mathieu Malaterre <malat at debian dot org> ---
Brushed-up example (with Makefile):

% more Makefile bytes.cc demo.cc
::::::::::::::
Makefile
::::::::::::::
CXXFLAGS :=3D -O2

demo: demo.o bytes.o
        $(CXX) $(CXXFLAGS) -o $@ $^ -lhwy

clean:
        rm -f bytes.o demo.o
::::::::::::::
bytes.cc
::::::::::::::
#include <cstring>

bool BytesEqual2(const void *bytes1, const void *bytes2, const size_t size)=
 {
  return memcmp(bytes1, bytes2, size) =3D=3D 0;
}
::::::::::::::
demo.cc
::::::::::::::
#include "hwy/aligned_allocator.h"
#include "hwy/highway.h"

#include <cstring>

bool BytesEqual2(const void *p1, const void *p2, const size_t size);

template <class D, class V>
void AssertVecEqual2(D d, const uint16_t *expected, const V &actual) {
  const size_t N =3D 2;
  auto actual_lanes =3D hwy::AllocateAligned<uint16_t>(N);
  Store(actual, d, actual_lanes.get());
  const uint8_t *expected_array =3D reinterpret_cast<const uint8_t *>(expec=
ted);
  const uint8_t *actual_array =3D
      reinterpret_cast<const uint8_t *>(actual_lanes.get());
  for (size_t i =3D 0; i < N; ++i) {
    const uint8_t *expected_ptr =3D expected_array + i * 2;
    const uint8_t *actual_ptr =3D actual_array + i * 2;
#if 1
    // trigger bug
    if (!BytesEqual2(expected_ptr, actual_ptr, 2)) {
#else
    // no bug
    if (std::memcmp(expected_ptr, actual_ptr, 2) !=3D 0) {
#endif
    abort();
  }
}
}

int main() {
  hwy::N_EMU128::FixedTag<uint16_t, 2> d;
  const size_t N =3D 2;
  hwy::AlignedFreeUniquePtr<uint16_t[]> in_lanes =3D
      hwy::AllocateAligned<uint16_t>(N);
  uint16_t expected_lanes[2];
  in_lanes[0] =3D 65535;
  in_lanes[1] =3D 32767;
  expected_lanes[0] =3D 65534;
  expected_lanes[1] =3D 16383;
  hwy::N_EMU128::Vec128<uint16_t, 2> v =3D Load(d, in_lanes.get());
  hwy::N_EMU128::Vec128<uint16_t, 2> actual =3D MulHigh(v, v);
  AssertVecEqual2(d, expected_lanes, actual);
}=