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Subject: [Bug tree-optimization/106322] tree-vectorize: Wrong code at O2
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Date: Mon, 08 Aug 2022 07:12:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106322

--- Comment #16 from Mathieu Malaterre <malat at debian dot org> ---
Simplified version:

% cat demo.cc
#include "hwy/highway.h"
#include "hwy/tests/test_util-inl.h"


struct TestMulHigh {
  template <typename T, class D>
  void operator()(T /*unused*/, D d) {
    const size_t N =3D 2;
    hwy::AlignedFreeUniquePtr<short unsigned int []> in_lanes =3D
hwy::AllocateAligned<T>(N);
    uint16_t expected_lanes[2];

    for (size_t i =3D 0; i < N; ++i) {
      in_lanes[i] =3D T(hwy::LimitsMax<T>() >> i);
    }
    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_ASSERT_VEC_EQ(d, in_lanes.get(), v);
    hwy::N_EMU128::Vec128<uint16_t, 2> actual =3D MulHigh(v, v);

    HWY_ASSERT_VEC_EQ(d, expected_lanes, actual);
  }
};

int main()
{
  TestMulHigh()(uint16_t(), hwy::N_EMU128::FixedTag<uint16_t, 2>());
}


Working:

% g++ -O2 -fno-tree-vectorize -o demo demo.cc -lhwy -lhwy_test

Not working:

% g++ -O2 -o demo demo.cc -lhwy -lhwy_test

With:

% apt-cache policy libhwy-dev
libhwy-dev:
  Installed: 1.0.0-5
  Candidate: 1.0.0-5
  Version table:
 *** 1.0.0-5 500
        500 http://deb.debian.org/debian sid/main i386 Packages
        100 /var/lib/dpkg/status=