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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110643] [13/14 Regression] aarch64: Miscompilation at O1
 level (O0 is working)
Date: Wed, 04 Oct 2023 15:55:34 +0000
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X-Bugzilla-Keywords: wrong-code
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110643

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |MOVED
             Status|WAITING                     |RESOLVED

--- Comment #22 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
template <typename T, size_t N, HWY_IF_FLOAT(T)>
HWY_API Mask128<T, N> IsInf(const Vec128<T, N> v) {
  const DFromV<decltype(v)> d;
  const RebindToSigned<decltype(d)> di;
  const VFromD<decltype(di)> vi =3D BitCast(di, v);
  // 'Shift left' to clear the sign bit, check for exponent=3Dmax and manti=
ssa=3D0.
  return RebindMask(d, Eq(Add(vi, vi), Set(di, hwy::MaxExponentTimes2<T>())=
));
}


Most likely should have been:
```
template <typename T, size_t N, HWY_IF_FLOAT(T)>
HWY_API Mask128<T, N> IsInf(const Vec128<T, N> v) {
  const DFromV<decltype(v)> d;
  const RebindToUnsigned<decltype(d)> du;
  const VFromD<decltype(du)> vi =3D BitCast(du, v);
  // 'Shift left' to clear the sign bit, check for exponent=3Dmax and manti=
ssa=3D0.
  return RebindMask(d, Eq(Add(vi, vi), Set(du, hwy::MaxExponentTimes2<T>())=
));
}
```

I noticed the bug happens in other places in highway for other targets too
(including x86_64).

this code is undefined due to an signed integer overflow and that is why us=
ing
unsigned is needed.


Yes -fsanitize=3Dundefined does not currently work for vectors (that is a k=
nown
limitation).=