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From: "tkoenig at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/97738] Optimizing division by value & - value for
 HAKMEM 175
Date: Fri, 06 Nov 2020 17:52:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97738

--- Comment #3 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Even faster code:

  ctz =3D __builtin_ctz (value);
  lowest_bit =3D value & - value;
  left_bits =3D value + lowest_bit;
  changed_bits =3D value ^ left_bits;
  right_bits =3D changed_bits >> (ctz + 2);
  return left_bits | right_bits;

The first two instructions get compiled directly (with -march=3Dnative)
to

        blsi    %edi, %edx
        tzcntl  %edi, %eax=