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From: "slyfox at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/110726] New: [14 Regression] wrong code on llvm-16
 around 'a |= a == 0'
Date: Tue, 18 Jul 2023 19:09:19 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 14.0
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X-Bugzilla-Severity: normal
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110726

            Bug ID: 110726
           Summary: [14 Regression] wrong code on llvm-16 around 'a |=3D a
                    =3D=3D 0'
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

This week's gcc r14-2600-g3a407070b610a8 fails llvm-16 test suite as:

      Failed Tests (1):
        LLVM-Unit ::
Support/./SupportTests/BlockFrequencyTest.SaturatingRightShift

It looks like the reproducer is trivial and happens even on -O0:

// $ cat bug.cc
int main(void) {
  unsigned long long freq =3D 0x10080ULL;

  freq >>=3D 2;
  freq |=3D freq =3D=3D 0;

  if (freq !=3D 0x4020ULL)
      __builtin_trap();
}

$ gcc-14 bug.cc -o a && ./a
Illegal instruction (core dumped)

$ $ gcc bug.cc -o a && ./a
<ok>

$ gcc -v
Using built-in specs.
COLLECT_GCC=3D/<<NIX>>/gcc-14.0.0/bin/gcc
COLLECT_LTO_WRAPPER=3D/<<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=3D/<<NIX>>/gcc-14.0.0
--with-gmp-include=3D/<<NIX>>/gmp-6.2.1-dev/include
--with-gmp-lib=3D/<<NIX>>/gmp-6.2.1/lib
--with-mpfr-include=3D/<<NIX>>/mpfr-4.2.0-dev/include
--with-mpfr-lib=3D/<<NIX>>/mpfr-4.2.0/lib --with-mpc=3D/<<NIX>>/libmpc-1.3.1
--with-native-system-header-dir=3D/<<NIX>>/glibc-2.37-8-dev/include
--with-build-sysroot=3D/ --program-prefix=3D --enable-lto --disable-libstdc=
xx-pch
--without-included-gettext --with-system-zlib --enable-checking=3Drelease
--enable-static --enable-languages=3Dc,c++ --disable-multilib --enable-plug=
in
--disable-libcc1 --with-isl=3D/<<NIX>>/isl-0.20 --disable-bootstrap
--build=3Dx86_64-unknown-linux-gnu --host=3Dx86_64-unknown-linux-gnu
--target=3Dx86_64-unknown-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 99999999 (experimental) (GCC)=