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From: "zsojka at seznam dot cz" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/103181] New: [9/10/11/12 Regression] wrong
 code at -O1 due to conditional division by 0 being executed
Date: Thu, 11 Nov 2021 04:47:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103181

            Bug ID: 103181
           Summary: [9/10/11/12 Regression] wrong code at -O1 due to
                    conditional division by 0 being executed
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu

Created attachment 51762
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51762&action=3Dedit
reduced testcase

Output:
$ x86_64-pc-linux-gnu-gcc testcase.c -O0 && ./a.out
$ x86_64-pc-linux-gnu-gcc testcase.c -O1 && ./a.out=20
Floating point exception
$ x86_64-pc-linux-gnu-gcc testcase.c -O2 && ./a.out
$ x86_64-pc-linux-gnu-gcc testcase.c -O3 && ./a.out

The right hand operand of || in
  v +=3D __builtin_bswap16 (s) || (S) (a / ((U){3, 0}));
is executed, even though s !=3D 0 and it may trap.

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=3D/repo/gcc-trunk/binary-latest-amd64//bin/x86_64-pc-linux-gnu-=
gcc
COLLECT_LTO_WRAPPER=3D/repo/gcc-trunk/binary-trunk-r12-5136-20211110203027-=
gabc2f01914d-checking-yes-rtl-df-extra-amd64/bin/../libexec/gcc/x86_64-pc-l=
inux-gnu/12.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=3Dc,c++
--enable-valgrind-annotations --disable-nls --enable-checking=3Dyes,rtl,df,=
extra
--with-cloog --with-ppl --with-isl --build=3Dx86_64-pc-linux-gnu
--host=3Dx86_64-pc-linux-gnu --target=3Dx86_64-pc-linux-gnu
--with-ld=3D/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=3D/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=3D/repo/gcc-trunk//binary-trunk-r12-5136-20211110203027-gabc2f0191=
4d-checking-yes-rtl-df-extra-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20211110 (experimental) (GCC)=