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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/97386] New: [8/9/10/11 Regression] wrong code
 with __builtin_bswap16() of rotated 64bit value
Date: Mon, 12 Oct 2020 14:38:17 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97386

            Bug ID: 97386
           Summary: [8/9/10/11 Regression] wrong code with
                    __builtin_bswap16() of rotated 64bit value
           Product: gcc
           Version: 11.0
            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: ---

Created attachment 49353
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D49353&action=3Dedit
reduced testcase

Output:
$ x86_64-pc-linux-gnu-gcc -O testcase.c
$ ./a.out=20
Aborted

The code in fact rotates 0xcccc00 instead of 0xcccc.

foo:
        mov     rcx, QWORD PTR c[rip]
        mov     eax, 13421568 # 0xcccc00
        rol     rax, cl
        ret

$ 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-g=
cc
COLLECT_LTO_WRAPPER=3D/repo/gcc-trunk/binary-trunk-r11-3806-20201012001625-=
g2baa36d4911-checking-yes-rtl-df-extra-amd64/bin/../libexec/gcc/x86_64-pc-l=
inux-gnu/11.0.0/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-r11-3806-20201012001625-g2baa36d49=
11-checking-yes-rtl-df-extra-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.0.0 20201012 (experimental) (GCC)=