[Bug target/78262] New: [7 Regression] wrong code with -fschedule-insns

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78262

            Bug ID: 78262
           Summary: [7 Regression] wrong code with -fschedule-insns
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu

Created attachment 39996
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39996&action=edit
reduced testcase

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

At the assembly level, the problem seems to be:
# testcase.c:12:   u128_0 = u128_0 << 127 | u128_0 >> 1;
        mov     rax, rcx        # tmp99, _2
        shrd    rcx, rbx, 1     # _2, _2,
        shrd    rbx, rax, 1     # _2, tmp99,
# testcase.c:13:   u128_0 >>= (u8)u128_0;
        shrd    rcx, rbx, cl    # _5, _5, _2
        shr     rbx, cl # _5, _2

^^^ the last shrd modifies rcx (and thus cl), which is used in the last shr
instruction - but it should use the original, unmodified value.

This might be a duplicate of some other bug that I cannot find now.

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-241953-checking-yes-rtl-df-extra-nographite-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--without-cloog --without-ppl --without-isl --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu
--with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-241953-checking-yes-rtl-df-extra-nographite-amd64
Thread model: posix
gcc version 7.0.0 20161108 (experimental) (GCC)