[llvm-bugs] [Bug 36943] New: wrong code with opt "-early-cse-memssa -instcombine -loop-rotate -loop-unroll -memcpyopt -gvn"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36943

            Bug ID: 36943
           Summary: wrong code with opt "-early-cse-memssa -instcombine
                    -loop-rotate -loop-unroll -memcpyopt -gvn"
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvm-bugs at lists.llvm.org

$ clangpolly -v
clang version 7.0.0 (http://llvm.org/git/clang.git
9a41408814f37f4f864fb3e57aa01919b4d871d8) (llvm/trunk 328613)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/su/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.4
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.2.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ 
$ clangpolly -O0 small.c; ./a.out
1
$ 
$ clangpolly -O3 -mllvm -disable-llvm-optzns -c -emit-llvm -o small.bc small.c
$ optpolly -early-cse-memssa -instcombine -loop-rotate -loop-unroll -memcpyopt
-gvn -o small-opt.bc small.bc
$ clangpolly small-opt.bc
$ ./a.out
0
$ 


----------------------------------


int printf (const char *, ...);

int a, b, c, d;

int main ()
{
  for (; b < 6; b++)
    {
      for (c = 8; c; c--)
        d = 1;
      a = d;
    }
  printf ("%d\n", a);
  return 0;
}

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