[llvm-bugs] [Bug 34760] New: wrong code with "opt -instcombine -early-cse-memssa -loop-rotate -loop-unroll -newgvn -simplifycfg -licm -loop-reroll"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34760

            Bug ID: 34760
           Summary: wrong code with "opt -instcombine -early-cse-memssa
                    -loop-rotate -loop-unroll -newgvn -simplifycfg -licm
                    -loop-reroll"
           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

This is tested with rev. 314335. 


$ clangpolly -v
clang version 6.0.0 (http://llvm.org/git/clang.git
31a16c4f5bc89d8e9ca6c0a52a34b98c18058b6b)
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 -O3 -mllvm -disable-llvm-optzns -c -emit-llvm -o small.bc small.c
$ optpolly -instcombine -early-cse-memssa -loop-rotate -loop-unroll -newgvn
-simplifycfg -licm -loop-reroll -o small-opt.bc small.bc
$ clangpolly small-opt.bc
$ ./a.out
8
$ 
$ clangpolly -O0 small.c; ./a.out
1
$ 


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


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

int a, b, c[1][8];

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

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