[llvm-bugs] [Bug 51125] New: wrong code at -O1 on x86_64-linux-gnu

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51125

            Bug ID: 51125
           Summary: wrong code at -O1 on x86_64-linux-gnu
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: zhendong.su at inf.ethz.ch
                CC: llvm-bugs at lists.llvm.org

[505] % clangtk -v
clang version 13.0.0 (https://github.com/llvm/llvm-project.git
5df48493f08930ad05d9746c65fd53e5131a08d0)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /local/suz-local/opfuzz/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
[506] % 
[506] % clangtk -O0 small.c; ./a.out
1
[507] % clangtk -O1 small.c
[508] % ./a.out
-1
[509] % cat small.c
int printf(const char *, ...);
int a = 1, b;
int main() {
 L:
  b = a;
  if (a) {
    unsigned c = a;
    a = -1;
    if (a == c)
      goto L;
  }
  printf("%d\n", b);
  return 0;
}

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