[llvm-bugs] [Bug 48859] New: wrong code at -O1 and above on x86_64-linux-gnu

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48859

            Bug ID: 48859
           Summary: wrong code at -O1 and above on x86_64-linux-gnu
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: zhendong.su at inf.ethz.ch
                CC: llvm-bugs at lists.llvm.org

[515] % clangtk -v
clang version 12.0.0 (https://github.com/llvm/llvm-project.git
022da61f6b30626708e5b4c1c009afb453d12ebe)
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
[516] % 
[516] % clangtk -O0 small.c; ./a.out
[517] % clangtk -O1 small.c
[518] % ./a.out
Aborted
[519] % 
[519] % cat small.c
int c;
void f(long p) { c = p; }

#pragma pack(1)
struct {
  long : 38;
  unsigned : 32;
  int a : 16;
} b;

int main() {
  f(b.a);
  if (c != 0)
    __builtin_abort ();
  return 0;
}

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