[llvm-bugs] [Bug 38125] New: clang miscompiles at -O2 and above on valid code

via llvm-bugs llvm-bugs at lists.llvm.org
Tue Jul 10 16:19:18 PDT 2018


            Bug ID: 38125
           Summary: clang miscompiles at -O2 and above on valid code
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: helloqirun at gmail.com
                CC: llvm-bugs at lists.llvm.org

It seems to be a recent regression.

$ clang-trunk -v
clang version 7.0.0 (trunk 336646)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin

$ clang-trunk abc.c ; ./a.out

$ clang-trunk -O2 abc.c ; ./a.out

$ cat abc.c
int printf(char *, ...);
int a, c;
unsigned short b;
short d;
void fn1(char p1) { a = a ^ p1; }
void fn2(long p1) {
  a = p1 & 5;
  fn1(p1 >> 56);
int main() {
  for (; c >= 0; c--)
    d = -3L;
  d |= b;
  printf("%d\n", b);
  printf("%X\n", a);

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