[llvm-bugs] [Bug 38214] New: clang miscompiles with "-newgvn" at -O2 on valid code

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38214

            Bug ID: 38214
           Summary: clang miscompiles with "-newgvn" at -O2 on valid code
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            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 happens at -O2 and -Os only. I have also tested r334040 and it miscompiles
as well.



$ clang-trunk -v
clang version 7.0.0 (trunk 337366)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin


$ clang-trunk abc.c  ;  ./a.out
-16

$ clang-trunk -mllvm -enable-newgvn -O3 abc.c  ; ./a.out
-16

$ clang-trunk -mllvm -enable-newgvn -O2 abc.c  ; ./a.out
0

$ cat abc.c
int printf(char *, ...);
char a, b;
char c[1];
int d, e;
char(f)(char g, char h) { return g + h; }
int __attribute__((noinline)) i(long g) { return g ? 1 : 0; }
int main() {
  char j = 0;
  for (; j != 15; j = f(j, 5)) {
    a = 0;
    for (; a < 11; ++a)
      if (a == b && j) {
        e = 0;
        for (; e < 8; e++)
          if (i((long)c))
            --d;
      }
  }
  printf("%d\n", d);
}

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