[llvm-bugs] [Bug 37748] New: Clang produces incorrect code with -O2 and higher

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37748

            Bug ID: 37748
           Summary: Clang produces incorrect code with -O2 and higher
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: Vsevolod.Livinskij at frtk.ru
                CC: llvm-bugs at lists.llvm.org

Created attachment 20413
  --> https://bugs.llvm.org/attachment.cgi?id=20413&action=edit
Reproducer.

Clang miscompiles with -O2 and higher.
opt-bisect-limit points to CodeGen Prepare on function

Reproducer:
>$ cat func.c
extern long a;
extern long b;
extern unsigned short c;
extern long d;
extern short e;

void foo() {
  a = (short)(e | (c & -32692));
  if (c / d)
    b = (e | (c & -32692)) > 0;
}
>$ cat driver.c
#include <stdio.h>

long a, b;
unsigned short c = 43589;
long d = 3;
short e;

void foo();

int main() {
  foo();
  printf("%ld\n", a);
}

Error:
>$ clang driver.c func.c ; ./a.out
-32700
>$ clang -O2 driver.c func.c ; ./a.out
32836

LLVM version:
clang version 7.0.0 (trunk 334268)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /llvm/bin-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64

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