[llvm-bugs] [Bug 34381] New: Clang produces incorrect code at -O0

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=34381

            Bug ID: 34381
           Summary: Clang produces incorrect code at -O0
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: Vsevolod.Livinskij at frtk.ru
                CC: llvm-bugs at lists.llvm.org

Clang produces wrong-code with -O0.
>$ cat driver.cpp 
#include <stdio.h>
extern const signed char var_11;
extern const unsigned int var_21;
extern const signed char var_29;
extern signed char var_370;
extern unsigned int var_390;

const signed char var_11 = 97;
const unsigned int var_21 = 3536697529U;
const signed char var_29 = 20;
signed char var_370 = 16;
unsigned int var_390 = 1082014357U;

extern void foo ();

int main () {
    foo ();
    printf("%llu\n", var_390);
    return 0;
}

>$ cat func.cpp 
extern const signed char var_11;
extern const unsigned int var_21;
extern const signed char var_29;
extern signed char var_370;
extern unsigned int var_390;

void foo() {
  var_390 = !char((var_21 < -var_29) + ~0);
  var_370 = short(var_11);
}

>$ clang++ -O1 driver.cpp func.cpp ; ./a.out 
1
>$ clang++ -O0 driver.cpp func.cpp ; ./a.out 
0

clang version 6.0.0 (trunk 311997)

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