[llvm-bugs] [Bug 37060] New: Clang miscompiles with -O1. (X86_DAG->DAG_Instruction_Selection_on_function)

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37060

            Bug ID: 37060
           Summary: Clang miscompiles with -O1.
                    (X86_DAG->DAG_Instruction_Selection_on_function)
           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 miscompiles testcase starting from optimization level -O1. opt-bisect
points to X86_DAG->DAG_Instruction_Selection_on_function.

Reproducer:
>$ cat main.c
#include <stdio.h>

const int b = 1545269876;
const int c = -1355305896;
const int * d = &(b);
int e = -1421384539;

extern void tf_0_foo();

int main () {
    tf_0_foo ();

    printf("%d\n", e);
    return 0;
}

>$ cat func.c
extern const int tf_0_var_6;
extern const int c;
extern int e;
extern const int * d;

void tf_0_foo() {
  short a = ~0 % c;
  e = (unsigned char)(a ^ *d);
}

Error:
>$ clang  -w -O0 main.c func.c ; ./a.out
139
>$ clang  -w -O3 main.c func.c ; ./a.out
-117

LLVM version:
clang version 7.0.0 (trunk 329488)
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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