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    <head>
      <base href="https://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Clang miscompiles with optimization level -O1 and higher"
   href="https://bugs.llvm.org/show_bug.cgi?id=37820">37820</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Clang miscompiles with optimization level -O1 and higher
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>enhancement
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>LLVM Codegen
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>Vsevolod.Livinskij@frtk.ru
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Created <span class=""><a href="attachment.cgi?id=20433" name="attach_20433" title="Reproducer.">attachment 20433</a> <a href="attachment.cgi?id=20433&action=edit" title="Reproducer.">[details]</a></span>
Reproducer.

Clang produces incorrect code with -O1 and higher.
Opt-bisect-limit points to X86 DAG->DAG Instruction Selection on function.

Reproducer:
<span class="quote">>$ cat func.c</span >
extern unsigned long a;
extern long b, c;
void foo() {
  b = (unsigned int)(a >> ((-16384L & c) + 4503359447364223024));
}

<span class="quote">>$ cat driver.c</span >
#include <stdio.h>

unsigned long a = 10144615248613568396UL;
long b, c = -4503359447364216586L;

void foo();

int main() {
  foo();
  printf("%lu\n", b);
}

Error:
<span class="quote">>$ clang -O0 driver.c func.c ; ./a.out</span >
36040
<span class="quote">>$ clang -O1 driver.c func.c ; ./a.out</span >
3640036552

LLVM version:
clang version 7.0.0 (trunk 334837)
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</pre>
        </div>
      </p>


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