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      <base href="https://bugs.llvm.org/">
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Incorrect optimization of assignment in present of memset"
   href="https://bugs.llvm.org/show_bug.cgi?id=34088">34088</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Incorrect optimization of assignment in present of memset
          </td>
        </tr>

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

        <tr>
          <th>Version</th>
          <td>5.0
          </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>normal
          </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>dpotapov@gmail.com
          </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=18914" name="attach_18914" title="An example to reproduce the problem.">attachment 18914</a> <a href="attachment.cgi?id=18914&action=edit" title="An example to reproduce the problem.">[details]</a></span>
An example to reproduce the problem.

During optimization clang removes assignments that should not be eliminated.
I have the following code:

  Init(&foo);
  buffer = foo.bar.buffer;
  memset(&foo, 0xCD, sizeof (foo));
  foo.bar.buffer = buffer;
  Print(&foo);

and if optimization is enabled, it becomes like this:

  Init(&foo);
  memset(&foo, 0xCD, sizeof (foo));
  Print(&foo);

The bug happens only with target: i386-pc-linux-gnu and for some layout of
structures. (Perhaps, it can happen on x86_64 too for different structures,
but I have not encountered it only on i386 architecture.)

I have attached a full example that demonstrates the problem. It includes
the following files:
test1.h - defines some structures.
test1.c - the main code that is incorrectly optimized
test2.c - defines Init() and Print()
Makefile - builds and runs the example code

If optimization is not enabled, the program prints as expected:
  ptr=(nil) size=0x0
however when any level optimization is enabled, I get the following output:
  ptr=0xcdcdcdcd size=0xcdcdcdcd
i.e. the initial value of 'buffer' set in Init() is overwritten by memset.

clang information:
$ clang-5.0 -m32 --version
clang version 5.0.0-svn309965-1~exp1 (branches/release_50)
Target: i386-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin</pre>
        </div>
      </p>


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