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      <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 - TargetLowering::computeKnownBitsForTargetNode - constant pool extraction"
   href="https://bugs.llvm.org/show_bug.cgi?id=45315">45315</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>TargetLowering::computeKnownBitsForTargetNode - constant pool extraction
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libraries
          </td>
        </tr>

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

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

        <tr>
          <th>OS</th>
          <td>Windows NT
          </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>Common Code Generator Code
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>llvm-dev@redking.me.uk
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>craig.topper@gmail.com, efriedma@quicinc.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>We can't safely extract the knownbits of target constant pools (e.g.
X86ISD::VBROADCAST_LOAD) because SimplifyDemandedBits may then attempt to
constant fold it, which then infinite loops as it gets relowered to
X86ISD::VBROADCAST_LOAD again......

As an initial stopgap, we could just not constant fold if SimplifyDemandedBits
encounters an opcode above FIRST_TARGET_MEMORY_OPCODE (or is a MemSDNode?) but
this doesn't address non-loading target patterns that might be used for
constant creation, so maybe we need some way to flag that a
computeKnownBitsForTargetNode call came from a lowered constant?</pre>
        </div>
      </p>


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