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    <head>
      <base href="https://llvm.org/bugs/" />
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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 --- - Comment describing isFsqrtCheap is probably wrong"
   href="https://llvm.org/bugs/show_bug.cgi?id=24572">24572</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Comment describing isFsqrtCheap is probably wrong
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>new-bugs
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </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>new bugs
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>schnetter@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Line 221 of include/llvm/Target/TargetLowering.h describes isFsqrtCheap, and
says

/// Return true if sqrt(x) is as cheap or cheaper than 1 / rsqrt(x)

This sounds wrong: When one calculates sqrt(x) via rsqrt(x), one does not use
1/rsqrt(x) -- rather, one uses x*rsqrt(x).

I did not check what code LLVM generates in this case, but I assume it does not
use a division.</pre>
        </div>
      </p>
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