<html>
    <head>
      <base href="http://llvm.org/bugs/" />
    </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 --- - magic numbers in MachineInstr.cpp"
   href="http://llvm.org/bugs/show_bug.cgi?id=20128">20128</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>magic numbers in MachineInstr.cpp
          </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>All
          </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>Common Code Generator Code
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>spatel+llvm@rotateright.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Around line 318:
        if (TiedTo != 15)

Not even a comment about what that '15' means, but later:

Around line 1162:
// MachineOperand::TiedTo is 4 bits wide.
const unsigned TiedMax = 15;

How about defining this constant in MachineOperand.h where the bitfield is
defined? 

Is there a way to determine bitfield size at compile-time?

If not, then do something like this?

#define BITS_IN_TIEDTO_FIELD 4
static const unsigned TiedMax = (1 << BITS_IN_TIEDTO_FIELD) - 1;

...and then use that const value in MachineInstr.cpp.</pre>
        </div>
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