r32.</em></td></tr>
<tr>
<td>REX.W + 1B /<em>r</em></td>
<td>SBB<em> r64, r/m64</em></td>
<td>RM</td>
<td>Valid</td>
<td>N.E.</td>
<td>Subtract with borrow <em>r/m64</em> from <em>r64.</em></td></tr></table>
<p><strong>NOTES:</strong></p>
<p>*</p>
<p>In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is used: AH, BH, CH, DH.</p>
<h3>Instruction Operand Encoding</h3>
<table>
<tr>
<td>Op/En</td>
<td>Operand 1</td>
<td>Operand 2</td>
<td>Operand 3</td>
<td>Operand 4<