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| <h5 class="subsubsection">9.24.2.3 Register Notation</h5> |
| |
| <p><a name="index-register-notation_002c-S12Z-1531"></a>Without a register prefix (see <a href="S12Z-Options.html#S12Z-Options">S12Z Options</a>), S12Z assembler code is expected in the traditional |
| format like this: |
| <pre class="smallexample"> lea s, (-2,s) |
| st d2, (0,s) |
| ld x, symbol |
| tfr d2, d6 |
| cmp d6, #1532 |
| </pre> |
| <p class="noindent">However, if <code>as</code> is started with (for example) ‘<samp><span class="samp">-mreg-prefix=%</span></samp>’ |
| then all register names must be prefixed with ‘<samp><span class="samp">%</span></samp>’ as follows: |
| <pre class="smallexample"> lea %s, (-2,%s) |
| st %d2, (0,%s) |
| ld %x, symbol |
| tfr %d2, %d6 |
| cmp %d6, #1532 |
| </pre> |
| <p>The register prefix feature is intended to be used by compilers |
| to avoid ambiguity between symbols and register names. |
| Consider the following assembler instruction: |
| <pre class="smallexample"> st d0, d1 |
| </pre> |
| <p class="noindent">The destination operand of this instruction could either refer to the register |
| ‘<samp><span class="samp">D1</span></samp>’, or it could refer to the symbol named “d1”. |
| If the latter is intended then <code>as</code> must be invoked with |
| ‘<samp><span class="samp">-mreg-prefix=</span><var>pfx</var></samp>’ and the code written as |
| <pre class="smallexample"> st <var>pfx</var>d0, d1 |
| </pre> |
| <p class="noindent">where <var>pfx</var> is the chosen register prefix. |
| For this reason, compiler back-ends should choose a register prefix which |
| cannot be confused with a symbol name. |
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