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<h3 class="section">4.1 <samp><span class="command">ld</span></samp> and the H8/300</h3>

<p><a name="index-H8_002f300-support-559"></a>For the H8/300, <samp><span class="command">ld</span></samp> can perform these global optimizations when
you specify the &lsquo;<samp><span class="samp">--relax</span></samp>&rsquo; command-line option.

     
<a name="index-relaxing-on-H8_002f300-560"></a>
<dl><dt><em>relaxing address modes</em><dd><samp><span class="command">ld</span></samp> finds all <code>jsr</code> and <code>jmp</code> instructions whose
targets are within eight bits, and turns them into eight-bit
program-counter relative <code>bsr</code> and <code>bra</code> instructions,
respectively.

     <p><a name="index-synthesizing-on-H8_002f300-561"></a><br><dt><em>synthesizing instructions</em><dd><!-- FIXME: specifically mov.b, or any mov instructions really? -->
<samp><span class="command">ld</span></samp> finds all <code>mov.b</code> instructions which use the
sixteen-bit absolute address form, but refer to the top
page of memory, and changes them to use the eight-bit address form. 
(That is: the linker turns &lsquo;<samp><span class="samp">mov.b </span><code>@</code><var>aa</var><span class="samp">:16</span></samp>&rsquo; into
&lsquo;<samp><span class="samp">mov.b </span><code>@</code><var>aa</var><span class="samp">:8</span></samp>&rsquo; whenever the address <var>aa</var> is in the
top page of memory).

     <br><dt><em>bit manipulation instructions</em><dd><samp><span class="command">ld</span></samp> finds all bit manipulation instructions like <code>band, bclr,
biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor</code>
which use 32 bit and 16 bit absolute address form, but refer to the top
page of memory, and changes them to use the 8 bit address form. 
(That is: the linker turns &lsquo;<samp><span class="samp">bset #xx:3,</span><code>@</code><var>aa</var><span class="samp">:32</span></samp>&rsquo; into
&lsquo;<samp><span class="samp">bset #xx:3,</span><code>@</code><var>aa</var><span class="samp">:8</span></samp>&rsquo; whenever the address <var>aa</var> is in
the top page of memory).

     <br><dt><em>system control instructions</em><dd><samp><span class="command">ld</span></samp> finds all <code>ldc.w, stc.w</code> instructions which use the
32 bit absolute address form, but refer to the top page of memory, and
changes them to use 16 bit address form. 
(That is: the linker turns &lsquo;<samp><span class="samp">ldc.w </span><code>@</code><var>aa</var><span class="samp">:32,ccr</span></samp>&rsquo; into
&lsquo;<samp><span class="samp">ldc.w </span><code>@</code><var>aa</var><span class="samp">:16,ccr</span></samp>&rsquo; whenever the address <var>aa</var> is in
the top page of memory). 
</dl>

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