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<title>LD: H8/300</title>
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<a name="H8_002f300"></a>
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<div class="header">
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<p>
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Next: <a href="M68HC11_002f68HC12.html#M68HC11_002f68HC12" accesskey="n" rel="next">M68HC11/68HC12</a>, Up: <a href="Machine-Dependent.html#Machine-Dependent" accesskey="u" rel="up">Machine Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="ld-and-the-H8_002f300"></a>
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<h3 class="section">5.1 <code>ld</code> and the H8/300</h3>
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<a name="index-H8_002f300-support"></a>
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<p>For the H8/300, <code>ld</code> can perform these global optimizations when
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you specify the ‘<samp>--relax</samp>’ command-line option.
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</p>
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<dl compact="compact">
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<dd><a name="index-relaxing-on-H8_002f300"></a>
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</dd>
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<dt><em>relaxing address modes</em></dt>
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<dd><p><code>ld</code> finds all <code>jsr</code> and <code>jmp</code> instructions whose
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targets are within eight bits, and turns them into eight-bit
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program-counter relative <code>bsr</code> and <code>bra</code> instructions,
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respectively.
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</p>
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<a name="index-synthesizing-on-H8_002f300"></a>
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</dd>
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<dt><em>synthesizing instructions</em></dt>
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<dd><p><code>ld</code> finds all <code>mov.b</code> instructions which use the
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sixteen-bit absolute address form, but refer to the top
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page of memory, and changes them to use the eight-bit address form.
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(That is: the linker turns ‘<samp>mov.b <code>@</code><var>aa</var>:16</samp>’ into
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‘<samp>mov.b <code>@</code><var>aa</var>:8</samp>’ whenever the address <var>aa</var> is in the
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top page of memory).
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</p>
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<p><code>ld</code> finds all <code>mov</code> instructions which use the register
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indirect with 32-bit displacement addressing mode, but use a small
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displacement inside 16-bit displacement range, and changes them to use
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the 16-bit displacement form. (That is: the linker turns ‘<samp>mov.b
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<code>@</code><var>d</var>:32,ERx</samp>’ into ‘<samp>mov.b <code>@</code><var>d</var>:16,ERx</samp>’
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whenever the displacement <var>d</var> is in the 16 bit signed integer
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range. Only implemented in ELF-format ld).
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</p>
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</dd>
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<dt><em>bit manipulation instructions</em></dt>
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<dd><p><code>ld</code> finds all bit manipulation instructions like <code>band, bclr,
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biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor</code>
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which use 32 bit and 16 bit absolute address form, but refer to the top
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page of memory, and changes them to use the 8 bit address form.
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(That is: the linker turns ‘<samp>bset #xx:3,<code>@</code><var>aa</var>:32</samp>’ into
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‘<samp>bset #xx:3,<code>@</code><var>aa</var>:8</samp>’ whenever the address <var>aa</var> is in
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the top page of memory).
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</p>
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</dd>
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<dt><em>system control instructions</em></dt>
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<dd><p><code>ld</code> finds all <code>ldc.w, stc.w</code> instructions which use the
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32 bit absolute address form, but refer to the top page of memory, and
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changes them to use 16 bit address form.
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(That is: the linker turns ‘<samp>ldc.w <code>@</code><var>aa</var>:32,ccr</samp>’ into
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‘<samp>ldc.w <code>@</code><var>aa</var>:16,ccr</samp>’ whenever the address <var>aa</var> is in
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the top page of memory).
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="M68HC11_002f68HC12.html#M68HC11_002f68HC12" accesskey="n" rel="next">M68HC11/68HC12</a>, Up: <a href="Machine-Dependent.html#Machine-Dependent" accesskey="u" rel="up">Machine Dependent</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p>
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