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| Next: <a href="i960.html#i960" accesskey="n" rel="next">i960</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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| <a name="ld-and-the-H8_002f300"></a> |
| <h3 class="section">4.1 <code>ld</code> and the H8/300</h3> |
| |
| <a name="index-H8_002f300-support"></a> |
| <p>For the H8/300, <code>ld</code> can perform these global optimizations when |
| you specify the ‘<samp>--relax</samp>’ command-line option. |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-relaxing-on-H8_002f300"></a> |
| </dd> |
| <dt><em>relaxing address modes</em></dt> |
| <dd><p><code>ld</code> 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"></a> |
| </dd> |
| <dt><em>synthesizing instructions</em></dt> |
| <dd><p><code>ld</code> 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 ‘<samp>mov.b <code>@</code><var>aa</var>:16</samp>’ into |
| ‘<samp>mov.b <code>@</code><var>aa</var>:8</samp>’ whenever the address <var>aa</var> is in the |
| top page of memory). |
| </p> |
| <p><code>ld</code> finds all <code>mov</code> instructions which use the register |
| indirect with 32-bit displacement addressing mode, but use a small |
| displacement inside 16-bit displacement range, and changes them to use |
| the 16-bit displacement form. (That is: the linker turns ‘<samp>mov.b |
| <code>@</code><var>d</var>:32,ERx</samp>’ into ‘<samp>mov.b <code>@</code><var>d</var>:16,ERx</samp>’ |
| whenever the displacement <var>d</var> is in the 16 bit signed integer |
| range. Only implemented in ELF-format ld). |
| </p> |
| </dd> |
| <dt><em>bit manipulation instructions</em></dt> |
| <dd><p><code>ld</code> 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 ‘<samp>bset #xx:3,<code>@</code><var>aa</var>:32</samp>’ into |
| ‘<samp>bset #xx:3,<code>@</code><var>aa</var>:8</samp>’ whenever the address <var>aa</var> is in |
| the top page of memory). |
| </p> |
| </dd> |
| <dt><em>system control instructions</em></dt> |
| <dd><p><code>ld</code> 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 ‘<samp>ldc.w <code>@</code><var>aa</var>:32,ccr</samp>’ into |
| ‘<samp>ldc.w <code>@</code><var>aa</var>:16,ccr</samp>’ whenever the address <var>aa</var> is in |
| the top page of memory). |
| </p></dd> |
| </dl> |
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| Next: <a href="i960.html#i960" accesskey="n" rel="next">i960</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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