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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Support relaxation of more x86 instructions"
href="http://llvm.org/bugs/show_bug.cgi?id=22662">22662</a>
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<th>Summary</th>
<td>Support relaxation of more x86 instructions
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>dwmw2@infradead.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>$ cat foo.S
.code16
movl (foo), %ebx
foo:
$ llvm-mc -filetype=obj foo.S | llvm-objdump -d -triple=i686-pc-linux-code16 -
<stdin>: file format ELF64-x86-64
Disassembly of section .text:
.text:
0: 67 66 8b 1d 00 00 00 00 movl 0, %ebx
We didn't need the 0x67 addr32 prefix for this. GCC does this:
0: 66 8b 1e 00 00 movl 0, %ebx
Although not strictly incorrect, this causes a problem for size-sensitive code;
the above example was taken from a boot sector implementation.
We should emit the 16-bit version by default. And if we do that, we're going to
need to handle relaxation for the case where it *isn't* sufficient.
We normally handle relaxation by converting to a *different* opcode. That isn't
sufficient here; we'll probably need a flag in the MCInst to indicate that it
should use addr32. Which is nice, since we already *wanted* to support the
explicit 'addr32' prefix...</pre>
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