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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - Incorrect/inefficient pushw encodings for x86-64 targets" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23996&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=VAGe2H-4hhWfxKhNV5mLgjIcXm9qZy4e788K38bJPlo&s=fqCf7jTKXuKXhUeyFGsG5kxze_NMjS_fYqK-P_14uHM&e=">23996</a>
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<th>Summary</th>
<td>Incorrect/inefficient pushw encodings for x86-64 targets
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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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
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<th>Reporter</th>
<td>david.l.kreitzer@intel.com
</td>
</tr>
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<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>Below is an illustration of the problems. The first pushw is incorrectly
encoded as pushq. The second pushw is encoded correctly but inefficiently as it
uses a 16-bit immediate rather than an 8-bit immediate.
Note also that the gas-generated instruction "66 6a 2a" is incorrectly printed
by llvm-objdump as pushq.
All 3 problems can be fixed by fixing the instruction descriptors for the
16-bit push immediate forms.
------------------------------
bash-4.3$ cat t.s
.section push,"x"
pushw $foo
pushw $42
bash-4.3$ llvm-mc t.s -filetype=obj -o - | llvm-objdump -d -
<stdin>: file format ELF64-x86-64
Disassembly of section push:
push:
0: 68 00 00 00 00 pushq $0
5: 66 68 2a 00 pushw $42
bash-4.3$ gcc -c t.s && llvm-objdump -d t.o
t.o: file format ELF64-x86-64
Disassembly of section push:
push:
0: 66 68 00 00 pushw $0
4: 66 6a 2a pushq $42</pre>
</div>
</p>
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