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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - PowerPC: Invalid merging of immediates for D-Form"
href="https://bugs.llvm.org/show_bug.cgi?id=49640">49640</a>
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<th>Summary</th>
<td>PowerPC: Invalid merging of immediates for D-Form
</td>
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<th>Product</th>
<td>libraries
</td>
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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>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: PowerPC
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>nemanja.i.ibm@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, nemanja.i.ibm@gmail.com
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=24661" name="attach_24661" title="Eigen test reduced by creduce">attachment 24661</a> <a href="attachment.cgi?id=24661&action=edit" title="Eigen test reduced by creduce">[details]</a></span>
Eigen test reduced by creduce
When a D-Form instruction is fed by an add-immediate, we attempt to merge the
two immediates to form a single displacement so we can remove the
add-immediate.
However, we don't check whether the new displacement fits into a 16-bit signed
immediate field early enough. Namely, we do a sign-extend from 16 bits first
which will discard high bits and then we check whether the result is a 16-bit
signed immediate. It of course will always be.
The check needs to be moved prior to the sign-extend.
Reduced test case from Eigen attached.
To reproduce the problem:
clang -S -O3 -mcpu=pwr9 badDForm.cpp -o - 2>/dev/null | grep stfs
stfs 0, 25400(7)
stfs 0, 30480(7)
stfs 0, -29976(7)
stfs 0, -24896(7)
stfs 0, -19816(7)
The correct values (with the peephole turned off):
clang -S -O3 -mcpu=pwr9 badDForm.cpp -o - -mllvm --disable-ppc-peephole
2>/dev/null | grep stfs
stfs 0, 0(7)
stfs 0, 5080(7)
stfs 0, 10160(7)
stfs 0, 15240(7)
stfs 0, 20320(7)</pre>
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