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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 --- - aarch64 backend uses x18 on ios"
href="https://llvm.org/bugs/show_bug.cgi?id=24588">24588</a>
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<th>Summary</th>
<td>aarch64 backend uses x18 on ios
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>Macintosh
</td>
</tr>
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<th>OS</th>
<td>other
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>andrew.b.adams@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=14780" name="attach_14780" title="A chunk of ll large enough to demonstrate the issue">attachment 14780</a> <a href="attachment.cgi?id=14780&action=edit" title="A chunk of ll large enough to demonstrate the issue">[details]</a></span>
A chunk of ll large enough to demonstrate the issue
This is a minor complaint, but it produces a very hard-to-debug error.
If you compile some .ll with a target triple aarch64-ios, then the aarch64
backend will happily use x18, even though that's reserved by the system on this
platform.
This causes crashes due to register-stomping. Clang avoids this by setting the
additional flag -mattr=+reserve-x18, but having IOS in the target triple seems
like it should be enough.
To reproduce, compile the attached .ll like so:
llc -mtriple aarch64-ios initmod.opengl_64.ll -filetype=asm -o - | grep x18
orr w0, wzr, #0x18
orr w0, wzr, #0x18
ldrsw x18, [x22, #40]
lsl x18, x18, #1
add x5, x5, x18
ldrsw x18, [x22, #40]
lsl x18, x18, #2
add x5, x5, x18
ldrsw x18, [x21, #40]
lsl x18, x18, #1
add x3, x3, x18
ldrsw x18, [x21, #40]
lsl x18, x18, #2
add x3, x3, x18
sxtw x18, w18
str w3, [x1, x18, lsl #2]
If you add -mattr=+reserve-x18, it does the right thing.
There's nothing very special about the attached ll - any sufficiently large
piece of ll should reproduce this.</pre>
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