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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - ARM: Negative offset support problem"
href="http://llvm.org/bugs/show_bug.cgi?id=20853">20853</a>
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<th>Summary</th>
<td>ARM: Negative offset support problem
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>Other
</td>
</tr>
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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>
</tr>
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<th>Component</th>
<td>llc
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>ioblakov@dev.rtsoft.ru
</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>Created <span class=""><a href="attachment.cgi?id=12990" name="attach_12990" title="Test">attachment 12990</a> <a href="attachment.cgi?id=12990&action=edit" title="Test">[details]</a></span>
Test
ARM compiler can use negative offset (imm12) only for a frame access.
The following example (n.c) shows problem:
int sum(int *p)
{
return p[-4] + p[-2] + p[0] + p[2] + p[4];
}
clang --target=arm -mcpu=cortex-a9 -S -mfloat-abi=soft -O3 n.c
sum:
sub r1, r0, #16 <<< instead of using [r0, #-16] to load a p[-4]
sub r2, r0, #8 <<< instead of using [r0, #-8] to load a p[-2]
ldr r1, [r1]
ldr r2, [r2]
ldr r3, [r0, #8]
add r1, r2, r1
ldr r2, [r0]
ldr r0, [r0, #16]
add r1, r1, r2
add r1, r1, r3
add r0, r1, r0
bx lr</pre>
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