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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Is there a way to force Using literal pool loads instead of MOVW/MOVT for global/constant value"
href="http://llvm.org/bugs/show_bug.cgi?id=17280">17280</a>
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<th>Summary</th>
<td>Is there a way to force Using literal pool loads instead of MOVW/MOVT for global/constant value
</td>
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<th>Product</th>
<td>new-bugs
</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>Linux
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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
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>mrcool0905@gmail.com
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=11232" name="attach_11232" title="sample code and disassembly dump">attachment 11232</a> <a href="attachment.cgi?id=11232&action=edit" title="sample code and disassembly dump">[details]</a></span>
sample code and disassembly dump
We are cross compiling to cortex-m4 cpu from linux with clang 3.3 and we are
really running of Text. Using literal pool loads instead of MOVW/MOVT would
save 2 bytes each time we load a big value, and I am trying to get it working.
Looking at the change from 5101 (ARMv6T2 and later should materialize
GlobalAddresses using MOVW/MOVT), this should be enabled with -Os for global
value, but it doesn't seem working when I compile the code with Os. After
hacking the llvm source code(add a opt to set UseMovt to false), I was able to
get it working on global value, but it still used MOVW/MOVT on constant value.
Seems like constant value code generation follows a different code path which
doesn't check UseMovt. And I noticed that cortex-m0 use literal pool load all
the time since it doesn't have MOVT instruction.
I am wondering if there is a way to force using literal pool loads instead of
MOVW/MOV, or if you can point me to the right place where we generate constant
value instructions, and I can make a patch for myself.
Attached is the sample code and disassembly dump.
Thanks,
Rui</pre>
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