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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - AARCH64 ADRP/ADD Code Size Regression between v6 and v7"
href="https://bugs.llvm.org/show_bug.cgi?id=42373">42373</a>
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<th>Summary</th>
<td>AARCH64 ADRP/ADD Code Size Regression between v6 and v7
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>7.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</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>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>rrmills@gmail.com
</td>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=22134" name="attach_22134" title="Example of simple code the reproduces issue">attachment 22134</a> <a href="attachment.cgi?id=22134&action=edit" title="Example of simple code the reproduces issue">[details]</a></span>
Example of simple code the reproduces issue
In developing for an extremely memory-constrained AARCH64 embedded environment,
I noticed a code size regression between versions 6 and 7. Specifically, I see
the regression when performing accesses into global structures.
Earlier versions (6 and older) would compile a single ADRP/ADD to the front of
the global struct at the beginning of a function. Accesses into the structures
would then be LDR/STR with offsets to the original calculated address.
Later versions are doing ADRP/ADD (followed by STR/LDR) combos on every access
into the struct.
The issue seems to come up in LLC. The IR produced by versions 6/7/8 seem
fundamentally identical. Furthermore, I can feed IR generated by llvm 6 into
LLC for versions 6, 7, and 8, and 7/8 produce the larger code. In all cases
I am compiling with '-Oz'
I have a bit more info in this thread on the llvm mailing list. I have also
attached a trivial example in which versions 7 and later will produce larger
code than versions 6 and older.
LLVM Mailing list thread:
<a href="http://lists.llvm.org/pipermail/llvm-dev/2019-May/132424.html">http://lists.llvm.org/pipermail/llvm-dev/2019-May/132424.html</a></pre>
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