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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [AArch64LoadStoreOptimizer] Pair loads of different widths; e.g., LDRW + LDRX"
href="https://llvm.org/bugs/show_bug.cgi?id=24507">24507</a>
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<th>Summary</th>
<td>[AArch64LoadStoreOptimizer] Pair loads of different widths; e.g., LDRW + LDRX
</td>
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<th>Product</th>
<td>libraries
</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>Windows NT
</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
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<th>Component</th>
<td>Backend: AArch64
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>mcrosier@codeaurora.org
</td>
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<th>CC</th>
<td>gberry@codeaurora.org, junbuml@codeaurora.org, llvm-bugs@lists.llvm.org, mcrosier@codeaurora.org, mssimpso@codeaurora.org
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<th>Classification</th>
<td>Unclassified
</td>
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<p>
<div>
<pre>From a hot loop in 400.perlbench:
4b345c: b9402ff0 ldr w16, [sp,#44]
4b3460: aa1703e2 mov x2, x23
4b3464: f9401bfa ldr x26, [sp,#48]
We should be able to form a ldp from the two load instructions, despite the
fact that the two are of different sizes. We'd need to zero out the upper bits
of x16, but I'm thinking a (ldp + and) is less expensive than (ldr + ldr).
We also need to think about more subtle things such as accessing data across
page boundaries that wouldn't have been accessed otherwise or accessing illegal
addresses (in the heap). I believe it's safe to access anything on the stack.
This optimization is specific to loads. We cannot easily do such an
optimization for stores.</pre>
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