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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Overestimated align on load"
href="https://bugs.llvm.org/show_bug.cgi?id=32230">32230</a>
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<th>Summary</th>
<td>Overestimated align on load
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</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>
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<th>Reporter</th>
<td>moconnor@directstream.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>This C++ code:
#include <cstdint>
using namespace std;
void test(uint8_t *ptr, long *buf, int const N) {
for (int I = 0; I < N - 7; ++I) {
uint64_t big = *(uint64_t *)(ptr + I);
buf[I] = big * big;
}
}
When compiled with:
clang++ -std=c++11 -S -emit-llvm -O2 -fno-unroll-loops test.cpp -o test.ll
Produces a:
%2 = load i64, i64* %1, align 8
Even when that load cannot be 8-byte aligned since it's stepping through `ptr`
a byte at a time.
I've tested this and seen this behavior on 3.8.0 and 4.0.0-rc4.
-fno-unroll-loops is only present to clean up the generated IR and doesn't
appear to affect the production of that load.</pre>
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