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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - saturating loops should exit early once the saturation condition is met"
href="https://bugs.llvm.org/show_bug.cgi?id=47147">47147</a>
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<th>Summary</th>
<td>saturating loops should exit early once the saturation condition is met
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Loop Optimizer
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>richard-llvm@metafoo.co.uk
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Example:
bool f(int *p, int *q) {
bool b = false;
for (; p != q; ++p)
if (*p <= 0) b = true;
return b;
}
... should probably be optimized to:
bool f(int *p, int *q) {
bool b = false;
for (; p != q; ++p)
if (*p <= 0) return true;
return false;
}
(that is, exit early once the loop has reached a saturation condition).
Currently neither LLVM nor GCC (nor ICC nor MSVC) performs this optimization.
Aside: the above loop is also not unrolled. But if it's rewritten as
for (int i = 0; i != q - p; ++i)
if (p[i] <= 0) b = true;
... then it gets unrolled 4x.</pre>
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