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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - reassociate multiplies with fast-math"
href="http://llvm.org/bugs/show_bug.cgi?id=21768">21768</a>
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<th>Summary</th>
<td>reassociate multiplies with fast-math
</td>
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<th>Product</th>
<td>libraries
</td>
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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>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>define float @foo(float %f0, float %f1, float %f2, float %f3) {
%mul0 = fmul fast float %f1, %f0
%mul1 = fmul fast float %mul0, %f2
%mul2 = fmul fast float %mul1, %f3
ret float %mul2
}
This should be optimized to:
define float @foo(float %f0, float %f1, float %f2, float %f3) {
%mul0 = fmul fast float %f0, %f1
%mul1 = fmul fast float %f2, %f3
%mul2 = fmul fast float %mul0, %mul1
ret float %mul2
}
Ie, instead of 3 dependent multiplies, we should have 2 independent fmuls
followed by the fmul of those results.
This can be generalized for N fmuls to form the optimal binary tree of
independent ops.</pre>
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</p>
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