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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [VectorCombine] transform shuffle of binops with common operand"
href="https://bugs.llvm.org/show_bug.cgi?id=52178">52178</a>
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<th>Summary</th>
<td>[VectorCombine] transform shuffle of binops with common operand
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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>All
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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
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Adapted/reduced from the regression test in <a href="https://reviews.llvm.org/D111800">https://reviews.llvm.org/D111800</a>
(that example could have further shuffle combining which would eliminate a
shuffle and almost definitely be a win):
define <3 x i3> @src(<3 x i3> %x, <3 x i3> %y, <3 x i3> %z) {
%a1 = sub <3 x i3> %x, %y
%a2 = sub <3 x i3> %x, %z
%r = shufflevector <3 x i3> %a1, <3 x i3> %a2, <3 x i32> <i32 0, i32 5, i32
3>
ret <3 x i3> %r
}
define <3 x i3> @tgt(<3 x i3> %x, <3 x i3> %y, <3 x i3> %z) {
%s1 = shufflevector <3 x i3> %x, <3 x i3> %x, <3 x i32> <i32 0, i32 5, i32 3>
%s2 = shufflevector <3 x i3> %y, <3 x i3> %z, <3 x i32> <i32 0, i32 5, i32 3>
%r2 = sub <3 x i3> %s1, %s2
ret <3 x i3> %r2
}
<a href="https://alive2.llvm.org/ce/z/d8zB4D">https://alive2.llvm.org/ce/z/d8zB4D</a>
Note: the shuffle of '%x' can be reduced to a unary shuffle; I left the mask
as-is to show that we're re-using the incoming shuffle mask.
As long as the shuffle is no more expensive than the binop, this should be a
win and would potentially allow subsequent combines.</pre>
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