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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] 12.0.0 Regression - foldShuffleOfHorizOp doesn't correctly handle 256-bit X86ISD::VBROADCAST"
href="https://bugs.llvm.org/show_bug.cgi?id=49971">49971</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[X86] 12.0.0 Regression - foldShuffleOfHorizOp doesn't correctly handle 256-bit X86ISD::VBROADCAST
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Windows NT
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>Blocks</th>
<td>49317
</td>
</tr></table>
<p>
<div>
<pre>Encountered by an internal test:
define <4 x double> @broadcast_hadd_pd(<4 x double> %0) {
%2 = tail call <4 x double> @llvm.x86.avx.hadd.pd.256(<4 x double> %0, <4 x
double> %0)
%3 = shufflevector <4 x double> %2, <4 x double> undef, <4 x i32> <i32 0, i32
1, i32 0, i32 1>
ret <4 x double> %3
}
declare <4 x double> @llvm.x86.avx.hadd.pd.256(<4 x double>, <4 x double>)
llc -march=znver2
trunk:
broadcast_hadd_pd:
vhaddpd %xmm0, %xmm0, %xmm0
vbroadcastsd %xmm0, %ymm0
retq
llvm12:
broadcast_hadd_pd:
vhaddpd %ymm0, %ymm0, %ymm0 ; WHERE DID THE SPLAT GO?
retq
llvm11:
broadcast_hadd_pd:
vhaddpd %xmm0, %xmm0, %xmm0
vpermpd $68, %ymm0, %ymm0 # ymm0 = ymm0[0,1,0,1]
retq
The issue is that foldShuffleOfHorizOp incorrectly assumes that a 256-bit
broadcast(vhaddpd(x,y)) can be replaced by vhaddpd(x,x).
The safest solution appears to be to drop X86ISD::VBROADCAST handling from
foldShuffleOfHorizOp entirely - canonicalizeShuffleMaskWithHorizOp already
handles it.
In trunk we've already removed all VBROADCAST/MOVDDUP handling from
foldShuffleOfHorizOp (2a0d5da917f1) but in 12.x we still need the MOVDDUP
support in some cases.</pre>
</div>
</p>
<div id="referenced">
<hr style="border: 1px dashed #969696">
<b>Referenced Bugs:</b>
<ul>
<li>
[<a class="bz_bug_link
bz_status_NEW "
title="NEW - [meta] 12.0.1 Release Blockers"
href="https://bugs.llvm.org/show_bug.cgi?id=49317">Bug 49317</a>] [meta] 12.0.1 Release Blockers
</li>
</ul>
</div>
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