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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] SimplifyDemandedBits failure to simplify PMULDQ/PMULUDQ"
href="https://bugs.llvm.org/show_bug.cgi?id=39178">39178</a>
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<th>Summary</th>
<td>[X86] SimplifyDemandedBits failure to simplify PMULDQ/PMULUDQ
</td>
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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>Windows NT
</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
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
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<th>CC</th>
<td>andrea.dibiagio@gmail.com, craig.topper@gmail.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
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<p>
<div>
<pre>define <2 x i64> @muludq_demanded_bits(<4 x i32>, <4 x i32>) {
%3 = shufflevector <4 x i32> %0, <4 x i32> <i32 undef, i32 0, i32 undef, i32
0>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
%4 = shufflevector <4 x i32> %1, <4 x i32> <i32 undef, i32 0, i32 undef, i32
0>, <4 x i32> <i32 0, i32 5, i32 2, i32 7>
%5 = bitcast <4 x i32> %3 to <2 x i64>
%6 = bitcast <4 x i32> %4 to <2 x i64>
%7 = mul <2 x i64> %6, %5
ret <2 x i64> %7
}
llc -mcpu=btver2
vpxor %xmm2, %xmm2, %xmm2
vpblendw $204, %xmm2, %xmm0, %xmm0 # xmm0 =
xmm0[0,1],xmm2[2,3],xmm0[4,5],xmm2[6,7]
vpblendw $204, %xmm2, %xmm1, %xmm1 # xmm1 =
xmm1[0,1],xmm2[2,3],xmm1[4,5],xmm2[6,7]
vpmuludq %xmm0, %xmm1, %xmm0
retq
The vpblendw can be removed as PMULDQ/PMULUDQ only use the bottom 32-bits of
each i64 element</pre>
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</p>
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