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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Failure to merge 2 * <2 x float> load + fadd and then split the result back to 2 * <2 x float>"
href="https://bugs.llvm.org/show_bug.cgi?id=42022">42022</a>
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<th>Summary</th>
<td>Failure to merge 2 * <2 x float> load + fadd and then split the result back to 2 * <2 x float>
</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
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
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<th>CC</th>
<td>a.bataev@hotmail.com, anton.a.afanasyev@gmail.com, craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<pre>Another missed vectorization opportunity for
struct Vector4 {
float x, y, z, w;
};
<a href="https://godbolt.org/z/lbAN92">https://godbolt.org/z/lbAN92</a>
// Bad: Failed to combine loads + split result
Vector4 Add(const Vector4 &a, const Vector4 &b) {
Vector4 r;
r.x = a.x + b.x;
r.y = a.y + b.y;
r.z = a.z + b.z;
r.w = a.w + b.w;
return r;
}
_Z3AddRK7Vector4S1_: # @_Z3AddRK7Vector4S1_
vmovsd (%rdi), %xmm0 # xmm0 = mem[0],zero
vmovsd (%rsi), %xmm2 # xmm2 = mem[0],zero
vmovsd 8(%rdi), %xmm1 # xmm1 = mem[0],zero
vaddps %xmm2, %xmm0, %xmm0
vmovsd 8(%rsi), %xmm2 # xmm2 = mem[0],zero
vaddps %xmm2, %xmm1, %xmm1
retq
Not sure whether this can be handled in the SLP or DAG but we should be able to
do something like:
_Z3AddRK7Vector4S1_: # @_Z3AddRK7Vector4S1_
vmovups (%rdi), %xmm0
vaddps (%rsi), %xmm0, %xmm0
vunpckhpd %xmm0, %xmm0, %xmm1 # xmm1 = xmm0[2,3,2,3]
retq</pre>
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