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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Messy code for insertelement on AVX2 vectors"
href="https://bugs.llvm.org/show_bug.cgi?id=50971">50971</a>
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<th>Summary</th>
<td>Messy code for insertelement on AVX2 vectors
</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
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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>efriedma@quicinc.com
</td>
</tr>
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<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
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<p>
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<pre>Examples:
#include <immintrin.h>
#define IDX 3
__m256d float1(__m256d a, __m256d b) { a[IDX] = b[0]; return a; }
__m256d float2(__m256d a, double b) { a[IDX] = b; return a; }
__m256d float3(__m256d a, double b) { return _mm256_blend_epi32(a,
_mm256_set1_pd(b), 3 << IDX * 2); }
__m256i int1(__m256i a, __m256i b) { a[IDX] = b[0]; return a; }
__m256i int2(__m256i a, long b) { a[IDX] = b; return a; }
__m256i int3(__m256i a, long b) { return _mm256_blend_epi32(a,
_mm256_set1_epi64x(b), 3 << IDX * 2); }
__m256i int4(__m256i a, long *b) { a[IDX] = *b; return a; }
__m256i int5(__m256i a, long *b) { return _mm256_blend_epi32(a,
_mm256_set1_epi64x(*b), 3 << IDX * 2); }
It looks like the lowering extracts an 128-bit vector, inserts into that, then
reconstructs the 256-bit vector. A broadcast+blend is almost always going to be
more efficient, I think.</pre>
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