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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - x86 backend widens v2f32 vectors only to do more work in software operations later for `sin`, `cos` etc."
href="https://bugs.llvm.org/show_bug.cgi?id=38527">38527</a>
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<th>Summary</th>
<td>x86 backend widens v2f32 vectors only to do more work in software operations later for `sin`, `cos` etc.
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>simonas+llvm.org@kazlauskas.me
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=20678" name="attach_20678" title="Simple fsin call on v2f32">attachment 20678</a> <a href="attachment.cgi?id=20678&action=edit" title="Simple fsin call on v2f32">[details]</a></span>
Simple fsin call on v2f32
Given the attached LLVM IR, running llc on it as such
<span class="quote">> llc winsimd.ll -O3 -filetype=asm -o -</span >
Will result in following assembly being generated
movq %rdi, %rbx
movsd (%rdi), %xmm0 # xmm0 = mem[0],zero
movaps %xmm0, (%rsp) # 16-byte Spill
callq sinf
movaps %xmm0, 16(%rsp) # 16-byte Spill
movaps (%rsp), %xmm0 # 16-byte Reload
callq sinf
movaps 16(%rsp), %xmm1 # 16-byte Reload
unpcklps %xmm0, %xmm1 # xmm1 =
xmm1[0],xmm0[0],xmm1[1],xmm0[1]
movaps %xmm1, 16(%rsp) # 16-byte Spill
movaps (%rsp), %xmm0 # 16-byte Reload
callq sinf
movaps %xmm0, 32(%rsp) # 16-byte Spill
pshufd $229, (%rsp), %xmm0 # 16-byte Folded Reload
# xmm0 = mem[1,1,2,3]
callq sinf
movdqa 32(%rsp), %xmm1 # 16-byte Reload
punpckldq %xmm0, %xmm1 # xmm1 =
xmm1[0],xmm0[0],xmm1[1],xmm0[1]
<snip>
Note how this generates 4 distinct calls to `sinf`, although 2 should be
sufficient. This happens, because the backend legalises the operation on v2f32
to v4f32, as indicated by `-debug` output from `llc`. However, the backend then
neglects to take care to not calculate `sinf` on the `undef` components of the
vector, resulting in extra work.</pre>
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