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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 - LLVM generates far less than ideal code for cold functions (when optimizing for size)"
href="https://bugs.llvm.org/show_bug.cgi?id=33249">33249</a>
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<th>Summary</th>
<td>LLVM generates far less than ideal code for cold functions (when optimizing for size)
</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>
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<th>OS</th>
<td>All
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>davide@freebsd.org
</td>
</tr>
<tr>
<th>CC</th>
<td>davidxl@google.com, filcab@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, rafael.espindola@gmail.com, simon.f.whittaker@gmail.com, wmi@google.com, xinliangli@gmail.com
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</tr></table>
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<pre><a href="https://godbolt.org/g/kgGJxw">https://godbolt.org/g/kgGJxw</a>
This function is cold, we should optimize for size (also at -O3), as GCC does:
winky(int): # @winky(int)
mov eax, 1
movd xmm2, eax
movd xmm0, edi
pshufd xmm1, xmm0, 0 # xmm1 = xmm0[0,0,0,0]
punpckldq xmm0, xmm2 # xmm0 =
xmm0[0],xmm2[0],xmm0[1],xmm2[1]
pshufd xmm2, xmm2, 80 # xmm2 = xmm2[0,0,1,1]
punpckldq xmm0, xmm2 # xmm0 =
xmm0[0],xmm2[0],xmm0[1],xmm2[1]
mov eax, 36
pshufd xmm2, xmm1, 245 # xmm2 = xmm1[1,1,3,3]
.LBB1_1: # =>This Inner Loop Header: Depth=1
pshufd xmm3, xmm0, 245 # xmm3 = xmm0[1,1,3,3]
pmuludq xmm0, xmm1
pshufd xmm0, xmm0, 232 # xmm0 = xmm0[0,2,2,3]
pmuludq xmm3, xmm2
pshufd xmm3, xmm3, 232 # xmm3 = xmm3[0,2,2,3]
punpckldq xmm0, xmm3 # xmm0 =
xmm0[0],xmm3[0],xmm0[1],xmm3[1]
add eax, -4
jne .LBB1_1
pshufd xmm1, xmm0, 78 # xmm1 = xmm0[2,3,0,1]
pshufd xmm2, xmm0, 245 # xmm2 = xmm0[1,1,3,3]
pmuludq xmm0, xmm1
pshufd xmm0, xmm0, 232 # xmm0 = xmm0[0,2,2,3]
pshufd xmm1, xmm1, 245 # xmm1 = xmm1[1,1,3,3]
pmuludq xmm1, xmm2
pshufd xmm1, xmm1, 232 # xmm1 = xmm1[0,2,2,3]
punpckldq xmm0, xmm1 # xmm0 =
xmm0[0],xmm1[0],xmm0[1],xmm1[1]
pshufd xmm1, xmm0, 229 # xmm1 = xmm0[1,1,2,3]
pmuludq xmm1, xmm0
pshufd xmm1, xmm1, 232 # xmm1 = xmm1[0,2,2,3]
pshufd xmm0, xmm0, 245 # xmm0 = xmm0[1,1,3,3]
pmuludq xmm0, xmm0
pshufd xmm0, xmm0, 232 # xmm0 = xmm0[0,2,2,3]
punpckldq xmm1, xmm0 # xmm1 =
xmm1[0],xmm0[0],xmm1[1],xmm0[1]
movd eax, xmm1
ret
vs
winky(int):
mov eax, edi
mov edx, 36
.L6:
imul eax, edi
dec edx
jne .L6
ret</pre>
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