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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 - Failure to simplify -min(-a, a) => max(-a, a)"
href="https://bugs.llvm.org/show_bug.cgi?id=39480">39480</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Failure to simplify -min(-a, a) => max(-a, a)
</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>Windows NT
</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>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>filcab@gmail.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com, tilkax@gmail.com
</td>
</tr></table>
<p>
<div>
<pre>#include <algorithm>
#include <x86intrin.h>
int min_neg_s32(int a)
{
return -std::min(-a, a);
}
__m128i min_neg_v4s32(__m128i a) {
return _mm_sub_epi32(_mm_setzero_si128(),
_mm_min_epi32(_mm_sub_epi32(_mm_setzero_si128(), a), a));
}
float min_neg_f32(float a)
{
return -std::min(-a, a);
}
<a href="https://godbolt.org/z/h4zTcS">https://godbolt.org/z/h4zTcS</a>
clang:
_Z11min_neg_s32i: # @_Z11min_neg_s32i
movl %edi, %eax
negl %eax
cmpl %edi, %eax
cmovgl %edi, %eax
negl %eax
retq
_Z13min_neg_v4s32Dv2_x: # @_Z13min_neg_v4s32Dv2_x
vpxor %xmm1, %xmm1, %xmm1
vpsubd %xmm0, %xmm1, %xmm2
vpminsd %xmm0, %xmm2, %xmm0
vpsubd %xmm0, %xmm1, %xmm0
retq
_Z11min_neg_f32f: # @_Z11min_neg_f32f
vmovaps .LCPI2_0(%rip), %xmm1 # xmm1 = [-0,-0,-0,-0]
vxorps %xmm1, %xmm0, %xmm2
vminss %xmm2, %xmm0, %xmm0
vxorps %xmm1, %xmm0, %xmm0
retq
gcc manages the scalar cases (s32 is interesting....) but not the vector case:
_Z11min_neg_s32i:
movl %edi, %eax
cltd
xorl %edx, %eax
subl %edx, %eax
ret
_Z13min_neg_v4s32Dv2_x:
vpxor %xmm1, %xmm1, %xmm1
vpsubd %xmm0, %xmm1, %xmm2
vpminsd %xmm0, %xmm2, %xmm0
vpsubd %xmm0, %xmm1, %xmm0
ret
_Z11min_neg_f32f:
vmovss %xmm0, %xmm0, %xmm1
vxorps .LC0(%rip), %xmm0, %xmm0
vmaxss %xmm1, %xmm0, %xmm0
ret</pre>
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