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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86, SSE] missing optimizations for pos/neg integer vector comparisons"
href="https://llvm.org/bugs/show_bug.cgi?id=26701">26701</a>
</td>
</tr>
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<th>Summary</th>
<td>[x86, SSE] missing optimizations for pos/neg integer vector comparisons
</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>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Checking if integer vector elements are positive or negative would seem to be a
common operation, but we don't handle this very well. We need to do extra work
because SSE/AVX only provide 2 integer comparison instructions (eq/gt):
define <4 x i32> @is_positive_using_signshift(<4 x i32> %x) {
%sign = ashr <4 x i32> %x, <i32 31, i32 31, i32 31, i32 31>
%not = xor <4 x i32> %sign, <i32 -1, i32 -1, i32 -1, i32 -1>
ret <4 x i32> %not
}
define <4 x i32> @is_positive_using_sge(<4 x i32> %x) {
%cmp = icmp sge <4 x i32> %x, zeroinitializer
%sext = sext <4 x i1> %cmp to <4 x i32>
ret <4 x i32> %sext
}
define <4 x i32> @is_positive_using_sgt(<4 x i32> %x) {
%cmp = icmp sgt <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
%sext = sext <4 x i1> %cmp to <4 x i32>
ret <4 x i32> %sext
}
define <4 x i32> @is_negative_using_signshift(<4 x i32> %x) {
%sign = ashr <4 x i32> %x, <i32 31, i32 31, i32 31, i32 31>
ret <4 x i32> %sign
}
define <4 x i32> @is_negative_using_slt(<4 x i32> %x) {
%cmp = icmp slt <4 x i32> %x, zeroinitializer
%sext = sext <4 x i1> %cmp to <4 x i32>
ret <4 x i32> %sext
}
define <4 x i32> @is_negative_using_sle(<4 x i32> %x) {
%cmp = icmp sle <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
%sext = sext <4 x i1> %cmp to <4 x i32>
ret <4 x i32> %sext
}
$ ./llc -o - pcmp.ll -mattr=avx
_is_positive_using_signshift:
vpsrad $31, %xmm0, %xmm0
vpcmpeqd %xmm1, %xmm1, %xmm1
vpxor %xmm1, %xmm0, %xmm0
retq
_is_positive_using_sge:
vpxor %xmm1, %xmm1, %xmm1
vpcmpgtd %xmm0, %xmm1, %xmm0
vpcmpeqd %xmm1, %xmm1, %xmm1
vpxor %xmm1, %xmm0, %xmm0
retq
_is_positive_using_sgt:
vpcmpeqd %xmm1, %xmm1, %xmm1
vpcmpgtd %xmm1, %xmm0, %xmm0
retq
_is_negative_using_signshift:
vpsrad $31, %xmm0, %xmm0
retq
_is_negative_using_slt:
vpxor %xmm1, %xmm1, %xmm1
vpcmpgtd %xmm0, %xmm1, %xmm0
retq
_is_negative_using_sle:
vpcmpeqd %xmm1, %xmm1, %xmm1
vpcmpgtd %xmm1, %xmm0, %xmm0
vpxor %xmm1, %xmm0, %xmm0
retq</pre>
</div>
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