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<base href="https://bugs.llvm.org/">
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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 - cmov regression"
href="https://bugs.llvm.org/show_bug.cgi?id=40646">40646</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>cmov regression
</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>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>Antonin.kriz@gmail.com
</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=21443" name="attach_21443" title="simple source file">attachment 21443</a> <a href="attachment.cgi?id=21443&action=edit" title="simple source file">[details]</a></span>
simple source file
clang has stopped using cmov instruction in the following
case(<a href="https://godbolt.org/z/CvPhJo">https://godbolt.org/z/CvPhJo</a>)
clang-trunk:
offset(ctx&, unsigned long):
mov rax, qword ptr [rdi + 8]
mov rcx, qword ptr [rdi + 16]
sub rax, rcx
cmp rax, rsi
setae al
jae .LBB0_1
mov rcx, qword ptr [rdi]
mov qword ptr [rdi], rcx
ret
.LBB0_1:
add rcx, rsi
mov qword ptr [rdi], rcx
ret
clang-5:
offset(ctx&, unsigned long):
mov rax, qword ptr [rdi + 8]
mov rcx, qword ptr [rdi + 16]
sub rax, rcx
add rcx, rsi
cmp rax, rsi
setae al
cmovb rcx, qword ptr [rdi]
mov qword ptr [rdi], rcx
ret
gcc-trunk:
offset(ctx&, unsigned long):
mov rdx, QWORD PTR [rdi+16]
mov rcx, QWORD PTR [rdi+8]
sub rcx, rdx
cmp rsi, rcx
setbe al
add rdx, rsi
cmp rsi, rcx
cmova rdx, QWORD PTR [rdi]
mov QWORD PTR [rdi], rdx
ret
Maybe there is a good reason why clang is not using cmov but according to this
measurement <a href="https://github.com/xiadz/cmov">https://github.com/xiadz/cmov</a>, cmov seems to be the better choice.</pre>
</div>
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