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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] clang::targets::X86TargetInfo::isCLZForZeroUndef should be BMI/LZCNT aware"
href="https://bugs.llvm.org/show_bug.cgi?id=40214">40214</a>
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<th>Summary</th>
<td>[X86] clang::targets::X86TargetInfo::isCLZForZeroUndef should be BMI/LZCNT aware
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
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<th>CC</th>
<td>andrea.dibiagio@gmail.com, craig.topper@gmail.com, filcab@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<pre>On x86 targets with BMI and LZCNT we should be able to return false from
isCLZForZeroUndef().
This would help avoid an issue we're seeing with ubsan warning that we have
zero inputs to clz/ctz in cases like:
#include <stdint.h>
uint64_t foo(uint64_t a0) {
uint64_t r0 = static_cast<uint64_t>( __builtin_clzll( a0 ) );
r0 = ( a0 ? r0 : 64 );
return r0;
}</pre>
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