https://bugs.llvm.org/show_bug.cgi?id=40214
Bug ID: 40214
Summary: [X86] clang::targets::X86TargetInfo::isCLZForZeroUndef
should be BMI/LZCNT aware
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected],
[email protected], [email protected]
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;
}
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