https://bugs.llvm.org/show_bug.cgi?id=42935
Bug ID: 42935
Summary: [X86] znver missing cmpxchg8b feature, resulting in
expanded atomicrmw
Product: libraries
Version: 9.0
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: nikita....@gmail.com
CC: craig.top...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk, spatel+l...@rotateright.com
define i64 @test(i64* %p) {
%x = atomicrmw sub i64* %p, i64 1 seq_cst
ret i64 %x
}
Under -mcpu=znver1 results in:
pushq %rax
.cfi_def_cfa_offset 16
movl $1, %esi
movl $5, %edx
callq __atomic_fetch_sub_8
popq %rcx
.cfi_def_cfa_offset 8
retq
While it should produce a "lock xaddq" instruction.
This issue was introduced in https://reviews.llvm.org/D59576, where the
CMPXCHG8B feature flag was not added to ZNFeatures.
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