[RyuJIT] Unnecessary nullcheck in Exchange_long benchmark #44087
Description
dotnet/performance/Perf.Interlocked.cs#L39:
private long _long = 0;
[MethodImpl(MethodImplOptions.NoInlining)]
public long Exchange_long() => Interlocked.Exchange(ref _long, 1);Codegen for Exchange_long:
cmp dword ptr [rcx], ecx ;; <--- nullcheck
lea rax, bword ptr [rcx+8]
mov edx, 1
xchg qword ptr [rax], rdx
mov rax, rdx
retthis code never throws NRE.
Is it #define CONSERVATIVE_NULL_CHECK_BYREF_CREATION 1's fault?
/cc @dotnet/jit-contrib @sandreenko
UPD: Same in MONO:
0: 50 push %rax
1: 48 85 ff test %rdi,%rdi ;; <----
4: 74 0b je 11 <xchange_long___+0x11>
6: b8 01 00 00 00 mov $0x1,%eax
b: 48 87 47 10 xchg %rax,0x10(%rdi)
f: 59 pop %rcx
10: c3 retq
11: 48 b8 60 e9 74 54 13 movabs $0x56135474e960,%rax
18: 56 00 00
1b: bf 32 01 00 00 mov $0x132,%edi
20: ff 10 callq *(%rax)
category:cq
theme:optimization
skill-level:beginner
cost:small
impact:small
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