Improve Interlocked.Exchange<T>

[mikedn]

Replace TypedReference with Unsafe.As, it generates far less code and, with the help of AggresiveInlining, it allows Exchange<T> to inline.

Fixes #16051

[mikedn]

The TypedReference based Exchange<T> generated

G_M49272_IG01:
       push     rdi
       push     rsi
       sub      rsp, 72
       mov      rsi, rcx
       lea      rdi, [rsp+20H]
       mov      ecx, 8
       xor      rax, rax
       rep stosd 
       mov      rcx, rsi
       mov      qword ptr [rsp+40H], rcx
       mov      gword ptr [rsp+70H], r8
G_M49272_IG02:
       mov      rcx, qword ptr [rcx+16]
       mov      rcx, qword ptr [rcx]
       mov      rax, rcx
       mov      r8d, eax
       and      r8d, 1
       test     r8d, r8d
       je       SHORT G_M49272_IG03
       mov      rax, qword ptr [rax-1]
G_M49272_IG03:
       test     r8d, r8d
       je       SHORT G_M49272_IG04
       mov      rcx, qword ptr [rcx-1]
G_M49272_IG04:
       mov      qword ptr [rsp+30H], rdx
       mov      qword ptr [rsp+38H], rax
       lea      rdx, bword ptr [rsp+70H]
       mov      qword ptr [rsp+20H], rdx
       mov      qword ptr [rsp+28H], rcx
       lea      rcx, bword ptr [rsp+30H]
       lea      rdx, bword ptr [rsp+20H]
       call     Interlocked:_Exchange(struct,struct)
       mov      rax, gword ptr [rsp+70H]
G_M49272_IG05:
       add      rsp, 72
       pop      rsi
       pop      rdi
       ret      
; Total bytes of code 123, prolog size 31 for method Interlocked:Exchange(byref,ref):ref

No wonder it was slower.

[jkotas]

Could you please also delete the TypedReference-based _Exchange ?

[mikedn]

Deleted TypedReference overloads.

[mikedn]

Now both Exchange<T> and CompareExchange<T> generate similar code, they both end up calling the object overload:

       488BCE               mov      rcx, rsi
       33D2                 xor      rdx, rdx
       E8BE174E5F           call     System.Threading.Interlocked:Exchange(byref,ref):ref
       488BCE               mov      rcx, rsi
       33D2                 xor      rdx, rdx
       4533C0               xor      r8, r8
       E8E1044E5F           call     System.Threading.Interlocked:CompareExchange(byref,ref,ref):ref

[jkotas]

Thank you!

[jkotas]

@dotnet-bot test Ubuntu x64 Checked Innerloop Build and Test please