CORINFO_HELP_ASSIGN_BYREF usage ?

[ycrumeyrolle]

Having this code:

        private ECParameters _parameters;

        public ECParameters ExportParameters()
        {
            var p = _parameters;
            return p;
        }

Which is supposed to be a copy of the struct ECParameters.

The ASM code is:

.NET Core 5.0.5 (CoreCLR 5.0.521.16609, CoreFX 5.0.521.16609), X64 RyuJIT

; ExportParameters()
       push      rdi
       push      rsi
       push      rbx
       sub       rsp,80
       mov       rbx,rdx
       lea       rsi,[rcx+10]
       lea       rdi,[rsp]
       mov       ecx,10
       rep movsq
       mov       rdi,rbx
       lea       rsi,[rsp]
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       movsq
       call      CORINFO_HELP_ASSIGN_BYREF
       call      CORINFO_HELP_ASSIGN_BYREF
       movsq
       call      CORINFO_HELP_ASSIGN_BYREF
       mov       rax,rbx
       add       rsp,80
       pop       rbx
       pop       rsi
       pop       rdi
       ret
; Total bytes of code 124

Where are the usage of all these CORINFO_HELP_ASSIGN_BYREF ?

[stephentoub]

ECParameters contains a bunch of byte[] fields (directly and indirectly via other structs it contains). You're seeing one CORINFO_HELP_ASSIGN_BYREF for every reference inside the struct that's being copied.