Jitter GC byref lifetime tracking missing a register

[janvorli]

The jitter misses tracking lifetime of the R15 register when jitting Microsoft.AspNetCore.Server.Kestrel.Http.SocketOutput:ProducingStart method, which leads to a GC hole. Here is a dump of the fragment of the jitted code with the lifetime annotation where it is visible that the R15 is not tracked and so if GC happens between the R15 assignment and the last instruction in the list below and the object pointed to by the initial RBX gets moved, the R15 is no longer valid.

New byrReg live regs=00000000 {}
byrReg -[rsi]
gcrReg +[rsi]
IN0010: 00005F 488BF7               mov      rsi, rdi
IN0011: 000062 448B772C             mov      r14d, dword ptr [rdi+44]
gcrReg -[rbx]
byrReg +[rbx]
IN0012: 000066 4881C388000000       add      rbx, 136
IN0013: 00006D 4C8BFB               mov      r15, rbx
gcrReg -[rdi]
byrReg +[rdi]
IN0014: 000070 498BFF               mov      rdi, r15
New gcrReg live regs=00000000 {}
gcrReg -[rsi]
New byrReg live regs=00000008 {rbx}
byrReg -[rdi]
IN0015: 000073 FF1500000000         call     [CORINFO_HELP_CHECKED_ASSIGN_REF]
IN0016: 000079 45897708             mov      dword ptr [r15+8], r14d