Fork channel

Create a new channel as a copy of main.

Rename channel

Rename main to:

Delete channel

Delete main? This cannot be undone.

simple-register-allocation-read-undef.mir
# RUN: llc < %s -x=mir -mtriple=x86_64-- -run-pass=simple-register-coalescing | FileCheck %s
---
name: f
body: |
  bb.0:
    JCC_1 %bb.2, 2, undef implicit killed $eflags
    JMP_1 %bb.1

  bb.1:
    %0 : gr64 = IMPLICIT_DEF
    NOOP implicit-def undef %1.sub_32bit : gr64
    NOOP implicit-def %1.sub_16bit : gr64
    JMP_1 %bb.3

  bb.2:
    NOOP implicit-def %0
    %1 = COPY %0

  bb.3:
    NOOP implicit killed %0
    NOOP implicit killed %1
...

# We should have a setting of both sub_32bit and sub_16bit. The first one
# should be undef and not dead, and the second should not be undef.

# CHECK-NOT:  dead
# CHECK:      NOOP implicit-def undef %1.sub_32bit
# CHECK-NOT:  undef
# CHECK-NEXT: NOOP implicit-def %1.sub_16bit