With D129208 applied but without this patch,
CodeGen/AMDGPU/subreg-intervals.mir fails machine verification
immediately after running LiveIntervals:
# Machine code for function test0: NoPHIs
0B bb.0:
16B S_NOP 0, implicit-def %0:sreg_64
32B S_NOP 0, implicit %0:sreg_64
48B S_NOP 0, implicit-def undef %0.sub0:sreg_64
64B S_NOP 0, implicit %0:sreg_64
# End machine code for function test0.
*** Bad machine code: Multiple connected components in live interval ***
- function: test0
- interval: %0 [16r,32r:0)[48r,64r:1) 0@16r 1@48r L000000000000000C [16r,32r:0) 0@16r L0000000000000003 [16r,32r:1)[48r,64r:0) 0@48r 1@16r weight:0.000000e+00