[PATCH] D49097: [RegisterCoalescer] Another fix for subrange join unreachable

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

I've reduced this testcase to this, although I think it can go a little further:

  ---
  name: coalescing_makes_lane_defined
  tracksRegLiveness: true
  body:             |
    bb.0:
      successors: %bb.1, %bb.2
  
      %0:sreg_32_xm0 = S_MOV_B32 0
      undef %1.sub2:sreg_128 = COPY %0
      undef %2.sub0:sreg_128 = S_MOV_B32 0
      undef %3.sub2:sreg_128 = COPY %0
      S_CBRANCH_SCC0 %bb.2, implicit undef $scc
  
    bb.1:
      successors: %bb.2
  
      undef %4.sub0:sreg_128 = S_MOV_B32 -1
      %4.sub2:sreg_128 = COPY killed %0
      %5:sreg_128 = COPY killed %4
      %6:sreg_128 = COPY killed %1
      %3:sreg_128 = COPY killed %6
      %2:sreg_128 = COPY killed %5
  
    bb.2:
      S_NOP 0, implicit killed %3
      S_ENDPGM implicit %2
  
  ...


Repository:
  rL LLVM

https://reviews.llvm.org/D49097