[llvm] [AMDGPU][Scheduler] Fix non-monotonic SlotIndex after schedule revert (PR #192039)

[Lucas Ramirez via llvm-commits]

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@@ -0,0 +1,643 @@
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx908 -run-pass=machine-scheduler -o /dev/null %s
+# Verify that modifyRegionSchedule does not leave non-monotonic SlotIndexes
+# when reverting a schedule. This used to crash with "register isn't live"
+# in GCNDownwardRPTracker::advanceBeforeNext().
+---
+name:            test_revert_slot_monotonicity
+tracksRegLiveness: true
+registers:
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lucas-rami wrote:

The list of registers should be removeable too.

https://github.com/llvm/llvm-project/pull/192039