[llvm] [AMDGPU] Support bottom-up postRA scheduing. (PR #135295)

[Matt Arsenault via llvm-commits]

================
@@ -69,6 +69,10 @@ class GCNHazardRecognizer final : public ScheduleHazardRecognizer {
   // Advance over a MachineInstr bundle. Look for hazards in the bundled
   // instructions.
   void processBundle();
+  // Recede over a MachineInstr bundle. Adds bundled instructions to the
+  // EmittedInstrs queue in bottom-up scheduling mode.
+  // TODO: Hazard detection is not yet implemented.
----------------
arsenm wrote:

I don't think this is something you can just leave for later. It's a problem if the hazard recognizer doesn't actually deal with the hazards 

https://github.com/llvm/llvm-project/pull/135295