[llvm] [RegisterCoalescer] Deferring deletion of instructions in `ErasedInstrs` until the end of an iteration (PR #79820)

[Quentin Dian via llvm-commits]

================
@@ -2156,7 +2159,9 @@ bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) {
   // CopyMI has been erased by joinIntervals at this point. Remove it from
   // ErasedInstrs since copyCoalesceWorkList() won't add a successful join back
   // to the work list. This keeps ErasedInstrs from growing needlessly.
-  ErasedInstrs.erase(CopyMI);
+  if (ErasedInstrs.erase(CopyMI))
+    // But we may encounter the instruction again in this iteration.
+    CurrentErasedInstrs.insert(CopyMI);
----------------
DianQK wrote:

>From the debugging results, it looks like `removePartialRedundancy` changes the contents of the work list.

https://github.com/llvm/llvm-project/pull/79820