[llvm] [MachineModuleInfo] add a grouping mechanism to defer deletion MF (PR #214525)

[Diana Picus via llvm-commits]

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@@ -103,10 +103,31 @@ MachineFunction &MachineModuleInfo::getOrCreateMachineFunction(Function &F) {
   return *MF;
 }
 
+// When a function is not grouped with any other function, we can delete its
+// MachineFunction immediately. When a function is grouped with other functions,
+// we can only delete its MachineFunction when all functions in the same group
+// have been finalized.
 void MachineModuleInfo::deleteMachineFunctionFor(Function &F) {
-  MachineFunctions.erase(&F);
+  FinalizedMFs.insert(&F);
   LastRequest = nullptr;
   LastResult = nullptr;
+  auto Leader = MFDeletionGrouping.findLeader(&F);
+  if (Leader == MFDeletionGrouping.member_end()) {
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rovka wrote:

Can you just do an `|| std::all_of(MFDeletionGrouping.members(Leader), lambda to check FinalizedMFs.count)` here?

https://github.com/llvm/llvm-project/pull/214525