[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
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rovka wrote:

Nit: This comment should be in the header.

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