[llvm] [CodeGen] Refactor and document ThunkInserter (PR #97468)

[Kristof Beyls via llvm-commits]

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@@ -95,19 +165,14 @@ bool ThunkInserter<Derived, InsertedThunksTy>::run(MachineModuleInfo &MMI,
                                                    MachineFunction &MF) {
   // If MF is not a thunk, check to see if we need to insert a thunk.
   if (!MF.getName().starts_with(getDerived().getThunkPrefix())) {
-    // Only add a thunk if one of the functions has the corresponding feature
-    // enabled in its subtarget, and doesn't enable external thunks. The target
-    // can use InsertedThunks to detect whether relevant thunks have already
-    // been inserted.
-    // FIXME: Conditionalize on indirect calls so we don't emit a thunk when
-    // nothing will end up calling it.
-    // FIXME: It's a little silly to look at every function just to enumerate
-    // the subtargets, but eventually we'll want to look at them for indirect
-    // calls, so maybe this is OK.
-    if (!getDerived().mayUseThunk(MF, InsertedThunks))
+    // Only add thunks if one of the functions may use them.
+    if (!getDerived().mayUseThunk(MF))
       return false;
 
-    InsertedThunks |= getDerived().insertThunks(MMI, MF);
+    // The target can use InsertedThunks to detect whether relevant thunks
+    // have already been inserted.
+    // FIXME: Make insertThunks return if MF was modified.
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kbeyls wrote:

I don't understand this FIXME well. Could you explain in a bit more detail what this FIXME is about?

https://github.com/llvm/llvm-project/pull/97468