[lld] [LLD][AArch64] Detach Landing Pad creation from Thunk creation (PR #116402)

[Fangrui Song via llvm-commits]

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@@ -2293,6 +2293,31 @@ bool ThunkCreator::normalizeExistingThunk(Relocation &rel, uint64_t src) {
   return false;
 }
 
+// When indirect branches are restricted, such as AArch64 BTI Thunks may need
+// to target a linker generated landing pad instead of the target. This needs
+// to be done once per pass as the need for a BTI thunk is dependent whether
+// a thunk is short or long. We iterate over all the thunks to make sure we
+// catch thunks that have been created but are no longer live. Non-live thunks
+// are not reachable via normalizeExistingThunk() but are still written.
+bool ThunkCreator::addSyntheticLandingPads() {
+  bool addressesChanged = false;
+  for (Thunk *t : allThunks) {
+    if (t->needsSyntheticLandingPad()) {
+      Thunk *lpt;
+      bool isNew;
+      auto &dr = cast<Defined>(t->destination);
+      std::tie(lpt, isNew) = getSyntheticLandingPad(dr, t->addend);
+      if (isNew) {
+        addressesChanged = true;
+        ThunkSection *ts = getISThunkSec(cast<InputSection>(dr.section));
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MaskRay wrote:

The used-once variable can be avoided

https://github.com/llvm/llvm-project/pull/116402