[lld] [lld-macho][arm64] Enhance safe ICF with thunk-based deduplication (PR #106573)

[via llvm-commits]

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@@ -251,6 +252,63 @@ void ICF::forEachClassRange(size_t begin, size_t end,
   }
 }
 
+// Given a range of identical icfInputs's, replace address significant functions
+// with a thunk that is just a direct branch to the first function in the
+// series. This way we end up we keep only one main body of the function but we
+// still retain address uniqueness of rellevant functions by having them be a
+// direct branch thunk rather than contain a full copy of the actual function
+// body.
+void ICF::applySafeThunksToRange(size_t begin, size_t end) {
+  // If we need to create a unique ICF thunk, use the first section as the
+  // section that all thunks will branch to.
+  ConcatInputSection *masterIsec = icfInputs[begin];
+  uint32_t thunkSize = target->getICFSafeThunkSize();
+  static std::mutex thunkInsertionMutex;
+
+  uint32_t keepUniqueCount = masterIsec->keepUnique ? 1 : 0;
+  for (size_t i = begin + 1; i < end; ++i) {
+    ConcatInputSection *isec = icfInputs[i];
+    if (isec->keepUnique)
+      ++keepUniqueCount;
+
+    // We create thunks for the 2nd, 3rd, ... keepUnique sections. The first
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alx32 wrote:

Great catch - fixed in latest revision. 

https://github.com/llvm/llvm-project/pull/106573