[lld] [lld][MachO] Tail merge strings (PR #161262)

[Ellis Hoag via llvm-commits]

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@@ -1776,8 +1817,24 @@ void DeduplicatedCStringSection::finalizeContents() {
     // only need to assign the offset.
     piece.outSecOff = it->second;
   }
-  for (CStringInputSection *isec : inputs)
+  for (CStringInputSection *isec : inputs) {
+    for (const auto &[i, piece] : llvm::enumerate(isec->pieces)) {
+      if (!piece.live)
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ellishg wrote:

That's true. If the string is in `tailMergeMap` then it will be live. However, we can skip the lookup if the string is dead, so this is more for performance than correctness.

https://github.com/llvm/llvm-project/pull/161262