[lld] [LLD][COFF] Detect weak reference cycles. (PR #104463)

[Fangrui Song via llvm-commits]

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@@ -126,9 +127,14 @@ DefinedImportThunk::DefinedImportThunk(COFFLinkerContext &ctx, StringRef name,
 
 Defined *Undefined::getWeakAlias() {
   // A weak alias may be a weak alias to another symbol, so check recursively.
-  for (Symbol *a = weakAlias; a; a = cast<Undefined>(a)->weakAlias)
+  SmallSet<Symbol *, 4> weakChain;
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MaskRay wrote:

DenseMap, which I believe has the least code size increase.

SmallPtrSet would be better than SmallSet but its small container case compiles to additional code than DenseMap.

https://github.com/llvm/llvm-project/pull/104463