[llvm] [TableGen] Add a DenseSet to track WriteRes that are referenced by some ReadAdvance. NFC (PR #124160)

[Min-Yih Hsu via llvm-commits]

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@@ -250,6 +250,9 @@ struct CodeGenProcModel {
   // Map from the ReadType field to the parent ReadAdvance record.
   DenseMap<const Record *, const Record *> ReadAdvanceMap;
 
+  // Set of WriteRes that are referenced by a ReadAdvance.
+  DenseSet<const Record *> ReadOfWriteSet;
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mshockwave wrote:

nit: should we use SmallPtrSet instead?

from programmers' manual: "...DenseSet is a great way to unique small values that are not simple pointers (use [SmallPtrSet](https://llvm.org/docs/ProgrammersManual.html#dss-smallptrset) for pointers)..."

https://github.com/llvm/llvm-project/pull/124160