[clang] [Clang] speed up -Wassign-enum via enumerator caching (PR #176560)

[Erich Keane via cfe-commits]

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@@ -3544,6 +3544,10 @@ class Sema final : public SemaBase {
   /// attribute.
   mutable llvm::DenseMap<const EnumDecl *, llvm::APInt> FlagBitsCache;
 
+  /// A cache of enumerator values for enums checked by -Wassign-enum.
+  llvm::DenseMap<const EnumDecl *, llvm::SmallVector<llvm::APSInt, 64>>
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erichkeane wrote:

IF you omit the size, SmallVector makes  'best guess', which is usually 4.  Probably worth just leaving it blank unless we have a REALLY good reason.  

https://github.com/llvm/llvm-project/pull/176560