[clang] [CIR] Emit promise declaration in coroutine (PR #166683)

[Andy Kaylor via cfe-commits]

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@@ -152,6 +152,9 @@ class CIRGenFunction : public CIRGenTypeCache {
   /// global initializers.
   mlir::Operation *curFn = nullptr;
 
+  /// Save Parameter Decl for coroutine.
+  llvm::SmallVector<const ParmVarDecl *, 4> fnArgs;
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andykaylor wrote:

Do we have a good reason for the 4 here?

https://github.com/llvm/llvm-project/pull/166683