feat(codegen): pass C-struct records by value as variadic arguments

A variadic EXTERN call is now arranged by clang per call, from the fixed
parameter count and the promoted argument types. C-struct records pass
unchanged in variadic positions, as C11 6.5.2.2p6-7 and 7.16.1.1p2
allow; a record that is not a C struct names the offending field.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2 files changed, 10 insertions, 4 deletions

diff --git a/include/cps/CodeGen.h b/include/cps/CodeGen.h
index 8f6a57b..b31cd3d 100644
--- a/include/cps/CodeGen.h
+++ b/include/cps/CodeGen.h
@@ -217,13 +217,17 @@ class CodeGen {
     llvm::Value *emitOperatorCall(const FuncSig &Signature, ExprAST *Left, ExprAST *Right = nullptr);
     llvm::Value *emitOperatorValues(const FuncSig &Signature, llvm::Value *Left,
                                      const TypeInfo *LeftType, llvm::Value *Right);
-    llvm::Value *emitVariadicArgument(ExprAST *Expr, const std::string &Callee, size_t Position);
+    llvm::Value *emitVariadicArgument(ExprAST *Expr, const std::string &Callee, size_t Position,
+                                      const TypeInfo *&Promoted);
+    // Variadic, if given, receives the promoted type of each variadic argument.
     bool marshalCallArgs(const FuncSig &Signature,
                          const std::vector<std::unique_ptr<ExprAST>> &ArgExprs,
                          int Line,
-                         std::vector<llvm::Value*> &Out);
+                         std::vector<llvm::Value*> &Out,
+                         std::vector<const TypeInfo *> *Variadic = nullptr);
     bool marshalCallArgs(const FuncSig &Signature, const std::vector<ExprAST*> &ArgExprs,
-                         int Line, std::vector<llvm::Value*> &Out);
+                         int Line, std::vector<llvm::Value*> &Out,
+                         std::vector<const TypeInfo *> *Variadic = nullptr);
     llvm::Value *symbolAddress(const SymbolInfo &Info);
     void emitAssignment(const LValueInfo &Target, ExprAST *Expr,
                         const SymbolInfo *Symbol = nullptr);
diff --git a/include/cps/FunctionGen.h b/include/cps/FunctionGen.h
index 8b63d67..6c5c7c0 100644
--- a/include/cps/FunctionGen.h
+++ b/include/cps/FunctionGen.h
@@ -122,7 +122,9 @@ public:
 
     llvm::Function *emitFunctionDef(FunctionDefAST *FuncAST, const std::function<void(StmtAST*)> &StmtEmitter, unsigned ScopeID);
 
-    llvm::Value *emitCall(const FuncSig &Sig, const std::vector<llvm::Value*> &Args);
+    // Variadic holds the promoted types of an EXTERN call's variadic arguments.
+    llvm::Value *emitCall(const FuncSig &Sig, const std::vector<llvm::Value*> &Args,
+                          const std::vector<const TypeInfo *> &Variadic = {});
 
     void emitReturn(llvm::Value *RetVal);
 };