[mlir][llvm] Add isVarArg flag to lookupOrCreateFn.

[ingomueller-net]

Summary

The function is a helper for looking up a function by name or creating
it if it doesn't exist. The arguments allow to specify the signature of
the function, if it needs to be created, but do not expose the varArg
parameter of LLVMFunctionType. This patch exposes adds an optional
parameter with a default value of false such that existing usage
continue to work as before.

mlir/include/mlir/Dialect/LLVMIR/FunctionCallUtils.h

 LLVM::LLVMFuncOp lookupOrCreateGenericFreeFn(ModuleOp moduleOp,
                                              bool opaquePointers);
 LLVM::LLVMFuncOp lookupOrCreateMemRefCopyFn(ModuleOp moduleOp, Type indexType,
                                             Type unrankedDescriptorType);
 
 /// Create a FuncOp with signature `resultType`(`paramTypes`)` and name `name`.
 LLVM::LLVMFuncOp lookupOrCreateFn(ModuleOp moduleOp, StringRef name,
                                   ArrayRef<Type> paramTypes = {},
-                                  Type resultType = {});
+                                  Type resultType = {}, bool isVarArg = false);
 
 } // namespace LLVM
 } // namespace mlir
 
 #endif // MLIR_DIALECT_LLVMIR_FUNCTIONCALLUTILS_H_

mlir/lib/Dialect/LLVMIR/IR/FunctionCallUtils.cpp

 static constexpr llvm::StringRef kGenericAlignedAlloc =
     "_mlir_memref_to_llvm_aligned_alloc";
 static constexpr llvm::StringRef kGenericFree = "_mlir_memref_to_llvm_free";
 static constexpr llvm::StringRef kMemRefCopy = "memrefCopy";
 
 /// Generic print function lookupOrCreate helper.
 LLVM::LLVMFuncOp mlir::LLVM::lookupOrCreateFn(ModuleOp moduleOp, StringRef name,
                                               ArrayRef<Type> paramTypes,
-                                              Type resultType) {
+                                              Type resultType, bool isVarArg) {
   auto func = moduleOp.lookupSymbol<LLVM::LLVMFuncOp>(name);
   if (func)
     return func;
   OpBuilder b(moduleOp.getBodyRegion());
   return b.create<LLVM::LLVMFuncOp>(
       moduleOp->getLoc(), name,
-      LLVM::LLVMFunctionType::get(resultType, paramTypes));
+      LLVM::LLVMFunctionType::get(resultType, paramTypes, isVarArg));
 }
 
 LLVM::LLVMFuncOp mlir::LLVM::lookupOrCreatePrintI64Fn(ModuleOp moduleOp) {
   return lookupOrCreateFn(moduleOp, kPrintI64,
                           IntegerType::get(moduleOp->getContext(), 64),
                           LLVM::LLVMVoidType::get(moduleOp->getContext()));
 }