[clang] [CIR] Add framework for CIR to LLVM IR lowering (PR #124650)

[Nathan Lanza via cfe-commits]

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@@ -0,0 +1,41 @@
+//====- LowerToLLVM.cpp - Lowering from CIR to LLVMIR ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements lowering of CIR operations to LLVMIR.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/CIR/LowerToLLVM.h"
+
+#include "mlir/IR/BuiltinOps.h"
+#include "mlir/Pass/Pass.h"
+#include "mlir/Pass/PassManager.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/TimeProfiler.h"
+
+
+using namespace cir;
+using namespace llvm;
+
+namespace cir {
+namespace direct {
+
+std::unique_ptr<llvm::Module>
+lowerDirectlyFromCIRToLLVMIR(mlir::ModuleOp theModule, LLVMContext &llvmCtx) {
+  llvm::TimeTraceScope scope("lower from CIR to LLVM directly");
+
+  auto ModuleName = theModule.getName();
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lanza wrote:

We need by code style rules for upstream pretty strictly. Almost-never-use-auto is one of them. So expand this out. 

Another is to make sure we're using the right casing throughout. TBH I forget which ruleset we use for this file as we have a partial compromise between MLIR in some places and Clang in others, but clang-tidy should be warning you about incorrect casings within llvm-project while upstreaming ClangIR.

https://github.com/llvm/llvm-project/pull/124650