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

[Aaron Ballman 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 MOp, LLVMContext &LLVMCtx) {
+  llvm::TimeTraceScope scope("lower from CIR to LLVM directly");
+
+  std::optional<StringRef> ModuleName = MOp.getName();
+  auto M = std::make_unique<llvm::Module>(
+      ModuleName ? *ModuleName : "CIRToLLVMModule", LLVMCtx);
+
+  if (!M)
+    report_fatal_error("Lowering from LLVMIR dialect to llvm IR failed!");
----------------
AaronBallman wrote:

"It depends" (sorry for the total non-answer, lol).

If the reason for the failure is because of user error, then we would want to thread in a DiagnosticsEngine so we can report diagnostics the usual way.

If the reason for the failure is because the CIR developer is holding things wrong, then we probably would want an assertion closer to the actual issue, and then silently return null here.

If the reason for the failure leads to "there's no way to recover from this, everything is in a horrible state", then report_fatal_error is more reasonable.

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