Codegen: Given a carbon file prints the assembly to the stdout (#2944)

Co-authored-by: Farzana Ahmed Siddique <fasiddique@google.com>

toolchain/codegen/codegen.cpp

@@ -0,0 +1,71 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "toolchain/codegen/codegen.h"
+
+#include <cstdio>
+
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetOptions.h"
+#include "llvm/TargetParser/Host.h"
+
+namespace Carbon {
+
+auto PrintAssemblyFromModule(llvm::Module& module,
+                             llvm::StringRef target_triple,
+                             llvm::raw_pwrite_stream& error_stream,
+                             llvm::raw_pwrite_stream& output_stream) -> bool {
+  // Initialize the target registry etc.
+  llvm::InitializeAllTargetInfos();
+  llvm::InitializeAllTargets();
+  llvm::InitializeAllTargetMCs();
+  llvm::InitializeAllAsmParsers();
+  llvm::InitializeAllAsmPrinters();
+
+  std::string error;
+  llvm::StringRef triple = target_triple;
+  std::string host_triple;
+  if (target_triple.empty()) {
+    host_triple = llvm::sys::getDefaultTargetTriple();
+    triple = host_triple;
+  }
+  const auto* target = llvm::TargetRegistry::lookupTarget(triple, error);
+
+  if (!target) {
+    error_stream << "ERROR: " << error << "\n";
+    return false;
+  }
+
+  constexpr llvm::StringLiteral CPU = "generic";
+  constexpr llvm::StringLiteral Features = "";
+
+  llvm::TargetOptions target_opts;
+  std::optional<llvm::Reloc::Model> reloc_model;
+  auto* target_machine = target->createTargetMachine(
+      target_triple, CPU, Features, target_opts, reloc_model);
+  module.setDataLayout(target_machine->createDataLayout());
+  module.setTargetTriple(target_triple);
+
+  // Using the legacy PM to generate the assembly since the new PM
+  // does not work with this yet.
+  // TODO: make the new PM work with the codegen pipeline.
+
+  llvm::legacy::PassManager pass;
+  auto file_type = llvm::CGFT_AssemblyFile;
+
+  if (target_machine->addPassesToEmitFile(pass, output_stream, nullptr,
+                                          file_type)) {
+    error_stream << "Nothing to write to object file\n";
+    return false;
+  }
+
+  pass.run(module);
+  delete target_machine;
+  return true;
+}
+}  // namespace Carbon