[offload][SYCL] Add SYCL Module splitting.

This patch adds SYCL Module splitting - the necessary step in the SYCL
compilation pipeline. Only 2 splitting modes are being added in this
patch: by kernel and by source.

The previous attempt was at llvm#119713. In this patch there is no
dependency in `TransformUtils` on "IPO" and on "Printing Passes". In
this patch a module splitting is self-contained and it doesn't introduce
linking issues.

Author: maksimsab

llvm/include/llvm/Transforms/Utils/SYCLSplitModule.h

@@ -0,0 +1,64 @@
+//===-------- SYCLSplitModule.h - module split ------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// Functionality to split a module into callgraphs. A callgraph here is a set
+// of entry points with all functions reachable from them via a call. The result
+// of the split is new modules containing corresponding callgraph.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_SYCLSPLITMODULE_H
+#define LLVM_TRANSFORMS_UTILS_SYCLSPLITMODULE_H
+
+#include "llvm/ADT/STLFunctionalExtras.h"
+#include "llvm/ADT/StringRef.h"
+
+#include <memory>
+#include <optional>
+#include <string>
+
+namespace llvm {
+
+class Module;
+
+enum class IRSplitMode {
+  IRSM_PER_TU,     // one module per translation unit
+  IRSM_PER_KERNEL, // one module per kernel
+  IRSM_NONE        // no splitting
+};
+
+/// \returns IRSplitMode value if \p S is recognized. Otherwise, std::nullopt is
+/// returned.
+std::optional<IRSplitMode> convertStringToSplitMode(StringRef S);
+
+/// The structure represents a split LLVM Module accompanied by additional
+/// information. Split Modules are being stored at disk due to the high RAM
+/// consumption during the whole splitting process.
+struct ModuleAndSYCLMetadata {
+  std::string ModuleFilePath;
+  std::string Symbols;
+
+  ModuleAndSYCLMetadata() = default;
+  ModuleAndSYCLMetadata(const ModuleAndSYCLMetadata &) = default;
+  ModuleAndSYCLMetadata &operator=(const ModuleAndSYCLMetadata &) = default;
+  ModuleAndSYCLMetadata(ModuleAndSYCLMetadata &&) = default;
+  ModuleAndSYCLMetadata &operator=(ModuleAndSYCLMetadata &&) = default;
+
+  ModuleAndSYCLMetadata(std::string_view File, std::string Symbols)
+      : ModuleFilePath(File), Symbols(std::move(Symbols)) {}
+};
+
+using PostSYCLSplitCallbackType =
+    function_ref<void(std::unique_ptr<Module> Part, std::string Symbols)>;
+
+/// Splits the given module \p M according to the given \p Settings.
+/// Every split image is being passed to \p Callback.
+void SYCLSplitModule(std::unique_ptr<Module> M, IRSplitMode Mode,
+                     PostSYCLSplitCallbackType Callback);
+
+} // namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_SYCLSPLITMODULE_H

llvm/include/llvm/Transforms/Utils/SYCLUtils.h

@@ -0,0 +1,26 @@
+//===------------ SYCLUtils.h - SYCL utility functions --------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// Utility functions for SYCL.
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_TRANSFORMS_UTILS_SYCLUTILS_H
+#define LLVM_TRANSFORMS_UTILS_SYCLUTILS_H
+
+#include <llvm/ADT/SmallString.h>
+#include <llvm/ADT/SmallVector.h>
+
+namespace llvm {
+
+class raw_ostream;
+
+using SYCLStringTable = SmallVector<SmallVector<SmallString<64>>>;
+
+void writeSYCLStringTable(const SYCLStringTable &Table, raw_ostream &OS);
+
+} // namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_SYCLUTILS_H

llvm/lib/Transforms/Utils/CMakeLists.txt

@@ -83,6 +83,8 @@ add_llvm_component_library(LLVMTransformUtils
   SizeOpts.cpp
   SplitModule.cpp
   StripNonLineTableDebugInfo.cpp
+  SYCLSplitModule.cpp
+  SYCLUtils.cpp
   SymbolRewriter.cpp
   UnifyFunctionExitNodes.cpp
   UnifyLoopExits.cpp