[offload][SYCL] Add Module splitting by categories.

llvm/include/llvm/Transforms/Utils/SplitModuleByCategory.h

@@ -0,0 +1,64 @@
+//===-------- SplitModuleByCategory.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 by categories.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORM_UTILS_SPLIT_MODULE_BY_CATEGORY_H
+#define LLVM_TRANSFORM_UTILS_SPLIT_MODULE_BY_CATEGORY_H
+
+#include "llvm/ADT/STLFunctionalExtras.h"
+
+#include <memory>
+#include <optional>
+#include <string>
+
+namespace llvm {
+
+class Module;
+class Function;
+
+/// Splits the given module \p M into parts. Each output part is passed to
+/// \p Callback for further possible processing. Each part corresponds to a
+/// subset of the module that is transitively reachable from some entry point
+/// group. Each entry point group is defined by \p EntryPointCategorizer (EPC)
+/// as follows: 1) If the function is not an entry point, then the Categorizer
+/// returns std::nullopt. Therefore, the function doesn't belong to any group.
+/// However, the function and global objects can still be associated with some
+/// output parts if they are transitively used from some entry points. 2) If the
+/// function belongs to an entry point group, then EPC returns an integer which
+/// is an identifier of the group. If two entry points belong to one group, then
+/// EPC returns the same identifier for both of them.
+///
+/// Let A and B be global objects in the module. The transitive dependency
+/// relation is defined such that: If global object A is used by global object B
+/// in any way (e.g., store, bitcast, phi node, call), then "A" -> "B".
+/// Transitivity is defined such that: If "A" -> "B" and "B" -> "C", then "A" ->
+/// "C". Examples of dependencies:
+/// - Function FA calls function FB
+/// - Function FA uses global variable GA
+/// - Global variable GA references (is initialized with) function FB
+/// - Function FA stores the address of function FB somewhere
+///
+/// The following cases are treated as dependencies between global objects:
+/// 1. Global object A is used by global object B in any way (store,
+///    bitcast, phi node, call, etc.): an "A" -> "B" edge will be added to the
+///    graph;
+/// 2. Function A performs an indirect call of a function with signature S, and
+///    there is a function B with signature S. An "A" -> "B" edge will be added
+///    to the graph;
+///
+/// FIXME: For now, the algorithm assumes no recursion in the input Module. This
+/// will be addressed in the near future.
+void splitModuleTransitiveFromEntryPoints(
+    std::unique_ptr<Module> M,
+    function_ref<std::optional<int>(const Function &F)> EntryPointCategorizer,
+    function_ref<void(std::unique_ptr<Module> Part)> Callback);
+
+} // namespace llvm
+
+#endif // LLVM_TRANSFORM_UTILS_SPLIT_MODULE_BY_CATEGORY_H

llvm/lib/Transforms/Utils/CMakeLists.txt

@@ -82,6 +82,7 @@ add_llvm_component_library(LLVMTransformUtils
   SimplifyLibCalls.cpp
   SizeOpts.cpp
   SplitModule.cpp
+  SplitModuleByCategory.cpp
   StripNonLineTableDebugInfo.cpp
   SymbolRewriter.cpp
   UnifyFunctionExitNodes.cpp

llvm/lib/Transforms/Utils/SplitModuleByCategory.cpp

@@ -0,0 +1,323 @@
+//===-------- SplitModuleByCategory.cpp - split a module by categories ----===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+// See comments in the header.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/SplitModuleByCategory.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+
+#include <map>
+#include <string>
+#include <utility>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "split-module-by-category"
+
+namespace {
+
+// A vector that contains a group of function with the same category.
+using EntryPointSet = SetVector<const Function *>;
+
+/// Represents a group of functions with one category.
+struct EntryPointGroup {
+  int ID;
+  EntryPointSet Functions;
+
+  EntryPointGroup() = default;
+
+  EntryPointGroup(int ID, EntryPointSet &&Functions = EntryPointSet())
+      : ID(ID), Functions(std::move(Functions)) {}
+
+  void clear() { Functions.clear(); }
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  LLVM_DUMP_METHOD void dump() const {
+    constexpr size_t INDENT = 4;
+    dbgs().indent(INDENT) << "ENTRY POINTS"
+                          << " " << ID << " {\n";
+    for (const Function *F : Functions)
+      dbgs().indent(INDENT) << "  " << F->getName() << "\n";
+
+    dbgs().indent(INDENT) << "}\n";
+  }
+#endif
+};
+
+/// Annotates an llvm::Module with information necessary to perform and track
+/// the result of code (llvm::Module instances) splitting:
+/// - entry points group from the module.
+class ModuleDesc {
+  std::unique_ptr<Module> M;
+  EntryPointGroup EntryPoints;
+
+public:
+  ModuleDesc(std::unique_ptr<Module> M,
+             EntryPointGroup &&EntryPoints = EntryPointGroup())
+      : M(std::move(M)), EntryPoints(std::move(EntryPoints)) {
+    assert(this->M && "Module should be non-null");
+  }
+
+  Module &getModule() { return *M; }
+  const Module &getModule() const { return *M; }
+
+  std::unique_ptr<Module> releaseModule() {
+    EntryPoints.clear();
+    return std::move(M);
+  }
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  LLVM_DUMP_METHOD void dump() const {
+    dbgs() << "ModuleDesc[" << M->getName() << "] {\n";
+    EntryPoints.dump();
+    dbgs() << "}\n";
+  }
+#endif
+};
+
+bool isKernel(const Function &F) {
+  return F.getCallingConv() == CallingConv::SPIR_KERNEL ||
+         F.getCallingConv() == CallingConv::AMDGPU_KERNEL ||
+         F.getCallingConv() == CallingConv::PTX_Kernel;
+}
+
+// Represents "dependency" or "use" graph of global objects (functions and
+// global variables) in a module. It is used during code split to
+// understand which global variables and functions (other than entry points)
+// should be included into a split module.
+//
+// Nodes of the graph represent LLVM's GlobalObjects, edges "A" -> "B" represent
+// the fact that if "A" is included into a module, then "B" should be included
+// as well.
+//
+// Examples of dependencies which are represented in this graph:
+// - Function FA calls function FB
+// - Function FA uses global variable GA
+// - Global variable GA references (initialized with) function FB
+// - Function FA stores address of a function FB somewhere
+//
+// The following cases are treated as dependencies between global objects:
+// 1. Global object A is used by a global object B in any way (store,
+//    bitcast, phi node, call, etc.): "A" -> "B" edge will be added to the
+//    graph;
+// 2. function A performs an indirect call of a function with signature S and
+//    there is a function B with signature S. "A" -> "B" edge will be added to
+//    the graph;
+class DependencyGraph {
+public:
+  using GlobalSet = SmallPtrSet<const GlobalValue *, 16>;
+
+  DependencyGraph(const Module &M) {
+    // Group functions by their signature to handle case (2) described above
+    DenseMap<const FunctionType *, DependencyGraph::GlobalSet>
+        FuncTypeToFuncsMap;
+    for (const Function &F : M.functions()) {
+      // Kernels can't be called (either directly or indirectly).
+      if (isKernel(F))
+        continue;
+
+      FuncTypeToFuncsMap[F.getFunctionType()].insert(&F);
+    }
+
+    for (const Function &F : M.functions()) {
+      // case (1), see comment above the class definition
+      for (const Value *U : F.users())
+        addUserToGraphRecursively(cast<const User>(U), &F);
+
+      // case (2), see comment above the class definition
+      for (const Instruction &I : instructions(F)) {
+        const CallBase *CB = dyn_cast<CallBase>(&I);
+        if (!CB || !CB->isIndirectCall()) // Direct calls were handled above
+          continue;
+
+        const FunctionType *Signature = CB->getFunctionType();
+        GlobalSet &PotentialCallees = FuncTypeToFuncsMap[Signature];
+        Graph[&F].insert(PotentialCallees.begin(), PotentialCallees.end());
+      }
+    }
+
+    // And every global variable (but their handling is a bit simpler)
+    for (const GlobalVariable &GV : M.globals())
+      for (const Value *U : GV.users())
+        addUserToGraphRecursively(cast<const User>(U), &GV);
+  }
+
+  iterator_range<GlobalSet::const_iterator>
+  dependencies(const GlobalValue *Val) const {
+    auto It = Graph.find(Val);
+    return (It == Graph.end())
+               ? make_range(EmptySet.begin(), EmptySet.end())
+               : make_range(It->second.begin(), It->second.end());
+  }
+
+private:
+  void addUserToGraphRecursively(const User *Root, const GlobalValue *V) {
+    SmallVector<const User *, 8> WorkList;
+    WorkList.push_back(Root);
+
+    while (!WorkList.empty()) {
+      const User *U = WorkList.pop_back_val();
+      if (const auto *I = dyn_cast<const Instruction>(U)) {
+        const Function *UFunc = I->getFunction();
+        Graph[UFunc].insert(V);
+      } else if (isa<const Constant>(U)) {
+        if (const auto *GV = dyn_cast<const GlobalVariable>(U))
+          Graph[GV].insert(V);
+        // This could be a global variable or some constant expression (like
+        // bitcast or gep). We trace users of this constant further to reach
+        // global objects they are used by and add them to the graph.
+        for (const User *UU : U->users())
+          WorkList.push_back(UU);
+      } else {
+        llvm_unreachable("Unhandled type of function user");
+      }
+    }
+  }
+
+  DenseMap<const GlobalValue *, GlobalSet> Graph;
+  SmallPtrSet<const GlobalValue *, 1> EmptySet;
+};
+
+void collectFunctionsAndGlobalVariablesToExtract(
+    SetVector<const GlobalValue *> &GVs, const Module &M,
+    const EntryPointGroup &ModuleEntryPoints, const DependencyGraph &DG) {
+  // We start with module entry points
+  for (const Function *F : ModuleEntryPoints.Functions)
+    GVs.insert(F);
+
+  // Non-discardable global variables are also include into the initial set
+  for (const GlobalVariable &GV : M.globals())
+    if (!GV.isDiscardableIfUnused())
+      GVs.insert(&GV);
+
+  // GVs has SetVector type. This type inserts a value only if it is not yet
+  // present there. So, recursion is not expected here.
+  size_t Idx = 0;
+  while (Idx < GVs.size()) {
+    const GlobalValue *Obj = GVs[Idx++];
+
+    for (const GlobalValue *Dep : DG.dependencies(Obj)) {
+      if (const auto *Func = dyn_cast<const Function>(Dep)) {
+        if (!Func->isDeclaration())
+          GVs.insert(Func);
+      } else {
+        GVs.insert(Dep); // Global variables are added unconditionally
+      }
+    }
+  }
+}
+
+ModuleDesc extractSubModule(const Module &M,
+                            const SetVector<const GlobalValue *> &GVs,
+                            EntryPointGroup &&ModuleEntryPoints) {
+  ValueToValueMapTy VMap;
+  // Clone definitions only for needed globals. Others will be added as
+  // declarations and removed later.
+  std::unique_ptr<Module> SubM = CloneModule(
+      M, VMap, [&](const GlobalValue *GV) { return GVs.contains(GV); });
+  // Replace entry points with cloned ones.
+  EntryPointSet NewEPs;
+  const EntryPointSet &EPs = ModuleEntryPoints.Functions;
+  llvm::for_each(
+      EPs, [&](const Function *F) { NewEPs.insert(cast<Function>(VMap[F])); });
+  ModuleEntryPoints.Functions = std::move(NewEPs);
+  return ModuleDesc{std::move(SubM), std::move(ModuleEntryPoints)};
+}
+
+// The function produces a copy of input LLVM IR module M with only those
+// functions and globals that can be called from entry points that are specified
+// in ModuleEntryPoints vector, in addition to the entry point functions.
+ModuleDesc extractCallGraph(const Module &M,
+                            EntryPointGroup &&ModuleEntryPoints,
+                            const DependencyGraph &DG) {
+  SetVector<const GlobalValue *> GVs;
+  collectFunctionsAndGlobalVariablesToExtract(GVs, M, ModuleEntryPoints, DG);
+
+  ModuleDesc SplitM = extractSubModule(M, GVs, std::move(ModuleEntryPoints));
+  LLVM_DEBUG(SplitM.dump());
+  return SplitM;
+}
+
+using EntryPointGroupVec = SmallVector<EntryPointGroup>;
+
+/// Module Splitter.
+/// It gets a module and a collection of entry points groups.
+/// Each group specifies subset entry points from input module that should be
+/// included in a split module.
+class ModuleSplitter {
+private:
+  std::unique_ptr<Module> M;
+  EntryPointGroupVec Groups;
+  DependencyGraph DG;
+
+private:
+  EntryPointGroup drawEntryPointGroup() {
+    assert(Groups.size() > 0 && "Reached end of entry point groups list.");
+    EntryPointGroup Group = std::move(Groups.back());
+    Groups.pop_back();
+    return Group;
+  }
+
+public:
+  ModuleSplitter(std::unique_ptr<Module> Module, EntryPointGroupVec &&GroupVec)
+      : M(std::move(Module)), Groups(std::move(GroupVec)), DG(*M) {
+    assert(!Groups.empty() && "Entry points groups collection is empty!");
+  }
+
+  /// Gets next subsequence of entry points in an input module and provides
+  /// split submodule containing these entry points and their dependencies.
+  ModuleDesc getNextSplit() {
+    return extractCallGraph(*M, drawEntryPointGroup(), DG);
+  }
+
+  /// Check that there are still submodules to split.
+  bool hasMoreSplits() const { return Groups.size() > 0; }
+};
+
+EntryPointGroupVec selectEntryPointGroups(
+    const Module &M, function_ref<std::optional<int>(const Function &F)> EPC) {
+  // std::map is used here to ensure stable ordering of entry point groups,
+  // which is based on their contents, this greatly helps LIT tests
+  // Note: EPC is allowed to return big identifiers. Therefore, we use
+  // std::map + SmallVector approach here.
+  std::map<int, EntryPointSet> EntryPointsMap;
+
+  for (const auto &F : M.functions())
+    if (std::optional<int> Category = EPC(F); Category)
+      EntryPointsMap[*Category].insert(&F);
+
+  EntryPointGroupVec Groups;
+  Groups.reserve(EntryPointsMap.size());
+  for (auto &[Key, EntryPoints] : EntryPointsMap)
+    Groups.emplace_back(Key, std::move(EntryPoints));
+
+  return Groups;
+}
+
+} // namespace
+
+void llvm::splitModuleTransitiveFromEntryPoints(
+    std::unique_ptr<Module> M,
+    function_ref<std::optional<int>(const Function &F)> EntryPointCategorizer,
+    function_ref<void(std::unique_ptr<Module> Part)> Callback) {
+  EntryPointGroupVec Groups = selectEntryPointGroups(*M, EntryPointCategorizer);
+  ModuleSplitter Splitter(std::move(M), std::move(Groups));
+  while (Splitter.hasMoreSplits()) {
+    ModuleDesc MD = Splitter.getNextSplit();
+    Callback(std::move(MD.releaseModule()));
+  }
+}