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264 lines
9.1 KiB
264 lines
9.1 KiB
//===- SplitModule.cpp - Split a module into partitions -------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the function llvm::SplitModule, which splits a module
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// into multiple linkable partitions. It can be used to implement parallel code
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// generation for link-time optimization.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "split-module"
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#include "llvm/Transforms/Utils/SplitModule.h"
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#include "llvm/ADT/EquivalenceClasses.h"
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#include "llvm/ADT/Hashing.h"
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#include "llvm/ADT/MapVector.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalAlias.h"
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#include "llvm/IR/GlobalObject.h"
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#include "llvm/IR/GlobalValue.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/MD5.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include <queue>
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using namespace llvm;
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namespace {
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typedef EquivalenceClasses<const GlobalValue *> ClusterMapType;
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typedef DenseMap<const Comdat *, const GlobalValue *> ComdatMembersType;
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typedef DenseMap<const GlobalValue *, unsigned> ClusterIDMapType;
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}
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static void addNonConstUser(ClusterMapType &GVtoClusterMap,
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const GlobalValue *GV, const User *U) {
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assert((!isa<Constant>(U) || isa<GlobalValue>(U)) && "Bad user");
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if (const Instruction *I = dyn_cast<Instruction>(U)) {
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const GlobalValue *F = I->getParent()->getParent();
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GVtoClusterMap.unionSets(GV, F);
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} else if (isa<GlobalIndirectSymbol>(U) || isa<Function>(U) ||
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isa<GlobalVariable>(U)) {
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GVtoClusterMap.unionSets(GV, cast<GlobalValue>(U));
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} else {
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llvm_unreachable("Underimplemented use case");
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}
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}
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// Adds all GlobalValue users of V to the same cluster as GV.
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static void addAllGlobalValueUsers(ClusterMapType &GVtoClusterMap,
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const GlobalValue *GV, const Value *V) {
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for (auto *U : V->users()) {
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SmallVector<const User *, 4> Worklist;
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Worklist.push_back(U);
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while (!Worklist.empty()) {
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const User *UU = Worklist.pop_back_val();
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// For each constant that is not a GV (a pure const) recurse.
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if (isa<Constant>(UU) && !isa<GlobalValue>(UU)) {
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Worklist.append(UU->user_begin(), UU->user_end());
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continue;
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}
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addNonConstUser(GVtoClusterMap, GV, UU);
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}
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}
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}
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// Find partitions for module in the way that no locals need to be
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// globalized.
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// Try to balance pack those partitions into N files since this roughly equals
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// thread balancing for the backend codegen step.
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static void findPartitions(Module *M, ClusterIDMapType &ClusterIDMap,
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unsigned N) {
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// At this point module should have the proper mix of globals and locals.
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// As we attempt to partition this module, we must not change any
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// locals to globals.
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DEBUG(dbgs() << "Partition module with (" << M->size() << ")functions\n");
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ClusterMapType GVtoClusterMap;
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ComdatMembersType ComdatMembers;
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auto recordGVSet = [&GVtoClusterMap, &ComdatMembers](GlobalValue &GV) {
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if (GV.isDeclaration())
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return;
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if (!GV.hasName())
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GV.setName("__llvmsplit_unnamed");
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// Comdat groups must not be partitioned. For comdat groups that contain
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// locals, record all their members here so we can keep them together.
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// Comdat groups that only contain external globals are already handled by
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// the MD5-based partitioning.
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if (const Comdat *C = GV.getComdat()) {
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auto &Member = ComdatMembers[C];
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if (Member)
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GVtoClusterMap.unionSets(Member, &GV);
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else
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Member = &GV;
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}
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// For aliases we should not separate them from their aliasees regardless
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// of linkage.
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if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(&GV)) {
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if (const GlobalObject *Base = GIS->getBaseObject())
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GVtoClusterMap.unionSets(&GV, Base);
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}
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if (const Function *F = dyn_cast<Function>(&GV)) {
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for (const BasicBlock &BB : *F) {
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BlockAddress *BA = BlockAddress::lookup(&BB);
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if (!BA || !BA->isConstantUsed())
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continue;
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addAllGlobalValueUsers(GVtoClusterMap, F, BA);
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}
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}
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if (GV.hasLocalLinkage())
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addAllGlobalValueUsers(GVtoClusterMap, &GV, &GV);
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};
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std::for_each(M->begin(), M->end(), recordGVSet);
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std::for_each(M->global_begin(), M->global_end(), recordGVSet);
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std::for_each(M->alias_begin(), M->alias_end(), recordGVSet);
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// Assigned all GVs to merged clusters while balancing number of objects in
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// each.
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auto CompareClusters = [](const std::pair<unsigned, unsigned> &a,
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const std::pair<unsigned, unsigned> &b) {
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if (a.second || b.second)
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return a.second > b.second;
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else
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return a.first > b.first;
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};
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std::priority_queue<std::pair<unsigned, unsigned>,
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std::vector<std::pair<unsigned, unsigned>>,
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decltype(CompareClusters)>
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BalancinQueue(CompareClusters);
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// Pre-populate priority queue with N slot blanks.
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for (unsigned i = 0; i < N; ++i)
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BalancinQueue.push(std::make_pair(i, 0));
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typedef std::pair<unsigned, ClusterMapType::iterator> SortType;
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SmallVector<SortType, 64> Sets;
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SmallPtrSet<const GlobalValue *, 32> Visited;
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// To guarantee determinism, we have to sort SCC according to size.
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// When size is the same, use leader's name.
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for (ClusterMapType::iterator I = GVtoClusterMap.begin(),
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E = GVtoClusterMap.end(); I != E; ++I)
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if (I->isLeader())
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Sets.push_back(
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std::make_pair(std::distance(GVtoClusterMap.member_begin(I),
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GVtoClusterMap.member_end()), I));
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std::sort(Sets.begin(), Sets.end(), [](const SortType &a, const SortType &b) {
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if (a.first == b.first)
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return a.second->getData()->getName() > b.second->getData()->getName();
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else
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return a.first > b.first;
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});
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for (auto &I : Sets) {
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unsigned CurrentClusterID = BalancinQueue.top().first;
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unsigned CurrentClusterSize = BalancinQueue.top().second;
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BalancinQueue.pop();
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DEBUG(dbgs() << "Root[" << CurrentClusterID << "] cluster_size(" << I.first
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<< ") ----> " << I.second->getData()->getName() << "\n");
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for (ClusterMapType::member_iterator MI =
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GVtoClusterMap.findLeader(I.second);
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MI != GVtoClusterMap.member_end(); ++MI) {
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if (!Visited.insert(*MI).second)
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continue;
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DEBUG(dbgs() << "----> " << (*MI)->getName()
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<< ((*MI)->hasLocalLinkage() ? " l " : " e ") << "\n");
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Visited.insert(*MI);
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ClusterIDMap[*MI] = CurrentClusterID;
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CurrentClusterSize++;
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}
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// Add this set size to the number of entries in this cluster.
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BalancinQueue.push(std::make_pair(CurrentClusterID, CurrentClusterSize));
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}
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}
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static void externalize(GlobalValue *GV) {
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if (GV->hasLocalLinkage()) {
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GV->setLinkage(GlobalValue::ExternalLinkage);
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GV->setVisibility(GlobalValue::HiddenVisibility);
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}
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// Unnamed entities must be named consistently between modules. setName will
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// give a distinct name to each such entity.
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if (!GV->hasName())
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GV->setName("__llvmsplit_unnamed");
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}
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// Returns whether GV should be in partition (0-based) I of N.
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static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) {
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if (auto *GIS = dyn_cast<GlobalIndirectSymbol>(GV))
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if (const GlobalObject *Base = GIS->getBaseObject())
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GV = Base;
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StringRef Name;
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if (const Comdat *C = GV->getComdat())
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Name = C->getName();
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else
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Name = GV->getName();
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// Partition by MD5 hash. We only need a few bits for evenness as the number
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// of partitions will generally be in the 1-2 figure range; the low 16 bits
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// are enough.
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MD5 H;
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MD5::MD5Result R;
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H.update(Name);
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H.final(R);
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return (R[0] | (R[1] << 8)) % N == I;
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}
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void llvm::SplitModule(
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std::unique_ptr<Module> M, unsigned N,
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function_ref<void(std::unique_ptr<Module> MPart)> ModuleCallback,
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bool PreserveLocals) {
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if (!PreserveLocals) {
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for (Function &F : *M)
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externalize(&F);
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for (GlobalVariable &GV : M->globals())
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externalize(&GV);
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for (GlobalAlias &GA : M->aliases())
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externalize(&GA);
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for (GlobalIFunc &GIF : M->ifuncs())
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externalize(&GIF);
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}
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// This performs splitting without a need for externalization, which might not
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// always be possible.
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ClusterIDMapType ClusterIDMap;
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findPartitions(M.get(), ClusterIDMap, N);
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// FIXME: We should be able to reuse M as the last partition instead of
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// cloning it.
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for (unsigned I = 0; I < N; ++I) {
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ValueToValueMapTy VMap;
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std::unique_ptr<Module> MPart(
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CloneModule(M.get(), VMap, [&](const GlobalValue *GV) {
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if (ClusterIDMap.count(GV))
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return (ClusterIDMap[GV] == I);
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else
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return isInPartition(GV, I, N);
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}));
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if (I != 0)
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MPart->setModuleInlineAsm("");
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ModuleCallback(std::move(MPart));
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}
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}
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