1 //===- SplitModule.cpp - Split a module into partitions -------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file defines the function llvm::SplitModule, which splits a module 11 // into multiple linkable partitions. It can be used to implement parallel code 12 // generation for link-time optimization. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #include "llvm/Transforms/Utils/SplitModule.h" 17 #include "llvm/ADT/Hashing.h" 18 #include "llvm/IR/Function.h" 19 #include "llvm/IR/GlobalAlias.h" 20 #include "llvm/IR/GlobalObject.h" 21 #include "llvm/IR/GlobalValue.h" 22 #include "llvm/IR/Module.h" 23 #include "llvm/Support/MD5.h" 24 #include "llvm/Support/raw_ostream.h" 25 #include "llvm/Transforms/Utils/Cloning.h" 26 27 using namespace llvm; 28 29 static void externalize(GlobalValue *GV) { 30 if (GV->hasLocalLinkage()) { 31 GV->setLinkage(GlobalValue::ExternalLinkage); 32 GV->setVisibility(GlobalValue::HiddenVisibility); 33 } 34 35 // Unnamed entities must be named consistently between modules. setName will 36 // give a distinct name to each such entity. 37 if (!GV->hasName()) 38 GV->setName("__llvmsplit_unnamed"); 39 } 40 41 // Returns whether GV should be in partition (0-based) I of N. 42 static bool isInPartition(const GlobalValue *GV, unsigned I, unsigned N) { 43 if (auto GA = dyn_cast<GlobalAlias>(GV)) 44 if (const GlobalObject *Base = GA->getBaseObject()) 45 GV = Base; 46 47 StringRef Name; 48 if (const Comdat *C = GV->getComdat()) 49 Name = C->getName(); 50 else 51 Name = GV->getName(); 52 53 // Partition by MD5 hash. We only need a few bits for evenness as the number 54 // of partitions will generally be in the 1-2 figure range; the low 16 bits 55 // are enough. 56 MD5 H; 57 MD5::MD5Result R; 58 H.update(Name); 59 H.final(R); 60 return (R[0] | (R[1] << 8)) % N == I; 61 } 62 63 void llvm::SplitModule( 64 std::unique_ptr<Module> M, unsigned N, 65 std::function<void(std::unique_ptr<Module> MPart)> ModuleCallback) { 66 for (Function &F : *M) 67 externalize(&F); 68 for (GlobalVariable &GV : M->globals()) 69 externalize(&GV); 70 for (GlobalAlias &GA : M->aliases()) 71 externalize(&GA); 72 73 // FIXME: We should be able to reuse M as the last partition instead of 74 // cloning it. 75 for (unsigned I = 0; I != N; ++I) { 76 ValueToValueMapTy VMap; 77 std::unique_ptr<Module> MPart( 78 CloneModule(M.get(), VMap, [=](const GlobalValue *GV) { 79 return isInPartition(GV, I, N); 80 })); 81 if (I != 0) 82 MPart->setModuleInlineAsm(""); 83 ModuleCallback(std::move(MPart)); 84 } 85 } 86
