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
externalize(GlobalValue * GV)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.
isInPartition(const GlobalValue * GV,unsigned I,unsigned 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
SplitModule(std::unique_ptr<Module> M,unsigned N,std::function<void (std::unique_ptr<Module> MPart)> ModuleCallback)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