1 //===- PartialInlining.cpp - Inline parts of functions --------------------===//
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 pass performs partial inlining, typically by inlining an if statement
11 // that surrounds the body of the function.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "llvm/Transforms/IPO/PartialInlining.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/IR/CFG.h"
18 #include "llvm/IR/Dominators.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/Module.h"
21 #include "llvm/Pass.h"
22 #include "llvm/Transforms/IPO.h"
23 #include "llvm/Transforms/Utils/Cloning.h"
24 #include "llvm/Transforms/Utils/CodeExtractor.h"
25 using namespace llvm;
26
27 #define DEBUG_TYPE "partialinlining"
28
29 STATISTIC(NumPartialInlined, "Number of functions partially inlined");
30
31 namespace {
32 struct PartialInlinerLegacyPass : public ModulePass {
33 static char ID; // Pass identification, replacement for typeid
PartialInlinerLegacyPass__anone84ee5620111::PartialInlinerLegacyPass34 PartialInlinerLegacyPass() : ModulePass(ID) {
35 initializePartialInlinerLegacyPassPass(*PassRegistry::getPassRegistry());
36 }
37
runOnModule__anone84ee5620111::PartialInlinerLegacyPass38 bool runOnModule(Module &M) override {
39 if (skipModule(M))
40 return false;
41 ModuleAnalysisManager DummyMAM;
42 auto PA = Impl.run(M, DummyMAM);
43 return !PA.areAllPreserved();
44 }
45
46 private:
47 PartialInlinerPass Impl;
48 };
49 }
50
51 char PartialInlinerLegacyPass::ID = 0;
52 INITIALIZE_PASS(PartialInlinerLegacyPass, "partial-inliner", "Partial Inliner",
53 false, false)
54
createPartialInliningPass()55 ModulePass *llvm::createPartialInliningPass() {
56 return new PartialInlinerLegacyPass();
57 }
58
unswitchFunction(Function * F)59 Function *PartialInlinerPass::unswitchFunction(Function *F) {
60 // First, verify that this function is an unswitching candidate...
61 BasicBlock *entryBlock = &F->front();
62 BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator());
63 if (!BR || BR->isUnconditional())
64 return nullptr;
65
66 BasicBlock* returnBlock = nullptr;
67 BasicBlock* nonReturnBlock = nullptr;
68 unsigned returnCount = 0;
69 for (BasicBlock *BB : successors(entryBlock)) {
70 if (isa<ReturnInst>(BB->getTerminator())) {
71 returnBlock = BB;
72 returnCount++;
73 } else
74 nonReturnBlock = BB;
75 }
76
77 if (returnCount != 1)
78 return nullptr;
79
80 // Clone the function, so that we can hack away on it.
81 ValueToValueMapTy VMap;
82 Function* duplicateFunction = CloneFunction(F, VMap);
83 duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
84 BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
85 BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
86 BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
87
88 // Go ahead and update all uses to the duplicate, so that we can just
89 // use the inliner functionality when we're done hacking.
90 F->replaceAllUsesWith(duplicateFunction);
91
92 // Special hackery is needed with PHI nodes that have inputs from more than
93 // one extracted block. For simplicity, just split the PHIs into a two-level
94 // sequence of PHIs, some of which will go in the extracted region, and some
95 // of which will go outside.
96 BasicBlock* preReturn = newReturnBlock;
97 newReturnBlock = newReturnBlock->splitBasicBlock(
98 newReturnBlock->getFirstNonPHI()->getIterator());
99 BasicBlock::iterator I = preReturn->begin();
100 Instruction *Ins = &newReturnBlock->front();
101 while (I != preReturn->end()) {
102 PHINode* OldPhi = dyn_cast<PHINode>(I);
103 if (!OldPhi) break;
104
105 PHINode *retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins);
106 OldPhi->replaceAllUsesWith(retPhi);
107 Ins = newReturnBlock->getFirstNonPHI();
108
109 retPhi->addIncoming(&*I, preReturn);
110 retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
111 newEntryBlock);
112 OldPhi->removeIncomingValue(newEntryBlock);
113
114 ++I;
115 }
116 newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
117
118 // Gather up the blocks that we're going to extract.
119 std::vector<BasicBlock*> toExtract;
120 toExtract.push_back(newNonReturnBlock);
121 for (BasicBlock &BB : *duplicateFunction)
122 if (&BB != newEntryBlock && &BB != newReturnBlock &&
123 &BB != newNonReturnBlock)
124 toExtract.push_back(&BB);
125
126 // The CodeExtractor needs a dominator tree.
127 DominatorTree DT;
128 DT.recalculate(*duplicateFunction);
129
130 // Extract the body of the if.
131 Function* extractedFunction
132 = CodeExtractor(toExtract, &DT).extractCodeRegion();
133
134 InlineFunctionInfo IFI;
135
136 // Inline the top-level if test into all callers.
137 std::vector<User *> Users(duplicateFunction->user_begin(),
138 duplicateFunction->user_end());
139 for (User *User : Users)
140 if (CallInst *CI = dyn_cast<CallInst>(User))
141 InlineFunction(CI, IFI);
142 else if (InvokeInst *II = dyn_cast<InvokeInst>(User))
143 InlineFunction(II, IFI);
144
145 // Ditch the duplicate, since we're done with it, and rewrite all remaining
146 // users (function pointers, etc.) back to the original function.
147 duplicateFunction->replaceAllUsesWith(F);
148 duplicateFunction->eraseFromParent();
149
150 ++NumPartialInlined;
151
152 return extractedFunction;
153 }
154
run(Module & M,ModuleAnalysisManager &)155 PreservedAnalyses PartialInlinerPass::run(Module &M, ModuleAnalysisManager &) {
156 std::vector<Function*> worklist;
157 worklist.reserve(M.size());
158 for (Function &F : M)
159 if (!F.use_empty() && !F.isDeclaration())
160 worklist.push_back(&F);
161
162 bool changed = false;
163 while (!worklist.empty()) {
164 Function* currFunc = worklist.back();
165 worklist.pop_back();
166
167 if (currFunc->use_empty()) continue;
168
169 bool recursive = false;
170 for (User *U : currFunc->users())
171 if (Instruction* I = dyn_cast<Instruction>(U))
172 if (I->getParent()->getParent() == currFunc) {
173 recursive = true;
174 break;
175 }
176 if (recursive) continue;
177
178
179 if (Function* newFunc = unswitchFunction(currFunc)) {
180 worklist.push_back(newFunc);
181 changed = true;
182 }
183
184 }
185
186 if (changed)
187 return PreservedAnalyses::none();
188 return PreservedAnalyses::all();
189 }
190