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 #define DEBUG_TYPE "partialinlining"
16 #include "llvm/Transforms/IPO.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/Module.h"
19 #include "llvm/Pass.h"
20 #include "llvm/Analysis/Dominators.h"
21 #include "llvm/Transforms/Utils/Cloning.h"
22 #include "llvm/Transforms/Utils/FunctionUtils.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/Support/CFG.h"
25 using namespace llvm;
26
27 STATISTIC(NumPartialInlined, "Number of functions partially inlined");
28
29 namespace {
30 struct PartialInliner : public ModulePass {
getAnalysisUsage__anon4a9c88210111::PartialInliner31 virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
32 static char ID; // Pass identification, replacement for typeid
PartialInliner__anon4a9c88210111::PartialInliner33 PartialInliner() : ModulePass(ID) {
34 initializePartialInlinerPass(*PassRegistry::getPassRegistry());
35 }
36
37 bool runOnModule(Module& M);
38
39 private:
40 Function* unswitchFunction(Function* F);
41 };
42 }
43
44 char PartialInliner::ID = 0;
45 INITIALIZE_PASS(PartialInliner, "partial-inliner",
46 "Partial Inliner", false, false)
47
createPartialInliningPass()48 ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); }
49
unswitchFunction(Function * F)50 Function* PartialInliner::unswitchFunction(Function* F) {
51 // First, verify that this function is an unswitching candidate...
52 BasicBlock* entryBlock = F->begin();
53 BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator());
54 if (!BR || BR->isUnconditional())
55 return 0;
56
57 BasicBlock* returnBlock = 0;
58 BasicBlock* nonReturnBlock = 0;
59 unsigned returnCount = 0;
60 for (succ_iterator SI = succ_begin(entryBlock), SE = succ_end(entryBlock);
61 SI != SE; ++SI)
62 if (isa<ReturnInst>((*SI)->getTerminator())) {
63 returnBlock = *SI;
64 returnCount++;
65 } else
66 nonReturnBlock = *SI;
67
68 if (returnCount != 1)
69 return 0;
70
71 // Clone the function, so that we can hack away on it.
72 ValueToValueMapTy VMap;
73 Function* duplicateFunction = CloneFunction(F, VMap,
74 /*ModuleLevelChanges=*/false);
75 duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
76 F->getParent()->getFunctionList().push_back(duplicateFunction);
77 BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
78 BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
79 BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
80
81 // Go ahead and update all uses to the duplicate, so that we can just
82 // use the inliner functionality when we're done hacking.
83 F->replaceAllUsesWith(duplicateFunction);
84
85 // Special hackery is needed with PHI nodes that have inputs from more than
86 // one extracted block. For simplicity, just split the PHIs into a two-level
87 // sequence of PHIs, some of which will go in the extracted region, and some
88 // of which will go outside.
89 BasicBlock* preReturn = newReturnBlock;
90 newReturnBlock = newReturnBlock->splitBasicBlock(
91 newReturnBlock->getFirstNonPHI());
92 BasicBlock::iterator I = preReturn->begin();
93 BasicBlock::iterator Ins = newReturnBlock->begin();
94 while (I != preReturn->end()) {
95 PHINode* OldPhi = dyn_cast<PHINode>(I);
96 if (!OldPhi) break;
97
98 PHINode* retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins);
99 OldPhi->replaceAllUsesWith(retPhi);
100 Ins = newReturnBlock->getFirstNonPHI();
101
102 retPhi->addIncoming(I, preReturn);
103 retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
104 newEntryBlock);
105 OldPhi->removeIncomingValue(newEntryBlock);
106
107 ++I;
108 }
109 newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
110
111 // Gather up the blocks that we're going to extract.
112 std::vector<BasicBlock*> toExtract;
113 toExtract.push_back(newNonReturnBlock);
114 for (Function::iterator FI = duplicateFunction->begin(),
115 FE = duplicateFunction->end(); FI != FE; ++FI)
116 if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
117 &*FI != newNonReturnBlock)
118 toExtract.push_back(FI);
119
120 // The CodeExtractor needs a dominator tree.
121 DominatorTree DT;
122 DT.runOnFunction(*duplicateFunction);
123
124 // Extract the body of the if.
125 Function* extractedFunction = ExtractCodeRegion(DT, toExtract);
126
127 InlineFunctionInfo IFI;
128
129 // Inline the top-level if test into all callers.
130 std::vector<User*> Users(duplicateFunction->use_begin(),
131 duplicateFunction->use_end());
132 for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
133 UI != UE; ++UI)
134 if (CallInst *CI = dyn_cast<CallInst>(*UI))
135 InlineFunction(CI, IFI);
136 else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
137 InlineFunction(II, IFI);
138
139 // Ditch the duplicate, since we're done with it, and rewrite all remaining
140 // users (function pointers, etc.) back to the original function.
141 duplicateFunction->replaceAllUsesWith(F);
142 duplicateFunction->eraseFromParent();
143
144 ++NumPartialInlined;
145
146 return extractedFunction;
147 }
148
runOnModule(Module & M)149 bool PartialInliner::runOnModule(Module& M) {
150 std::vector<Function*> worklist;
151 worklist.reserve(M.size());
152 for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
153 if (!FI->use_empty() && !FI->isDeclaration())
154 worklist.push_back(&*FI);
155
156 bool changed = false;
157 while (!worklist.empty()) {
158 Function* currFunc = worklist.back();
159 worklist.pop_back();
160
161 if (currFunc->use_empty()) continue;
162
163 bool recursive = false;
164 for (Function::use_iterator UI = currFunc->use_begin(),
165 UE = currFunc->use_end(); UI != UE; ++UI)
166 if (Instruction* I = dyn_cast<Instruction>(*UI))
167 if (I->getParent()->getParent() == currFunc) {
168 recursive = true;
169 break;
170 }
171 if (recursive) continue;
172
173
174 if (Function* newFunc = unswitchFunction(currFunc)) {
175 worklist.push_back(newFunc);
176 changed = true;
177 }
178
179 }
180
181 return changed;
182 }
183