PartialInlining.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
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/ADT/Statistic.h"
18#include "llvm/IR/CFG.h"
19#include "llvm/IR/Dominators.h"
20#include "llvm/IR/Instructions.h"
21#include "llvm/IR/Module.h"
22#include "llvm/Pass.h"
23#include "llvm/Transforms/Utils/Cloning.h"
24#include "llvm/Transforms/Utils/CodeExtractor.h"
25using namespace llvm;
26
27STATISTIC(NumPartialInlined, "Number of functions partially inlined");
28
29namespace {
30  struct PartialInliner : public ModulePass {
31    void getAnalysisUsage(AnalysisUsage &AU) const override { }
32    static char ID; // Pass identification, replacement for typeid
33    PartialInliner() : ModulePass(ID) {
34      initializePartialInlinerPass(*PassRegistry::getPassRegistry());
35    }
36
37    bool runOnModule(Module& M) override;
38
39  private:
40    Function* unswitchFunction(Function* F);
41  };
42}
43
44char PartialInliner::ID = 0;
45INITIALIZE_PASS(PartialInliner, "partial-inliner",
46                "Partial Inliner", false, false)
47
48ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); }
49
50Function* 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.recalculate(*duplicateFunction);
123
124  // Extract the body of the if.
125  Function* extractedFunction
126    = CodeExtractor(toExtract, &DT).extractCodeRegion();
127
128  InlineFunctionInfo IFI;
129
130  // Inline the top-level if test into all callers.
131  std::vector<User *> Users(duplicateFunction->user_begin(),
132                            duplicateFunction->user_end());
133  for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
134       UI != UE; ++UI)
135    if (CallInst *CI = dyn_cast<CallInst>(*UI))
136      InlineFunction(CI, IFI);
137    else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
138      InlineFunction(II, IFI);
139
140  // Ditch the duplicate, since we're done with it, and rewrite all remaining
141  // users (function pointers, etc.) back to the original function.
142  duplicateFunction->replaceAllUsesWith(F);
143  duplicateFunction->eraseFromParent();
144
145  ++NumPartialInlined;
146
147  return extractedFunction;
148}
149
150bool PartialInliner::runOnModule(Module& M) {
151  std::vector<Function*> worklist;
152  worklist.reserve(M.size());
153  for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
154    if (!FI->use_empty() && !FI->isDeclaration())
155      worklist.push_back(&*FI);
156
157  bool changed = false;
158  while (!worklist.empty()) {
159    Function* currFunc = worklist.back();
160    worklist.pop_back();
161
162    if (currFunc->use_empty()) continue;
163
164    bool recursive = false;
165    for (User *U : currFunc->users())
166      if (Instruction* I = dyn_cast<Instruction>(U))
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