PartialInlining.cpp revision d5f50da7f06199c03de1294981e35cfd1c4d53dd 
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/Compiler.h"
25#include "llvm/Support/CFG.h"
26using namespace llvm;
27
28STATISTIC(NumPartialInlined, "Number of functions partially inlined");
29
30namespace {
31  struct VISIBILITY_HIDDEN PartialInliner : public ModulePass {
32    virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
33    static char ID; // Pass identification, replacement for typeid
34    PartialInliner() : ModulePass(&ID) {}
35
36    bool runOnModule(Module& M);
37
38  private:
39    Function* unswitchFunction(Function* F);
40  };
41}
42
43char PartialInliner::ID = 0;
44static RegisterPass<PartialInliner> X("partial-inliner", "Partial Inliner");
45
46ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); }
47
48Function* PartialInliner::unswitchFunction(Function* F) {
49  // First, verify that this function is an unswitching candidate...
50  BasicBlock* entryBlock = F->begin();
51  if (!isa<BranchInst>(entryBlock->getTerminator()))
52    return 0;
53
54  BasicBlock* returnBlock = 0;
55  BasicBlock* nonReturnBlock = 0;
56  unsigned returnCount = 0;
57  for (succ_iterator SI = succ_begin(entryBlock), SE = succ_end(entryBlock);
58       SI != SE; ++SI)
59    if (isa<ReturnInst>((*SI)->getTerminator())) {
60      returnBlock = *SI;
61      returnCount++;
62    } else
63      nonReturnBlock = *SI;
64
65  if (returnCount != 1)
66    return 0;
67
68  // Clone the function, so that we can hack away on it.
69  DenseMap<const Value*, Value*> ValueMap;
70  Function* duplicateFunction = CloneFunction(F, ValueMap);
71  duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
72  F->getParent()->getFunctionList().push_back(duplicateFunction);
73  BasicBlock* newEntryBlock = cast<BasicBlock>(ValueMap[entryBlock]);
74  BasicBlock* newReturnBlock = cast<BasicBlock>(ValueMap[returnBlock]);
75  BasicBlock* newNonReturnBlock = cast<BasicBlock>(ValueMap[nonReturnBlock]);
76
77  // Go ahead and update all uses to the duplicate, so that we can just
78  // use the inliner functionality when we're done hacking.
79  F->replaceAllUsesWith(duplicateFunction);
80
81  // Special hackery is needed with PHI nodes that have inputs from more than
82  // one extracted block.  For simplicity, just split the PHIs into a two-level
83  // sequence of PHIs, some of which will go in the extracted region, and some
84  // of which will go outside.
85  BasicBlock* preReturn = newReturnBlock;
86  newReturnBlock = newReturnBlock->splitBasicBlock(
87                                              newReturnBlock->getFirstNonPHI());
88  BasicBlock::iterator I = preReturn->begin();
89  BasicBlock::iterator Ins = newReturnBlock->begin();
90  while (I != preReturn->end()) {
91    PHINode* OldPhi = dyn_cast<PHINode>(I);
92    if (!OldPhi) break;
93
94    PHINode* retPhi = PHINode::Create(OldPhi->getType(), "", Ins);
95    OldPhi->replaceAllUsesWith(retPhi);
96    Ins = newReturnBlock->getFirstNonPHI();
97
98    retPhi->addIncoming(I, preReturn);
99    retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
100                        newEntryBlock);
101    OldPhi->removeIncomingValue(newEntryBlock);
102
103    ++I;
104  }
105  newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
106
107  // Gather up the blocks that we're going to extract.
108  std::vector<BasicBlock*> toExtract;
109  toExtract.push_back(newNonReturnBlock);
110  for (Function::iterator FI = duplicateFunction->begin(),
111       FE = duplicateFunction->end(); FI != FE; ++FI)
112    if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
113        &*FI != newNonReturnBlock)
114      toExtract.push_back(FI);
115
116  // The CodeExtractor needs a dominator tree.
117  DominatorTree DT;
118  DT.runOnFunction(*duplicateFunction);
119
120  // Extract the body of the the if.
121  Function* extractedFunction = ExtractCodeRegion(DT, toExtract);
122
123  // Inline the top-level if test into all callers.
124  std::vector<User*> Users(duplicateFunction->use_begin(),
125                           duplicateFunction->use_end());
126  for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
127       UI != UE; ++UI)
128    if (CallInst* CI = dyn_cast<CallInst>(*UI))
129      InlineFunction(CI);
130    else if (InvokeInst* II = dyn_cast<InvokeInst>(*UI))
131      InlineFunction(II);
132
133  // Ditch the duplicate, since we're done with it, and rewrite all remaining
134  // users (function pointers, etc.) back to the original function.
135  duplicateFunction->replaceAllUsesWith(F);
136  duplicateFunction->eraseFromParent();
137
138  ++NumPartialInlined;
139
140  return extractedFunction;
141}
142
143bool PartialInliner::runOnModule(Module& M) {
144  std::vector<Function*> worklist;
145  worklist.reserve(M.size());
146  for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
147    if (!FI->use_empty() && !FI->isDeclaration())
148    worklist.push_back(&*FI);
149
150  bool changed = false;
151  while (!worklist.empty()) {
152    Function* currFunc = worklist.back();
153    worklist.pop_back();
154
155    if (currFunc->use_empty()) continue;
156
157    bool recursive = false;
158    for (Function::use_iterator UI = currFunc->use_begin(),
159         UE = currFunc->use_end(); UI != UE; ++UI)
160      if (Instruction* I = dyn_cast<Instruction>(UI))
161        if (I->getParent()->getParent() == currFunc) {
162          recursive = true;
163          break;
164        }
165    if (recursive) continue;
166
167
168    if (Function* newFunc = unswitchFunction(currFunc)) {
169      worklist.push_back(newFunc);
170      changed = true;
171    }
172
173  }
174
175  return changed;
176}
177