PartialInlining.cpp revision 492d06efde44a4e38a6ed321ada4af5a75494df6 
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 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  BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator());
52  if (!BR || BR->isUnconditional())
53    return 0;
54
55  BasicBlock* returnBlock = 0;
56  BasicBlock* nonReturnBlock = 0;
57  unsigned returnCount = 0;
58  for (succ_iterator SI = succ_begin(entryBlock), SE = succ_end(entryBlock);
59       SI != SE; ++SI)
60    if (isa<ReturnInst>((*SI)->getTerminator())) {
61      returnBlock = *SI;
62      returnCount++;
63    } else
64      nonReturnBlock = *SI;
65
66  if (returnCount != 1)
67    return 0;
68
69  // Clone the function, so that we can hack away on it.
70  DenseMap<const Value*, Value*> ValueMap;
71  Function* duplicateFunction = CloneFunction(F, ValueMap);
72  duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
73  F->getParent()->getFunctionList().push_back(duplicateFunction);
74  BasicBlock* newEntryBlock = cast<BasicBlock>(ValueMap[entryBlock]);
75  BasicBlock* newReturnBlock = cast<BasicBlock>(ValueMap[returnBlock]);
76  BasicBlock* newNonReturnBlock = cast<BasicBlock>(ValueMap[nonReturnBlock]);
77
78  // Go ahead and update all uses to the duplicate, so that we can just
79  // use the inliner functionality when we're done hacking.
80  F->replaceAllUsesWith(duplicateFunction);
81
82  // Special hackery is needed with PHI nodes that have inputs from more than
83  // one extracted block.  For simplicity, just split the PHIs into a two-level
84  // sequence of PHIs, some of which will go in the extracted region, and some
85  // of which will go outside.
86  BasicBlock* preReturn = newReturnBlock;
87  newReturnBlock = newReturnBlock->splitBasicBlock(
88                                              newReturnBlock->getFirstNonPHI());
89  BasicBlock::iterator I = preReturn->begin();
90  BasicBlock::iterator Ins = newReturnBlock->begin();
91  while (I != preReturn->end()) {
92    PHINode* OldPhi = dyn_cast<PHINode>(I);
93    if (!OldPhi) break;
94
95    PHINode* retPhi = PHINode::Create(OldPhi->getType(), "", Ins);
96    OldPhi->replaceAllUsesWith(retPhi);
97    Ins = newReturnBlock->getFirstNonPHI();
98
99    retPhi->addIncoming(I, preReturn);
100    retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
101                        newEntryBlock);
102    OldPhi->removeIncomingValue(newEntryBlock);
103
104    ++I;
105  }
106  newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
107
108  // Gather up the blocks that we're going to extract.
109  std::vector<BasicBlock*> toExtract;
110  toExtract.push_back(newNonReturnBlock);
111  for (Function::iterator FI = duplicateFunction->begin(),
112       FE = duplicateFunction->end(); FI != FE; ++FI)
113    if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
114        &*FI != newNonReturnBlock)
115      toExtract.push_back(FI);
116
117  // The CodeExtractor needs a dominator tree.
118  DominatorTree DT;
119  DT.runOnFunction(*duplicateFunction);
120
121  // Extract the body of the the if.
122  Function* extractedFunction = ExtractCodeRegion(DT, toExtract);
123
124  // Inline the top-level if test into all callers.
125  std::vector<User*> Users(duplicateFunction->use_begin(),
126                           duplicateFunction->use_end());
127  for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
128       UI != UE; ++UI)
129    if (CallInst* CI = dyn_cast<CallInst>(*UI))
130      InlineFunction(CI);
131    else if (InvokeInst* II = dyn_cast<InvokeInst>(*UI))
132      InlineFunction(II);
133
134  // Ditch the duplicate, since we're done with it, and rewrite all remaining
135  // users (function pointers, etc.) back to the original function.
136  duplicateFunction->replaceAllUsesWith(F);
137  duplicateFunction->eraseFromParent();
138
139  ++NumPartialInlined;
140
141  return extractedFunction;
142}
143
144bool PartialInliner::runOnModule(Module& M) {
145  std::vector<Function*> worklist;
146  worklist.reserve(M.size());
147  for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
148    if (!FI->use_empty() && !FI->isDeclaration())
149    worklist.push_back(&*FI);
150
151  bool changed = false;
152  while (!worklist.empty()) {
153    Function* currFunc = worklist.back();
154    worklist.pop_back();
155
156    if (currFunc->use_empty()) continue;
157
158    bool recursive = false;
159    for (Function::use_iterator UI = currFunc->use_begin(),
160         UE = currFunc->use_end(); UI != UE; ++UI)
161      if (Instruction* I = dyn_cast<Instruction>(UI))
162        if (I->getParent()->getParent() == currFunc) {
163          recursive = true;
164          break;
165        }
166    if (recursive) continue;
167
168
169    if (Function* newFunc = unswitchFunction(currFunc)) {
170      worklist.push_back(newFunc);
171      changed = true;
172    }
173
174  }
175
176  return changed;
177}
178