PartialInlining.cpp revision 6cb8c23db1c3becdce6dfbf1b7f1677faca4251e 
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"
25using namespace llvm;
26
27STATISTIC(NumPartialInlined, "Number of functions partially inlined");
28
29namespace {
30  struct PartialInliner : public ModulePass {
31    virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
32    static char ID; // Pass identification, replacement for typeid
33    PartialInliner() : ModulePass(ID) {}
34
35    bool runOnModule(Module& M);
36
37  private:
38    Function* unswitchFunction(Function* F);
39  };
40}
41
42char PartialInliner::ID = 0;
43INITIALIZE_PASS(PartialInliner, "partial-inliner",
44                "Partial Inliner", false, false);
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  ValueMap<const Value*, Value*> VMap;
71  Function* duplicateFunction = CloneFunction(F, VMap,
72                                              /*ModuleLevelChanges=*/false);
73  duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
74  F->getParent()->getFunctionList().push_back(duplicateFunction);
75  BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
76  BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
77  BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
78
79  // Go ahead and update all uses to the duplicate, so that we can just
80  // use the inliner functionality when we're done hacking.
81  F->replaceAllUsesWith(duplicateFunction);
82
83  // Special hackery is needed with PHI nodes that have inputs from more than
84  // one extracted block.  For simplicity, just split the PHIs into a two-level
85  // sequence of PHIs, some of which will go in the extracted region, and some
86  // of which will go outside.
87  BasicBlock* preReturn = newReturnBlock;
88  newReturnBlock = newReturnBlock->splitBasicBlock(
89                                              newReturnBlock->getFirstNonPHI());
90  BasicBlock::iterator I = preReturn->begin();
91  BasicBlock::iterator Ins = newReturnBlock->begin();
92  while (I != preReturn->end()) {
93    PHINode* OldPhi = dyn_cast<PHINode>(I);
94    if (!OldPhi) break;
95
96    PHINode* retPhi = PHINode::Create(OldPhi->getType(), "", Ins);
97    OldPhi->replaceAllUsesWith(retPhi);
98    Ins = newReturnBlock->getFirstNonPHI();
99
100    retPhi->addIncoming(I, preReturn);
101    retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
102                        newEntryBlock);
103    OldPhi->removeIncomingValue(newEntryBlock);
104
105    ++I;
106  }
107  newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
108
109  // Gather up the blocks that we're going to extract.
110  std::vector<BasicBlock*> toExtract;
111  toExtract.push_back(newNonReturnBlock);
112  for (Function::iterator FI = duplicateFunction->begin(),
113       FE = duplicateFunction->end(); FI != FE; ++FI)
114    if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
115        &*FI != newNonReturnBlock)
116      toExtract.push_back(FI);
117
118  // The CodeExtractor needs a dominator tree.
119  DominatorTree DT;
120  DT.runOnFunction(*duplicateFunction);
121
122  // Extract the body of the if.
123  Function* extractedFunction = ExtractCodeRegion(DT, toExtract);
124
125  InlineFunctionInfo IFI;
126
127  // Inline the top-level if test into all callers.
128  std::vector<User*> Users(duplicateFunction->use_begin(),
129                           duplicateFunction->use_end());
130  for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
131       UI != UE; ++UI)
132    if (CallInst *CI = dyn_cast<CallInst>(*UI))
133      InlineFunction(CI, IFI);
134    else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
135      InlineFunction(II, IFI);
136
137  // Ditch the duplicate, since we're done with it, and rewrite all remaining
138  // users (function pointers, etc.) back to the original function.
139  duplicateFunction->replaceAllUsesWith(F);
140  duplicateFunction->eraseFromParent();
141
142  ++NumPartialInlined;
143
144  return extractedFunction;
145}
146
147bool PartialInliner::runOnModule(Module& M) {
148  std::vector<Function*> worklist;
149  worklist.reserve(M.size());
150  for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
151    if (!FI->use_empty() && !FI->isDeclaration())
152      worklist.push_back(&*FI);
153
154  bool changed = false;
155  while (!worklist.empty()) {
156    Function* currFunc = worklist.back();
157    worklist.pop_back();
158
159    if (currFunc->use_empty()) continue;
160
161    bool recursive = false;
162    for (Function::use_iterator UI = currFunc->use_begin(),
163         UE = currFunc->use_end(); UI != UE; ++UI)
164      if (Instruction* I = dyn_cast<Instruction>(*UI))
165        if (I->getParent()->getParent() == currFunc) {
166          recursive = true;
167          break;
168        }
169    if (recursive) continue;
170
171
172    if (Function* newFunc = unswitchFunction(currFunc)) {
173      worklist.push_back(newFunc);
174      changed = true;
175    }
176
177  }
178
179  return changed;
180}
181