lib/Transforms/IPO/PartialInlining.cpp

   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"
  26 using namespace llvm;
  27
  28 STATISTIC(NumPartialInlined, "Number of functions partially inlined");
  29
  30 namespace {
  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
  43 char PartialInliner::ID = 0;
  44 static RegisterPass<PartialInliner> X("partial-inliner", "Partial Inliner");
  45
  46 ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); }
  47
  48 Function* 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
 143 bool 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 }