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