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 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   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
 144 bool 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 }