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      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/ADT/Statistic.h"
     18 #include "llvm/Analysis/Dominators.h"
     19 #include "llvm/IR/Instructions.h"
     20 #include "llvm/IR/Module.h"
     21 #include "llvm/Pass.h"
     22 #include "llvm/Support/CFG.h"
     23 #include "llvm/Transforms/Utils/Cloning.h"
     24 #include "llvm/Transforms/Utils/CodeExtractor.h"
     25 using namespace llvm;
     26 
     27 STATISTIC(NumPartialInlined, "Number of functions partially inlined");
     28 
     29 namespace {
     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       initializePartialInlinerPass(*PassRegistry::getPassRegistry());
     35     }
     36 
     37     bool runOnModule(Module& M);
     38 
     39   private:
     40     Function* unswitchFunction(Function* F);
     41   };
     42 }
     43 
     44 char PartialInliner::ID = 0;
     45 INITIALIZE_PASS(PartialInliner, "partial-inliner",
     46                 "Partial Inliner", false, false)
     47 
     48 ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); }
     49 
     50 Function* PartialInliner::unswitchFunction(Function* F) {
     51   // First, verify that this function is an unswitching candidate...
     52   BasicBlock* entryBlock = F->begin();
     53   BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator());
     54   if (!BR || BR->isUnconditional())
     55     return 0;
     56 
     57   BasicBlock* returnBlock = 0;
     58   BasicBlock* nonReturnBlock = 0;
     59   unsigned returnCount = 0;
     60   for (succ_iterator SI = succ_begin(entryBlock), SE = succ_end(entryBlock);
     61        SI != SE; ++SI)
     62     if (isa<ReturnInst>((*SI)->getTerminator())) {
     63       returnBlock = *SI;
     64       returnCount++;
     65     } else
     66       nonReturnBlock = *SI;
     67 
     68   if (returnCount != 1)
     69     return 0;
     70 
     71   // Clone the function, so that we can hack away on it.
     72   ValueToValueMapTy VMap;
     73   Function* duplicateFunction = CloneFunction(F, VMap,
     74                                               /*ModuleLevelChanges=*/false);
     75   duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
     76   F->getParent()->getFunctionList().push_back(duplicateFunction);
     77   BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
     78   BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
     79   BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
     80 
     81   // Go ahead and update all uses to the duplicate, so that we can just
     82   // use the inliner functionality when we're done hacking.
     83   F->replaceAllUsesWith(duplicateFunction);
     84 
     85   // Special hackery is needed with PHI nodes that have inputs from more than
     86   // one extracted block.  For simplicity, just split the PHIs into a two-level
     87   // sequence of PHIs, some of which will go in the extracted region, and some
     88   // of which will go outside.
     89   BasicBlock* preReturn = newReturnBlock;
     90   newReturnBlock = newReturnBlock->splitBasicBlock(
     91                                               newReturnBlock->getFirstNonPHI());
     92   BasicBlock::iterator I = preReturn->begin();
     93   BasicBlock::iterator Ins = newReturnBlock->begin();
     94   while (I != preReturn->end()) {
     95     PHINode* OldPhi = dyn_cast<PHINode>(I);
     96     if (!OldPhi) break;
     97 
     98     PHINode* retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins);
     99     OldPhi->replaceAllUsesWith(retPhi);
    100     Ins = newReturnBlock->getFirstNonPHI();
    101 
    102     retPhi->addIncoming(I, preReturn);
    103     retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
    104                         newEntryBlock);
    105     OldPhi->removeIncomingValue(newEntryBlock);
    106 
    107     ++I;
    108   }
    109   newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
    110 
    111   // Gather up the blocks that we're going to extract.
    112   std::vector<BasicBlock*> toExtract;
    113   toExtract.push_back(newNonReturnBlock);
    114   for (Function::iterator FI = duplicateFunction->begin(),
    115        FE = duplicateFunction->end(); FI != FE; ++FI)
    116     if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
    117         &*FI != newNonReturnBlock)
    118       toExtract.push_back(FI);
    119 
    120   // The CodeExtractor needs a dominator tree.
    121   DominatorTree DT;
    122   DT.runOnFunction(*duplicateFunction);
    123 
    124   // Extract the body of the if.
    125   Function* extractedFunction
    126     = CodeExtractor(toExtract, &DT).extractCodeRegion();
    127 
    128   InlineFunctionInfo IFI;
    129 
    130   // Inline the top-level if test into all callers.
    131   std::vector<User*> Users(duplicateFunction->use_begin(),
    132                            duplicateFunction->use_end());
    133   for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
    134        UI != UE; ++UI)
    135     if (CallInst *CI = dyn_cast<CallInst>(*UI))
    136       InlineFunction(CI, IFI);
    137     else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
    138       InlineFunction(II, IFI);
    139 
    140   // Ditch the duplicate, since we're done with it, and rewrite all remaining
    141   // users (function pointers, etc.) back to the original function.
    142   duplicateFunction->replaceAllUsesWith(F);
    143   duplicateFunction->eraseFromParent();
    144 
    145   ++NumPartialInlined;
    146 
    147   return extractedFunction;
    148 }
    149 
    150 bool PartialInliner::runOnModule(Module& M) {
    151   std::vector<Function*> worklist;
    152   worklist.reserve(M.size());
    153   for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
    154     if (!FI->use_empty() && !FI->isDeclaration())
    155       worklist.push_back(&*FI);
    156 
    157   bool changed = false;
    158   while (!worklist.empty()) {
    159     Function* currFunc = worklist.back();
    160     worklist.pop_back();
    161 
    162     if (currFunc->use_empty()) continue;
    163 
    164     bool recursive = false;
    165     for (Function::use_iterator UI = currFunc->use_begin(),
    166          UE = currFunc->use_end(); UI != UE; ++UI)
    167       if (Instruction* I = dyn_cast<Instruction>(*UI))
    168         if (I->getParent()->getParent() == currFunc) {
    169           recursive = true;
    170           break;
    171         }
    172     if (recursive) continue;
    173 
    174 
    175     if (Function* newFunc = unswitchFunction(currFunc)) {
    176       worklist.push_back(newFunc);
    177       changed = true;
    178     }
    179 
    180   }
    181 
    182   return changed;
    183 }
    184