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 #include "llvm/Transforms/IPO.h"
  16 #include "llvm/ADT/Statistic.h"
  17 #include "llvm/IR/CFG.h"
  18 #include "llvm/IR/Dominators.h"
  19 #include "llvm/IR/Instructions.h"
  20 #include "llvm/IR/Module.h"
  21 #include "llvm/Pass.h"
  22 #include "llvm/Transforms/Utils/Cloning.h"
  23 #include "llvm/Transforms/Utils/CodeExtractor.h"
  24 using namespace llvm;
  25
  26 #define DEBUG_TYPE "partialinlining"
  27
  28 STATISTIC(NumPartialInlined, "Number of functions partially inlined");
  29
  30 namespace {
  31   struct PartialInliner : public ModulePass {
  32     void getAnalysisUsage(AnalysisUsage &AU) const override { }
  33     static char ID; // Pass identification, replacement for typeid
  34     PartialInliner() : ModulePass(ID) {
  35       initializePartialInlinerPass(*PassRegistry::getPassRegistry());
  36     }
  37
  38     bool runOnModule(Module& M) override;
  39
  40   private:
  41     Function* unswitchFunction(Function* F);
  42   };
  43 }
  44
  45 char PartialInliner::ID = 0;
  46 INITIALIZE_PASS(PartialInliner, "partial-inliner",
  47                 "Partial Inliner", false, false)
  48
  49 ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); }
  50
  51 Function* PartialInliner::unswitchFunction(Function* F) {
  52   // First, verify that this function is an unswitching candidate...
  53   BasicBlock* entryBlock = F->begin();
  54   BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator());
  55   if (!BR || BR->isUnconditional())
  56     return nullptr;
  57
  58   BasicBlock* returnBlock = nullptr;
  59   BasicBlock* nonReturnBlock = nullptr;
  60   unsigned returnCount = 0;
  61   for (BasicBlock *Succ : successors(entryBlock))
  62     if (isa<ReturnInst>(Succ->getTerminator())) {
  63       returnBlock = Succ;
  64       returnCount++;
  65     } else
  66       nonReturnBlock = Succ;
  67
  68   if (returnCount != 1)
  69     return nullptr;
  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.recalculate(*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->user_begin(),
 132                             duplicateFunction->user_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 (User *U : currFunc->users())
 166       if (Instruction* I = dyn_cast<Instruction>(U))
 167         if (I->getParent()->getParent() == currFunc) {
 168           recursive = true;
 169           break;
 170         }
 171     if (recursive) continue;
 172
 173
 174     if (Function* newFunc = unswitchFunction(currFunc)) {
 175       worklist.push_back(newFunc);
 176       changed = true;
 177     }
 178
 179   }
 180
 181   return changed;
 182 }