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->front();
  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 *BB : successors(entryBlock)) {
  62     if (isa<ReturnInst>(BB->getTerminator())) {
  63       returnBlock = BB;
  64       returnCount++;
  65     } else
  66       nonReturnBlock = BB;
  67   }
  68
  69   if (returnCount != 1)
  70     return nullptr;
  71
  72   // Clone the function, so that we can hack away on it.
  73   ValueToValueMapTy VMap;
  74   Function* duplicateFunction = CloneFunction(F, VMap,
  75                                               /*ModuleLevelChanges=*/false);
  76   duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
  77   F->getParent()->getFunctionList().push_back(duplicateFunction);
  78   BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
  79   BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
  80   BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
  81
  82   // Go ahead and update all uses to the duplicate, so that we can just
  83   // use the inliner functionality when we're done hacking.
  84   F->replaceAllUsesWith(duplicateFunction);
  85
  86   // Special hackery is needed with PHI nodes that have inputs from more than
  87   // one extracted block.  For simplicity, just split the PHIs into a two-level
  88   // sequence of PHIs, some of which will go in the extracted region, and some
  89   // of which will go outside.
  90   BasicBlock* preReturn = newReturnBlock;
  91   newReturnBlock = newReturnBlock->splitBasicBlock(
  92       newReturnBlock->getFirstNonPHI()->getIterator());
  93   BasicBlock::iterator I = preReturn->begin();
  94   Instruction *Ins = &newReturnBlock->front();
  95   while (I != preReturn->end()) {
  96     PHINode* OldPhi = dyn_cast<PHINode>(I);
  97     if (!OldPhi) break;
  98
  99     PHINode *retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins);
 100     OldPhi->replaceAllUsesWith(retPhi);
 101     Ins = newReturnBlock->getFirstNonPHI();
 102
 103     retPhi->addIncoming(&*I, preReturn);
 104     retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
 105                         newEntryBlock);
 106     OldPhi->removeIncomingValue(newEntryBlock);
 107
 108     ++I;
 109   }
 110   newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
 111
 112   // Gather up the blocks that we're going to extract.
 113   std::vector<BasicBlock*> toExtract;
 114   toExtract.push_back(newNonReturnBlock);
 115   for (Function::iterator FI = duplicateFunction->begin(),
 116        FE = duplicateFunction->end(); FI != FE; ++FI)
 117     if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
 118         &*FI != newNonReturnBlock)
 119       toExtract.push_back(&*FI);
 120
 121   // The CodeExtractor needs a dominator tree.
 122   DominatorTree DT;
 123   DT.recalculate(*duplicateFunction);
 124
 125   // Extract the body of the if.
 126   Function* extractedFunction
 127     = CodeExtractor(toExtract, &DT).extractCodeRegion();
 128
 129   InlineFunctionInfo IFI;
 130
 131   // Inline the top-level if test into all callers.
 132   std::vector<User *> Users(duplicateFunction->user_begin(),
 133                             duplicateFunction->user_end());
 134   for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
 135        UI != UE; ++UI)
 136     if (CallInst *CI = dyn_cast<CallInst>(*UI))
 137       InlineFunction(CI, IFI);
 138     else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
 139       InlineFunction(II, IFI);
 140
 141   // Ditch the duplicate, since we're done with it, and rewrite all remaining
 142   // users (function pointers, etc.) back to the original function.
 143   duplicateFunction->replaceAllUsesWith(F);
 144   duplicateFunction->eraseFromParent();
 145
 146   ++NumPartialInlined;
 147
 148   return extractedFunction;
 149 }
 150
 151 bool PartialInliner::runOnModule(Module& M) {
 152   std::vector<Function*> worklist;
 153   worklist.reserve(M.size());
 154   for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
 155     if (!FI->use_empty() && !FI->isDeclaration())
 156       worklist.push_back(&*FI);
 157
 158   bool changed = false;
 159   while (!worklist.empty()) {
 160     Function* currFunc = worklist.back();
 161     worklist.pop_back();
 162
 163     if (currFunc->use_empty()) continue;
 164
 165     bool recursive = false;
 166     for (User *U : currFunc->users())
 167       if (Instruction* I = dyn_cast<Instruction>(U))
 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 }