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/CFG.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
  35     bool runOnModule(Module& M);
  36
  37   private:
  38     Function* unswitchFunction(Function* F);
  39   };
  40 }
  41
  42 char PartialInliner::ID = 0;
  43 INITIALIZE_PASS(PartialInliner, "partial-inliner",
  44                 "Partial Inliner", false, false);
  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   ValueMap<const Value*, Value*> VMap;
  71   Function* duplicateFunction = CloneFunction(F, VMap,
  72                                               /*ModuleLevelChanges=*/false);
  73   duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
  74   F->getParent()->getFunctionList().push_back(duplicateFunction);
  75   BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
  76   BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
  77   BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
  78
  79   // Go ahead and update all uses to the duplicate, so that we can just
  80   // use the inliner functionality when we're done hacking.
  81   F->replaceAllUsesWith(duplicateFunction);
  82
  83   // Special hackery is needed with PHI nodes that have inputs from more than
  84   // one extracted block.  For simplicity, just split the PHIs into a two-level
  85   // sequence of PHIs, some of which will go in the extracted region, and some
  86   // of which will go outside.
  87   BasicBlock* preReturn = newReturnBlock;
  88   newReturnBlock = newReturnBlock->splitBasicBlock(
  89                                               newReturnBlock->getFirstNonPHI());
  90   BasicBlock::iterator I = preReturn->begin();
  91   BasicBlock::iterator Ins = newReturnBlock->begin();
  92   while (I != preReturn->end()) {
  93     PHINode* OldPhi = dyn_cast<PHINode>(I);
  94     if (!OldPhi) break;
  95
  96     PHINode* retPhi = PHINode::Create(OldPhi->getType(), "", Ins);
  97     OldPhi->replaceAllUsesWith(retPhi);
  98     Ins = newReturnBlock->getFirstNonPHI();
  99
 100     retPhi->addIncoming(I, preReturn);
 101     retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
 102                         newEntryBlock);
 103     OldPhi->removeIncomingValue(newEntryBlock);
 104
 105     ++I;
 106   }
 107   newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
 108
 109   // Gather up the blocks that we're going to extract.
 110   std::vector<BasicBlock*> toExtract;
 111   toExtract.push_back(newNonReturnBlock);
 112   for (Function::iterator FI = duplicateFunction->begin(),
 113        FE = duplicateFunction->end(); FI != FE; ++FI)
 114     if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
 115         &*FI != newNonReturnBlock)
 116       toExtract.push_back(FI);
 117
 118   // The CodeExtractor needs a dominator tree.
 119   DominatorTree DT;
 120   DT.runOnFunction(*duplicateFunction);
 121
 122   // Extract the body of the if.
 123   Function* extractedFunction = ExtractCodeRegion(DT, toExtract);
 124
 125   InlineFunctionInfo IFI;
 126
 127   // Inline the top-level if test into all callers.
 128   std::vector<User*> Users(duplicateFunction->use_begin(),
 129                            duplicateFunction->use_end());
 130   for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
 131        UI != UE; ++UI)
 132     if (CallInst *CI = dyn_cast<CallInst>(*UI))
 133       InlineFunction(CI, IFI);
 134     else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
 135       InlineFunction(II, IFI);
 136
 137   // Ditch the duplicate, since we're done with it, and rewrite all remaining
 138   // users (function pointers, etc.) back to the original function.
 139   duplicateFunction->replaceAllUsesWith(F);
 140   duplicateFunction->eraseFromParent();
 141
 142   ++NumPartialInlined;
 143
 144   return extractedFunction;
 145 }
 146
 147 bool PartialInliner::runOnModule(Module& M) {
 148   std::vector<Function*> worklist;
 149   worklist.reserve(M.size());
 150   for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
 151     if (!FI->use_empty() && !FI->isDeclaration())
 152       worklist.push_back(&*FI);
 153
 154   bool changed = false;
 155   while (!worklist.empty()) {
 156     Function* currFunc = worklist.back();
 157     worklist.pop_back();
 158
 159     if (currFunc->use_empty()) continue;
 160
 161     bool recursive = false;
 162     for (Function::use_iterator UI = currFunc->use_begin(),
 163          UE = currFunc->use_end(); UI != UE; ++UI)
 164       if (Instruction* I = dyn_cast<Instruction>(*UI))
 165         if (I->getParent()->getParent() == currFunc) {
 166           recursive = true;
 167           break;
 168         }
 169     if (recursive) continue;
 170
 171
 172     if (Function* newFunc = unswitchFunction(currFunc)) {
 173       worklist.push_back(newFunc);
 174       changed = true;
 175     }
 176
 177   }
 178
 179   return changed;
 180 }