lib/Transforms/IPO/BlockExtractor.cpp

   1 //===- BlockExtractor.cpp - Extracts blocks into their own functions ------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This pass extracts the specified basic blocks from the module into their
  10 // own functions.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/ADT/STLExtras.h"
  15 #include "llvm/ADT/Statistic.h"
  16 #include "llvm/IR/Instructions.h"
  17 #include "llvm/IR/Module.h"
  18 #include "llvm/Pass.h"
  19 #include "llvm/Support/CommandLine.h"
  20 #include "llvm/Support/Debug.h"
  21 #include "llvm/Support/MemoryBuffer.h"
  22 #include "llvm/Transforms/IPO.h"
  23 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  24 #include "llvm/Transforms/Utils/CodeExtractor.h"
  25
  26 using namespace llvm;
  27
  28 #define DEBUG_TYPE "block-extractor"
  29
  30 STATISTIC(NumExtracted, "Number of basic blocks extracted");
  31
  32 static cl::opt<std::string> BlockExtractorFile(
  33     "extract-blocks-file", cl::value_desc("filename"),
  34     cl::desc("A file containing list of basic blocks to extract"), cl::Hidden);
  35
  36 cl::opt<bool> BlockExtractorEraseFuncs("extract-blocks-erase-funcs",
  37                                        cl::desc("Erase the existing functions"),
  38                                        cl::Hidden);
  39 namespace {
  40 class BlockExtractor : public ModulePass {
  41   SmallVector<SmallVector<BasicBlock *, 16>, 4> GroupsOfBlocks;
  42   bool EraseFunctions;
  43   /// Map a function name to groups of blocks.
  44   SmallVector<std::pair<std::string, SmallVector<std::string, 4>>, 4>
  45       BlocksByName;
  46
  47   void init(const SmallVectorImpl<SmallVector<BasicBlock *, 16>>
  48                 &GroupsOfBlocksToExtract) {
  49     for (const SmallVectorImpl<BasicBlock *> &GroupOfBlocks :
  50          GroupsOfBlocksToExtract) {
  51       SmallVector<BasicBlock *, 16> NewGroup;
  52       NewGroup.append(GroupOfBlocks.begin(), GroupOfBlocks.end());
  53       GroupsOfBlocks.emplace_back(NewGroup);
  54     }
  55     if (!BlockExtractorFile.empty())
  56       loadFile();
  57   }
  58
  59 public:
  60   static char ID;
  61   BlockExtractor(const SmallVectorImpl<BasicBlock *> &BlocksToExtract,
  62                  bool EraseFunctions)
  63       : ModulePass(ID), EraseFunctions(EraseFunctions) {
  64     // We want one group per element of the input list.
  65     SmallVector<SmallVector<BasicBlock *, 16>, 4> MassagedGroupsOfBlocks;
  66     for (BasicBlock *BB : BlocksToExtract) {
  67       SmallVector<BasicBlock *, 16> NewGroup;
  68       NewGroup.push_back(BB);
  69       MassagedGroupsOfBlocks.push_back(NewGroup);
  70     }
  71     init(MassagedGroupsOfBlocks);
  72   }
  73
  74   BlockExtractor(const SmallVectorImpl<SmallVector<BasicBlock *, 16>>
  75                      &GroupsOfBlocksToExtract,
  76                  bool EraseFunctions)
  77       : ModulePass(ID), EraseFunctions(EraseFunctions) {
  78     init(GroupsOfBlocksToExtract);
  79   }
  80
  81   BlockExtractor() : BlockExtractor(SmallVector<BasicBlock *, 0>(), false) {}
  82   bool runOnModule(Module &M) override;
  83
  84 private:
  85   void loadFile();
  86   void splitLandingPadPreds(Function &F);
  87 };
  88 } // end anonymous namespace
  89
  90 char BlockExtractor::ID = 0;
  91 INITIALIZE_PASS(BlockExtractor, "extract-blocks",
  92                 "Extract basic blocks from module", false, false)
  93
  94 ModulePass *llvm::createBlockExtractorPass() { return new BlockExtractor(); }
  95 ModulePass *llvm::createBlockExtractorPass(
  96     const SmallVectorImpl<BasicBlock *> &BlocksToExtract, bool EraseFunctions) {
  97   return new BlockExtractor(BlocksToExtract, EraseFunctions);
  98 }
  99 ModulePass *llvm::createBlockExtractorPass(
 100     const SmallVectorImpl<SmallVector<BasicBlock *, 16>>
 101         &GroupsOfBlocksToExtract,
 102     bool EraseFunctions) {
 103   return new BlockExtractor(GroupsOfBlocksToExtract, EraseFunctions);
 104 }
 105
 106 /// Gets all of the blocks specified in the input file.
 107 void BlockExtractor::loadFile() {
 108   auto ErrOrBuf = MemoryBuffer::getFile(BlockExtractorFile);
 109   if (ErrOrBuf.getError())
 110     report_fatal_error("BlockExtractor couldn't load the file.");
 111   // Read the file.
 112   auto &Buf = *ErrOrBuf;
 113   SmallVector<StringRef, 16> Lines;
 114   Buf->getBuffer().split(Lines, '\n', /*MaxSplit=*/-1,
 115                          /*KeepEmpty=*/false);
 116   for (const auto &Line : Lines) {
 117     SmallVector<StringRef, 4> LineSplit;
 118     Line.split(LineSplit, ' ', /*MaxSplit=*/-1,
 119                /*KeepEmpty=*/false);
 120     if (LineSplit.empty())
 121       continue;
 122     SmallVector<StringRef, 4> BBNames;
 123     LineSplit[1].split(BBNames, ';', /*MaxSplit=*/-1,
 124                        /*KeepEmpty=*/false);
 125     if (BBNames.empty())
 126       report_fatal_error("Missing bbs name");
 127     BlocksByName.push_back({LineSplit[0], {BBNames.begin(), BBNames.end()}});
 128   }
 129 }
 130
 131 /// Extracts the landing pads to make sure all of them have only one
 132 /// predecessor.
 133 void BlockExtractor::splitLandingPadPreds(Function &F) {
 134   for (BasicBlock &BB : F) {
 135     for (Instruction &I : BB) {
 136       if (!isa<InvokeInst>(&I))
 137         continue;
 138       InvokeInst *II = cast<InvokeInst>(&I);
 139       BasicBlock *Parent = II->getParent();
 140       BasicBlock *LPad = II->getUnwindDest();
 141
 142       // Look through the landing pad's predecessors. If one of them ends in an
 143       // 'invoke', then we want to split the landing pad.
 144       bool Split = false;
 145       for (auto PredBB : predecessors(LPad)) {
 146         if (PredBB->isLandingPad() && PredBB != Parent &&
 147             isa<InvokeInst>(Parent->getTerminator())) {
 148           Split = true;
 149           break;
 150         }
 151       }
 152
 153       if (!Split)
 154         continue;
 155
 156       SmallVector<BasicBlock *, 2> NewBBs;
 157       SplitLandingPadPredecessors(LPad, Parent, ".1", ".2", NewBBs);
 158     }
 159   }
 160 }
 161
 162 bool BlockExtractor::runOnModule(Module &M) {
 163
 164   bool Changed = false;
 165
 166   // Get all the functions.
 167   SmallVector<Function *, 4> Functions;
 168   for (Function &F : M) {
 169     splitLandingPadPreds(F);
 170     Functions.push_back(&F);
 171   }
 172
 173   // Get all the blocks specified in the input file.
 174   unsigned NextGroupIdx = GroupsOfBlocks.size();
 175   GroupsOfBlocks.resize(NextGroupIdx + BlocksByName.size());
 176   for (const auto &BInfo : BlocksByName) {
 177     Function *F = M.getFunction(BInfo.first);
 178     if (!F)
 179       report_fatal_error("Invalid function name specified in the input file");
 180     for (const auto &BBInfo : BInfo.second) {
 181       auto Res = llvm::find_if(*F, [&](const BasicBlock &BB) {
 182         return BB.getName().equals(BBInfo);
 183       });
 184       if (Res == F->end())
 185         report_fatal_error("Invalid block name specified in the input file");
 186       GroupsOfBlocks[NextGroupIdx].push_back(&*Res);
 187     }
 188     ++NextGroupIdx;
 189   }
 190
 191   // Extract each group of basic blocks.
 192   for (auto &BBs : GroupsOfBlocks) {
 193     SmallVector<BasicBlock *, 32> BlocksToExtractVec;
 194     for (BasicBlock *BB : BBs) {
 195       // Check if the module contains BB.
 196       if (BB->getParent()->getParent() != &M)
 197         report_fatal_error("Invalid basic block");
 198       LLVM_DEBUG(dbgs() << "BlockExtractor: Extracting "
 199                         << BB->getParent()->getName() << ":" << BB->getName()
 200                         << "\n");
 201       BlocksToExtractVec.push_back(BB);
 202       if (const InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
 203         BlocksToExtractVec.push_back(II->getUnwindDest());
 204       ++NumExtracted;
 205       Changed = true;
 206     }
 207     Function *F = CodeExtractor(BlocksToExtractVec).extractCodeRegion();
 208     if (F)
 209       LLVM_DEBUG(dbgs() << "Extracted group '" << (*BBs.begin())->getName()
 210                         << "' in: " << F->getName() << '\n');
 211     else
 212       LLVM_DEBUG(dbgs() << "Failed to extract for group '"
 213                         << (*BBs.begin())->getName() << "'\n");
 214   }
 215
 216   // Erase the functions.
 217   if (EraseFunctions || BlockExtractorEraseFuncs) {
 218     for (Function *F : Functions) {
 219       LLVM_DEBUG(dbgs() << "BlockExtractor: Trying to delete " << F->getName()
 220                         << "\n");
 221       F->deleteBody();
 222     }
 223     // Set linkage as ExternalLinkage to avoid erasing unreachable functions.
 224     for (Function &F : M)
 225       F.setLinkage(GlobalValue::ExternalLinkage);
 226     Changed = true;
 227   }
 228
 229   return Changed;
 230 }