C++ BranchInst::setMetadata方法代码示例

/// buildCFICheck - emits __cfi_check for the current module.
void CrossDSOCFI::buildCFICheck() {
  // FIXME: verify that __cfi_check ends up near the end of the code section,
  // but before the jump slots created in LowerBitSets.
  llvm::DenseSet<uint64_t> BitSetIds;
  NamedMDNode *BitSetNM = M->getNamedMetadata("llvm.bitsets");

  if (BitSetNM)
    for (unsigned I = 0, E = BitSetNM->getNumOperands(); I != E; ++I)
      if (ConstantInt *TypeId = extractBitSetTypeId(BitSetNM->getOperand(I)))
        BitSetIds.insert(TypeId->getZExtValue());

  LLVMContext &Ctx = M->getContext();
  Constant *C = M->getOrInsertFunction(
      "__cfi_check",
      FunctionType::get(
          Type::getVoidTy(Ctx),
          {Type::getInt64Ty(Ctx), PointerType::getUnqual(Type::getInt8Ty(Ctx))},
          false));
  Function *F = dyn_cast<Function>(C);
  F->setAlignment(4096);
  auto args = F->arg_begin();
  Argument &CallSiteTypeId = *(args++);
  CallSiteTypeId.setName("CallSiteTypeId");
  Argument &Addr = *(args++);
  Addr.setName("Addr");
  assert(args == F->arg_end());

  BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F);

  BasicBlock *TrapBB = BasicBlock::Create(Ctx, "trap", F);
  IRBuilder<> IRBTrap(TrapBB);
  Function *TrapFn = Intrinsic::getDeclaration(M, Intrinsic::trap);
  llvm::CallInst *TrapCall = IRBTrap.CreateCall(TrapFn);
  TrapCall->setDoesNotReturn();
  TrapCall->setDoesNotThrow();
  IRBTrap.CreateUnreachable();

  BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F);
  IRBuilder<> IRBExit(ExitBB);
  IRBExit.CreateRetVoid();

  IRBuilder<> IRB(BB);
  SwitchInst *SI = IRB.CreateSwitch(&CallSiteTypeId, TrapBB, BitSetIds.size());
  for (uint64_t TypeId : BitSetIds) {
    ConstantInt *CaseTypeId = ConstantInt::get(Type::getInt64Ty(Ctx), TypeId);
    BasicBlock *TestBB = BasicBlock::Create(Ctx, "test", F);
    IRBuilder<> IRBTest(TestBB);
    Function *BitsetTestFn =
        Intrinsic::getDeclaration(M, Intrinsic::bitset_test);

    Value *Test = IRBTest.CreateCall(
        BitsetTestFn, {&Addr, MetadataAsValue::get(
                                  Ctx, ConstantAsMetadata::get(CaseTypeId))});
    BranchInst *BI = IRBTest.CreateCondBr(Test, ExitBB, TrapBB);
    BI->setMetadata(LLVMContext::MD_prof, VeryLikelyWeights);

    SI->addCase(CaseTypeId, TestBB);
    ++TypeIds;
  }
}

/// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
/// but also creates the ElseBlock.
/// Before:
///   Head
///   SplitBefore
///   Tail
/// After:
///   Head
///   if (Cond)
///     ThenBlock
///   else
///     ElseBlock
///   SplitBefore
///   Tail
void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
                                         TerminatorInst **ThenTerm,
                                         TerminatorInst **ElseTerm,
                                         MDNode *BranchWeights) {
  BasicBlock *Head = SplitBefore->getParent();
  BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
  TerminatorInst *HeadOldTerm = Head->getTerminator();
  LLVMContext &C = Head->getContext();
  BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
  BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
  *ThenTerm = BranchInst::Create(Tail, ThenBlock);
  *ElseTerm = BranchInst::Create(Tail, ElseBlock);
  BranchInst *HeadNewTerm =
    BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
  HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
  ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
}

TerminatorInst *llvm::SplitBlockAndInsertIfThen(Instruction *Cmp,
    bool Unreachable, MDNode *BranchWeights) {
  Instruction *SplitBefore = Cmp->getNextNode();
  BasicBlock *Head = SplitBefore->getParent();
  BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
  TerminatorInst *HeadOldTerm = Head->getTerminator();
  LLVMContext &C = Head->getContext();
  BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
  TerminatorInst *CheckTerm;
  if (Unreachable)
    CheckTerm = new UnreachableInst(C, ThenBlock);
  else
    CheckTerm = BranchInst::Create(Tail, ThenBlock);
  BranchInst *HeadNewTerm =
    BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cmp);
  HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
  ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
  return CheckTerm;
}

TerminatorInst *
llvm::SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore,
                                bool Unreachable, MDNode *BranchWeights,
                                DominatorTree *DT, LoopInfo *LI) {
  BasicBlock *Head = SplitBefore->getParent();
  BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
  TerminatorInst *HeadOldTerm = Head->getTerminator();
  LLVMContext &C = Head->getContext();
  BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
  TerminatorInst *CheckTerm;
  if (Unreachable)
    CheckTerm = new UnreachableInst(C, ThenBlock);
  else
    CheckTerm = BranchInst::Create(Tail, ThenBlock);
  CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
  BranchInst *HeadNewTerm =
    BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
  HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
  ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);

  if (DT) {
    if (DomTreeNode *OldNode = DT->getNode(Head)) {
      std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());

      DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
      for (DomTreeNode *Child : Children)
        DT->changeImmediateDominator(Child, NewNode);

      // Head dominates ThenBlock.
      DT->addNewBlock(ThenBlock, Head);
    }
  }

  if (LI) {
    if (Loop *L = LI->getLoopFor(Head)) {
      L->addBasicBlockToLoop(ThenBlock, *LI);
      L->addBasicBlockToLoop(Tail, *LI);
    }
  }

  return CheckTerm;
}

//.........这里部分代码省略.........
  //   LoopBody
  //   If (!cond) goto Exit
  // InsertBot:
  //   LoopBody
  //   If (!cond) goto Exit
  // InsertBot.next:
  // NewPreHeader:
  // ...
  // Header:
  //  LoopBody
  //  If (cond) goto Header
  // Exit:

  BasicBlock *InsertTop = SplitEdge(PreHeader, Header, DT, LI);
  BasicBlock *InsertBot =
      SplitBlock(InsertTop, InsertTop->getTerminator(), DT, LI);
  BasicBlock *NewPreHeader =
      SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);

  InsertTop->setName(Header->getName() + ".peel.begin");
  InsertBot->setName(Header->getName() + ".peel.next");
  NewPreHeader->setName(PreHeader->getName() + ".peel.newph");

  ValueToValueMapTy LVMap;

  // If we have branch weight information, we'll want to update it for the
  // newly created branches.
  BranchInst *LatchBR =
      cast<BranchInst>(cast<BasicBlock>(Latch)->getTerminator());
  unsigned HeaderIdx = (LatchBR->getSuccessor(0) == Header ? 0 : 1);

  uint64_t TrueWeight, FalseWeight;
  uint64_t ExitWeight = 0, BackEdgeWeight = 0;
  if (LatchBR->extractProfMetadata(TrueWeight, FalseWeight)) {
    ExitWeight = HeaderIdx ? TrueWeight : FalseWeight;
    BackEdgeWeight = HeaderIdx ? FalseWeight : TrueWeight;
  }

  // For each peeled-off iteration, make a copy of the loop.
  for (unsigned Iter = 0; Iter < PeelCount; ++Iter) {
    SmallVector<BasicBlock *, 8> NewBlocks;
    ValueToValueMapTy VMap;

    // The exit weight of the previous iteration is the header entry weight
    // of the current iteration. So this is exactly how many dynamic iterations
    // the current peeled-off static iteration uses up.
    // FIXME: due to the way the distribution is constructed, we need a
    // guard here to make sure we don't end up with non-positive weights.
    if (ExitWeight < BackEdgeWeight)
      BackEdgeWeight -= ExitWeight;
    else
      BackEdgeWeight = 1;

    cloneLoopBlocks(L, Iter, InsertTop, InsertBot, Exit,
                    NewBlocks, LoopBlocks, VMap, LVMap, LI);
    updateBranchWeights(InsertBot, cast<BranchInst>(VMap[LatchBR]), Iter,
                        PeelCount, ExitWeight);

    InsertTop = InsertBot;
    InsertBot = SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
    InsertBot->setName(Header->getName() + ".peel.next");

    F->getBasicBlockList().splice(InsertTop->getIterator(),
                                  F->getBasicBlockList(),
                                  NewBlocks[0]->getIterator(), F->end());

    // Remap to use values from the current iteration instead of the
    // previous one.
    remapInstructionsInBlocks(NewBlocks, VMap);
  }

  // Now adjust the phi nodes in the loop header to get their initial values
  // from the last peeled-off iteration instead of the preheader.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PHI = cast<PHINode>(I);
    Value *NewVal = PHI->getIncomingValueForBlock(Latch);
    Instruction *LatchInst = dyn_cast<Instruction>(NewVal);
    if (LatchInst && L->contains(LatchInst))
      NewVal = LVMap[LatchInst];

    PHI->setIncomingValue(PHI->getBasicBlockIndex(NewPreHeader), NewVal);
  }

  // Adjust the branch weights on the loop exit.
  if (ExitWeight) {
    MDBuilder MDB(LatchBR->getContext());
    MDNode *WeightNode =
        HeaderIdx ? MDB.createBranchWeights(ExitWeight, BackEdgeWeight)
                  : MDB.createBranchWeights(BackEdgeWeight, ExitWeight);
    LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
  }

  // If the loop is nested, we changed the parent loop, update SE.
  if (Loop *ParentLoop = L->getParentLoop())
    SE->forgetLoop(ParentLoop);

  NumPeeled++;

  return true;
}

/// buildCFICheck - emits __cfi_check for the current module.
void CrossDSOCFI::buildCFICheck(Module &M) {
  // FIXME: verify that __cfi_check ends up near the end of the code section,
  // but before the jump slots created in LowerTypeTests.
  llvm::DenseSet<uint64_t> TypeIds;
  SmallVector<MDNode *, 2> Types;
  for (GlobalObject &GO : M.global_objects()) {
    Types.clear();
    GO.getMetadata(LLVMContext::MD_type, Types);
    for (MDNode *Type : Types) {
      // Sanity check. GO must not be a function declaration.
      assert(!isa<Function>(&GO) || !cast<Function>(&GO)->isDeclaration());

      if (ConstantInt *TypeId = extractNumericTypeId(Type))
        TypeIds.insert(TypeId->getZExtValue());
    }
  }

  LLVMContext &Ctx = M.getContext();
  Constant *C = M.getOrInsertFunction(
      "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx),
      Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx), nullptr);
  Function *F = dyn_cast<Function>(C);
  F->setAlignment(4096);
  auto args = F->arg_begin();
  Value &CallSiteTypeId = *(args++);
  CallSiteTypeId.setName("CallSiteTypeId");
  Value &Addr = *(args++);
  Addr.setName("Addr");
  Value &CFICheckFailData = *(args++);
  CFICheckFailData.setName("CFICheckFailData");
  assert(args == F->arg_end());

  BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F);
  BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F);

  BasicBlock *TrapBB = BasicBlock::Create(Ctx, "fail", F);
  IRBuilder<> IRBFail(TrapBB);
  Constant *CFICheckFailFn = M.getOrInsertFunction(
      "__cfi_check_fail", Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx),
      Type::getInt8PtrTy(Ctx), nullptr);
  IRBFail.CreateCall(CFICheckFailFn, {&CFICheckFailData, &Addr});
  IRBFail.CreateBr(ExitBB);

  IRBuilder<> IRBExit(ExitBB);
  IRBExit.CreateRetVoid();

  IRBuilder<> IRB(BB);
  SwitchInst *SI = IRB.CreateSwitch(&CallSiteTypeId, TrapBB, TypeIds.size());
  for (uint64_t TypeId : TypeIds) {
    ConstantInt *CaseTypeId = ConstantInt::get(Type::getInt64Ty(Ctx), TypeId);
    BasicBlock *TestBB = BasicBlock::Create(Ctx, "test", F);
    IRBuilder<> IRBTest(TestBB);
    Function *BitsetTestFn = Intrinsic::getDeclaration(&M, Intrinsic::type_test);

    Value *Test = IRBTest.CreateCall(
        BitsetTestFn, {&Addr, MetadataAsValue::get(
                                  Ctx, ConstantAsMetadata::get(CaseTypeId))});
    BranchInst *BI = IRBTest.CreateCondBr(Test, ExitBB, TrapBB);
    BI->setMetadata(LLVMContext::MD_prof, VeryLikelyWeights);

    SI->addCase(CaseTypeId, TestBB);
    ++NumTypeIds;
  }
}

//.........这里部分代码省略.........

  uint64_t TrueWeight, FalseWeight;
  uint64_t ExitWeight = 0, CurHeaderWeight = 0;
  if (LatchBR->extractProfMetadata(TrueWeight, FalseWeight)) {
    ExitWeight = HeaderIdx ? TrueWeight : FalseWeight;
    // The # of times the loop body executes is the sum of the exit block
    // weight and the # of times the backedges are taken.
    CurHeaderWeight = TrueWeight + FalseWeight;
  }

  // For each peeled-off iteration, make a copy of the loop.
  for (unsigned Iter = 0; Iter < PeelCount; ++Iter) {
    SmallVector<BasicBlock *, 8> NewBlocks;
    ValueToValueMapTy VMap;

    // Subtract the exit weight from the current header weight -- the exit
    // weight is exactly the weight of the previous iteration's header.
    // FIXME: due to the way the distribution is constructed, we need a
    // guard here to make sure we don't end up with non-positive weights.
    if (ExitWeight < CurHeaderWeight)
      CurHeaderWeight -= ExitWeight;
    else
      CurHeaderWeight = 1;

    cloneLoopBlocks(L, Iter, InsertTop, InsertBot, Exit,
                    NewBlocks, LoopBlocks, VMap, LVMap, DT, LI);

    // Remap to use values from the current iteration instead of the
    // previous one.
    remapInstructionsInBlocks(NewBlocks, VMap);

    if (DT) {
      // Latches of the cloned loops dominate over the loop exit, so idom of the
      // latter is the first cloned loop body, as original PreHeader dominates
      // the original loop body.
      if (Iter == 0)
        DT->changeImmediateDominator(Exit, cast<BasicBlock>(LVMap[Latch]));
#ifdef EXPENSIVE_CHECKS
      assert(DT->verify(DominatorTree::VerificationLevel::Fast));
#endif
    }

    auto *LatchBRCopy = cast<BranchInst>(VMap[LatchBR]);
    updateBranchWeights(InsertBot, LatchBRCopy, Iter,
                        PeelCount, ExitWeight);
    // Remove Loop metadata from the latch branch instruction
    // because it is not the Loop's latch branch anymore.
    LatchBRCopy->setMetadata(LLVMContext::MD_loop, nullptr);

    InsertTop = InsertBot;
    InsertBot = SplitBlock(InsertBot, InsertBot->getTerminator(), DT, LI);
    InsertBot->setName(Header->getName() + ".peel.next");

    F->getBasicBlockList().splice(InsertTop->getIterator(),
                                  F->getBasicBlockList(),
                                  NewBlocks[0]->getIterator(), F->end());
  }

  // Now adjust the phi nodes in the loop header to get their initial values
  // from the last peeled-off iteration instead of the preheader.
  for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
    PHINode *PHI = cast<PHINode>(I);
    Value *NewVal = PHI->getIncomingValueForBlock(Latch);
    Instruction *LatchInst = dyn_cast<Instruction>(NewVal);
    if (LatchInst && L->contains(LatchInst))
      NewVal = LVMap[LatchInst];

    PHI->setIncomingValue(PHI->getBasicBlockIndex(NewPreHeader), NewVal);
  }

  // Adjust the branch weights on the loop exit.
  if (ExitWeight) {
    // The backedge count is the difference of current header weight and
    // current loop exit weight. If the current header weight is smaller than
    // the current loop exit weight, we mark the loop backedge weight as 1.
    uint64_t BackEdgeWeight = 0;
    if (ExitWeight < CurHeaderWeight)
      BackEdgeWeight = CurHeaderWeight - ExitWeight;
    else
      BackEdgeWeight = 1;
    MDBuilder MDB(LatchBR->getContext());
    MDNode *WeightNode =
        HeaderIdx ? MDB.createBranchWeights(ExitWeight, BackEdgeWeight)
                  : MDB.createBranchWeights(BackEdgeWeight, ExitWeight);
    LatchBR->setMetadata(LLVMContext::MD_prof, WeightNode);
  }

  if (Loop *ParentLoop = L->getParentLoop())
    L = ParentLoop;

  // We modified the loop, update SE.
  SE->forgetTopmostLoop(L);

  // FIXME: Incrementally update loop-simplify
  simplifyLoop(L, DT, LI, SE, AC, PreserveLCSSA);

  NumPeeled++;

  return true;
}