C++ BranchInst::setCondition方法代码示例

// Tries to remove a sanity check; returns true if it worked.
bool AsapPass::optimizeCheckAway(llvm::Instruction *Inst) {
    BranchInst *BI = cast<BranchInst>(Inst);
    assert(BI->isConditional() && "Sanity check must be conditional branch.");
    
    unsigned int RegularBranch = getRegularBranch(BI, SCI);
    
    bool Changed = false;
    if (RegularBranch == 0) {
        BI->setCondition(ConstantInt::getTrue(Inst->getContext()));
        Changed = true;
    } else if (RegularBranch == 1) {
        BI->setCondition(ConstantInt::getFalse(Inst->getContext()));
        Changed = true;
    } else {
        // This can happen, e.g., in the following case:
        //     array[-1] = a + b;
        // is transformed into
        //     if (a + b overflows)
        //         report_overflow()
        //     else
        //         report_index_out_of_bounds();
        // In this case, removing the sanity check does not help much, so we
        // just do nothing.
        // Thanks to Will Dietz for his explanation at
        // http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-April/071958.html
        dbgs() << "Warning: Sanity check with no regular branch found.\n";
        dbgs() << "The sanity check has been kept intact.\n";
    }
    
    if (PrintRemovedChecks && Changed) {
        DebugLoc DL = getSanityCheckDebugLoc(BI, RegularBranch);
        printDebugLoc(DL, BI->getContext(), dbgs());
        dbgs() << ": SanityCheck with cost ";
        dbgs() << *BI->getMetadata("cost")->getOperand(0);

        if (MDNode *IA = DL.getInlinedAt()) {
            dbgs() << " (inlined at ";
            printDebugLoc(DebugLoc(IA), BI->getContext(), dbgs());
            dbgs() << ")";
        }

        BasicBlock *Succ = BI->getSuccessor(RegularBranch == 0 ? 1 : 0);
        if (const CallInst *CI = SCI->findSanityCheckCall(Succ)) {
            dbgs() << " " << CI->getCalledFunction()->getName();
        }
        dbgs() << "\n";
    }

    return Changed;
}

/// \brief Insert the missing branch conditions
void StructurizeCFG::insertConditions(bool Loops) {
  BranchVector &Conds = Loops ? LoopConds : Conditions;
  Value *Default = Loops ? BoolTrue : BoolFalse;
  SSAUpdater PhiInserter;

  for (BranchVector::iterator I = Conds.begin(),
       E = Conds.end(); I != E; ++I) {

    BranchInst *Term = *I;
    assert(Term->isConditional());

    BasicBlock *Parent = Term->getParent();
    BasicBlock *SuccTrue = Term->getSuccessor(0);
    BasicBlock *SuccFalse = Term->getSuccessor(1);

    PhiInserter.Initialize(Boolean, "");
    PhiInserter.AddAvailableValue(&Func->getEntryBlock(), Default);
    PhiInserter.AddAvailableValue(Loops ? SuccFalse : Parent, Default);

    BBPredicates &Preds = Loops ? LoopPreds[SuccFalse] : Predicates[SuccTrue];

    NearestCommonDominator Dominator(DT);
    Dominator.addBlock(Parent, false);

    Value *ParentValue = 0;
    for (BBPredicates::iterator PI = Preds.begin(), PE = Preds.end();
         PI != PE; ++PI) {

      if (PI->first == Parent) {
        ParentValue = PI->second;
        break;
      }
      PhiInserter.AddAvailableValue(PI->first, PI->second);
      Dominator.addBlock(PI->first);
    }

    if (ParentValue) {
      Term->setCondition(ParentValue);
    } else {
      if (!Dominator.wasResultExplicitMentioned())
        PhiInserter.AddAvailableValue(Dominator.getResult(), Default);

      Term->setCondition(PhiInserter.GetValueInMiddleOfBlock(Parent));
    }
  }
}

//.........这里部分代码省略.........
    	BasicBlock * safeHeader, * defHeader;
    	if (clonedBlockMap.count(firstTarget)) {
    		defHeader = firstTarget;
    		safeHeader = clonedBlockMap[firstTarget];
    		assert(safeHeader == secondTarget);
    	} else {
    		assert(clonedBlockMap.count(secondTarget));
    		defHeader = secondTarget;
			safeHeader = clonedBlockMap[secondTarget];
			assert(safeHeader == firstTarget);
    	}

    	SPM_DEBUG( dbgs() << "FASan: (Unsupported) second array in safe region controlled by " << * preHeaderBranch << "\n" );
    	Loop * defLoop = LI_->getLoopFor(defHeader);
    	assert(defLoop && "default region is not a loop!");

		Loop::block_iterator itBodyBlock,S,E;
		S = defLoop->block_begin();
		E = defLoop->block_end();

	// mark accesses in cloned region as safe
    	for (itBodyBlock = S;itBodyBlock != E; ++itBodyBlock) {
    		BasicBlock * defBodyBlock = *itBodyBlock;
    		BasicBlock * safeBodyBlock = clonedBlockMap[defBodyBlock];

    		for(auto & inst : *safeBodyBlock) {
				markSafeArrayUse(&inst, CI.Array);
			}
    	}

    // add conjunctive test
    	Value * oldCond = preHeaderBranch->getCondition();
    	Value * joinedCond = IRB.CreateAnd(oldCond, CR, "allsafe");
    	preHeaderBranch->setCondition(joinedCond);

    } else {

	  // get loop
		Loop* finalLoop = CI.FinalLoop;
		Loop::block_iterator itBodyBlock,S,E;
		S = finalLoop->block_begin();
		E = finalLoop->block_end();

	  // clone loop body (cloned loop will run unchecked)
		ValueToValueMapTy cloneMap;

		BasicBlock * clonedHeader = 0;
		std::vector<BasicBlock*> clonedBlocks;

		for (itBodyBlock = S;itBodyBlock != E; ++itBodyBlock) {

			const BasicBlock * bodyBlock = *itBodyBlock;
			BasicBlock * clonedBlock = CloneBasicBlock(bodyBlock, cloneMap, "_checked", &F, 0);

			cloneMap[bodyBlock] = clonedBlock;
			clonedBlockMap[bodyBlock] = clonedBlock;
			clonedBlocks.push_back(clonedBlock);

			if (bodyBlock == finalLoop->getHeader()) {
				clonedHeader = clonedBlock;
				SPM_DEBUG( dbgs() << "FASan: loop header case at " << bodyBlock->getName() << "\n" );
			} else {
				SPM_DEBUG( dbgs() << "FASan: non-header block at " << bodyBlock->getName() << "\n" );
			}
		}

//.........这里部分代码省略.........

    // We now have a loop-invariant count of loop iterations (which is not the
    // constant zero) for which we know that this loop will not exit via this
    // exisiting block.

    // We need to make sure that this block will run on every loop iteration.
    // For this to be true, we must dominate all blocks with backedges. Such
    // blocks are in-loop predecessors to the header block.
    bool NotAlways = false;
    for (pred_iterator PI = pred_begin(L->getHeader()),
         PIE = pred_end(L->getHeader()); PI != PIE; ++PI) {
      if (!L->contains(*PI))
        continue;

      if (!DT->dominates(*I, *PI)) {
        NotAlways = true;
        break;
      }
    }

    if (NotAlways)
      continue;

    // Make sure this blocks ends with a conditional branch.
    Instruction *TI = (*I)->getTerminator();
    if (!TI)
      continue;

    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
      if (!BI->isConditional())
        continue;

      CountedExitBranch = BI;
    } else
      continue;

    // Note that this block may not be the loop latch block, even if the loop
    // has a latch block.
    CountedExitBlock = *I;
    ExitCount = EC;
    break;
  }

  if (!CountedExitBlock)
    return MadeChange;

  BasicBlock *Preheader = L->getLoopPreheader();

  // If we don't have a preheader, then insert one. If we already have a
  // preheader, then we can use it (except if the preheader contains a use of
  // the CTR register because some such uses might be reordered by the
  // selection DAG after the mtctr instruction).
  if (!Preheader || mightUseCTR(TT, Preheader))
    Preheader = InsertPreheaderForLoop(L, this);
  if (!Preheader)
    return MadeChange;

  DEBUG(dbgs() << "Preheader for exit count: " << Preheader->getName() << "\n");

  // Insert the count into the preheader and replace the condition used by the
  // selected branch.
  MadeChange = true;

  SCEVExpander SCEVE(*SE, "loopcnt");
  LLVMContext &C = SE->getContext();
  Type *CountType = TT.isArch64Bit() ? Type::getInt64Ty(C) :
                                       Type::getInt32Ty(C);
  if (!ExitCount->getType()->isPointerTy() &&
      ExitCount->getType() != CountType)
    ExitCount = SE->getZeroExtendExpr(ExitCount, CountType);
  ExitCount = SE->getAddExpr(ExitCount,
                             SE->getConstant(CountType, 1)); 
  Value *ECValue = SCEVE.expandCodeFor(ExitCount, CountType,
                                       Preheader->getTerminator());

  IRBuilder<> CountBuilder(Preheader->getTerminator());
  Module *M = Preheader->getParent()->getParent();
  Value *MTCTRFunc = Intrinsic::getDeclaration(M, Intrinsic::ppc_mtctr,
                                               CountType);
  CountBuilder.CreateCall(MTCTRFunc, ECValue);

  IRBuilder<> CondBuilder(CountedExitBranch);
  Value *DecFunc =
    Intrinsic::getDeclaration(M, Intrinsic::ppc_is_decremented_ctr_nonzero);
  Value *NewCond = CondBuilder.CreateCall(DecFunc);
  Value *OldCond = CountedExitBranch->getCondition();
  CountedExitBranch->setCondition(NewCond);

  // The false branch must exit the loop.
  if (!L->contains(CountedExitBranch->getSuccessor(0)))
    CountedExitBranch->swapSuccessors();

  // The old condition may be dead now, and may have even created a dead PHI
  // (the original induction variable).
  RecursivelyDeleteTriviallyDeadInstructions(OldCond);
  DeleteDeadPHIs(CountedExitBlock);

  ++NumCTRLoops;
  return MadeChange;
}

//.........这里部分代码省略.........
     // the IDom in that case.
     for (BasicBlock *SuccBB: successors(BB))
       if (ImmediateSuccessorsOfExitBlocks.insert(SuccBB).second) {
         if (DT->getNode(SuccBB)->getIDom()->getBlock() == Header) {
           assert(!SuccBB->getSinglePredecessor() &&
                  "BB should be the IDom then!");
           DT->changeImmediateDominator(SuccBB, PreHeader);
         }
       }
    }
  }

  // Loop structure should be the following:
  //  Epilog             Prolog
  //
  // PreHeader         PreHeader
  // NewPreHeader      PrologPreHeader
  //   Header            PrologHeader
  //   ...               ...
  //   Latch             PrologLatch
  // NewExit           PrologExit
  // EpilogPreHeader   NewPreHeader
  //   EpilogHeader      Header
  //   ...               ...
  //   EpilogLatch       Latch
  // LatchExit              LatchExit

  // Rewrite the cloned instruction operands to use the values created when the
  // clone is created.
  for (BasicBlock *BB : NewBlocks) {
    for (Instruction &I : *BB) {
      RemapInstruction(&I, VMap,
                       RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
    }
  }

  if (UseEpilogRemainder) {
    // Connect the epilog code to the original loop and update the
    // PHI functions.
    ConnectEpilog(L, ModVal, NewExit, LatchExit, PreHeader,
                  EpilogPreHeader, NewPreHeader, VMap, DT, LI,
                  PreserveLCSSA);

    // Update counter in loop for unrolling.
    // I should be multiply of Count.
    IRBuilder<> B2(NewPreHeader->getTerminator());
    Value *TestVal = B2.CreateSub(TripCount, ModVal, "unroll_iter");
    BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
    B2.SetInsertPoint(LatchBR);
    PHINode *NewIdx = PHINode::Create(TestVal->getType(), 2, "niter",
                                      Header->getFirstNonPHI());
    Value *IdxSub =
        B2.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
                     NewIdx->getName() + ".nsub");
    Value *IdxCmp;
    if (LatchBR->getSuccessor(0) == Header)
      IdxCmp = B2.CreateIsNotNull(IdxSub, NewIdx->getName() + ".ncmp");
    else
      IdxCmp = B2.CreateIsNull(IdxSub, NewIdx->getName() + ".ncmp");
    NewIdx->addIncoming(TestVal, NewPreHeader);
    NewIdx->addIncoming(IdxSub, Latch);
    LatchBR->setCondition(IdxCmp);
  } else {
    // Connect the prolog code to the original loop and update the
    // PHI functions.
    ConnectProlog(L, BECount, Count, PrologExit, LatchExit, PreHeader,
                  NewPreHeader, VMap, DT, LI, PreserveLCSSA);
  }

  // If this loop is nested, then the loop unroller changes the code in the
  // parent loop, so the Scalar Evolution pass needs to be run again.
  if (Loop *ParentLoop = L->getParentLoop())
    SE->forgetLoop(ParentLoop);

  // Canonicalize to LoopSimplifyForm both original and remainder loops. We
  // cannot rely on the LoopUnrollPass to do this because it only does
  // canonicalization for parent/subloops and not the sibling loops.
  if (OtherExits.size() > 0) {
    // Generate dedicated exit blocks for the original loop, to preserve
    // LoopSimplifyForm.
    formDedicatedExitBlocks(L, DT, LI, PreserveLCSSA);
    // Generate dedicated exit blocks for the remainder loop if one exists, to
    // preserve LoopSimplifyForm.
    if (remainderLoop)
      formDedicatedExitBlocks(remainderLoop, DT, LI, PreserveLCSSA);
  }

  if (remainderLoop && UnrollRemainder) {
    DEBUG(dbgs() << "Unrolling remainder loop\n");
    UnrollLoop(remainderLoop, /*Count*/Count - 1, /*TripCount*/Count - 1,
               /*Force*/false, /*AllowRuntime*/false,
               /*AllowExpensiveTripCount*/false, /*PreserveCondBr*/true,
               /*PreserveOnlyFirst*/false, /*TripMultiple*/1,
               /*PeelCount*/0, /*UnrollRemainder*/false, LI, SE, DT, AC, ORE,
               PreserveLCSSA);
  }

  NumRuntimeUnrolled++;
  return true;
}

//.........这里部分代码省略.........
  // Branch to either remainder (extra iterations) loop or unrolling loop.
  B.CreateCondBr(BranchVal, RemainderLoop, UnrollingLoop);
  PreHeaderBR->eraseFromParent();
  Function *F = Header->getParent();
  // Get an ordered list of blocks in the loop to help with the ordering of the
  // cloned blocks in the prolog/epilog code
  LoopBlocksDFS LoopBlocks(L);
  LoopBlocks.perform(LI);

  //
  // For each extra loop iteration, create a copy of the loop's basic blocks
  // and generate a condition that branches to the copy depending on the
  // number of 'left over' iterations.
  //
  std::vector<BasicBlock *> NewBlocks;
  ValueToValueMapTy VMap;

  // For unroll factor 2 remainder loop will have 1 iterations.
  // Do not create 1 iteration loop.
  bool CreateRemainderLoop = (Count != 2);

  // Clone all the basic blocks in the loop. If Count is 2, we don't clone
  // the loop, otherwise we create a cloned loop to execute the extra
  // iterations. This function adds the appropriate CFG connections.
  BasicBlock *InsertBot = UseEpilogRemainder ? Exit : PrologExit;
  BasicBlock *InsertTop = UseEpilogRemainder ? EpilogPreHeader : PrologPreHeader;
  CloneLoopBlocks(L, ModVal, CreateRemainderLoop, UseEpilogRemainder, InsertTop,
                  InsertBot, NewPreHeader, NewBlocks, LoopBlocks, VMap, LI);

  // Insert the cloned blocks into the function.
  F->getBasicBlockList().splice(InsertBot->getIterator(),
                                F->getBasicBlockList(),
                                NewBlocks[0]->getIterator(),
                                F->end());

  // Loop structure should be the following:
  //  Epilog             Prolog
  //
  // PreHeader         PreHeader
  // NewPreHeader      PrologPreHeader
  //   Header            PrologHeader
  //   ...               ...
  //   Latch             PrologLatch
  // NewExit           PrologExit
  // EpilogPreHeader   NewPreHeader
  //   EpilogHeader      Header
  //   ...               ...
  //   EpilogLatch       Latch
  // Exit              Exit

  // Rewrite the cloned instruction operands to use the values created when the
  // clone is created.
  for (BasicBlock *BB : NewBlocks) {
    for (Instruction &I : *BB) {
      RemapInstruction(&I, VMap,
                       RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
    }
  }

  if (UseEpilogRemainder) {
    // Connect the epilog code to the original loop and update the
    // PHI functions.
    ConnectEpilog(L, ModVal, NewExit, Exit, PreHeader,
                  EpilogPreHeader, NewPreHeader, VMap, DT, LI,
                  PreserveLCSSA);

    // Update counter in loop for unrolling.
    // I should be multiply of Count.
    IRBuilder<> B2(NewPreHeader->getTerminator());
    Value *TestVal = B2.CreateSub(TripCount, ModVal, "unroll_iter");
    BranchInst *LatchBR = cast<BranchInst>(Latch->getTerminator());
    B2.SetInsertPoint(LatchBR);
    PHINode *NewIdx = PHINode::Create(TestVal->getType(), 2, "niter",
                                      Header->getFirstNonPHI());
    Value *IdxSub =
        B2.CreateSub(NewIdx, ConstantInt::get(NewIdx->getType(), 1),
                     NewIdx->getName() + ".nsub");
    Value *IdxCmp;
    if (LatchBR->getSuccessor(0) == Header)
      IdxCmp = B2.CreateIsNotNull(IdxSub, NewIdx->getName() + ".ncmp");
    else
      IdxCmp = B2.CreateIsNull(IdxSub, NewIdx->getName() + ".ncmp");
    NewIdx->addIncoming(TestVal, NewPreHeader);
    NewIdx->addIncoming(IdxSub, Latch);
    LatchBR->setCondition(IdxCmp);
  } else {
    // Connect the prolog code to the original loop and update the
    // PHI functions.
    ConnectProlog(L, BECount, Count, PrologExit, PreHeader, NewPreHeader,
                  VMap, DT, LI, PreserveLCSSA);
  }

  // If this loop is nested, then the loop unroller changes the code in the
  // parent loop, so the Scalar Evolution pass needs to be run again.
  if (Loop *ParentLoop = L->getParentLoop())
    SE->forgetLoop(ParentLoop);

  NumRuntimeUnrolled++;
  return true;
}

//.........这里部分代码省略.........
    // constant zero) for which we know that this loop will not exit via this
    // existing block.

    // We need to make sure that this block will run on every loop iteration.
    // For this to be true, we must dominate all blocks with backedges. Such
    // blocks are in-loop predecessors to the header block.
    bool NotAlways = false;
    for (pred_iterator PI = pred_begin(L->getHeader()),
         PIE = pred_end(L->getHeader()); PI != PIE; ++PI) {
      if (!L->contains(*PI))
        continue;

      if (!DT->dominates(*I, *PI)) {
        NotAlways = true;
        break;
      }
    }

    if (NotAlways)
      continue;

    // Make sure this blocks ends with a conditional branch.
    Instruction *TI = (*I)->getTerminator();
    if (!TI)
      continue;

    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
      if (!BI->isConditional())
        continue;

      CountedExitBranch = BI;
    } else
      continue;

    // Note that this block may not be the loop latch block, even if the loop
    // has a latch block.
    CountedExitBlock = *I;
    ExitCount = EC;
    break;
  }

  if (!CountedExitBlock)
    return MadeChange;

  BasicBlock *Preheader = L->getLoopPreheader();

  // If we don't have a preheader, then insert one. If we already have a
  // preheader, then we can use it (except if the preheader contains a use of
  // the CTR register because some such uses might be reordered by the
  // selection DAG after the mtctr instruction).
  if (!Preheader || mightUseCTR(Preheader))
    Preheader = InsertPreheaderForLoop(L, DT, LI, PreserveLCSSA);
  if (!Preheader)
    return MadeChange;

  LLVM_DEBUG(dbgs() << "Preheader for exit count: " << Preheader->getName()
                    << "\n");

  // Insert the count into the preheader and replace the condition used by the
  // selected branch.
  MadeChange = true;

  SCEVExpander SCEVE(*SE, *DL, "loopcnt");
  LLVMContext &C = SE->getContext();
  Type *CountType = TM->isPPC64() ? Type::getInt64Ty(C) : Type::getInt32Ty(C);
  if (!ExitCount->getType()->isPointerTy() &&
      ExitCount->getType() != CountType)
    ExitCount = SE->getZeroExtendExpr(ExitCount, CountType);
  ExitCount = SE->getAddExpr(ExitCount, SE->getOne(CountType));
  Value *ECValue =
      SCEVE.expandCodeFor(ExitCount, CountType, Preheader->getTerminator());

  IRBuilder<> CountBuilder(Preheader->getTerminator());
  Module *M = Preheader->getParent()->getParent();
  Function *MTCTRFunc =
      Intrinsic::getDeclaration(M, Intrinsic::ppc_mtctr, CountType);
  CountBuilder.CreateCall(MTCTRFunc, ECValue);

  IRBuilder<> CondBuilder(CountedExitBranch);
  Function *DecFunc =
      Intrinsic::getDeclaration(M, Intrinsic::ppc_is_decremented_ctr_nonzero);
  Value *NewCond = CondBuilder.CreateCall(DecFunc, {});
  Value *OldCond = CountedExitBranch->getCondition();
  CountedExitBranch->setCondition(NewCond);

  // The false branch must exit the loop.
  if (!L->contains(CountedExitBranch->getSuccessor(0)))
    CountedExitBranch->swapSuccessors();

  // The old condition may be dead now, and may have even created a dead PHI
  // (the original induction variable).
  RecursivelyDeleteTriviallyDeadInstructions(OldCond);
  // Run through the basic blocks of the loop and see if any of them have dead
  // PHIs that can be removed.
  for (auto I : L->blocks())
    DeleteDeadPHIs(I);

  ++NumCTRLoops;
  return MadeChange;
}