/// SplitLandingPadPredecessors - This method transforms the landing pad, /// OrigBB, by introducing two new basic blocks into the function. One of those /// new basic blocks gets the predecessors listed in Preds. The other basic /// block gets the remaining predecessors of OrigBB. The landingpad instruction /// OrigBB is clone into both of the new basic blocks. The new blocks are given /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. /// /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular, /// it does not preserve LoopSimplify (because it's complicated to handle the /// case where one of the edges being split is an exit of a loop with other /// exits). /// void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB, ArrayRef<BasicBlock*> Preds, const char *Suffix1, const char *Suffix2, Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs) { assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!"); // Create a new basic block for OrigBB's predecessors listed in Preds. Insert // it right before the original block. BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(), OrigBB->getName() + Suffix1, OrigBB->getParent(), OrigBB); NewBBs.push_back(NewBB1); // The new block unconditionally branches to the old block. BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1); // Move the edges from Preds to point to NewBB1 instead of OrigBB. for (unsigned i = 0, e = Preds.size(); i != e; ++i) { // This is slightly more strict than necessary; the minimum requirement // is that there be no more than one indirectbr branching to BB. And // all BlockAddress uses would need to be updated. assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) && "Cannot split an edge from an IndirectBrInst"); Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1); } // Update DominatorTree, LoopInfo, and LCCSA analysis information. bool HasLoopExit = false; UpdateAnalysisInformation(OrigBB, NewBB1, Preds, P, HasLoopExit); // Update the PHI nodes in OrigBB with the values coming from NewBB1. UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, P, HasLoopExit); // Move the remaining edges from OrigBB to point to NewBB2. SmallVector<BasicBlock*, 8> NewBB2Preds; for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB); i != e; ) { BasicBlock *Pred = *i++; if (Pred == NewBB1) continue; assert(!isa<IndirectBrInst>(Pred->getTerminator()) && "Cannot split an edge from an IndirectBrInst"); NewBB2Preds.push_back(Pred); e = pred_end(OrigBB); } BasicBlock *NewBB2 = 0; if (!NewBB2Preds.empty()) { // Create another basic block for the rest of OrigBB's predecessors. NewBB2 = BasicBlock::Create(OrigBB->getContext(), OrigBB->getName() + Suffix2, OrigBB->getParent(), OrigBB); NewBBs.push_back(NewBB2); // The new block unconditionally branches to the old block. BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2); // Move the remaining edges from OrigBB to point to NewBB2. for (SmallVectorImpl<BasicBlock*>::iterator i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i) (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2); // Update DominatorTree, LoopInfo, and LCCSA analysis information. HasLoopExit = false; UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, P, HasLoopExit); // Update the PHI nodes in OrigBB with the values coming from NewBB2. UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, P, HasLoopExit); } LandingPadInst *LPad = OrigBB->getLandingPadInst(); Instruction *Clone1 = LPad->clone(); Clone1->setName(Twine("lpad") + Suffix1); NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1); if (NewBB2) { Instruction *Clone2 = LPad->clone(); Clone2->setName(Twine("lpad") + Suffix2); NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2); // Create a PHI node for the two cloned landingpad instructions. PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad); PN->addIncoming(Clone1, NewBB1); PN->addIncoming(Clone2, NewBB2); LPad->replaceAllUsesWith(PN); LPad->eraseFromParent(); } else { // There is no second clone. Just replace the landing pad with the first // clone. LPad->replaceAllUsesWith(Clone1); LPad->eraseFromParent(); } }