/// SplitCriticalEdge - If this edge is a critical edge, insert a new node to /// split the critical edge. This will update DominatorTree information if it /// is available, thus calling this pass will not invalidate either of them. /// This returns the new block if the edge was split, null otherwise. /// /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the /// specified successor will be merged into the same critical edge block. /// This is most commonly interesting with switch instructions, which may /// have many edges to any one destination. This ensures that all edges to that /// dest go to one block instead of each going to a different block, but isn't /// the standard definition of a "critical edge". /// /// It is invalid to call this function on a critical edge that starts at an /// IndirectBrInst. Splitting these edges will almost always create an invalid /// program because the address of the new block won't be the one that is jumped /// to. /// BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P, bool MergeIdenticalEdges, bool DontDeleteUselessPhis, bool SplitLandingPads) { if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0; assert(!isa<IndirectBrInst>(TI) && "Cannot split critical edge from IndirectBrInst"); BasicBlock *TIBB = TI->getParent(); BasicBlock *DestBB = TI->getSuccessor(SuccNum); // Splitting the critical edge to a landing pad block is non-trivial. Don't do // it in this generic function. if (DestBB->isLandingPad()) return 0; // Create a new basic block, linking it into the CFG. BasicBlock *NewBB = BasicBlock::Create(TI->getContext(), TIBB->getName() + "." + DestBB->getName() + "_crit_edge"); // Create our unconditional branch. BranchInst *NewBI = BranchInst::Create(DestBB, NewBB); NewBI->setDebugLoc(TI->getDebugLoc()); // Branch to the new block, breaking the edge. TI->setSuccessor(SuccNum, NewBB); // Insert the block into the function... right after the block TI lives in. Function &F = *TIBB->getParent(); Function::iterator FBBI = TIBB; F.getBasicBlockList().insert(++FBBI, NewBB); // If there are any PHI nodes in DestBB, we need to update them so that they // merge incoming values from NewBB instead of from TIBB. { unsigned BBIdx = 0; for (BasicBlock::iterator I = DestBB->begin(); isa<PHINode>(I); ++I) { // We no longer enter through TIBB, now we come in through NewBB. // Revector exactly one entry in the PHI node that used to come from // TIBB to come from NewBB. PHINode *PN = cast<PHINode>(I); // Reuse the previous value of BBIdx if it lines up. In cases where we // have multiple phi nodes with *lots* of predecessors, this is a speed // win because we don't have to scan the PHI looking for TIBB. This // happens because the BB list of PHI nodes are usually in the same // order. if (PN->getIncomingBlock(BBIdx) != TIBB) BBIdx = PN->getBasicBlockIndex(TIBB); PN->setIncomingBlock(BBIdx, NewBB); } } // If there are any other edges from TIBB to DestBB, update those to go // through the split block, making those edges non-critical as well (and // reducing the number of phi entries in the DestBB if relevant). if (MergeIdenticalEdges) { for (unsigned i = SuccNum+1, e = TI->getNumSuccessors(); i != e; ++i) { if (TI->getSuccessor(i) != DestBB) continue; // Remove an entry for TIBB from DestBB phi nodes. DestBB->removePredecessor(TIBB, DontDeleteUselessPhis); // We found another edge to DestBB, go to NewBB instead. TI->setSuccessor(i, NewBB); } } // If we don't have a pass object, we can't update anything... if (P == 0) return NewBB; DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>(); // If we have nothing to update, just return. if (DT == 0 && LI == 0) return NewBB; // Now update analysis information. Since the only predecessor of NewBB is // the TIBB, TIBB clearly dominates NewBB. TIBB usually doesn't dominate // anything, as there are other successors of DestBB. However, if all other // predecessors of DestBB are already dominated by DestBB (e.g. DestBB is a // loop header) then NewBB dominates DestBB. SmallVector<BasicBlock*, 8> OtherPreds; // If there is a PHI in the block, loop over predecessors with it, which is // faster than iterating pred_begin/end. if (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) if (PN->getIncomingBlock(i) != NewBB) OtherPreds.push_back(PN->getIncomingBlock(i)); } else { for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB); I != E; ++I) { BasicBlock *P = *I; if (P != NewBB) OtherPreds.push_back(P); } } bool NewBBDominatesDestBB = true; // Should we update DominatorTree information? if (DT) { DomTreeNode *TINode = DT->getNode(TIBB); // The new block is not the immediate dominator for any other nodes, but // TINode is the immediate dominator for the new node. // if (TINode) { // Don't break unreachable code! DomTreeNode *NewBBNode = DT->addNewBlock(NewBB, TIBB); DomTreeNode *DestBBNode = 0; // If NewBBDominatesDestBB hasn't been computed yet, do so with DT. if (!OtherPreds.empty()) { DestBBNode = DT->getNode(DestBB); while (!OtherPreds.empty() && NewBBDominatesDestBB) { if (DomTreeNode *OPNode = DT->getNode(OtherPreds.back())) NewBBDominatesDestBB = DT->dominates(DestBBNode, OPNode); OtherPreds.pop_back(); } OtherPreds.clear(); } // If NewBBDominatesDestBB, then NewBB dominates DestBB, otherwise it // doesn't dominate anything. if (NewBBDominatesDestBB) { if (!DestBBNode) DestBBNode = DT->getNode(DestBB); DT->changeImmediateDominator(DestBBNode, NewBBNode); } } } // Update LoopInfo if it is around. if (LI) { if (Loop *TIL = LI->getLoopFor(TIBB)) { // If one or the other blocks were not in a loop, the new block is not // either, and thus LI doesn't need to be updated. if (Loop *DestLoop = LI->getLoopFor(DestBB)) { if (TIL == DestLoop) { // Both in the same loop, the NewBB joins loop. DestLoop->addBasicBlockToLoop(NewBB, LI->getBase()); } else if (TIL->contains(DestLoop)) { // Edge from an outer loop to an inner loop. Add to the outer loop. TIL->addBasicBlockToLoop(NewBB, LI->getBase()); } else if (DestLoop->contains(TIL)) { // Edge from an inner loop to an outer loop. Add to the outer loop. DestLoop->addBasicBlockToLoop(NewBB, LI->getBase()); } else { // Edge from two loops with no containment relation. Because these // are natural loops, we know that the destination block must be the // header of its loop (adding a branch into a loop elsewhere would // create an irreducible loop). assert(DestLoop->getHeader() == DestBB && "Should not create irreducible loops!"); if (Loop *P = DestLoop->getParentLoop()) P->addBasicBlockToLoop(NewBB, LI->getBase()); } } // If TIBB is in a loop and DestBB is outside of that loop, split the // other exit blocks of the loop that also have predecessors outside // the loop, to maintain a LoopSimplify guarantee. if (!TIL->contains(DestBB) && P->mustPreserveAnalysisID(LoopSimplifyID)) { assert(!TIL->contains(NewBB) && "Split point for loop exit is contained in loop!"); // Update LCSSA form in the newly created exit block. if (P->mustPreserveAnalysisID(LCSSAID)) createPHIsForSplitLoopExit(TIBB, NewBB, DestBB); // For each unique exit block... // FIXME: This code is functionally equivalent to the corresponding // loop in LoopSimplify. SmallVector<BasicBlock *, 4> ExitBlocks; TIL->getExitBlocks(ExitBlocks); for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { // Collect all the preds that are inside the loop, and note // whether there are any preds outside the loop. SmallVector<BasicBlock *, 4> Preds; bool HasPredOutsideOfLoop = false; BasicBlock *Exit = ExitBlocks[i]; for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I) { BasicBlock *P = *I; if (TIL->contains(P)) { if (isa<IndirectBrInst>(P->getTerminator())) { Preds.clear(); break; } Preds.push_back(P); } else { HasPredOutsideOfLoop = true; } } // If there are any preds not in the loop, we'll need to split // the edges. The Preds.empty() check is needed because a block // may appear multiple times in the list. We can't use // getUniqueExitBlocks above because that depends on LoopSimplify // form, which we're in the process of restoring! if (!Preds.empty() && HasPredOutsideOfLoop) { if (!Exit->isLandingPad()) { BasicBlock *NewExitBB = SplitBlockPredecessors(Exit, Preds, "split", P); if (P->mustPreserveAnalysisID(LCSSAID)) createPHIsForSplitLoopExit(Preds, NewExitBB, Exit); } else if (SplitLandingPads) { SmallVector<BasicBlock*, 8> NewBBs; SplitLandingPadPredecessors(Exit, Preds, ".split1", ".split2", P, NewBBs); if (P->mustPreserveAnalysisID(LCSSAID)) createPHIsForSplitLoopExit(Preds, NewBBs[0], Exit); } } } } // LCSSA form was updated above for the case where LoopSimplify is // available, which means that all predecessors of loop exit blocks // are within the loop. Without LoopSimplify form, it would be // necessary to insert a new phi. assert((!P->mustPreserveAnalysisID(LCSSAID) || P->mustPreserveAnalysisID(LoopSimplifyID)) && "SplitCriticalEdge doesn't know how to update LCCSA form " "without LoopSimplify!"); } } return NewBB; }
/// SplitCriticalEdge - If this edge is a critical edge, insert a new node to /// split the critical edge. This will update DominatorTree and /// DominatorFrontier information if it is available, thus calling this pass /// will not invalidate either of them. This returns the new block if the edge /// was split, null otherwise. /// /// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the /// specified successor will be merged into the same critical edge block. /// This is most commonly interesting with switch instructions, which may /// have many edges to any one destination. This ensures that all edges to that /// dest go to one block instead of each going to a different block, but isn't /// the standard definition of a "critical edge". /// /// It is invalid to call this function on a critical edge that starts at an /// IndirectBrInst. Splitting these edges will almost always create an invalid /// program because the address of the new block won't be the one that is jumped /// to. /// BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P, bool MergeIdenticalEdges) { if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0; assert(!isa<IndirectBrInst>(TI) && "Cannot split critical edge from IndirectBrInst"); BasicBlock *TIBB = TI->getParent(); BasicBlock *DestBB = TI->getSuccessor(SuccNum); // Create a new basic block, linking it into the CFG. BasicBlock *NewBB = BasicBlock::Create(TI->getContext(), TIBB->getName() + "." + DestBB->getName() + "_crit_edge"); // Create our unconditional branch. BranchInst::Create(DestBB, NewBB); // Branch to the new block, breaking the edge. TI->setSuccessor(SuccNum, NewBB); // Insert the block into the function... right after the block TI lives in. Function &F = *TIBB->getParent(); Function::iterator FBBI = TIBB; F.getBasicBlockList().insert(++FBBI, NewBB); // If there are any PHI nodes in DestBB, we need to update them so that they // merge incoming values from NewBB instead of from TIBB. if (PHINode *APHI = dyn_cast<PHINode>(DestBB->begin())) { // This conceptually does: // foreach (PHINode *PN in DestBB) // PN->setIncomingBlock(PN->getIncomingBlock(TIBB), NewBB); // but is optimized for two cases. if (APHI->getNumIncomingValues() <= 8) { // Small # preds case. unsigned BBIdx = 0; for (BasicBlock::iterator I = DestBB->begin(); isa<PHINode>(I); ++I) { // We no longer enter through TIBB, now we come in through NewBB. // Revector exactly one entry in the PHI node that used to come from // TIBB to come from NewBB. PHINode *PN = cast<PHINode>(I); // Reuse the previous value of BBIdx if it lines up. In cases where we // have multiple phi nodes with *lots* of predecessors, this is a speed // win because we don't have to scan the PHI looking for TIBB. This // happens because the BB list of PHI nodes are usually in the same // order. if (PN->getIncomingBlock(BBIdx) != TIBB) BBIdx = PN->getBasicBlockIndex(TIBB); PN->setIncomingBlock(BBIdx, NewBB); } } else { // However, the foreach loop is slow for blocks with lots of predecessors // because PHINode::getIncomingBlock is O(n) in # preds. Instead, walk // the user list of TIBB to find the PHI nodes. SmallPtrSet<PHINode*, 16> UpdatedPHIs; for (Value::use_iterator UI = TIBB->use_begin(), E = TIBB->use_end(); UI != E; ) { Value::use_iterator Use = UI++; if (PHINode *PN = dyn_cast<PHINode>(Use)) { // Remove one entry from each PHI. if (PN->getParent() == DestBB && UpdatedPHIs.insert(PN)) PN->setOperand(Use.getOperandNo(), NewBB); } } } } // If there are any other edges from TIBB to DestBB, update those to go // through the split block, making those edges non-critical as well (and // reducing the number of phi entries in the DestBB if relevant). if (MergeIdenticalEdges) { for (unsigned i = SuccNum+1, e = TI->getNumSuccessors(); i != e; ++i) { if (TI->getSuccessor(i) != DestBB) continue; // Remove an entry for TIBB from DestBB phi nodes. DestBB->removePredecessor(TIBB); // We found another edge to DestBB, go to NewBB instead. TI->setSuccessor(i, NewBB); } } // If we don't have a pass object, we can't update anything... if (P == 0) return NewBB; DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>(); DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>(); LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>(); ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>(); // If we have nothing to update, just return. if (DT == 0 && DF == 0 && LI == 0 && PI == 0) return NewBB; // Now update analysis information. Since the only predecessor of NewBB is // the TIBB, TIBB clearly dominates NewBB. TIBB usually doesn't dominate // anything, as there are other successors of DestBB. However, if all other // predecessors of DestBB are already dominated by DestBB (e.g. DestBB is a // loop header) then NewBB dominates DestBB. SmallVector<BasicBlock*, 8> OtherPreds; // If there is a PHI in the block, loop over predecessors with it, which is // faster than iterating pred_begin/end. if (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) if (PN->getIncomingBlock(i) != NewBB) OtherPreds.push_back(PN->getIncomingBlock(i)); } else { for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB); I != E; ++I) if (*I != NewBB) OtherPreds.push_back(*I); } bool NewBBDominatesDestBB = true; // Should we update DominatorTree information? if (DT) { DomTreeNode *TINode = DT->getNode(TIBB); // The new block is not the immediate dominator for any other nodes, but // TINode is the immediate dominator for the new node. // if (TINode) { // Don't break unreachable code! DomTreeNode *NewBBNode = DT->addNewBlock(NewBB, TIBB); DomTreeNode *DestBBNode = 0; // If NewBBDominatesDestBB hasn't been computed yet, do so with DT. if (!OtherPreds.empty()) { DestBBNode = DT->getNode(DestBB); while (!OtherPreds.empty() && NewBBDominatesDestBB) { if (DomTreeNode *OPNode = DT->getNode(OtherPreds.back())) NewBBDominatesDestBB = DT->dominates(DestBBNode, OPNode); OtherPreds.pop_back(); } OtherPreds.clear(); } // If NewBBDominatesDestBB, then NewBB dominates DestBB, otherwise it // doesn't dominate anything. if (NewBBDominatesDestBB) { if (!DestBBNode) DestBBNode = DT->getNode(DestBB); DT->changeImmediateDominator(DestBBNode, NewBBNode); } } } // Should we update DominanceFrontier information? if (DF) { // If NewBBDominatesDestBB hasn't been computed yet, do so with DF. if (!OtherPreds.empty()) { // FIXME: IMPLEMENT THIS! llvm_unreachable("Requiring domfrontiers but not idom/domtree/domset." " not implemented yet!"); } // Since the new block is dominated by its only predecessor TIBB, // it cannot be in any block's dominance frontier. If NewBB dominates // DestBB, its dominance frontier is the same as DestBB's, otherwise it is // just {DestBB}. DominanceFrontier::DomSetType NewDFSet; if (NewBBDominatesDestBB) { DominanceFrontier::iterator I = DF->find(DestBB); if (I != DF->end()) { DF->addBasicBlock(NewBB, I->second); if (I->second.count(DestBB)) { // However NewBB's frontier does not include DestBB. DominanceFrontier::iterator NF = DF->find(NewBB); DF->removeFromFrontier(NF, DestBB); } } else DF->addBasicBlock(NewBB, DominanceFrontier::DomSetType()); } else { DominanceFrontier::DomSetType NewDFSet; NewDFSet.insert(DestBB); DF->addBasicBlock(NewBB, NewDFSet); } } // Update LoopInfo if it is around. if (LI) { if (Loop *TIL = LI->getLoopFor(TIBB)) { // If one or the other blocks were not in a loop, the new block is not // either, and thus LI doesn't need to be updated. if (Loop *DestLoop = LI->getLoopFor(DestBB)) { if (TIL == DestLoop) { // Both in the same loop, the NewBB joins loop. DestLoop->addBasicBlockToLoop(NewBB, LI->getBase()); } else if (TIL->contains(DestLoop)) { // Edge from an outer loop to an inner loop. Add to the outer loop. TIL->addBasicBlockToLoop(NewBB, LI->getBase()); } else if (DestLoop->contains(TIL)) { // Edge from an inner loop to an outer loop. Add to the outer loop. DestLoop->addBasicBlockToLoop(NewBB, LI->getBase()); } else { // Edge from two loops with no containment relation. Because these // are natural loops, we know that the destination block must be the // header of its loop (adding a branch into a loop elsewhere would // create an irreducible loop). assert(DestLoop->getHeader() == DestBB && "Should not create irreducible loops!"); if (Loop *P = DestLoop->getParentLoop()) P->addBasicBlockToLoop(NewBB, LI->getBase()); } } // If TIBB is in a loop and DestBB is outside of that loop, split the // other exit blocks of the loop that also have predecessors outside // the loop, to maintain a LoopSimplify guarantee. if (!TIL->contains(DestBB) && P->mustPreserveAnalysisID(LoopSimplifyID)) { assert(!TIL->contains(NewBB) && "Split point for loop exit is contained in loop!"); // Update LCSSA form in the newly created exit block. if (P->mustPreserveAnalysisID(LCSSAID)) { SmallVector<BasicBlock *, 1> OrigPred; OrigPred.push_back(TIBB); CreatePHIsForSplitLoopExit(OrigPred, NewBB, DestBB); } // For each unique exit block... SmallVector<BasicBlock *, 4> ExitBlocks; TIL->getExitBlocks(ExitBlocks); for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { // Collect all the preds that are inside the loop, and note // whether there are any preds outside the loop. SmallVector<BasicBlock *, 4> Preds; bool HasPredOutsideOfLoop = false; BasicBlock *Exit = ExitBlocks[i]; for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I) if (TIL->contains(*I)) Preds.push_back(*I); else HasPredOutsideOfLoop = true; // If there are any preds not in the loop, we'll need to split // the edges. The Preds.empty() check is needed because a block // may appear multiple times in the list. We can't use // getUniqueExitBlocks above because that depends on LoopSimplify // form, which we're in the process of restoring! if (!Preds.empty() && HasPredOutsideOfLoop) { BasicBlock *NewExitBB = SplitBlockPredecessors(Exit, Preds.data(), Preds.size(), "split", P); if (P->mustPreserveAnalysisID(LCSSAID)) CreatePHIsForSplitLoopExit(Preds, NewExitBB, Exit); } } } // LCSSA form was updated above for the case where LoopSimplify is // available, which means that all predecessors of loop exit blocks // are within the loop. Without LoopSimplify form, it would be // necessary to insert a new phi. assert((!P->mustPreserveAnalysisID(LCSSAID) || P->mustPreserveAnalysisID(LoopSimplifyID)) && "SplitCriticalEdge doesn't know how to update LCCSA form " "without LoopSimplify!"); } } // Update ProfileInfo if it is around. if (PI) PI->splitEdge(TIBB, DestBB, NewBB, MergeIdenticalEdges); return NewBB; }
std::pair<polly::BBPair, BranchInst *> polly::executeScopConditionally(Scop &S, Value *RTC, DominatorTree &DT, RegionInfo &RI, LoopInfo &LI) { Region &R = S.getRegion(); PollyIRBuilder Builder(S.getEntry()); // Before: // // \ / // // EnteringBB // // _____|_____ // // / EntryBB \ // // | (region) | // // \_ExitingBB_/ // // | // // ExitBB // // / \ // // Create a fork block. BasicBlock *EnteringBB = S.getEnteringBlock(); BasicBlock *EntryBB = S.getEntry(); assert(EnteringBB && "Must be a simple region"); BasicBlock *SplitBlock = splitEdge(EnteringBB, EntryBB, ".split_new_and_old", &DT, &LI, &RI); SplitBlock->setName("polly.split_new_and_old"); // If EntryBB is the exit block of the region that includes Prev, exclude // SplitBlock from that region by making it itself the exit block. This is // trivially possible because there is just one edge to EnteringBB. // This is necessary because we will add an outgoing edge from SplitBlock, // which would violate the single exit block requirement of PrevRegion. Region *PrevRegion = RI.getRegionFor(EnteringBB); while (PrevRegion->getExit() == EntryBB) { PrevRegion->replaceExit(SplitBlock); PrevRegion = PrevRegion->getParent(); } RI.setRegionFor(SplitBlock, PrevRegion); // Create a join block BasicBlock *ExitingBB = S.getExitingBlock(); BasicBlock *ExitBB = S.getExit(); assert(ExitingBB && "Must be a simple region"); BasicBlock *MergeBlock = splitEdge(ExitingBB, ExitBB, ".merge_new_and_old", &DT, &LI, &RI); MergeBlock->setName("polly.merge_new_and_old"); // Exclude the join block from the region. R.replaceExitRecursive(MergeBlock); RI.setRegionFor(MergeBlock, R.getParent()); // \ / // // EnteringBB // // | // // SplitBlock // // _____|_____ // // / EntryBB \ // // | (region) | // // \_ExitingBB_/ // // | // // MergeBlock // // | // // ExitBB // // / \ // // Create the start and exiting block. Function *F = SplitBlock->getParent(); BasicBlock *StartBlock = BasicBlock::Create(F->getContext(), "polly.start", F); BasicBlock *ExitingBlock = BasicBlock::Create(F->getContext(), "polly.exiting", F); SplitBlock->getTerminator()->eraseFromParent(); Builder.SetInsertPoint(SplitBlock); BranchInst *CondBr = Builder.CreateCondBr(RTC, StartBlock, S.getEntry()); if (Loop *L = LI.getLoopFor(SplitBlock)) { L->addBasicBlockToLoop(StartBlock, LI); L->addBasicBlockToLoop(ExitingBlock, LI); } DT.addNewBlock(StartBlock, SplitBlock); DT.addNewBlock(ExitingBlock, StartBlock); RI.setRegionFor(StartBlock, RI.getRegionFor(SplitBlock)); RI.setRegionFor(ExitingBlock, RI.getRegionFor(SplitBlock)); // \ / // // EnteringBB // // | // // SplitBlock---------\ // // _____|_____ | // // / EntryBB \ StartBlock // // | (region) | | // // \_ExitingBB_/ ExitingBlock // // | // // MergeBlock // // | // // ExitBB // // / \ // // Connect start block to exiting block. Builder.SetInsertPoint(StartBlock); Builder.CreateBr(ExitingBlock); DT.changeImmediateDominator(ExitingBlock, StartBlock); // Connect exiting block to join block. Builder.SetInsertPoint(ExitingBlock); Builder.CreateBr(MergeBlock); DT.changeImmediateDominator(MergeBlock, SplitBlock); // \ / // // EnteringBB // // | // // SplitBlock---------\ // // _____|_____ | // // / EntryBB \ StartBlock // // | (region) | | // // \_ExitingBB_/ ExitingBlock // // | | // // MergeBlock---------/ // // | // // ExitBB // // / \ // // // Split the edge between SplitBlock and EntryBB, to avoid a critical edge. splitEdge(SplitBlock, EntryBB, ".pre_entry_bb", &DT, &LI, &RI); // \ / // // EnteringBB // // | // // SplitBlock---------\ // // | | // // PreEntryBB | // // _____|_____ | // // / EntryBB \ StartBlock // // | (region) | | // // \_ExitingBB_/ ExitingBlock // // | | // // MergeBlock---------/ // // | // // ExitBB // // / \ // return std::make_pair(std::make_pair(StartBlock, ExitingBlock), CondBr); }