| //===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass is an extremely simple version of the SimplifyCFG pass. Its sole |
| // job is to delete LLVM basic blocks that are not reachable from the entry |
| // node. To do this, it performs a simple depth first traversal of the CFG, |
| // then deletes any unvisited nodes. |
| // |
| // Note that this pass is really a hack. In particular, the instruction |
| // selectors for various targets should just not generate code for unreachable |
| // blocks. Until LLVM has a more systematic way of defining instruction |
| // selectors, however, we cannot really expect them to handle additional |
| // complexity. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/CodeGen/Passes.h" |
| #include "llvm/Constant.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Function.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Type.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/ProfileInfo.h" |
| #include "llvm/CodeGen/MachineDominators.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineModuleInfo.h" |
| #include "llvm/CodeGen/MachineLoopInfo.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Target/TargetInstrInfo.h" |
| #include "llvm/ADT/DepthFirstIterator.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| using namespace llvm; |
| |
| namespace { |
| class UnreachableBlockElim : public FunctionPass { |
| virtual bool runOnFunction(Function &F); |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| UnreachableBlockElim() : FunctionPass(ID) { |
| initializeUnreachableBlockElimPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addPreserved<DominatorTree>(); |
| AU.addPreserved<ProfileInfo>(); |
| } |
| }; |
| } |
| char UnreachableBlockElim::ID = 0; |
| INITIALIZE_PASS(UnreachableBlockElim, "unreachableblockelim", |
| "Remove unreachable blocks from the CFG", false, false) |
| |
| FunctionPass *llvm::createUnreachableBlockEliminationPass() { |
| return new UnreachableBlockElim(); |
| } |
| |
| bool UnreachableBlockElim::runOnFunction(Function &F) { |
| SmallPtrSet<BasicBlock*, 8> Reachable; |
| |
| // Mark all reachable blocks. |
| for (df_ext_iterator<Function*, SmallPtrSet<BasicBlock*, 8> > I = |
| df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable); I != E; ++I) |
| /* Mark all reachable blocks */; |
| |
| // Loop over all dead blocks, remembering them and deleting all instructions |
| // in them. |
| std::vector<BasicBlock*> DeadBlocks; |
| for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) |
| if (!Reachable.count(I)) { |
| BasicBlock *BB = I; |
| DeadBlocks.push_back(BB); |
| while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { |
| PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); |
| BB->getInstList().pop_front(); |
| } |
| for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) |
| (*SI)->removePredecessor(BB); |
| BB->dropAllReferences(); |
| } |
| |
| // Actually remove the blocks now. |
| ProfileInfo *PI = getAnalysisIfAvailable<ProfileInfo>(); |
| for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) { |
| if (PI) PI->removeBlock(DeadBlocks[i]); |
| DeadBlocks[i]->eraseFromParent(); |
| } |
| |
| return DeadBlocks.size(); |
| } |
| |
| |
| namespace { |
| class UnreachableMachineBlockElim : public MachineFunctionPass { |
| virtual bool runOnMachineFunction(MachineFunction &F); |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const; |
| MachineModuleInfo *MMI; |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| UnreachableMachineBlockElim() : MachineFunctionPass(ID) {} |
| }; |
| } |
| char UnreachableMachineBlockElim::ID = 0; |
| |
| INITIALIZE_PASS(UnreachableMachineBlockElim, "unreachable-mbb-elimination", |
| "Remove unreachable machine basic blocks", false, false) |
| |
| char &llvm::UnreachableMachineBlockElimID = UnreachableMachineBlockElim::ID; |
| |
| void UnreachableMachineBlockElim::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addPreserved<MachineLoopInfo>(); |
| AU.addPreserved<MachineDominatorTree>(); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) { |
| SmallPtrSet<MachineBasicBlock*, 8> Reachable; |
| bool ModifiedPHI = false; |
| |
| MMI = getAnalysisIfAvailable<MachineModuleInfo>(); |
| MachineDominatorTree *MDT = getAnalysisIfAvailable<MachineDominatorTree>(); |
| MachineLoopInfo *MLI = getAnalysisIfAvailable<MachineLoopInfo>(); |
| |
| // Mark all reachable blocks. |
| for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> > |
| I = df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable); |
| I != E; ++I) |
| /* Mark all reachable blocks */; |
| |
| // Loop over all dead blocks, remembering them and deleting all instructions |
| // in them. |
| std::vector<MachineBasicBlock*> DeadBlocks; |
| for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) { |
| MachineBasicBlock *BB = I; |
| |
| // Test for deadness. |
| if (!Reachable.count(BB)) { |
| DeadBlocks.push_back(BB); |
| |
| // Update dominator and loop info. |
| if (MLI) MLI->removeBlock(BB); |
| if (MDT && MDT->getNode(BB)) MDT->eraseNode(BB); |
| |
| while (BB->succ_begin() != BB->succ_end()) { |
| MachineBasicBlock* succ = *BB->succ_begin(); |
| |
| MachineBasicBlock::iterator start = succ->begin(); |
| while (start != succ->end() && start->isPHI()) { |
| for (unsigned i = start->getNumOperands() - 1; i >= 2; i-=2) |
| if (start->getOperand(i).isMBB() && |
| start->getOperand(i).getMBB() == BB) { |
| start->RemoveOperand(i); |
| start->RemoveOperand(i-1); |
| } |
| |
| start++; |
| } |
| |
| BB->removeSuccessor(BB->succ_begin()); |
| } |
| } |
| } |
| |
| // Actually remove the blocks now. |
| for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) |
| DeadBlocks[i]->eraseFromParent(); |
| |
| // Cleanup PHI nodes. |
| for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) { |
| MachineBasicBlock *BB = I; |
| // Prune unneeded PHI entries. |
| SmallPtrSet<MachineBasicBlock*, 8> preds(BB->pred_begin(), |
| BB->pred_end()); |
| MachineBasicBlock::iterator phi = BB->begin(); |
| while (phi != BB->end() && phi->isPHI()) { |
| for (unsigned i = phi->getNumOperands() - 1; i >= 2; i-=2) |
| if (!preds.count(phi->getOperand(i).getMBB())) { |
| phi->RemoveOperand(i); |
| phi->RemoveOperand(i-1); |
| ModifiedPHI = true; |
| } |
| |
| if (phi->getNumOperands() == 3) { |
| unsigned Input = phi->getOperand(1).getReg(); |
| unsigned Output = phi->getOperand(0).getReg(); |
| |
| MachineInstr* temp = phi; |
| ++phi; |
| temp->eraseFromParent(); |
| ModifiedPHI = true; |
| |
| if (Input != Output) { |
| MachineRegisterInfo &MRI = F.getRegInfo(); |
| MRI.constrainRegClass(Input, MRI.getRegClass(Output)); |
| MRI.replaceRegWith(Output, Input); |
| } |
| |
| continue; |
| } |
| |
| ++phi; |
| } |
| } |
| |
| F.RenumberBlocks(); |
| |
| return (DeadBlocks.size() || ModifiedPHI); |
| } |