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infrastructure. This was essentially work toward PGO based on a design that had several flaws, partially dating from a time when LLVM had a different architecture, and with an effort to modernize it abandoned without being completed. Since then, it has bitrotted for several years further. The result is nearly unusable, and isn't helping any of the modern PGO efforts. Instead, it is getting in the way, adding confusion about PGO in LLVM and distracting everyone with maintenance on essentially dead code. Removing it paves the way for modern efforts around PGO. Among other effects, this removes the last of the runtime libraries from LLVM. Those are being developed in the separate 'compiler-rt' project now, with somewhat different licensing specifically more approriate for runtimes. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191835 91177308-0d34-0410-b5e6-96231b3b80d8
212 lines
7.1 KiB
C++
212 lines
7.1 KiB
C++
//===-- UnreachableBlockElim.cpp - Remove unreachable blocks for codegen --===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass is an extremely simple version of the SimplifyCFG pass. Its sole
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// job is to delete LLVM basic blocks that are not reachable from the entry
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// node. To do this, it performs a simple depth first traversal of the CFG,
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// then deletes any unvisited nodes.
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//
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// Note that this pass is really a hack. In particular, the instruction
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// selectors for various targets should just not generate code for unreachable
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// blocks. Until LLVM has a more systematic way of defining instruction
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// selectors, however, we cannot really expect them to handle additional
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// complexity.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/CodeGen/MachineDominators.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineModuleInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Target/TargetInstrInfo.h"
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using namespace llvm;
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namespace {
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class UnreachableBlockElim : public FunctionPass {
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virtual bool runOnFunction(Function &F);
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public:
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static char ID; // Pass identification, replacement for typeid
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UnreachableBlockElim() : FunctionPass(ID) {
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initializeUnreachableBlockElimPass(*PassRegistry::getPassRegistry());
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreserved<DominatorTree>();
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}
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};
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}
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char UnreachableBlockElim::ID = 0;
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INITIALIZE_PASS(UnreachableBlockElim, "unreachableblockelim",
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"Remove unreachable blocks from the CFG", false, false)
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FunctionPass *llvm::createUnreachableBlockEliminationPass() {
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return new UnreachableBlockElim();
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}
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bool UnreachableBlockElim::runOnFunction(Function &F) {
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SmallPtrSet<BasicBlock*, 8> Reachable;
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// Mark all reachable blocks.
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for (df_ext_iterator<Function*, SmallPtrSet<BasicBlock*, 8> > I =
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df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable); I != E; ++I)
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/* Mark all reachable blocks */;
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// Loop over all dead blocks, remembering them and deleting all instructions
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// in them.
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std::vector<BasicBlock*> DeadBlocks;
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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if (!Reachable.count(I)) {
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BasicBlock *BB = I;
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DeadBlocks.push_back(BB);
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while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
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PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
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BB->getInstList().pop_front();
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}
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for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
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(*SI)->removePredecessor(BB);
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BB->dropAllReferences();
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}
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// Actually remove the blocks now.
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for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i) {
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DeadBlocks[i]->eraseFromParent();
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}
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return DeadBlocks.size();
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}
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namespace {
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class UnreachableMachineBlockElim : public MachineFunctionPass {
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virtual bool runOnMachineFunction(MachineFunction &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const;
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MachineModuleInfo *MMI;
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public:
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static char ID; // Pass identification, replacement for typeid
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UnreachableMachineBlockElim() : MachineFunctionPass(ID) {}
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};
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}
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char UnreachableMachineBlockElim::ID = 0;
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INITIALIZE_PASS(UnreachableMachineBlockElim, "unreachable-mbb-elimination",
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"Remove unreachable machine basic blocks", false, false)
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char &llvm::UnreachableMachineBlockElimID = UnreachableMachineBlockElim::ID;
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void UnreachableMachineBlockElim::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addPreserved<MachineLoopInfo>();
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AU.addPreserved<MachineDominatorTree>();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
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SmallPtrSet<MachineBasicBlock*, 8> Reachable;
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bool ModifiedPHI = false;
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MMI = getAnalysisIfAvailable<MachineModuleInfo>();
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MachineDominatorTree *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
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MachineLoopInfo *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
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// Mark all reachable blocks.
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for (df_ext_iterator<MachineFunction*, SmallPtrSet<MachineBasicBlock*, 8> >
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I = df_ext_begin(&F, Reachable), E = df_ext_end(&F, Reachable);
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I != E; ++I)
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/* Mark all reachable blocks */;
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// Loop over all dead blocks, remembering them and deleting all instructions
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// in them.
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std::vector<MachineBasicBlock*> DeadBlocks;
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for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
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MachineBasicBlock *BB = I;
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// Test for deadness.
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if (!Reachable.count(BB)) {
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DeadBlocks.push_back(BB);
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// Update dominator and loop info.
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if (MLI) MLI->removeBlock(BB);
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if (MDT && MDT->getNode(BB)) MDT->eraseNode(BB);
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while (BB->succ_begin() != BB->succ_end()) {
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MachineBasicBlock* succ = *BB->succ_begin();
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MachineBasicBlock::iterator start = succ->begin();
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while (start != succ->end() && start->isPHI()) {
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for (unsigned i = start->getNumOperands() - 1; i >= 2; i-=2)
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if (start->getOperand(i).isMBB() &&
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start->getOperand(i).getMBB() == BB) {
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start->RemoveOperand(i);
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start->RemoveOperand(i-1);
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}
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start++;
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}
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BB->removeSuccessor(BB->succ_begin());
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}
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}
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}
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// Actually remove the blocks now.
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for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++i)
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DeadBlocks[i]->eraseFromParent();
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// Cleanup PHI nodes.
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for (MachineFunction::iterator I = F.begin(), E = F.end(); I != E; ++I) {
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MachineBasicBlock *BB = I;
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// Prune unneeded PHI entries.
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SmallPtrSet<MachineBasicBlock*, 8> preds(BB->pred_begin(),
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BB->pred_end());
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MachineBasicBlock::iterator phi = BB->begin();
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while (phi != BB->end() && phi->isPHI()) {
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for (unsigned i = phi->getNumOperands() - 1; i >= 2; i-=2)
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if (!preds.count(phi->getOperand(i).getMBB())) {
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phi->RemoveOperand(i);
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phi->RemoveOperand(i-1);
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ModifiedPHI = true;
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}
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if (phi->getNumOperands() == 3) {
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unsigned Input = phi->getOperand(1).getReg();
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unsigned Output = phi->getOperand(0).getReg();
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MachineInstr* temp = phi;
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++phi;
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temp->eraseFromParent();
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ModifiedPHI = true;
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if (Input != Output) {
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MachineRegisterInfo &MRI = F.getRegInfo();
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MRI.constrainRegClass(Input, MRI.getRegClass(Output));
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MRI.replaceRegWith(Output, Input);
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}
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continue;
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}
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++phi;
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}
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}
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F.RenumberBlocks();
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return (DeadBlocks.size() || ModifiedPHI);
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}
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