--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/CodeGen/UnreachableBlockElim.cpp	Thu Dec 12 13:56:28 2013 +0900
@@ -0,0 +1,211 @@
+//===-- 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/ADT/DepthFirstIterator.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Target/TargetInstrInfo.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>();
+    }
+  };
+}
+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.
+  for (unsigned i = 0, e = DeadBlocks.size(); i != e; ++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);
+}