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diff --git a/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
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+//===- SimplifyCFGPass.cpp - CFG Simplification Pass ----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements dead code elimination and basic block merging, along
+// with a collection of other peephole control flow optimizations.  For example:
+//
+//   * Removes basic blocks with no predecessors.
+//   * Merges a basic block into its predecessor if there is only one and the
+//     predecessor only has one successor.
+//   * Eliminates PHI nodes for basic blocks with a single predecessor.
+//   * Eliminates a basic block that only contains an unconditional branch.
+//   * Changes invoke instructions to nounwind functions to be calls.
+//   * Change things like "if (x) if (y)" into "if (x&y)".
+//   * etc..
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "simplifycfg"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/Module.h"
+#include "llvm/Attributes.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+STATISTIC(NumSimpl, "Number of blocks simplified");
+
+namespace {
+  struct VISIBILITY_HIDDEN CFGSimplifyPass : public FunctionPass {
+    static char ID; // Pass identification, replacement for typeid
+    CFGSimplifyPass() : FunctionPass(&ID) {}
+
+    virtual bool runOnFunction(Function &F);
+  };
+}
+
+char CFGSimplifyPass::ID = 0;
+static RegisterPass<CFGSimplifyPass> X("simplifycfg", "Simplify the CFG");
+
+// Public interface to the CFGSimplification pass
+FunctionPass *llvm::createCFGSimplificationPass() {
+  return new CFGSimplifyPass();
+}
+
+/// ChangeToUnreachable - Insert an unreachable instruction before the specified
+/// instruction, making it and the rest of the code in the block dead.
+static void ChangeToUnreachable(Instruction *I) {
+  BasicBlock *BB = I->getParent();
+  // Loop over all of the successors, removing BB's entry from any PHI
+  // nodes.
+  for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+    (*SI)->removePredecessor(BB);
+  
+  new UnreachableInst(I);
+  
+  // All instructions after this are dead.
+  BasicBlock::iterator BBI = I, BBE = BB->end();
+  while (BBI != BBE) {
+    if (!BBI->use_empty())
+      BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
+    BB->getInstList().erase(BBI++);
+  }
+}
+
+/// ChangeToCall - Convert the specified invoke into a normal call.
+static void ChangeToCall(InvokeInst *II) {
+  BasicBlock *BB = II->getParent();
+  SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
+  CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args.begin(),
+                                       Args.end(), "", II);
+  NewCall->takeName(II);
+  NewCall->setCallingConv(II->getCallingConv());
+  NewCall->setAttributes(II->getAttributes());
+  II->replaceAllUsesWith(NewCall);
+
+  // Follow the call by a branch to the normal destination.
+  BranchInst::Create(II->getNormalDest(), II);
+
+  // Update PHI nodes in the unwind destination
+  II->getUnwindDest()->removePredecessor(BB);
+  BB->getInstList().erase(II);
+}
+
+static bool MarkAliveBlocks(BasicBlock *BB,
+                            SmallPtrSet<BasicBlock*, 128> &Reachable) {
+  
+  SmallVector<BasicBlock*, 128> Worklist;
+  Worklist.push_back(BB);
+  bool Changed = false;
+  while (!Worklist.empty()) {
+    BB = Worklist.back();
+    Worklist.pop_back();
+    
+    if (!Reachable.insert(BB))
+      continue;
+
+    // Do a quick scan of the basic block, turning any obviously unreachable
+    // instructions into LLVM unreachable insts.  The instruction combining pass
+    // canonicalizes unreachable insts into stores to null or undef.
+    for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
+      if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
+        if (CI->doesNotReturn()) {
+          // If we found a call to a no-return function, insert an unreachable
+          // instruction after it.  Make sure there isn't *already* one there
+          // though.
+          ++BBI;
+          if (!isa<UnreachableInst>(BBI)) {
+            ChangeToUnreachable(BBI);
+            Changed = true;
+          }
+          break;
+        }
+      }
+      
+      if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
+        if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
+            isa<UndefValue>(SI->getOperand(1))) {
+          ChangeToUnreachable(SI);
+          Changed = true;
+          break;
+        }
+    }
+
+    // Turn invokes that call 'nounwind' functions into ordinary calls.
+    if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
+      if (II->doesNotThrow()) {
+        ChangeToCall(II);
+        Changed = true;
+      }
+
+    Changed |= ConstantFoldTerminator(BB);
+    for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+      Worklist.push_back(*SI);
+  }
+  return Changed;
+}
+
+/// RemoveUnreachableBlocksFromFn - Remove blocks that are not reachable, even 
+/// if they are in a dead cycle.  Return true if a change was made, false 
+/// otherwise.
+static bool RemoveUnreachableBlocksFromFn(Function &F) {
+  SmallPtrSet<BasicBlock*, 128> Reachable;
+  bool Changed = MarkAliveBlocks(F.begin(), Reachable);
+  
+  // If there are unreachable blocks in the CFG...
+  if (Reachable.size() == F.size())
+    return Changed;
+  
+  assert(Reachable.size() < F.size());
+  NumSimpl += F.size()-Reachable.size();
+  
+  // Loop over all of the basic blocks that are not reachable, dropping all of
+  // their internal references...
+  for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
+    if (Reachable.count(BB))
+      continue;
+    
+    for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+      if (Reachable.count(*SI))
+        (*SI)->removePredecessor(BB);
+    BB->dropAllReferences();
+  }
+  
+  for (Function::iterator I = ++F.begin(); I != F.end();)
+    if (!Reachable.count(I))
+      I = F.getBasicBlockList().erase(I);
+    else
+      ++I;
+  
+  return true;
+}
+
+/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
+/// iterating until no more changes are made.
+static bool IterativeSimplifyCFG(Function &F) {
+  bool Changed = false;
+  bool LocalChange = true;
+  while (LocalChange) {
+    LocalChange = false;
+    
+    // Loop over all of the basic blocks (except the first one) and remove them
+    // if they are unneeded...
+    //
+    for (Function::iterator BBIt = ++F.begin(); BBIt != F.end(); ) {
+      if (SimplifyCFG(BBIt++)) {
+        LocalChange = true;
+        ++NumSimpl;
+      }
+    }
+    Changed |= LocalChange;
+  }
+  return Changed;
+}
+
+// It is possible that we may require multiple passes over the code to fully
+// simplify the CFG.
+//
+bool CFGSimplifyPass::runOnFunction(Function &F) {
+  bool EverChanged = RemoveUnreachableBlocksFromFn(F);
+  EverChanged |= IterativeSimplifyCFG(F);
+  
+  // If neither pass changed anything, we're done.
+  if (!EverChanged) return false;
+
+  // IterativeSimplifyCFG can (rarely) make some loops dead.  If this happens,
+  // RemoveUnreachableBlocksFromFn is needed to nuke them, which means we should
+  // iterate between the two optimizations.  We structure the code like this to
+  // avoid reruning IterativeSimplifyCFG if the second pass of 
+  // RemoveUnreachableBlocksFromFn doesn't do anything.
+  if (!RemoveUnreachableBlocksFromFn(F))
+    return true;
+  
+  do {
+    EverChanged = IterativeSimplifyCFG(F);
+    EverChanged |= RemoveUnreachableBlocksFromFn(F);
+  } while (EverChanged);
+  
+  return true;
+}