--- a/lib/Transforms/Scalar/TailRecursionElimination.cpp	Mon Oct 27 20:20:15 2014 +0900
+++ b/lib/Transforms/Scalar/TailRecursionElimination.cpp	Thu Feb 19 15:19:25 2015 +0900
@@ -63,6 +63,7 @@
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/CallSite.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Function.h"
@@ -86,6 +87,7 @@
 namespace {
   struct TailCallElim : public FunctionPass {
     const TargetTransformInfo *TTI;
+    const DataLayout *DL;
 
     static char ID; // Pass identification, replacement for typeid
     TailCallElim() : FunctionPass(ID) {
@@ -136,7 +138,7 @@
 char TailCallElim::ID = 0;
 INITIALIZE_PASS_BEGIN(TailCallElim, "tailcallelim",
                       "Tail Call Elimination", false, false)
-INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_END(TailCallElim, "tailcallelim",
                     "Tail Call Elimination", false, false)
 
@@ -153,7 +155,7 @@
 #endif
 
 void TailCallElim::getAnalysisUsage(AnalysisUsage &AU) const {
-  AU.addRequired<TargetTransformInfo>();
+  AU.addRequired<TargetTransformInfoWrapperPass>();
 }
 
 /// \brief Scan the specified function for alloca instructions.
@@ -176,6 +178,8 @@
   if (skipOptnoneFunction(F))
     return false;
 
+  DL = F.getParent()->getDataLayout();
+
   bool AllCallsAreTailCalls = false;
   bool Modified = markTails(F, AllCallsAreTailCalls);
   if (AllCallsAreTailCalls)
@@ -194,7 +198,7 @@
 
     auto AddUsesToWorklist = [&](Value *V) {
       for (auto &U : V->uses()) {
-        if (!Visited.insert(&U))
+        if (!Visited.insert(&U).second)
           continue;
         Worklist.push_back(&U);
       }
@@ -406,7 +410,7 @@
   // right, so don't even try to convert it...
   if (F.getFunctionType()->isVarArg()) return false;
 
-  TTI = &getAnalysis<TargetTransformInfo>();
+  TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
   BasicBlock *OldEntry = nullptr;
   bool TailCallsAreMarkedTail = false;
   SmallVector<PHINode*, 8> ArgumentPHIs;
@@ -424,18 +428,28 @@
   // alloca' is changed from being a static alloca to being a dynamic alloca.
   // Until this is resolved, disable this transformation if that would ever
   // happen.  This bug is PR962.
+  SmallVector<BasicBlock*, 8> BBToErase;
   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
     if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
       bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
                                           ArgumentPHIs, !CanTRETailMarkedCall);
-      if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
+      if (!Change && BB->getFirstNonPHIOrDbg() == Ret) {
         Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
                                           TailCallsAreMarkedTail, ArgumentPHIs,
                                           !CanTRETailMarkedCall);
+        // FoldReturnAndProcessPred may have emptied some BB. Remember to
+        // erase them.
+        if (Change && BB->empty())
+          BBToErase.push_back(BB);
+
+      }
       MadeChange |= Change;
     }
   }
 
+  for (auto BB: BBToErase)
+    BB->eraseFromParent();
+
   // If we eliminated any tail recursions, it's possible that we inserted some
   // silly PHI nodes which just merge an initial value (the incoming operand)
   // with themselves.  Check to see if we did and clean up our mess if so.  This
@@ -474,7 +488,7 @@
       // being loaded from.
       if (CI->mayWriteToMemory() ||
           !isSafeToLoadUnconditionally(L->getPointerOperand(), L,
-                                       L->getAlignment()))
+                                       L->getAlignment(), DL))
         return false;
     }
   }
@@ -843,8 +857,20 @@
     if (CallInst *CI = FindTRECandidate(BI, CannotTailCallElimCallsMarkedTail)){
       DEBUG(dbgs() << "FOLDING: " << *BB
             << "INTO UNCOND BRANCH PRED: " << *Pred);
-      EliminateRecursiveTailCall(CI, FoldReturnIntoUncondBranch(Ret, BB, Pred),
-                                 OldEntry, TailCallsAreMarkedTail, ArgumentPHIs,
+      ReturnInst *RI = FoldReturnIntoUncondBranch(Ret, BB, Pred);
+
+      // Cleanup: if all predecessors of BB have been eliminated by
+      // FoldReturnIntoUncondBranch, we would like to delete it, but we
+      // can not just nuke it as it is being used as an iterator by our caller.
+      // Just empty it, and the caller will erase it when it is safe to do so.
+      // It is important to empty it, because the ret instruction in there is
+      // still using a value which EliminateRecursiveTailCall will attempt
+      // to remove.
+      if (!BB->hasAddressTaken() && pred_begin(BB) == pred_end(BB))
+        BB->getInstList().clear();
+
+      EliminateRecursiveTailCall(CI, RI, OldEntry, TailCallsAreMarkedTail,
+                                 ArgumentPHIs,
                                  CannotTailCallElimCallsMarkedTail);
       ++NumRetDuped;
       Change = true;