Index: llvm/trunk/include/llvm/IR/Instructions.h
===================================================================
--- llvm/trunk/include/llvm/IR/Instructions.h
+++ llvm/trunk/include/llvm/IR/Instructions.h
@@ -2738,6 +2738,14 @@
     block_begin()[i] = BB;
   }
 
+  /// Replace every incoming basic block \p Old to basic block \p New.
+  void replaceIncomingBlockWith(BasicBlock *Old, BasicBlock *New) {
+    assert(New && Old && "PHI node got a null basic block!");
+    for (unsigned Op = 0, NumOps = getNumOperands(); Op != NumOps; ++Op)
+      if (getIncomingBlock(Op) == Old)
+        setIncomingBlock(Op, New);
+  }
+
   /// Add an incoming value to the end of the PHI list
   ///
   void addIncoming(Value *V, BasicBlock *BB) {
Index: llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
+++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
@@ -7221,11 +7221,8 @@
       std::swap(TBB, FBB);
 
     // Replace the old BB with the new BB.
-    for (PHINode &PN : TBB->phis()) {
-      int i;
-      while ((i = PN.getBasicBlockIndex(&BB)) >= 0)
-        PN.setIncomingBlock(i, TmpBB);
-    }
+    for (PHINode &PN : TBB->phis())
+      PN.replaceIncomingBlockWith(&BB, TmpBB);
 
     // Add another incoming edge form the new BB.
     for (PHINode &PN : FBB->phis()) {
Index: llvm/trunk/lib/IR/BasicBlock.cpp
===================================================================
--- llvm/trunk/lib/IR/BasicBlock.cpp
+++ llvm/trunk/lib/IR/BasicBlock.cpp
@@ -431,13 +431,8 @@
     // Loop over any phi nodes in the basic block, updating the BB field of
     // incoming values...
     BasicBlock *Successor = *I;
-    for (auto &PN : Successor->phis()) {
-      int Idx = PN.getBasicBlockIndex(this);
-      while (Idx != -1) {
-        PN.setIncomingBlock((unsigned)Idx, New);
-        Idx = PN.getBasicBlockIndex(this);
-      }
-    }
+    for (auto &PN : Successor->phis())
+      PN.replaceIncomingBlockWith(this, New);
   }
   return New;
 }
@@ -455,9 +450,7 @@
       PHINode *PN = dyn_cast<PHINode>(II);
       if (!PN)
         break;
-      int i;
-      while ((i = PN->getBasicBlockIndex(this)) >= 0)
-        PN->setIncomingBlock(i, New);
+      PN->replaceIncomingBlockWith(this, New);
     }
   }
 }
Index: llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ llvm/trunk/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -536,12 +536,6 @@
     Optional<const SCEV *> HighLimit;
   };
 
-  // A utility function that does a `replaceUsesOfWith' on the incoming block
-  // set of a `PHINode' -- replaces instances of `Block' in the `PHINode's
-  // incoming block list with `ReplaceBy'.
-  static void replacePHIBlock(PHINode *PN, BasicBlock *Block,
-                              BasicBlock *ReplaceBy);
-
   // Compute a safe set of limits for the main loop to run in -- effectively the
   // intersection of `Range' and the iteration space of the original loop.
   // Return None if unable to compute the set of subranges.
@@ -643,13 +637,6 @@
 
 } // end anonymous namespace
 
-void LoopConstrainer::replacePHIBlock(PHINode *PN, BasicBlock *Block,
-                                      BasicBlock *ReplaceBy) {
-  for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
-    if (PN->getIncomingBlock(i) == Block)
-      PN->setIncomingBlock(i, ReplaceBy);
-}
-
 /// Given a loop with an deccreasing induction variable, is it possible to
 /// safely calculate the bounds of a new loop using the given Predicate.
 static bool isSafeDecreasingBound(const SCEV *Start,
@@ -1339,7 +1326,7 @@
   // The latch exit now has a branch from `RRI.ExitSelector' instead of
   // `LS.Latch'.  The PHI nodes need to be updated to reflect that.
   for (PHINode &PN : LS.LatchExit->phis())
-    replacePHIBlock(&PN, LS.Latch, RRI.ExitSelector);
+    PN.replaceIncomingBlockWith(LS.Latch, RRI.ExitSelector);
 
   return RRI;
 }
@@ -1363,8 +1350,7 @@
   BranchInst::Create(LS.Header, Preheader);
 
   for (PHINode &PN : LS.Header->phis())
-    for (unsigned i = 0, e = PN.getNumIncomingValues(); i < e; ++i)
-      replacePHIBlock(&PN, OldPreheader, Preheader);
+    PN.replaceIncomingBlockWith(OldPreheader, Preheader);
 
   return Preheader;
 }
Index: llvm/trunk/lib/Transforms/Scalar/LoopInterchange.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopInterchange.cpp
+++ llvm/trunk/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -1281,13 +1281,8 @@
 
 static void updateIncomingBlock(BasicBlock *CurrBlock, BasicBlock *OldPred,
                                 BasicBlock *NewPred) {
-  for (PHINode &PHI : CurrBlock->phis()) {
-    unsigned Num = PHI.getNumIncomingValues();
-    for (unsigned i = 0; i < Num; ++i) {
-      if (PHI.getIncomingBlock(i) == OldPred)
-        PHI.setIncomingBlock(i, NewPred);
-    }
-  }
+  for (PHINode &PHI : CurrBlock->phis())
+    PHI.replaceIncomingBlockWith(OldPred, NewPred);
 }
 
 /// Update BI to jump to NewBB instead of OldBB. Records updates to