Index: llvm/include/llvm/IR/Dominators.h
===================================================================
--- llvm/include/llvm/IR/Dominators.h
+++ llvm/include/llvm/IR/Dominators.h
@@ -165,6 +165,9 @@
   // Ensure base-class overloads are visible.
   using Base::dominates;
 
+  /// Return true if the (end of the) basic block BB dominates the use U.
+  bool dominates(const BasicBlock *BB, const Use &U) const;
+
   /// Return true if value Def dominates use U, in the sense that Def is
   /// available at U, and could be substituted as the used value without
   /// violating the SSA dominance requirement.
Index: llvm/lib/IR/Dominators.cpp
===================================================================
--- llvm/lib/IR/Dominators.cpp
+++ llvm/lib/IR/Dominators.cpp
@@ -112,6 +112,16 @@
            PAC.preservedSet<CFGAnalyses>());
 }
 
+bool DominatorTree::dominates(const BasicBlock *BB, const Use &U) const {
+  Instruction *UserInst = cast<Instruction>(U.getUser());
+  if (auto *PN = dyn_cast<PHINode>(UserInst))
+    // A phi use using a value from a block is dominated by the end of that
+    // block.  Note that the phi's parent block may not be.
+    return dominates(BB, PN->getIncomingBlock(U));
+  else
+    return properlyDominates(BB, UserInst->getParent());
+}
+
 // dominates - Return true if Def dominates a use in User. This performs
 // the special checks necessary if Def and User are in the same basic block.
 // Note that Def doesn't dominate a use in Def itself!
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -2693,11 +2693,10 @@
 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
                                         DominatorTree &DT,
                                         const BasicBlock *BB) {
-  auto ProperlyDominates = [&DT](const BasicBlock *BB, const Use &U) {
-    auto *I = cast<Instruction>(U.getUser())->getParent();
-    return DT.properlyDominates(BB, I);
+  auto Dominates = [&DT](const BasicBlock *BB, const Use &U) {
+    return DT.dominates(BB, U);
   };
-  return ::replaceDominatedUsesWith(From, To, BB, ProperlyDominates);
+  return ::replaceDominatedUsesWith(From, To, BB, Dominates);
 }
 
 bool llvm::callsGCLeafFunction(const CallBase *Call,
Index: llvm/test/Transforms/GVN/phi.ll
===================================================================
--- llvm/test/Transforms/GVN/phi.ll
+++ llvm/test/Transforms/GVN/phi.ll
@@ -37,10 +37,8 @@
 ; CHECK:       untaken:
 ; CHECK-NEXT:    br label [[MERGE]]
 ; CHECK:       merge:
-; CHECK-NEXT:    [[PHI1:%.*]] = phi i64 [ [[A]], [[TAKEN]] ], [ [[B:%.*]], [[UNTAKEN]] ]
-; CHECK-NEXT:    [[PHI2:%.*]] = phi i64 [ 0, [[TAKEN]] ], [ [[B]], [[UNTAKEN]] ]
-; CHECK-NEXT:    [[RET:%.*]] = sub i64 [[PHI1]], [[PHI2]]
-; CHECK-NEXT:    ret i64 [[RET]]
+; CHECK-NEXT:    [[PHI1:%.*]] = phi i64 [ 0, [[TAKEN]] ], [ [[B:%.*]], [[UNTAKEN]] ]
+; CHECK-NEXT:    ret i64 0
 ;
   br i1 %c, label %taken, label %untaken
 taken:
@@ -134,8 +132,7 @@
 ; CHECK:       untaken:
 ; CHECK-NEXT:    br label [[MERGE]]
 ; CHECK:       merge:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i64 [ [[A]], [[TAKEN]] ], [ 0, [[UNTAKEN]] ]
-; CHECK-NEXT:    ret i64 [[PHI]]
+; CHECK-NEXT:    ret i64 0
 ;
   br i1 %c, label %taken, label %untaken
 taken:
@@ -159,8 +156,7 @@
 ; CHECK:       untaken:
 ; CHECK-NEXT:    br label [[MERGE]]
 ; CHECK:       merge:
-; CHECK-NEXT:    [[PHI:%.*]] = phi i64 [ [[A]], [[TAKEN]] ], [ 0, [[UNTAKEN]] ]
-; CHECK-NEXT:    ret i64 [[PHI]]
+; CHECK-NEXT:    ret i64 0
 ;
   br i1 %c, label %taken, label %untaken
 taken: