-

diff --git a/include/llvm/Analysis/VectorUtils.h b/include/llvm/Analysis/VectorUtils.h
index a73f9fc..6bd11aa 100644
--- a/include/llvm/Analysis/VectorUtils.h
+++ b/include/llvm/Analysis/VectorUtils.h
@@ -115,6 +115,14 @@ computeMinimumValueSizes(ArrayRef<BasicBlock*> Blocks,
                          const TargetTransformInfo *TTI=nullptr);
 
 /// \returns \p I after propagating metadata from \p VL.
+///
+/// Specifically, let Kinds = [MD_tbaa, MD_alias_scope, MD_noalias, MD_fpmath,
+/// MD_nontemporal].  For K in Kinds, we get the MDNode for K from each of the
+/// elements of VL, compute their "intersection" (i.e., the most generic
+/// metadata value that covers all of the individual values), and set I's
+/// metadata for M equal to the intersection value.
+///
+/// This function always sets a (possibly null) value for each K in Kinds.
 Instruction *propagateMetadata(Instruction *I, ArrayRef<Value *> VL);
 
 } // llvm namespace
diff --git a/lib/Analysis/VectorUtils.cpp b/lib/Analysis/VectorUtils.cpp
index 55cc538..e0f968d 100644
--- a/lib/Analysis/VectorUtils.cpp
+++ b/lib/Analysis/VectorUtils.cpp
@@ -454,14 +454,12 @@ Instruction *llvm::propagateMetadata(Instruction *Inst, ArrayRef<Value *> VL) {
   SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
   I0->getAllMetadataOtherThanDebugLoc(Metadata);
 
-  for (unsigned I = 0, N = Metadata.size(); I != N; ++I) {
-    unsigned Kind = Metadata[I].first;
-    MDNode *MD = Metadata[I].second;
-
-    for (int J = 1, E = VL.size(); MD && J != E; ++J) {
-      const Instruction *IJ = cast<Instruction>(VL[J]);
-      MDNode *IMD = IJ->getMetadata(Kind);
-
+  for (auto Kind : {LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
+                    LLVMContext::MD_noalias, LLVMContext::MD_fpmath,
+                    LLVMContext::MD_nontemporal}) {
+    MDNode *MD = I0->getMetadata(Kind);
+    for (int I = 1, N = VL.size(); I != N; ++I) {
+      MDNode *IMD = cast<Instruction>(VL[I])->getMetadata(Kind);
       switch (Kind) {
       case LLVMContext::MD_tbaa:
         MD = MDNode::getMostGenericTBAA(MD, IMD);
@@ -479,11 +477,9 @@ Instruction *llvm::propagateMetadata(Instruction *Inst, ArrayRef<Value *> VL) {
         MD = MDNode::intersect(MD, IMD);
         break;
       default:
-        MD = nullptr; // Remove unknown metadata.
-        break;
+        assert(false && "Unreachable");
       }
     }
-
     Inst->setMetadata(Kind, MD);
   }