diff --git a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp b/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
--- a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
+++ b/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
@@ -213,6 +213,27 @@
   LLVM_DEBUG(dbgs() << "ARG PROMOTION:  Promoting to:" << *NF << "\n"
                     << "From: " << *F);
 
+  uint64_t LargestVectorWidth = 0;
+  for (auto *I : Params)
+    if (auto *VT = dyn_cast<llvm::VectorType>(I))
+      LargestVectorWidth = std::max(
+          LargestVectorWidth, VT->getPrimitiveSizeInBits().getKnownMinSize());
+
+  auto UpdateMLVW = [LargestVectorWidth, F](AttributeList &PAL) {
+    Attribute MLVW = PAL.getFnAttr("min-legal-vector-width");
+    if (MLVW.isValid()) {
+      uint64_t OldWidth;
+      MLVW.getValueAsString().getAsInteger(0, OldWidth);
+      if (LargestVectorWidth > OldWidth) {
+        PAL = PAL.addFnAttribute(F->getContext(), "min-legal-vector-width",
+                                 llvm::utostr(LargestVectorWidth));
+        return true;
+      }
+    }
+    return false;
+  };
+  UpdateMLVW(PAL);
+
   // Recompute the parameter attributes list based on the new arguments for
   // the function.
   NF->setAttributes(AttributeList::get(F->getContext(), PAL.getFnAttrs(),
@@ -308,6 +329,10 @@
     Args.clear();
     ArgAttrVec.clear();
 
+    AttributeList PAL = CB.getCaller()->getAttributes();
+    if (UpdateMLVW(PAL))
+      CB.getCaller()->setAttributes(PAL);
+
     // Update the callgraph to know that the callsite has been transformed.
     if (ReplaceCallSite)
       (*ReplaceCallSite)(CB, *NewCS);
diff --git a/llvm/test/Transforms/ArgumentPromotion/byval-3.ll b/llvm/test/Transforms/ArgumentPromotion/byval-3.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/ArgumentPromotion/byval-3.ll
@@ -0,0 +1,25 @@
+; RUN: opt < %s -passes=argpromotion -S | FileCheck %s
+
+; CHECK-LABEL: define i32 @foo() #0 {
+; CHECK-NEXT:      %.val = load <32 x half>, <32 x half>* undef, align 4
+; CHECK-NEXT:      call void @bar(<32 x half> %.val)
+; CHECK-NEXT:      ret i32 0
+; CHECK-NEXT:    }
+
+; CHECK-LABEL: define internal void @bar(<32 x half> %.0.val) #0 {
+; CHECK-NEXT:      ret void
+; CHECK-NEXT:    }
+
+; CHECK:    attributes #0 = { uwtable "min-legal-vector-width"="512" }
+
+define i32 @foo() #0 {
+  call void @bar(<32 x half>* undef)
+  ret i32 0
+}
+
+define internal void @bar(<32 x half>*) #0 {
+  %2 = load <32 x half>, <32 x half>* %0, align 4
+  ret void
+}
+
+attributes #0 = { uwtable "min-legal-vector-width"="0" }