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
@@ -218,9 +218,29 @@
   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](const AttributeList &PAL,
+                                            AttributeList &NewPAL) {
+    Attribute MLVW = PAL.getFnAttr("min-legal-vector-width");
+    if (MLVW.isValid()) {
+      uint64_t OldWidth;
+      MLVW.getValueAsString().getAsInteger(0, OldWidth);
+      if (LargestVectorWidth > OldWidth)
+        NewPAL = PAL.addFnAttribute(F->getContext(), "min-legal-vector-width",
+                                    llvm::utostr(LargestVectorWidth));
+    }
+  };
+  AttributeList NewPAL;
+  UpdateMLVW(PAL, NewPAL);
+
   // Recompute the parameter attributes list based on the new arguments for
   // the function.
-  NF->setAttributes(AttributeList::get(F->getContext(), PAL.getFnAttrs(),
+  NF->setAttributes(AttributeList::get(F->getContext(), NewPAL.getFnAttrs(),
                                        PAL.getRetAttrs(), ArgAttrVec));
   ArgAttrVec.clear();
 
@@ -305,9 +325,10 @@
       NewCall->setTailCallKind(cast<CallInst>(&CB)->getTailCallKind());
       NewCS = NewCall;
     }
+    UpdateMLVW(CallPAL, NewPAL);
     NewCS->setCallingConv(CB.getCallingConv());
     NewCS->setAttributes(AttributeList::get(F->getContext(),
-                                            CallPAL.getFnAttrs(),
+                                            NewPAL.getFnAttrs(),
                                             CallPAL.getRetAttrs(), ArgAttrVec));
     NewCS->copyMetadata(CB, {LLVMContext::MD_prof, LLVMContext::MD_dbg});
     Args.clear();
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) #1
+; CHECK-NEXT:      ret i32 0
+; CHECK-NEXT:    }
+
+; CHECK-LABEL: define internal void @bar(<32 x half> %.0.val) #1 {
+; CHECK-NEXT:      ret void
+; CHECK-NEXT:    }
+
+; CHECK:    attributes #1 = { 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" }