diff --git a/llvm/include/llvm/IR/IRBuilder.h b/llvm/include/llvm/IR/IRBuilder.h
index 5344a93efb33..fed2cbfa8648 100644
--- a/llvm/include/llvm/IR/IRBuilder.h
+++ b/llvm/include/llvm/IR/IRBuilder.h
@@ -438,22 +438,26 @@ public:
   /// \brief Create and insert an element unordered-atomic memcpy between the
   /// specified pointers.
   ///
+  /// DstAlign/SrcAlign are the alignments of the Dst/Src pointers, respectively.
+  ///
   /// If the pointers aren't i8*, they will be converted.  If a TBAA tag is
   /// specified, it will be added to the instruction. Likewise with alias.scope
   /// and noalias tags.
   CallInst *CreateElementUnorderedAtomicMemCpy(
-      Value *Dst, Value *Src, uint64_t Size, uint32_t ElementSize,
-      MDNode *TBAATag = nullptr, MDNode *TBAAStructTag = nullptr,
-      MDNode *ScopeTag = nullptr, MDNode *NoAliasTag = nullptr) {
+      Value *Dst, unsigned DstAlign, Value *Src, unsigned SrcAlign,
+      uint64_t Size, uint32_t ElementSize, MDNode *TBAATag = nullptr,
+      MDNode *TBAAStructTag = nullptr, MDNode *ScopeTag = nullptr,
+      MDNode *NoAliasTag = nullptr) {
     return CreateElementUnorderedAtomicMemCpy(
-        Dst, Src, getInt64(Size), ElementSize, TBAATag, TBAAStructTag, ScopeTag,
-        NoAliasTag);
+        Dst, DstAlign, Src, SrcAlign, getInt64(Size), ElementSize, TBAATag,
+        TBAAStructTag, ScopeTag, NoAliasTag);
   }
 
   CallInst *CreateElementUnorderedAtomicMemCpy(
-      Value *Dst, Value *Src, Value *Size, uint32_t ElementSize,
-      MDNode *TBAATag = nullptr, MDNode *TBAAStructTag = nullptr,
-      MDNode *ScopeTag = nullptr, MDNode *NoAliasTag = nullptr);
+      Value *Dst, unsigned DstAlign, Value *Src, unsigned SrcAlign, Value *Size,
+      uint32_t ElementSize, MDNode *TBAATag = nullptr,
+      MDNode *TBAAStructTag = nullptr, MDNode *ScopeTag = nullptr,
+      MDNode *NoAliasTag = nullptr);
 
   /// \brief Create and insert a memmove between the specified
   /// pointers.
diff --git a/llvm/lib/IR/IRBuilder.cpp b/llvm/lib/IR/IRBuilder.cpp
index 89338c8b8498..027c0255bcec 100644
--- a/llvm/lib/IR/IRBuilder.cpp
+++ b/llvm/lib/IR/IRBuilder.cpp
@@ -135,8 +135,13 @@ CreateMemCpy(Value *Dst, Value *Src, Value *Size, unsigned Align,
 }
 
 CallInst *IRBuilderBase::CreateElementUnorderedAtomicMemCpy(
-    Value *Dst, Value *Src, Value *Size, uint32_t ElementSize, MDNode *TBAATag,
-    MDNode *TBAAStructTag, MDNode *ScopeTag, MDNode *NoAliasTag) {
+    Value *Dst, unsigned DstAlign, Value *Src, unsigned SrcAlign, Value *Size,
+    uint32_t ElementSize, MDNode *TBAATag, MDNode *TBAAStructTag,
+    MDNode *ScopeTag, MDNode *NoAliasTag) {
+  assert(DstAlign >= ElementSize &&
+         "Pointer alignment must be at least element size");
+  assert(SrcAlign >= ElementSize &&
+         "Pointer alignment must be at least element size");
   Dst = getCastedInt8PtrValue(Dst);
   Src = getCastedInt8PtrValue(Src);
 
@@ -148,6 +153,10 @@ CallInst *IRBuilderBase::CreateElementUnorderedAtomicMemCpy(
 
   CallInst *CI = createCallHelper(TheFn, Ops, this);
 
+  // Set the alignment of the pointer args.
+  CI->addParamAttr(0, Attribute::getWithAlignment(CI->getContext(), DstAlign));
+  CI->addParamAttr(1, Attribute::getWithAlignment(CI->getContext(), SrcAlign));
+
   // Set the TBAA info if present.
   if (TBAATag)
     CI->setMetadata(LLVMContext::MD_tbaa, TBAATag);
diff --git a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
index eb5f3cc47cef..7234b97f64d4 100644
--- a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -1063,16 +1063,12 @@ bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
     if (StoreSize > TTI->getAtomicMemIntrinsicMaxElementSize())
       return false;
 
+    // Create the call.
+    // Note that unordered atomic loads/stores are *required* by the spec to
+    // have an alignment but non-atomic loads/stores may not.
     NewCall = Builder.CreateElementUnorderedAtomicMemCpy(
-        StoreBasePtr, LoadBasePtr, NumBytes, StoreSize);
-
-    // Propagate alignment info onto the pointer args. Note that unordered
-    // atomic loads/stores are *required* by the spec to have an alignment
-    // but non-atomic loads/stores may not.
-    NewCall->addParamAttr(0, Attribute::getWithAlignment(NewCall->getContext(),
-                                                         SI->getAlignment()));
-    NewCall->addParamAttr(1, Attribute::getWithAlignment(NewCall->getContext(),
-                                                         LI->getAlignment()));
+        StoreBasePtr, SI->getAlignment(), LoadBasePtr, LI->getAlignment(),
+        NumBytes, StoreSize);
   }
   NewCall->setDebugLoc(SI->getDebugLoc());