Index: lib/CodeGen/CGAtomic.cpp
===================================================================
--- lib/CodeGen/CGAtomic.cpp
+++ lib/CodeGen/CGAtomic.cpp
@@ -665,6 +665,20 @@
     MemTy = AT->getValueType();
   CharUnits sizeChars, alignChars;
   std::tie(sizeChars, alignChars) = getContext().getTypeInfoInChars(AtomicTy);
+
+  // Get alignment from declaration.
+  if (const auto *UO = dyn_cast<UnaryOperator>(E->getPtr()))
+    if (UO->getOpcode() == UO_AddrOf) {
+      CharUnits alignDecl;
+      if (const auto *DRE = dyn_cast<DeclRefExpr>(UO->getSubExpr()))
+        alignDecl =
+            getContext().toCharUnitsFromBits(DRE->getDecl()->getMaxAlignment());
+      else if (const auto *ME = dyn_cast<MemberExpr>(UO->getSubExpr()))
+        alignDecl = getContext().toCharUnitsFromBits(
+            ME->getMemberDecl()->getMaxAlignment());
+      alignChars = std::max(alignChars, alignDecl);
+    }
+
   uint64_t Size = sizeChars.getQuantity();
   unsigned MaxInlineWidthInBits = getTarget().getMaxAtomicInlineWidth();
   bool UseLibcall = (sizeChars != alignChars ||
Index: test/CodeGenCXX/atomic-align.cpp
===================================================================
--- test/CodeGenCXX/atomic-align.cpp
+++ test/CodeGenCXX/atomic-align.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 %s -std=c++11 -emit-llvm -o - -triple=x86_64-linux-gnu | FileCheck %s
+
+struct AM {
+  int f1, f2;
+};
+alignas(8) AM m;
+AM load1() {
+  AM am;
+  // m is declared to align to 8bytes, so generate load atomic instead
+  // of libcall.
+  // CHECK-LABEL: @_Z5load1v
+  // CHECK: load atomic {{.*}} monotonic
+  __atomic_load(&m, &am, 0);
+  return am;
+}
+
+struct BM {
+  int f1;
+  alignas(8) AM f2;
+};
+BM bm;
+AM load2() {
+  AM am;
+  // BM::f2 is declared to align to 8bytes, so generate load atomic instead
+  // of libcall.
+  // CHECK-LABEL: @_Z5load2v
+  // CHECK: load atomic {{.*}} monotonic
+  __atomic_load(&bm.f2, &am, 0);
+  return am;
+}