Index: clang/lib/CodeGen/CGCall.cpp
===================================================================
--- clang/lib/CodeGen/CGCall.cpp
+++ clang/lib/CodeGen/CGCall.cpp
@@ -2048,6 +2048,22 @@
       // allows it to work on indirect virtual function calls.
       if (AttrOnCallSite && TargetDecl->hasAttr<NoMergeAttr>())
         FuncAttrs.addAttribute(llvm::Attribute::NoMerge);
+
+      // Add known guaranteed alignment for allocation functions
+      if (unsigned BuiltinID = Fn->getBuiltinID()) {
+        switch (BuiltinID) {
+        case Builtin::BImalloc:
+        case Builtin::BIcalloc:
+        case Builtin::BIrealloc:
+        case Builtin::BIstrdup:
+        case Builtin::BIstrndup:
+          RetAttrs.addAlignmentAttr(Context.getTargetInfo().getNewAlign() /
+                                    Context.getTargetInfo().getCharWidth());
+          break;
+        default:
+          break;
+        }
+      }
     }
 
     // 'const', 'pure' and 'noalias' attributed functions are also nounwind.