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diff --git a/include/llvm/ExecutionEngine/Orc/Legacy.h b/include/llvm/ExecutionEngine/Orc/Legacy.h
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+++ b/include/llvm/ExecutionEngine/Orc/Legacy.h
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+//===--- Legacy.h -- Adapters for ExecutionEngine API interop ---*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Contains core ORC APIs.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_EXECUTIONENGINE_ORC_LEGACY_H
+#define LLVM_EXECUTIONENGINE_ORC_LEGACY_H
+
+#include "llvm/ExecutionEngine/JITSymbol.h"
+#include "llvm/ExecutionEngine/Orc/Core.h"
+
+namespace llvm {
+namespace orc {
+
+/// SymbolResolver is a composable interface for looking up symbol flags
+///        and addresses using the AsynchronousSymbolQuery type. It will
+///        eventually replace the LegacyJITSymbolResolver interface as the
+///        stardard ORC symbol resolver type.
+///
+/// FIXME: SymbolResolvers should go away and be replaced with VSOs with
+///        defenition generators.
+class SymbolResolver {
+public:
+  virtual ~SymbolResolver() = default;
+
+  /// Returns the flags for each symbol in Symbols that can be found,
+  ///        along with the set of symbol that could not be found.
+  virtual SymbolFlagsMap lookupFlags(const SymbolNameSet &Symbols) = 0;
+
+  /// For each symbol in Symbols that can be found, assigns that symbols
+  ///        value in Query. Returns the set of symbols that could not be found.
+  virtual SymbolNameSet lookup(std::shared_ptr<AsynchronousSymbolQuery> Query,
+                               SymbolNameSet Symbols) = 0;
+
+private:
+  virtual void anchor();
+};
+
+/// Implements SymbolResolver with a pair of supplied function objects
+///        for convenience. See createSymbolResolver.
+template <typename LookupFlagsFn, typename LookupFn>
+class LambdaSymbolResolver final : public SymbolResolver {
+public:
+  template <typename LookupFlagsFnRef, typename LookupFnRef>
+  LambdaSymbolResolver(LookupFlagsFnRef &&LookupFlags, LookupFnRef &&Lookup)
+      : LookupFlags(std::forward<LookupFlagsFnRef>(LookupFlags)),
+        Lookup(std::forward<LookupFnRef>(Lookup)) {}
+
+  SymbolFlagsMap lookupFlags(const SymbolNameSet &Symbols) final {
+    return LookupFlags(Symbols);
+  }
+
+  SymbolNameSet lookup(std::shared_ptr<AsynchronousSymbolQuery> Query,
+                       SymbolNameSet Symbols) final {
+    return Lookup(std::move(Query), std::move(Symbols));
+  }
+
+private:
+  LookupFlagsFn LookupFlags;
+  LookupFn Lookup;
+};
+
+/// Creates a SymbolResolver implementation from the pair of supplied
+///        function objects.
+template <typename LookupFlagsFn, typename LookupFn>
+std::unique_ptr<LambdaSymbolResolver<
+    typename std::remove_cv<
+        typename std::remove_reference<LookupFlagsFn>::type>::type,
+    typename std::remove_cv<
+        typename std::remove_reference<LookupFn>::type>::type>>
+createSymbolResolver(LookupFlagsFn &&LookupFlags, LookupFn &&Lookup) {
+  using LambdaSymbolResolverImpl = LambdaSymbolResolver<
+      typename std::remove_cv<
+          typename std::remove_reference<LookupFlagsFn>::type>::type,
+      typename std::remove_cv<
+          typename std::remove_reference<LookupFn>::type>::type>;
+  return llvm::make_unique<LambdaSymbolResolverImpl>(
+      std::forward<LookupFlagsFn>(LookupFlags), std::forward<LookupFn>(Lookup));
+}
+
+class JITSymbolResolverAdapter : public JITSymbolResolver {
+public:
+  JITSymbolResolverAdapter(ExecutionSession &ES, SymbolResolver &R,
+                           MaterializationResponsibility *MR);
+  Expected<LookupFlagsResult> lookupFlags(const LookupSet &Symbols) override;
+  Expected<LookupResult> lookup(const LookupSet &Symbols) override;
+
+private:
+  ExecutionSession &ES;
+  std::set<SymbolStringPtr> ResolvedStrings;
+  SymbolResolver &R;
+  MaterializationResponsibility *MR;
+};
+
+/// Use the given legacy-style FindSymbol function (i.e. a function that
+///        takes a const std::string& or StringRef and returns a JITSymbol) to
+///        find the flags for each symbol in Symbols and store their flags in
+///        SymbolFlags. If any JITSymbol returned by FindSymbol is in an error
+///        state the function returns immediately with that error, otherwise it
+///        returns the set of symbols not found.
+///
+/// Useful for implementing lookupFlags bodies that query legacy resolvers.
+template <typename FindSymbolFn>
+Expected<SymbolFlagsMap> lookupFlagsWithLegacyFn(const SymbolNameSet &Symbols,
+                                                 FindSymbolFn FindSymbol) {
+  SymbolFlagsMap SymbolFlags;
+
+  for (auto &S : Symbols) {
+    if (JITSymbol Sym = FindSymbol(*S))
+      SymbolFlags[S] = Sym.getFlags();
+    else if (auto Err = Sym.takeError())
+      return std::move(Err);
+  }
+
+  return SymbolFlags;
+}
+
+/// Use the given legacy-style FindSymbol function (i.e. a function that
+///        takes a const std::string& or StringRef and returns a JITSymbol) to
+///        find the address and flags for each symbol in Symbols and store the
+///        result in Query. If any JITSymbol returned by FindSymbol is in an
+///        error then Query.notifyFailed(...) is called with that error and the
+///        function returns immediately. On success, returns the set of symbols
+///        not found.
+///
+/// Useful for implementing lookup bodies that query legacy resolvers.
+template <typename FindSymbolFn>
+SymbolNameSet
+lookupWithLegacyFn(ExecutionSession &ES, AsynchronousSymbolQuery &Query,
+                   const SymbolNameSet &Symbols, FindSymbolFn FindSymbol) {
+  SymbolNameSet SymbolsNotFound;
+  bool NewSymbolsResolved = false;
+
+  for (auto &S : Symbols) {
+    if (JITSymbol Sym = FindSymbol(*S)) {
+      if (auto Addr = Sym.getAddress()) {
+        Query.resolve(S, JITEvaluatedSymbol(*Addr, Sym.getFlags()));
+        Query.notifySymbolReady();
+        NewSymbolsResolved = true;
+      } else {
+        ES.legacyFailQuery(Query, Addr.takeError());
+        return SymbolNameSet();
+      }
+    } else if (auto Err = Sym.takeError()) {
+      ES.legacyFailQuery(Query, std::move(Err));
+      return SymbolNameSet();
+    } else
+      SymbolsNotFound.insert(S);
+  }
+
+  if (NewSymbolsResolved && Query.isFullyResolved())
+    Query.handleFullyResolved();
+
+  if (NewSymbolsResolved && Query.isFullyReady())
+    Query.handleFullyReady();
+
+  return SymbolsNotFound;
+}
+
+/// An ORC SymbolResolver implementation that uses a legacy
+///        findSymbol-like function to perform lookup;
+template <typename LegacyLookupFn>
+class LegacyLookupFnResolver final : public SymbolResolver {
+public:
+  using ErrorReporter = std::function<void(Error)>;
+
+  LegacyLookupFnResolver(ExecutionSession &ES, LegacyLookupFn LegacyLookup,
+                         ErrorReporter ReportError)
+      : ES(ES), LegacyLookup(std::move(LegacyLookup)),
+        ReportError(std::move(ReportError)) {}
+
+  SymbolFlagsMap lookupFlags(const SymbolNameSet &Symbols) final {
+    if (auto SymbolFlags = lookupFlagsWithLegacyFn(Symbols, LegacyLookup))
+      return std::move(*SymbolFlags);
+    else {
+      ReportError(SymbolFlags.takeError());
+      return SymbolFlagsMap();
+    }
+  }
+
+  SymbolNameSet lookup(std::shared_ptr<AsynchronousSymbolQuery> Query,
+                       SymbolNameSet Symbols) final {
+    return lookupWithLegacyFn(ES, *Query, Symbols, LegacyLookup);
+  }
+
+private:
+  ExecutionSession &ES;
+  LegacyLookupFn LegacyLookup;
+  ErrorReporter ReportError;
+};
+
+template <typename LegacyLookupFn>
+std::shared_ptr<LegacyLookupFnResolver<LegacyLookupFn>>
+createLegacyLookupResolver(ExecutionSession &ES, LegacyLookupFn LegacyLookup,
+                           std::function<void(Error)> ErrorReporter) {
+  return std::make_shared<LegacyLookupFnResolver<LegacyLookupFn>>(
+      ES, std::move(LegacyLookup), std::move(ErrorReporter));
+}
+
+} // End namespace orc
+} // End namespace llvm
+
+#endif // LLVM_EXECUTIONENGINE_ORC_LEGACY_H