Index: lib/Transforms/Coroutines/CoroEarly.cpp
===================================================================
--- lib/Transforms/Coroutines/CoroEarly.cpp
+++ lib/Transforms/Coroutines/CoroEarly.cpp
@@ -12,12 +12,69 @@
 //===----------------------------------------------------------------------===//
 
 #include "CoroInternal.h"
+#include "llvm/IR/CallSite.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "coro-early"
 
+namespace {
+// Created on demand if CoroEarly pass has work to do.
+class Lowerer : public coro::LowererBase {
+  void lowerResumeOrDestroy(CallSite CS, CoroSubFnInst::ResumeKind);
+
+public:
+  Lowerer(Module &M) : LowererBase(M) {}
+  static std::unique_ptr<Lowerer> createIfNeeded(Module &M);
+  bool lowerEarlyIntrinsics(Function &F);
+};
+}
+
+// Replace a direct call to coro.resume or coro.destroy with an indirect call to
+// an address returned by coro.subfn.addr intrinsic. This is done so that
+// CGPassManager recognizes devirtualization when CoroElide pass replaces a call
+// to coro.subfn.addr with an appropriate function address.
+void Lowerer::lowerResumeOrDestroy(CallSite CS,
+                                   CoroSubFnInst::ResumeKind Index) {
+  Value *ResumeAddr =
+      makeSubFnCall(CS.getArgOperand(0), Index, CS.getInstruction());
+  CS.setCalledFunction(ResumeAddr);
+  CS.setCallingConv(CallingConv::Fast);
+}
+
+bool Lowerer::lowerEarlyIntrinsics(Function &F) {
+  bool Changed = false;
+  for (auto IB = inst_begin(F), IE = inst_end(F); IB != IE;) {
+    Instruction &I = *IB++;
+    if (auto *II = dyn_cast<IntrinsicInst>(&I)) {
+      switch (II->getIntrinsicID()) {
+      default:
+        continue;
+      case Intrinsic::coro_resume:
+        lowerResumeOrDestroy(II, CoroSubFnInst::ResumeIndex);
+        break;
+      case Intrinsic::coro_destroy:
+        lowerResumeOrDestroy(II, CoroSubFnInst::DestroyIndex);
+        break;
+      }
+      Changed = true;
+    }
+  }
+  return Changed;
+}
+
+// This pass has work to do only if we find intrinsics we are going to lower in
+// the module.
+std::unique_ptr<Lowerer> Lowerer::createIfNeeded(Module &M) {
+  if (M.getNamedValue(CORO_RESUME_STR) || M.getNamedValue(CORO_DESTROY_STR))
+    return llvm::make_unique<Lowerer>(M);
+
+  return {};
+}
+
 //===----------------------------------------------------------------------===//
 //                              Top Level Driver
 //===----------------------------------------------------------------------===//
@@ -25,12 +82,25 @@
 namespace {
 
 struct CoroEarly : public FunctionPass {
-  static char ID; // Pass identification, replacement for typeid
+  static char ID; // Pass identification, replacement for typeid.
   CoroEarly() : FunctionPass(ID) {}
 
-  bool runOnFunction(Function &F) override { return false; }
+  std::unique_ptr<Lowerer> L;
+
+  bool doInitialization(Module &M) override {
+    L = Lowerer::createIfNeeded(M);
+    return false;
+  }
+
+  bool runOnFunction(Function &F) override {
+    if (!L)
+      return false;
+
+    return L->lowerEarlyIntrinsics(F);
+  }
+
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.setPreservesAll();
+    AU.setPreservesCFG();
   }
 };
 
Index: lib/Transforms/Coroutines/CoroInstr.h
===================================================================
--- /dev/null
+++ lib/Transforms/Coroutines/CoroInstr.h
@@ -0,0 +1,67 @@
+//===-- CoroInstr.h - Coroutine Intrinsics Instruction Wrappers -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This file defines classes that make it really easy to deal with intrinsic
+// functions with the isa/dyncast family of functions.  In particular, this
+// allows you to do things like:
+//
+//     if (auto *SF = dyn_cast<CoroSubFnInst>(Inst))
+//        ... SF->getFrame() ... SF->getAlloc() ...
+//
+// All intrinsic function calls are instances of the call instruction, so these
+// are all subclasses of the CallInst class.  Note that none of these classes
+// has state or virtual methods, which is an important part of this gross/neat
+// hack working.
+//
+// The helpful comment above is borrowed from llvm/IntrinsicInst.h, we keep
+// coroutine intrinsic wrappers here since they are only used by the passes in
+// the Coroutine library.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IntrinsicInst.h"
+
+namespace llvm {
+
+#define CORO_DESTROY_STR "llvm.coro.destroy"
+#define CORO_RESUME_STR "llvm.coro.resume"
+
+/// This class represents the llvm.coro.subfn.addr instruction.
+class LLVM_LIBRARY_VISIBILITY CoroSubFnInst : public IntrinsicInst {
+  enum { FrameArg, IndexArg };
+
+public:
+  enum ResumeKind {
+    ResumeIndex,
+    DestroyIndex,
+    IndexLast,
+    IndexFirst = ResumeIndex
+  };
+
+  Value *getFrame() const { return getArgOperand(FrameArg); }
+  ResumeKind getIndex() const {
+    int64_t Index = getRawIndex()->getValue().getSExtValue();
+    assert(Index >= IndexFirst && Index < IndexLast &&
+           "unexpected CoroSubFnInst index argument");
+    return static_cast<ResumeKind>(Index);
+  }
+
+  ConstantInt *getRawIndex() const {
+    return cast<ConstantInt>(getArgOperand(IndexArg));
+  }
+
+  // Methods to support type inquiry through isa, cast, and dyn_cast:
+  static inline bool classof(const IntrinsicInst *I) {
+    return I->getIntrinsicID() == Intrinsic::coro_subfn_addr;
+  }
+  static inline bool classof(const Value *V) {
+    return isa<IntrinsicInst>(V) && classof(cast<IntrinsicInst>(V));
+  }
+};
+
+} // End namespace llvm.
Index: lib/Transforms/Coroutines/CoroInternal.h
===================================================================
--- lib/Transforms/Coroutines/CoroInternal.h
+++ lib/Transforms/Coroutines/CoroInternal.h
@@ -12,10 +12,14 @@
 #ifndef LLVM_LIB_TRANSFORMS_COROUTINES_COROINTERNAL_H
 #define LLVM_LIB_TRANSFORMS_COROUTINES_COROINTERNAL_H
 
+#include "CoroInstr.h"
 #include "llvm/Transforms/Coroutines.h"
 
 namespace llvm {
 
+class FunctionType;
+class LLVMContext;
+class Module;
 class PassRegistry;
 
 void initializeCoroEarlyPass(PassRegistry &);
@@ -23,6 +27,19 @@
 void initializeCoroElidePass(PassRegistry &);
 void initializeCoroCleanupPass(PassRegistry &);
 
-}
+namespace coro {
+
+// Keeps data and helper functions for lowering coroutine intrinsics.
+struct LowererBase {
+  Module &TheModule;
+  LLVMContext &Context;
+  FunctionType *const ResumeFnType;
+
+  LowererBase(Module &M);
+  Value *makeSubFnCall(Value *Arg, int Index, Instruction *InsertPt);
+};
+
+} // End namespace coro.
+} // End namespace llvm
 
 #endif
Index: lib/Transforms/Coroutines/Coroutines.cpp
===================================================================
--- lib/Transforms/Coroutines/Coroutines.cpp
+++ lib/Transforms/Coroutines/Coroutines.cpp
@@ -66,3 +66,31 @@
   Builder.addExtension(PassManagerBuilder::EP_OptimizerLast,
                        addCoroutineOptimizerLastPasses);
 }
+
+// Construct the lowerer base class and initialize its members.
+coro::LowererBase::LowererBase(Module &M)
+    : TheModule(M), Context(M.getContext()),
+      ResumeFnType(FunctionType::get(Type::getVoidTy(Context),
+                                     Type::getInt8PtrTy(Context),
+                                     /*isVarArg=*/false)) {}
+
+// Creates a sequence of instructions to obtain a resume function address using
+// llvm.coro.subfn.addr. It generates the following sequence:
+//
+//    call i8* @llvm.coro.subfn.addr(i8* %Arg, i8 %index)
+//    bitcast i8* %2 to void(i8*)*
+
+Value *coro::LowererBase::makeSubFnCall(Value *Arg, int Index,
+                                        Instruction *InsertPt) {
+  auto *IndexVal = ConstantInt::get(Type::getInt8Ty(Context), Index);
+  auto *Fn = Intrinsic::getDeclaration(&TheModule, Intrinsic::coro_subfn_addr);
+
+  assert(Index >= CoroSubFnInst::IndexFirst &&
+         Index < CoroSubFnInst::IndexLast &&
+         "makeSubFnCall: Index value out of range");
+  auto *Call = CallInst::Create(Fn, {Arg, IndexVal}, "", InsertPt);
+
+  auto *Bitcast =
+      new BitCastInst(Call, ResumeFnType->getPointerTo(), "", InsertPt);
+  return Bitcast;
+}
Index: test/Transforms/Coroutines/coro-early.ll
===================================================================
--- /dev/null
+++ test/Transforms/Coroutines/coro-early.ll
@@ -0,0 +1,24 @@
+; Tests that CoroEarly pass correctly lowers coro.resume and coro.destroy
+; intrinsics.
+; RUN: opt < %s -S -coro-early | FileCheck %s
+
+; CHECK-LABEL: @callResume
+define void @callResume(i8* %hdl) {
+; CHECK-NEXT: entry
+entry:
+; CHECK-NEXT: %0 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 0)
+; CHECK-NEXT: %1 = bitcast i8* %0 to void (i8*)*
+; CHECK-NEXT: call fastcc void %1(i8* %hdl)
+  call void @llvm.coro.resume(i8* %hdl)
+
+; CHECK-NEXT: %2 = call i8* @llvm.coro.subfn.addr(i8* %hdl, i8 1)
+; CHECK-NEXT: %3 = bitcast i8* %2 to void (i8*)*
+; CHECK-NEXT: call fastcc void %3(i8* %hdl)
+  call void @llvm.coro.destroy(i8* %hdl)
+
+  ret void
+; CHECK-NEXT: ret void
+}
+
+declare void @llvm.coro.resume(i8*)
+declare void @llvm.coro.destroy(i8*)