Index: include/llvm/CodeGen/GlobalISel/GISelAccessor.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/GISelAccessor.h
+++ include/llvm/CodeGen/GlobalISel/GISelAccessor.h
@@ -17,6 +17,7 @@
 
 namespace llvm {
 class CallLowering;
+class InstructionSelector;
 class RegisterBankInfo;
 
 /// The goal of this helper class is to gather the accessor to all
@@ -27,6 +28,9 @@
 struct GISelAccessor {
   virtual ~GISelAccessor() {}
   virtual const CallLowering *getCallLowering() const { return nullptr;}
+  virtual const InstructionSelector *getInstructionSelector() const {
+    return nullptr;
+  }
   virtual const RegisterBankInfo *getRegBankInfo() const { return nullptr;}
 };
 } // End namespace llvm;
Index: include/llvm/CodeGen/GlobalISel/InstructionSelect.h
===================================================================
--- /dev/null
+++ include/llvm/CodeGen/GlobalISel/InstructionSelect.h
@@ -0,0 +1,39 @@
+//== llvm/CodeGen/GlobalISel/InstructionSelect.h -----------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file This file describes the interface of the MachineFunctionPass
+/// responsible for selecting (possibly generic) machine instructions to
+/// target-specific instructions.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_GLOBALISEL_INSTRUCTIONSELECT_H
+#define LLVM_CODEGEN_GLOBALISEL_INSTRUCTIONSELECT_H
+
+#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+
+namespace llvm {
+/// This pass is responsible for selecting generic machine instructions to
+/// target-specific instructions.  It relies on the InstructionSelector provided
+/// by the target.
+/// Selection is done by examining blocks in post-order, and instructions in
+/// reverse order.
+///
+/// \post for all inst in MF: not isPreISelGenericOpcode(inst.opcode)
+class InstructionSelect : public MachineFunctionPass {
+public:
+  static char ID;
+  const char *getPassName() const override { return "InstructionSelect"; }
+
+  InstructionSelect();
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+};
+} // End namespace llvm.
+
+#endif
Index: include/llvm/CodeGen/GlobalISel/InstructionSelector.h
===================================================================
--- /dev/null
+++ include/llvm/CodeGen/GlobalISel/InstructionSelector.h
@@ -0,0 +1,44 @@
+//==-- llvm/CodeGen/GlobalISel/InstructionSelector.h -------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file This file declares the API for the instruction selector.
+/// This class is responsible for selecting machine instructions.
+/// It's implemented by the target. It's used by the InstructionSelect pass.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_GLOBALISEL_INSTRUCTIONSELECTOR_H
+#define LLVM_CODEGEN_GLOBALISEL_INSTRUCTIONSELECTOR_H
+
+namespace llvm {
+class MachineInstr;
+class TargetInstrInfo;
+class TargetRegisterInfo;
+
+/// Provides the logic to select generic machine instructions.
+class InstructionSelector {
+public:
+  virtual ~InstructionSelector() {}
+
+  /// Select the (possibly generic) instruction \p I to only use target-specific
+  /// opcodes. It is OK to insert multiple instructions, but they cannot be
+  /// generic pre-isel instructions.
+  ///
+  /// \returns whether selection succeeded.
+  /// \pre  I.getParent() && I.getParent()->getParent()
+  /// \post if returns true: !isPreISelGenericOpcode(I.getOpcode())
+  virtual bool select(MachineInstr &I) const = 0;
+
+protected:
+  InstructionSelector();
+};
+
+} // End namespace llvm.
+
+#endif
Index: include/llvm/CodeGen/GlobalISel/RegisterBankInfo.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/RegisterBankInfo.h
+++ include/llvm/CodeGen/GlobalISel/RegisterBankInfo.h
@@ -479,6 +479,15 @@
     return &A != &B;
   }
 
+  /// Constrain the (possibly generic) virtual register \p Reg to \p RC.
+  ///
+  /// \pre \p Reg is a virtual register that either has a bank or a class.
+  /// \returns The constrained register class, or nullptr if there is none.
+  /// \note This is a generic variant of MachineRegisterInfo::constrainRegClass
+  static const TargetRegisterClass *
+  constrainGenericRegister(unsigned Reg, const TargetRegisterClass &RC,
+                           MachineRegisterInfo &MRI);
+
   /// Identifier used when the related instruction mapping instance
   /// is generated by target independent code.
   /// Make sure not to use that identifier to avoid possible collision.
Index: include/llvm/CodeGen/TargetPassConfig.h
===================================================================
--- include/llvm/CodeGen/TargetPassConfig.h
+++ include/llvm/CodeGen/TargetPassConfig.h
@@ -226,6 +226,8 @@
   /// class or register banks.
   virtual bool addRegBankSelect() { return true; }
 
+  virtual bool addGlobalInstructionSelect() { return true; }
+
   /// Add the complete, standard set of LLVM CodeGen passes.
   /// Fully developed targets will not generally override this.
   virtual void addMachinePasses();
Index: include/llvm/InitializePasses.h
===================================================================
--- include/llvm/InitializePasses.h
+++ include/llvm/InitializePasses.h
@@ -155,6 +155,7 @@
 void initializeInstSimplifierPass(PassRegistry&);
 void initializeInstrProfilingLegacyPassPass(PassRegistry &);
 void initializeInstructionCombiningPassPass(PassRegistry&);
+void initializeInstructionSelectPass(PassRegistry &);
 void initializeInterleavedAccessPass(PassRegistry &);
 void initializeInternalizeLegacyPassPass(PassRegistry&);
 void initializeIntervalPartitionPass(PassRegistry&);
Index: include/llvm/Target/TargetSubtargetInfo.h
===================================================================
--- include/llvm/Target/TargetSubtargetInfo.h
+++ include/llvm/Target/TargetSubtargetInfo.h
@@ -25,6 +25,7 @@
 
 class CallLowering;
 class DataLayout;
+class InstructionSelector;
 class MachineFunction;
 class MachineInstr;
 class RegisterBankInfo;
@@ -88,6 +89,11 @@
     return nullptr;
   }
   virtual const CallLowering *getCallLowering() const { return nullptr; }
+
+  virtual const InstructionSelector *getInstructionSelector() const {
+    return nullptr;
+  }
+
   /// Target can subclass this hook to select a different DAG scheduler.
   virtual RegisterScheduler::FunctionPassCtor
       getDAGScheduler(CodeGenOpt::Level) const {
Index: lib/CodeGen/GlobalISel/CMakeLists.txt
===================================================================
--- lib/CodeGen/GlobalISel/CMakeLists.txt
+++ lib/CodeGen/GlobalISel/CMakeLists.txt
@@ -1,6 +1,8 @@
 # List of all GlobalISel files.
 set(GLOBAL_ISEL_FILES
       IRTranslator.cpp
+      InstructionSelect.cpp
+      InstructionSelector.cpp
       MachineIRBuilder.cpp
       RegBankSelect.cpp
       RegisterBank.cpp
Index: lib/CodeGen/GlobalISel/GlobalISel.cpp
===================================================================
--- lib/CodeGen/GlobalISel/GlobalISel.cpp
+++ lib/CodeGen/GlobalISel/GlobalISel.cpp
@@ -26,5 +26,6 @@
 void llvm::initializeGlobalISel(PassRegistry &Registry) {
   initializeIRTranslatorPass(Registry);
   initializeRegBankSelectPass(Registry);
+  initializeInstructionSelectPass(Registry);
 }
 #endif // LLVM_BUILD_GLOBAL_ISEL
Index: lib/CodeGen/GlobalISel/InstructionSelect.cpp
===================================================================
--- /dev/null
+++ lib/CodeGen/GlobalISel/InstructionSelect.cpp
@@ -0,0 +1,81 @@
+//===- llvm/CodeGen/GlobalISel/InstructionSelect.cpp - InstructionSelect ---==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file implements the InstructionSelect class.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/Function.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
+
+#define DEBUG_TYPE "instruction-select"
+
+using namespace llvm;
+
+char InstructionSelect::ID = 0;
+INITIALIZE_PASS(InstructionSelect, DEBUG_TYPE,
+                "Select target instructions out of generic instructions",
+                false, false);
+
+InstructionSelect::InstructionSelect() : MachineFunctionPass(ID) {
+  initializeInstructionSelectPass(*PassRegistry::getPassRegistry());
+}
+
+static void reportSelectionError(const MachineInstr &MI, const Twine &Message) {
+  const MachineFunction &MF = *MI.getParent()->getParent();
+  std::string ErrStorage;
+  raw_string_ostream Err(ErrStorage);
+  Err << Message << ":\nIn function: " << MF.getName() << '\n' << MI << '\n';
+  report_fatal_error(Err.str());
+}
+
+bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
+  DEBUG(dbgs() << "Selecting function: " << MF.getName() << '\n');
+
+  const InstructionSelector *ISel = MF.getSubtarget().getInstructionSelector();
+  assert(ISel && "Cannot work without InstructionSelector");
+
+  // FIXME: freezeReservedRegs is now done in IRTranslator, but there are many
+  // other MF/MFI fields we need to initialize.
+  // FIXME: We could introduce new blocks and will need to fix the outer loop.
+  for (MachineBasicBlock *MBB : post_order(&MF)) {
+    for (MachineBasicBlock::reverse_iterator MII = MBB->rbegin(),
+                                             End = MBB->rend();
+         MII != End;) {
+      MachineInstr &MI = *MII++;
+      DEBUG(dbgs() << "Selecting: " << MI << '\n');
+      if (!ISel->select(MI))
+        reportSelectionError(MI, "Cannot select");
+      // FIXME: It would be nice to dump all inserted instructions.  It's not
+      // obvious how, esp. considering select() can insert after MI.
+    }
+  }
+
+  // Check that we did select everything. Do this separately to make sure we
+  // didn't miss any newly inserted instructions.
+  // FIXME: This (and other checks) should move into a verifier.
+  // FIXME: That would also let us selectively enable it.
+  for (MachineBasicBlock &MBB : MF) {
+    for (MachineInstr &MI : MBB) {
+      if (isPreISelGenericOpcode(MI.getOpcode())) {
+        reportSelectionError(
+            MI, "Generic instruction survived instruction selection");
+      }
+    }
+  }
+
+  // FIXME: Should we accurately track changes?
+  return true;
+}
Index: lib/CodeGen/GlobalISel/InstructionSelector.cpp
===================================================================
--- /dev/null
+++ lib/CodeGen/GlobalISel/InstructionSelector.cpp
@@ -0,0 +1,19 @@
+//===- llvm/CodeGen/GlobalISel/InstructionSelector.cpp -----------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file implements the InstructionSelector class.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
+
+#define DEBUG_TYPE "instructionselector"
+
+using namespace llvm;
+
+InstructionSelector::InstructionSelector() {}
Index: lib/CodeGen/GlobalISel/RegisterBankInfo.cpp
===================================================================
--- lib/CodeGen/GlobalISel/RegisterBankInfo.cpp
+++ lib/CodeGen/GlobalISel/RegisterBankInfo.cpp
@@ -197,6 +197,25 @@
   return &RegBank;
 }
 
+const TargetRegisterClass *RegisterBankInfo::constrainGenericRegister(
+    unsigned Reg, const TargetRegisterClass &RC, MachineRegisterInfo &MRI) {
+
+  // If the register already has a class, fallback to MRI::constrainRegClass.
+  auto &RegClassOrBank = MRI.getRegClassOrRegBank(Reg);
+  if (RegClassOrBank.is<const TargetRegisterClass *>())
+    return MRI.constrainRegClass(Reg, &RC);
+
+  const RegisterBank *RB = RegClassOrBank.get<const RegisterBank *>();
+  assert(RB && "Generic register does not have a register bank");
+
+  // Otherwise, all we can do is ensure the bank covers the class, and set it.
+  if (!RB->covers(RC))
+    return nullptr;
+
+  MRI.setRegClass(Reg, &RC);
+  return &RC;
+}
+
 RegisterBankInfo::InstructionMapping
 RegisterBankInfo::getInstrMappingImpl(const MachineInstr &MI) const {
   RegisterBankInfo::InstructionMapping Mapping(DefaultMappingID, /*Cost*/ 1,
Index: lib/CodeGen/LLVMTargetMachine.cpp
===================================================================
--- lib/CodeGen/LLVMTargetMachine.cpp
+++ lib/CodeGen/LLVMTargetMachine.cpp
@@ -172,6 +172,9 @@
     if (PassConfig->addRegBankSelect())
       return nullptr;
 
+    if (PassConfig->addGlobalInstructionSelect())
+      return nullptr;
+
   } else if (PassConfig->addInstSelector())
     return nullptr;
 
Index: lib/CodeGen/MachineRegisterInfo.cpp
===================================================================
--- lib/CodeGen/MachineRegisterInfo.cpp
+++ lib/CodeGen/MachineRegisterInfo.cpp
@@ -38,6 +38,27 @@
 void
 MachineRegisterInfo::setRegClass(unsigned Reg, const TargetRegisterClass *RC) {
   assert(RC && RC->isAllocatable() && "Invalid RC for virtual register");
+
+#ifdef LLVM_BUILD_GLOBAL_ISEL
+  // FIXME: This is completely unnecessary post-isel. Perhaps we should use
+  // a different vreg numbering scheme for generic vregs?  That would make
+  // this kind of check very cheap.
+  // Alternatively, we could introduce separate methods for gvregs. The naive
+  // way (different names) can easily become awkward to use, so maybe this is
+  // a good opportunity to introduce dedicated vreg types, that cast away to
+  // unsigned, but let us overload on the type?
+
+  // If Reg was generic and we were tracking a size, we don't need to anymore.
+  auto &SizeMap = getVRegToSize();
+  auto SizeIt = SizeMap.find(Reg);
+  if (SizeIt != SizeMap.end()) {
+    // FIXME: Can banks have sizes that aren't multiples of 8?
+    assert(SizeIt->second == (RC->getSize() * 8) &&
+           "Can't change virtual register size only by giving it a class");
+    SizeMap.erase(SizeIt);
+  }
+#endif
+
   VRegInfo[Reg].first = RC;
 }
 
Index: lib/Target/AArch64/AArch64InstructionSelector.h
===================================================================
--- /dev/null
+++ lib/Target/AArch64/AArch64InstructionSelector.h
@@ -0,0 +1,40 @@
+//===- AArch64InstructionSelector --------------------------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file declares the targeting of the InstructionSelector class for
+/// AArch64.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_AARCH64_AARCH64INSTRUCTIONSELECTOR_H
+#define LLVM_LIB_TARGET_AARCH64_AARCH64INSTRUCTIONSELECTOR_H
+
+#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
+
+namespace llvm {
+class AArch64InstrInfo;
+class AArch64RegisterBankInfo;
+// FIXME: Why on earth is this a struct?
+struct AArch64RegisterInfo;
+class AArch64Subtarget;
+
+class AArch64InstructionSelector : public InstructionSelector {
+public:
+  AArch64InstructionSelector(const AArch64Subtarget &STI,
+                             const AArch64RegisterBankInfo &RBI);
+
+  virtual bool select(MachineInstr &I) const override;
+
+private:
+  const AArch64InstrInfo &TII;
+  const AArch64RegisterInfo &TRI;
+  const AArch64RegisterBankInfo &RBI;
+};
+
+} // End llvm namespace.
+#endif
Index: lib/Target/AArch64/AArch64InstructionSelector.cpp
===================================================================
--- /dev/null
+++ lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -0,0 +1,186 @@
+//===- AArch64InstructionSelector.cpp ----------------------------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file implements the targeting of the InstructionSelector class for
+/// AArch64.
+/// \todo This should be generated by TableGen.
+//===----------------------------------------------------------------------===//
+
+#include "AArch64InstructionSelector.h"
+#include "AArch64InstrInfo.h"
+#include "AArch64RegisterBankInfo.h"
+#include "AArch64RegisterInfo.h"
+#include "AArch64Subtarget.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+#define DEBUG_TYPE "aarch64-isel"
+
+using namespace llvm;
+
+#ifndef LLVM_BUILD_GLOBAL_ISEL
+#error "You shouldn't build this"
+#endif
+
+AArch64InstructionSelector::AArch64InstructionSelector(
+    const AArch64Subtarget &STI, const AArch64RegisterBankInfo &RBI)
+    : InstructionSelector(), TII(*STI.getInstrInfo()),
+      TRI(*STI.getRegisterInfo()), RBI(RBI) {}
+
+/// Select the AArch64 opcode for the basic binary operation \p GenericOpc
+/// (such as G_OR or G_ADD), appropriate for the register bank \p RegBankID
+/// and of size \p OpSize.
+/// \returns \p GenericOpc if the combination is unsupported.
+static unsigned selectBinaryOp(unsigned GenericOpc, unsigned RegBankID,
+                               unsigned OpSize) {
+  switch (RegBankID) {
+  case AArch64::GPRRegBankID:
+    switch (OpSize) {
+    case 32:
+      switch (GenericOpc) {
+      case TargetOpcode::G_OR:
+        return AArch64::ORRWrr;
+      case TargetOpcode::G_ADD:
+        return AArch64::ADDWrr;
+      default:
+        return GenericOpc;
+      }
+    case 64:
+      switch (GenericOpc) {
+      case TargetOpcode::G_OR:
+        return AArch64::ORRXrr;
+      case TargetOpcode::G_ADD:
+        return AArch64::ADDXrr;
+      default:
+        return GenericOpc;
+      }
+    }
+  };
+  return GenericOpc;
+}
+
+/// Mutate the newly-selected instruction \p I to constrain its (possibly
+/// generic) virtual register operands to the instruction's register class.
+/// This could involve inserting COPYs before (for uses) or after (for defs).
+/// This requires the number of operands to match the instruction description.
+///
+/// FIXME: We need to somehow generalize this logic, but it's not obvious
+/// how. For instance, it's true for the simplest instructions only that the
+/// number and order of operands is the same pre- and post-isel.
+static void fixupSelectedInstRegOperands(MachineInstr &I,
+                                         const AArch64InstrInfo &TII,
+                                         const AArch64RegisterInfo &TRI,
+                                         const AArch64RegisterBankInfo &RBI) {
+  MachineBasicBlock &MBB = *I.getParent();
+  MachineFunction &MF = *MBB.getParent();
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+
+  for (unsigned OpI = 0, OpE = I.getNumExplicitOperands(); OpI != OpE; ++OpI) {
+    MachineOperand &MO = I.getOperand(OpI);
+    DEBUG(dbgs() << "Converting operand: " << MO << '\n');
+
+    assert(MO.isReg() && "Unsupported binop non-reg operand");
+
+    const TargetRegisterClass *RC = TII.getRegClass(I.getDesc(), OpI, &TRI, MF);
+    assert(RC && "Selected inst should have regclass operand");
+
+    // If the operand is a vreg, we should constrain its regclass, and only
+    // insert COPYs if that's impossible.
+    // If the operand is a physreg, we only insert COPYs if the register class
+    // doesn't contain the register.
+    if (TRI.isVirtualRegister(MO.getReg())) {
+      if (RBI.constrainGenericRegister(MO.getReg(), *RC, MRI))
+        continue;
+    } else {
+      if (RC->contains(MO.getReg()))
+        continue;
+    }
+
+    const unsigned NewReg = MRI.createVirtualRegister(RC);
+    if (MO.isDef()) {
+      BuildMI(MBB, std::next(MachineBasicBlock::iterator(I)), I.getDebugLoc(),
+              TII.get(TargetOpcode::COPY), MO.getReg())
+          .addReg(NewReg);
+      MO.setReg(NewReg);
+    } else {
+      BuildMI(MBB, I, I.getDebugLoc(), TII.get(TargetOpcode::COPY), NewReg)
+          .addReg(MO.getReg());
+    }
+  }
+}
+
+bool AArch64InstructionSelector::select(MachineInstr &I) const {
+  // FIXME: Is this check really necessary?
+  assert(I.getParent() && "Instruction should be in a basic block!");
+  assert(I.getParent()->getParent() && "Instruction should be in a function!");
+
+  MachineBasicBlock &MBB = *I.getParent();
+  MachineFunction &MF = *MBB.getParent();
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+
+  // FIXME: Is there *really* nothing to be done here?  This assumes that
+  // no upstream pass introduces things like generic vreg on copies or
+  // target-specific instructions.
+  // We should document (and verify) that assumption.
+  if (!isPreISelGenericOpcode(I.getOpcode()))
+    return true;
+
+  assert(I.getNumOperands() == I.getNumExplicitOperands() &&
+         "Generic instruction has unexpected implicit operands");
+
+  // FIXME: This goes away when we stop using Type.
+  const Type *Ty = I.getType();
+  assert(Ty && "Generic instruction doesn't have a type");
+  assert(!Ty->isAggregateType() &&
+         "Generic instruction still has an aggregate type at selection time");
+
+  // The size (in bits) of the operation, or 0 for the label type.
+  const unsigned OpSize = Ty->getPrimitiveSizeInBits();
+
+  switch (I.getOpcode()) {
+  case TargetOpcode::G_OR:
+  case TargetOpcode::G_ADD: {
+    DEBUG(dbgs() << "AArch64: Selecting: binop\n");
+
+    const unsigned DefReg = I.getOperand(0).getReg();
+    // FIXME: Can generic operations have physical registers operands? If so,
+    // this will need to be taught about that, and we'll need to get the bank
+    // out of the minimal class for the register.
+    // Either way, this needs to be documented (and possibly verified).
+    assert(TRI.isVirtualRegister(DefReg) && "Only supports vregs");
+
+    const RegisterBank *RBPtr = RBI.getRegBank(DefReg, MRI, TRI);
+    assert(RBPtr && "Generic register hasn't been selected to a bank or class");
+    const RegisterBank &RB = *RBPtr;
+
+    assert(OpSize && "Generic binary instruction type isn't primitive");
+    const unsigned NewOpc = selectBinaryOp(I.getOpcode(), RB.getID(), OpSize);
+
+    if (NewOpc == I.getOpcode())
+      return false;
+
+    I.setDesc(TII.get(NewOpc));
+    // FIXME: Should the type be always reset in setDesc?
+    I.setType(nullptr);
+
+    // Now that we selected an opcode, we need to fixup the register operands
+    // to use appropriate classes, inserting COPYs if necessary.
+    fixupSelectedInstRegOperands(I, TII, TRI, RBI);
+    return true;
+  }
+  }
+
+  return false;
+}
Index: lib/Target/AArch64/AArch64Subtarget.h
===================================================================
--- lib/Target/AArch64/AArch64Subtarget.h
+++ lib/Target/AArch64/AArch64Subtarget.h
@@ -17,6 +17,7 @@
 #include "AArch64FrameLowering.h"
 #include "AArch64ISelLowering.h"
 #include "AArch64InstrInfo.h"
+#include "AArch64RegisterBankInfo.h"
 #include "AArch64RegisterInfo.h"
 #include "AArch64SelectionDAGInfo.h"
 #include "llvm/CodeGen/GlobalISel/GISelAccessor.h"
@@ -147,7 +148,8 @@
     return &getInstrInfo()->getRegisterInfo();
   }
   const CallLowering *getCallLowering() const override;
-  const RegisterBankInfo *getRegBankInfo() const override;
+  const InstructionSelector *getInstructionSelector() const override;
+  const AArch64RegisterBankInfo *getRegBankInfo() const override;
   const Triple &getTargetTriple() const { return TargetTriple; }
   bool enableMachineScheduler() const override { return true; }
   bool enablePostRAScheduler() const override {
Index: lib/Target/AArch64/AArch64Subtarget.cpp
===================================================================
--- lib/Target/AArch64/AArch64Subtarget.cpp
+++ lib/Target/AArch64/AArch64Subtarget.cpp
@@ -98,9 +98,14 @@
   return GISel->getCallLowering();
 }
 
-const RegisterBankInfo *AArch64Subtarget::getRegBankInfo() const {
+const InstructionSelector *AArch64Subtarget::getInstructionSelector() const {
   assert(GISel && "Access to GlobalISel APIs not set");
-  return GISel->getRegBankInfo();
+  return GISel->getInstructionSelector();
+}
+
+const AArch64RegisterBankInfo *AArch64Subtarget::getRegBankInfo() const {
+  assert(GISel && "Access to GlobalISel APIs not set");
+  return static_cast<const AArch64RegisterBankInfo *>(GISel->getRegBankInfo());
 }
 
 /// Find the target operand flags that describe how a global value should be
Index: lib/Target/AArch64/AArch64TargetMachine.cpp
===================================================================
--- lib/Target/AArch64/AArch64TargetMachine.cpp
+++ lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -12,11 +12,13 @@
 
 #include "AArch64.h"
 #include "AArch64CallLowering.h"
+#include "AArch64InstructionSelector.h"
 #include "AArch64RegisterBankInfo.h"
 #include "AArch64TargetMachine.h"
 #include "AArch64TargetObjectFile.h"
 #include "AArch64TargetTransformInfo.h"
 #include "llvm/CodeGen/GlobalISel/IRTranslator.h"
+#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
 #include "llvm/CodeGen/GlobalISel/RegBankSelect.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/RegAllocRegistry.h"
@@ -195,10 +197,14 @@
 namespace {
 struct AArch64GISelActualAccessor : public GISelAccessor {
   std::unique_ptr<CallLowering> CallLoweringInfo;
+  std::unique_ptr<InstructionSelector> InstSelector;
   std::unique_ptr<RegisterBankInfo> RegBankInfo;
   const CallLowering *getCallLowering() const override {
     return CallLoweringInfo.get();
   }
+  const InstructionSelector *getInstructionSelector() const override {
+    return InstSelector.get();
+  }
   const RegisterBankInfo *getRegBankInfo() const override {
     return RegBankInfo.get();
   }
@@ -233,8 +239,15 @@
         new AArch64GISelActualAccessor();
     GISel->CallLoweringInfo.reset(
         new AArch64CallLowering(*I->getTargetLowering()));
-    GISel->RegBankInfo.reset(
-        new AArch64RegisterBankInfo(*I->getRegisterInfo()));
+
+    auto *RBI = new AArch64RegisterBankInfo(*I->getRegisterInfo());
+
+    // FIXME: At this point, we can't rely on Subtarget having RBI.
+    // It's awkward to mix passing RBI and the Subtarget; should we pass
+    // TII/TRI as well?
+    GISel->InstSelector.reset(new AArch64InstructionSelector(*I, *RBI));
+
+    GISel->RegBankInfo.reset(RBI);
 #endif
     I->setGISelAccessor(*GISel);
   }
@@ -277,6 +290,7 @@
 #ifdef LLVM_BUILD_GLOBAL_ISEL
   bool addIRTranslator() override;
   bool addRegBankSelect() override;
+  bool addGlobalInstructionSelect() override;
 #endif
   bool addILPOpts() override;
   void addPreRegAlloc() override;
@@ -378,6 +392,10 @@
   addPass(new RegBankSelect());
   return false;
 }
+bool AArch64PassConfig::addGlobalInstructionSelect() {
+  addPass(new InstructionSelect());
+  return false;
+}
 #endif
 
 bool AArch64PassConfig::addILPOpts() {
Index: lib/Target/AArch64/CMakeLists.txt
===================================================================
--- lib/Target/AArch64/CMakeLists.txt
+++ lib/Target/AArch64/CMakeLists.txt
@@ -19,6 +19,7 @@
 # List of all GlobalISel files.
 set(GLOBAL_ISEL_FILES
       AArch64CallLowering.cpp
+      AArch64InstructionSelector.cpp
       AArch64RegisterBankInfo.cpp
       )
 
Index: lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
+++ lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
@@ -315,6 +315,7 @@
 #ifdef LLVM_BUILD_GLOBAL_ISEL
   bool addIRTranslator() override;
   bool addRegBankSelect() override;
+  bool addGlobalInstructionSelect() override;
 #endif
   void addFastRegAlloc(FunctionPass *RegAllocPass) override;
   void addOptimizedRegAlloc(FunctionPass *RegAllocPass) override;
@@ -515,6 +516,10 @@
 bool GCNPassConfig::addRegBankSelect() {
   return false;
 }
+
+bool GCNPassConfig::addGlobalInstructionSelect() {
+  return false;
+}
 #endif
 
 void GCNPassConfig::addPreRegAlloc() {
Index: test/CodeGen/AArch64/GlobalISel/arm64-instructionselect.mir
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/GlobalISel/arm64-instructionselect.mir
@@ -0,0 +1,151 @@
+# RUN: llc -O0 -run-pass=instruction-select -global-isel %s -o - | FileCheck %s
+# REQUIRES: global-isel
+
+# Test the instruction selector.
+# As we support more instructions, we need to split this up.
+
+--- |
+  target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+  target triple = "aarch64-apple-ios"
+
+  define void @add_i32_gpr() { ret void }
+  define void @add_i64_gpr() { ret void }
+
+  define void @or_i32_gpr() { ret void }
+  define void @or_i64_gpr() { ret void }
+
+  define void @or_i64_gpr_copy_fpr_use() { ret void }
+
+...
+
+---
+# Check that we select a 32-bit GPR G_ADD into ADDWrr on GPR32.
+# Also check that we constrain the register class of the COPY to GPR32.
+# CHECK-LABEL: name: add_i32_gpr
+name:            add_i32_gpr
+alignment:       2
+isSSA:           true
+
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gpr32 }
+# CHECK-NEXT:  - { id: 1, class: gpr32 }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+
+# CHECK:  body:
+# CHECK:    %0 = COPY %w0
+# CHECK:    %1 = ADDWrr %0, %0
+body:             |
+  bb.0:
+    liveins: %w0
+
+    %0(32) = COPY %w0
+    %1(32) = G_ADD i32 %0, %0
+...
+
+---
+# Same as add_i32_gpr, for 64-bit operations.
+# CHECK-LABEL: name: add_i64_gpr
+name:            add_i64_gpr
+alignment:       2
+isSSA:           true
+
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gpr64 }
+# CHECK-NEXT:  - { id: 1, class: gpr64 }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+
+# CHECK:  body:
+# CHECK:    %0 = COPY %x0
+# CHECK:    %1 = ADDXrr %0, %0
+body:             |
+  bb.0:
+    liveins: %x0
+
+    %0(64) = COPY %x0
+    %1(64) = G_ADD i64 %0, %0
+...
+
+---
+# Same as add_i32_gpr, for G_OR operations.
+# CHECK-LABEL: name: or_i32_gpr
+name:            or_i32_gpr
+alignment:       2
+isSSA:           true
+
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gpr32 }
+# CHECK-NEXT:  - { id: 1, class: gpr32 }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+
+# CHECK:  body:
+# CHECK:    %0 = COPY %w0
+# CHECK:    %1 = ORRWrr %0, %0
+body:             |
+  bb.0:
+    liveins: %w0
+
+    %0(32) = COPY %w0
+    %1(32) = G_OR i32 %0, %0
+...
+
+---
+# Same as add_i64_gpr, for G_OR operations.
+# CHECK-LABEL: name: or_i64_gpr
+name:            or_i64_gpr
+alignment:       2
+isSSA:           true
+
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gpr64 }
+# CHECK-NEXT:  - { id: 1, class: gpr64 }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+
+# CHECK:  body:
+# CHECK:    %0 = COPY %x0
+# CHECK:    %1 = ORRXrr %0, %0
+body:             |
+  bb.0:
+    liveins: %x0
+
+    %0(64) = COPY %x0
+    %1(64) = G_OR i64 %0, %0
+...
+
+---
+# Check that we emit a FPR64->GPR64 COPY for a GPR G_OR with an FPR use.
+# CHECK-LABEL: name: or_i64_gpr_copy_fpr_use
+name:            or_i64_gpr_copy_fpr_use
+alignment:       2
+isSSA:           true
+
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gpr64 }
+# CHECK-NEXT:  - { id: 1, class: fpr64 }
+# CHECK-NEXT:  - { id: 2, class: gpr64 }
+# CHECK-NEXT:  - { id: 3, class: gpr64 }
+registers:
+  - { id: 0, class: gpr }
+  - { id: 1, class: fpr64 }
+  - { id: 2, class: gpr }
+
+# CHECK:  body:
+# CHECK:    %0 = COPY %x0
+# CHECK:    %1 = COPY %d0
+# CHECK:    %3 = COPY %1
+# CHECK:    %2 = ORRXrr %0, %1
+body:             |
+  bb.0:
+    liveins: %x0, %d0
+
+    %0(64) = COPY %x0
+    %1 = COPY %d0
+    %2(64) = G_OR i64 %0, %1
+...