Index: lib/CodeGen/GlobalISel/InstructionSelector.cpp
===================================================================
--- lib/CodeGen/GlobalISel/InstructionSelector.cpp
+++ lib/CodeGen/GlobalISel/InstructionSelector.cpp
@@ -55,6 +55,13 @@
     // constrainOperandRegClass does that for us.
     MO.setReg(constrainOperandRegClass(MF, TRI, MRI, TII, RBI, I, I.getDesc(),
                                        Reg, OpI));
+
+    // Tie uses to defs as indicated in MCInstrDesc.
+    if (MO.isUse()) {
+      int DefIdx = I.getDesc().getOperandConstraint(OpI, MCOI::TIED_TO);
+      if (DefIdx != -1)
+        I.tieOperands(DefIdx, OpI);
+    }
   }
   return true;
 }
Index: lib/Target/X86/CMakeLists.txt
===================================================================
--- lib/Target/X86/CMakeLists.txt
+++ lib/Target/X86/CMakeLists.txt
@@ -12,6 +12,7 @@
 tablegen(LLVM X86GenSubtargetInfo.inc -gen-subtarget)
 if(LLVM_BUILD_GLOBAL_ISEL)
   tablegen(LLVM X86GenRegisterBank.inc -gen-register-bank)
+  tablegen(LLVM X86GenGlobalISel.inc -gen-global-isel)
 endif()
 
 add_public_tablegen_target(X86CommonTableGen)
@@ -21,6 +22,7 @@
   X86CallLowering.cpp
   X86LegalizerInfo.cpp
   X86RegisterBankInfo.cpp
+  X86InstructionSelector.cpp
   )
 
 if(LLVM_BUILD_GLOBAL_ISEL)
Index: lib/Target/X86/X86InstructionSelector.h
===================================================================
--- /dev/null
+++ lib/Target/X86/X86InstructionSelector.h
@@ -0,0 +1,47 @@
+//===- X86InstructionSelector --------------------------------*- 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 X86.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_X86_X86INSTRUCTIONSELECTOR_H
+#define LLVM_LIB_TARGET_X86_X86INSTRUCTIONSELECTOR_H
+
+#include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
+
+namespace llvm {
+
+class X86InstrInfo;
+class X86RegisterBankInfo;
+class X86RegisterInfo;
+class X86Subtarget;
+class X86TargetMachine;
+
+class X86InstructionSelector : public InstructionSelector {
+public:
+  X86InstructionSelector(const X86TargetMachine &TM, const X86Subtarget &STI,
+                         const X86RegisterBankInfo &RBI);
+
+  bool select(MachineInstr &I) const override;
+
+private:
+  /// tblgen-erated 'select' implementation, used as the initial selector for
+  /// the patterns that don't require complex C++.
+  bool selectImpl(MachineInstr &I) const;
+
+  const X86TargetMachine &TM;
+  const X86Subtarget &STI;
+  const X86InstrInfo &TII;
+  const X86RegisterInfo &TRI;
+  const X86RegisterBankInfo &RBI;
+};
+
+} // end namespace llvm
+
+#endif // LLVM_LIB_TARGET_X86_X86INSTRUCTIONSELECTOR_H
Index: lib/Target/X86/X86InstructionSelector.cpp
===================================================================
--- /dev/null
+++ lib/Target/X86/X86InstructionSelector.cpp
@@ -0,0 +1,135 @@
+//===- X86InstructionSelector.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
+/// X86.
+/// \todo This should be generated by TableGen.
+//===----------------------------------------------------------------------===//
+
+#include "X86InstructionSelector.h"
+#include "X86InstrInfo.h"
+#include "X86RegisterBankInfo.h"
+#include "X86RegisterInfo.h"
+#include "X86Subtarget.h"
+#include "X86TargetMachine.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 "X86-isel"
+
+using namespace llvm;
+
+#ifndef LLVM_BUILD_GLOBAL_ISEL
+#error "You shouldn't build this"
+#endif
+
+#include "X86GenGlobalISel.inc"
+
+X86InstructionSelector::X86InstructionSelector(const X86TargetMachine &TM,
+                                               const X86Subtarget &STI,
+                                               const X86RegisterBankInfo &RBI)
+    : InstructionSelector(), TM(TM), STI(STI), TII(*STI.getInstrInfo()),
+      TRI(*STI.getRegisterInfo()), RBI(RBI) {}
+
+// FIXME: This should be target-independent, inferred from the types declared
+// for each class in the bank.
+static const TargetRegisterClass *
+getRegClassForTypeOnBank(LLT Ty, const RegisterBank &RB) {
+  if (RB.getID() == X86::GPRRegBankID) {
+    if (Ty.getSizeInBits() <= 32)
+      return &X86::GR32RegClass;
+    if (Ty.getSizeInBits() == 64)
+      return &X86::GR64RegClass;
+  }
+
+  llvm_unreachable("Unknown RegBank!");
+  return nullptr;
+}
+
+// Set X86 Opcode and constrain DestReg.
+static bool selectCopy(MachineInstr &I, const TargetInstrInfo &TII,
+                       MachineRegisterInfo &MRI, const TargetRegisterInfo &TRI,
+                       const RegisterBankInfo &RBI) {
+
+  unsigned DstReg = I.getOperand(0).getReg();
+  if (TargetRegisterInfo::isPhysicalRegister(DstReg)) {
+    assert(I.isCopy() && "Generic operators do not allow physical registers");
+    return true;
+  }
+
+  const RegisterBank &RegBank = *RBI.getRegBank(DstReg, MRI, TRI);
+  const unsigned DstSize = MRI.getType(DstReg).getSizeInBits();
+  unsigned SrcReg = I.getOperand(1).getReg();
+  const unsigned SrcSize = RBI.getSizeInBits(SrcReg, MRI, TRI);
+  (void)SrcSize;
+  assert((!TargetRegisterInfo::isPhysicalRegister(SrcReg) || I.isCopy()) &&
+         "No phys reg on generic operators");
+  assert((DstSize == SrcSize ||
+          // Copies are a mean to setup initial types, the number of
+          // bits may not exactly match.
+          (TargetRegisterInfo::isPhysicalRegister(SrcReg) &&
+           DstSize <= RBI.getSizeInBits(SrcReg, MRI, TRI))) &&
+         "Copy with different width?!");
+
+  const TargetRegisterClass *RC = nullptr;
+
+  switch (RegBank.getID()) {
+  case X86::GPRRegBankID:
+    assert((DstSize <= 64) && "GPRs cannot get more than 64-bit width values.");
+    RC = getRegClassForTypeOnBank(MRI.getType(DstReg), RegBank);
+    break;
+  default:
+    llvm_unreachable("Unknown RegBank!");
+    break;
+  }
+
+  // No need to constrain SrcReg. It will get constrained when
+  // we hit another of its use or its defs.
+  // Copies do not have constraints.
+  if (!RBI.constrainGenericRegister(DstReg, *RC, MRI)) {
+    DEBUG(dbgs() << "Failed to constrain " << TII.getName(I.getOpcode())
+                 << " operand\n");
+    return false;
+  }
+  I.setDesc(TII.get(X86::COPY));
+  return true;
+}
+
+bool X86InstructionSelector::select(MachineInstr &I) const {
+  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();
+
+  unsigned Opcode = I.getOpcode();
+  if (!isPreISelGenericOpcode(Opcode)) {
+    // Certain non-generic instructions also need some special handling.
+
+    if (I.isCopy())
+      return selectCopy(I, TII, MRI, TRI, RBI);
+
+    // TODO: handle more cases - LOAD_STACK_GUARD, PHI
+    return true;
+  }
+
+  if (I.getNumOperands() != I.getNumExplicitOperands()) {
+
+    llvm_unreachable("Generic instruction has unexpected implicit operands\n");
+  }
+
+  return selectImpl(I);
+}
Index: lib/Target/X86/X86LegalizerInfo.cpp
===================================================================
--- lib/Target/X86/X86LegalizerInfo.cpp
+++ lib/Target/X86/X86LegalizerInfo.cpp
@@ -38,12 +38,13 @@
   const LLT s16 = LLT::scalar(16);
   const LLT s32 = LLT::scalar(32);
 
-  for (auto Ty : {s8, s16, s32})
+  for (auto Ty : {s8, s16, s32}) {
     setAction({TargetOpcode::G_ADD, Ty}, Legal);
+    setAction({TargetOpcode::G_SUB, Ty}, Legal);
+  }
 }
-void
 
-X86LegalizerInfo::setLegalizerInfo64bit() {
+void X86LegalizerInfo::setLegalizerInfo64bit() {
 
   if (!Subtarget.is64Bit())
     return;
@@ -51,4 +52,5 @@
   const LLT s64 = LLT::scalar(64);
 
   setAction({TargetOpcode::G_ADD, s64}, Legal);
+  setAction({TargetOpcode::G_SUB, s64}, Legal);
 }
Index: lib/Target/X86/X86RegisterBankInfo.cpp
===================================================================
--- lib/Target/X86/X86RegisterBankInfo.cpp
+++ lib/Target/X86/X86RegisterBankInfo.cpp
@@ -111,6 +111,7 @@
 
   switch (Opc) {
   case TargetOpcode::G_ADD:
+  case TargetOpcode::G_SUB:
     return getOperandsMapping(MI, false);
     break;
   default:
Index: lib/Target/X86/X86TargetMachine.cpp
===================================================================
--- lib/Target/X86/X86TargetMachine.cpp
+++ lib/Target/X86/X86TargetMachine.cpp
@@ -15,6 +15,7 @@
 #include "X86.h"
 #include "X86CallLowering.h"
 #include "X86LegalizerInfo.h"
+#include "X86InstructionSelector.h"
 #ifdef LLVM_BUILD_GLOBAL_ISEL
 #include "X86RegisterBankInfo.h"
 #endif
@@ -34,6 +35,7 @@
 #include "llvm/CodeGen/GlobalISel/IRTranslator.h"
 #include "llvm/CodeGen/GlobalISel/Legalizer.h"
 #include "llvm/CodeGen/GlobalISel/RegBankSelect.h"
+#include "llvm/CodeGen/GlobalISel/InstructionSelect.h"
 #include "llvm/CodeGen/MachineScheduler.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/CodeGen/TargetPassConfig.h"
@@ -211,14 +213,14 @@
   std::unique_ptr<CallLowering> CallLoweringInfo;
   std::unique_ptr<LegalizerInfo> Legalizer;
   std::unique_ptr<RegisterBankInfo> RegBankInfo;
+  std::unique_ptr<InstructionSelector> InstSelector;
 
   const CallLowering *getCallLowering() const override {
     return CallLoweringInfo.get();
   }
 
   const InstructionSelector *getInstructionSelector() const override {
-    //TODO: Implement
-    return nullptr;
+    return InstSelector.get();
   }
 
   const LegalizerInfo *getLegalizerInfo() const override {
@@ -282,6 +284,7 @@
 
     auto *RBI = new X86RegisterBankInfo(*I->getRegisterInfo());
     GISel->RegBankInfo.reset(RBI);
+    GISel->InstSelector.reset(new X86InstructionSelector(*this, *I, *RBI));
 
 #endif
     I->setGISelAccessor(*GISel);
@@ -391,7 +394,7 @@
 }
 
 bool X86PassConfig::addGlobalInstructionSelect() {
-  //TODO: Implement
+  addPass(new InstructionSelect());
   return false;
 }
 #endif
Index: test/CodeGen/X86/GlobalISel/binop-isel.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/GlobalISel/binop-isel.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=x86_64-linux-gnu -global-isel < %s -o - | FileCheck %s
+
+define i32 @test_add_i32(i32 %arg1, i32 %arg2) {
+; CHECK-LABEL: test_add_i32:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    # kill: %EDI<def> %EDI<kill> %RDI<def>
+; CHECK-NEXT:    # kill: %ESI<def> %ESI<kill> %RSI<def>
+; CHECK-NEXT:    leal (%rsi,%rdi), %eax
+; CHECK-NEXT:    retq
+  %ret = add i32 %arg1, %arg2
+  ret i32 %ret
+}
+
+define i32 @test_sub_i32(i32 %arg1, i32 %arg2) {
+; CHECK-LABEL: test_sub_i32:
+; CHECK:       # BB#0:
+; CHECK-NEXT:    subl %esi, %edi
+; CHECK-NEXT:    movl %edi, %eax
+; CHECK-NEXT:    retq
+  %ret = sub i32 %arg1, %arg2
+  ret i32 %ret
+}
Index: test/CodeGen/X86/GlobalISel/legalize-sub.mir
===================================================================
--- /dev/null
+++ test/CodeGen/X86/GlobalISel/legalize-sub.mir
@@ -0,0 +1,40 @@
+# RUN: llc -mtriple=x86_64-linux-gnu -global-isel -run-pass=legalizer %s -o - | FileCheck %s 
+
+--- |
+  ; ModuleID = '<stdin>'
+  source_filename = "<stdin>"
+  target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64--linux-gnu"
+  
+  define i32 @test_sub_i32(i32 %arg1, i32 %arg2) {
+    %ret = sub i32 %arg1, %arg2
+    ret i32 %ret
+  }
+
+...
+---
+name:            test_sub_i32
+alignment:       4
+legalized:       false
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+registers:       
+  - { id: 0, class: _ }
+  - { id: 1, class: _ }
+  - { id: 2, class: _ }
+body:             |
+  bb.1 (%ir-block.0):
+    liveins: %edi, %esi
+    ;  CHECK-LABEL: name: test_sub_i32
+    ;  CHECK: [[VAL1:%.*]](s32) = COPY %edi  
+    ;  CHECK: [[VAL2:%.*]](s32) = COPY %esi
+    ;  CHECK: [[RES:%.*]](s32) = G_SUB [[VAL1:%.*]], [[VAL2:%.*]]
+
+    %0(s32) = COPY %edi
+    %1(s32) = COPY %esi
+    %2(s32) = G_SUB %0, %1
+    %eax = COPY %2(s32)
+    RET 0, implicit %eax
+
+...
Index: test/CodeGen/X86/GlobalISel/x86_64-instructionselect.mir
===================================================================
--- /dev/null
+++ test/CodeGen/X86/GlobalISel/x86_64-instructionselect.mir
@@ -0,0 +1,64 @@
+# RUN: llc -mtriple=x86_64-linux-gnu -global-isel -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck %s
+
+--- |
+  define i32 @test_add_i32(i32 %arg1, i32 %arg2) {
+    %ret = add i32 %arg1, %arg2
+    ret i32 %ret
+  }
+  
+  define i32 @test_sub_i32(i32 %arg1, i32 %arg2) {
+    %ret = sub i32 %arg1, %arg2
+    ret i32 %ret
+  }
+
+...
+
+---
+name:            test_add_i32
+legalized:       true
+regBankSelected: true
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gr32 }
+# CHECK-NEXT:  - { id: 1, class: gr32 }
+# CHECK-NEXT:  - { id: 2, class: gr32 }
+registers:       
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+  - { id: 2, class: gpr }
+# CHECK:      %0 = COPY %edi
+# CHECK-NEXT: %1 = COPY %esi
+# CHECK-NEXT: %2 = ADD32rr %0, %1
+body:             |
+  bb.1 (%ir-block.0):
+    liveins: %edi, %esi
+  
+    %0(s32) = COPY %edi
+    %1(s32) = COPY %esi
+    %2(s32) = G_ADD %0, %1
+
+...
+
+---
+name:            test_sub_i32
+legalized:       true
+regBankSelected: true
+# CHECK:      registers:
+# CHECK-NEXT:  - { id: 0, class: gr32 }
+# CHECK-NEXT:  - { id: 1, class: gr32 }
+# CHECK-NEXT:  - { id: 2, class: gr32 }
+registers:       
+  - { id: 0, class: gpr }
+  - { id: 1, class: gpr }
+  - { id: 2, class: gpr }
+# CHECK:      %0 = COPY %edi
+# CHECK-NEXT: %1 = COPY %esi
+# CHECK-NEXT: %2 = SUB32rr %0, %1
+body:             |
+  bb.1 (%ir-block.0):
+    liveins: %edi, %esi
+  
+    %0(s32) = COPY %edi
+    %1(s32) = COPY %esi
+    %2(s32) = G_SUB %0, %1
+
+...