compiler/optimizing/register_allocator_test.cc

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "builder.h"
#include "code_generator.h"
#include "code_generator_x86.h"
#include "dex_file.h"
#include "dex_instruction.h"
#include "nodes.h"
#include "optimizing_unit_test.h"
#include "register_allocator.h"
#include "ssa_liveness_analysis.h"
#include "ssa_phi_elimination.h"
#include "utils/arena_allocator.h"

#include "gtest/gtest.h"

namespace art {

// Note: the register allocator tests rely on the fact that constants have live
// intervals and registers get allocated to them.

static bool Check(const uint16_t* data) {
  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HGraphBuilder builder(&allocator);
  const DexFile::CodeItem* item = reinterpret_cast<const DexFile::CodeItem*>(data);
  HGraph* graph = builder.BuildGraph(*item);
  graph->TryBuildingSsa();
  x86::CodeGeneratorX86 codegen(graph);
  SsaLivenessAnalysis liveness(*graph, &codegen);
  liveness.Analyze();
  RegisterAllocator register_allocator(&allocator, &codegen, liveness);
  register_allocator.AllocateRegisters();
  return register_allocator.Validate(false);
}

/**
 * Unit testing of RegisterAllocator::ValidateIntervals. Register allocator
 * tests are based on this validation method.
 */
TEST(RegisterAllocatorTest, ValidateIntervals) {
  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HGraph* graph = new (&allocator) HGraph(&allocator);
  x86::CodeGeneratorX86 codegen(graph);
  GrowableArray<LiveInterval*> intervals(&allocator, 0);

  // Test with two intervals of the same range.
  {
    static constexpr size_t ranges[][2] = {{0, 42}};
    intervals.Add(BuildInterval(ranges, arraysize(ranges), &allocator, 0));
    intervals.Add(BuildInterval(ranges, arraysize(ranges), &allocator, 1));
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));

    intervals.Get(1)->SetRegister(0);
    ASSERT_FALSE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));
    intervals.Reset();
  }

  // Test with two non-intersecting intervals.
  {
    static constexpr size_t ranges1[][2] = {{0, 42}};
    intervals.Add(BuildInterval(ranges1, arraysize(ranges1), &allocator, 0));
    static constexpr size_t ranges2[][2] = {{42, 43}};
    intervals.Add(BuildInterval(ranges2, arraysize(ranges2), &allocator, 1));
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));

    intervals.Get(1)->SetRegister(0);
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));
    intervals.Reset();
  }

  // Test with two non-intersecting intervals, with one with a lifetime hole.
  {
    static constexpr size_t ranges1[][2] = {{0, 42}, {45, 48}};
    intervals.Add(BuildInterval(ranges1, arraysize(ranges1), &allocator, 0));
    static constexpr size_t ranges2[][2] = {{42, 43}};
    intervals.Add(BuildInterval(ranges2, arraysize(ranges2), &allocator, 1));
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));

    intervals.Get(1)->SetRegister(0);
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));
    intervals.Reset();
  }

  // Test with intersecting intervals.
  {
    static constexpr size_t ranges1[][2] = {{0, 42}, {44, 48}};
    intervals.Add(BuildInterval(ranges1, arraysize(ranges1), &allocator, 0));
    static constexpr size_t ranges2[][2] = {{42, 47}};
    intervals.Add(BuildInterval(ranges2, arraysize(ranges2), &allocator, 1));
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));

    intervals.Get(1)->SetRegister(0);
    ASSERT_FALSE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));
    intervals.Reset();
  }

  // Test with siblings.
  {
    static constexpr size_t ranges1[][2] = {{0, 42}, {44, 48}};
    intervals.Add(BuildInterval(ranges1, arraysize(ranges1), &allocator, 0));
    intervals.Get(0)->SplitAt(43);
    static constexpr size_t ranges2[][2] = {{42, 47}};
    intervals.Add(BuildInterval(ranges2, arraysize(ranges2), &allocator, 1));
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));

    intervals.Get(1)->SetRegister(0);
    // Sibling of the first interval has no register allocated to it.
    ASSERT_TRUE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));

    intervals.Get(0)->GetNextSibling()->SetRegister(0);
    ASSERT_FALSE(RegisterAllocator::ValidateIntervals(
        intervals, 0, 0, codegen, &allocator, true, false));
  }
}

TEST(RegisterAllocatorTest, CFG1) {
  /*
   * Test the following snippet:
   *  return 0;
   *
   * Which becomes the following graph:
   *       constant0
   *       goto
   *        |
   *       return
   *        |
   *       exit
   */
  const uint16_t data[] = ONE_REGISTER_CODE_ITEM(
    Instruction::CONST_4 | 0 | 0,
    Instruction::RETURN);

  ASSERT_TRUE(Check(data));
}

TEST(RegisterAllocatorTest, Loop1) {
  /*
   * Test the following snippet:
   *  int a = 0;
   *  while (a == a) {
   *    a = 4;
   *  }
   *  return 5;
   *
   * Which becomes the following graph:
   *       constant0
   *       constant4
   *       constant5
   *       goto
   *        |
   *       goto
   *        |
   *       phi
   *       equal
   *       if +++++
   *        |       \ +
   *        |     goto
   *        |
   *       return
   *        |
   *       exit
   */

  const uint16_t data[] = TWO_REGISTERS_CODE_ITEM(
    Instruction::CONST_4 | 0 | 0,
    Instruction::IF_EQ, 4,
    Instruction::CONST_4 | 4 << 12 | 0,
    Instruction::GOTO | 0xFD00,
    Instruction::CONST_4 | 5 << 12 | 1 << 8,
    Instruction::RETURN | 1 << 8);

  ASSERT_TRUE(Check(data));
}

TEST(RegisterAllocatorTest, Loop2) {
  /*
   * Test the following snippet:
   *  int a = 0;
   *  while (a == 8) {
   *    a = 4 + 5;
   *  }
   *  return 6 + 7;
   *
   * Which becomes the following graph:
   *       constant0
   *       constant4
   *       constant5
   *       constant6
   *       constant7
   *       constant8
   *       goto
   *        |
   *       goto
   *        |
   *       phi
   *       equal
   *       if +++++
   *        |       \ +
   *        |      4 + 5
   *        |      goto
   *        |
   *       6 + 7
   *       return
   *        |
   *       exit
   */

  const uint16_t data[] = TWO_REGISTERS_CODE_ITEM(
    Instruction::CONST_4 | 0 | 0,
    Instruction::CONST_4 | 8 << 12 | 1 << 8,
    Instruction::IF_EQ | 1 << 8, 7,
    Instruction::CONST_4 | 4 << 12 | 0 << 8,
    Instruction::CONST_4 | 5 << 12 | 1 << 8,
    Instruction::ADD_INT, 1 << 8 | 0,
    Instruction::GOTO | 0xFA00,
    Instruction::CONST_4 | 6 << 12 | 1 << 8,
    Instruction::CONST_4 | 7 << 12 | 1 << 8,
    Instruction::ADD_INT, 1 << 8 | 0,
    Instruction::RETURN | 1 << 8);

  ASSERT_TRUE(Check(data));
}

static HGraph* BuildSSAGraph(const uint16_t* data, ArenaAllocator* allocator) {
  HGraphBuilder builder(allocator);
  const DexFile::CodeItem* item = reinterpret_cast<const DexFile::CodeItem*>(data);
  HGraph* graph = builder.BuildGraph(*item);
  graph->TryBuildingSsa();
  return graph;
}

TEST(RegisterAllocatorTest, Loop3) {
  /*
   * Test the following snippet:
   *  int a = 0
   *  do {
   *    b = a;
   *    a++;
   *  } while (a != 5)
   *  return b;
   *
   * Which becomes the following graph:
   *       constant0
   *       constant1
   *       constant5
   *       goto
   *        |
   *       goto
   *        |++++++++++++
   *       phi          +
   *       a++          +
   *       equals       +
   *       if           +
   *        |++++++++++++
   *       return
   *        |
   *       exit
   */

  const uint16_t data[] = THREE_REGISTERS_CODE_ITEM(
    Instruction::CONST_4 | 0 | 0,
    Instruction::ADD_INT_LIT8 | 1 << 8, 1 << 8,
    Instruction::CONST_4 | 5 << 12 | 2 << 8,
    Instruction::IF_NE | 1 << 8 | 2 << 12, 3,
    Instruction::RETURN | 0 << 8,
    Instruction::MOVE | 1 << 12 | 0 << 8,
    Instruction::GOTO | 0xF900);

  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HGraph* graph = BuildSSAGraph(data, &allocator);
  x86::CodeGeneratorX86 codegen(graph);
  SsaLivenessAnalysis liveness(*graph, &codegen);
  liveness.Analyze();
  RegisterAllocator register_allocator(&allocator, &codegen, liveness);
  register_allocator.AllocateRegisters();
  ASSERT_TRUE(register_allocator.Validate(false));

  HBasicBlock* loop_header = graph->GetBlocks().Get(2);
  HPhi* phi = loop_header->GetFirstPhi()->AsPhi();

  LiveInterval* phi_interval = phi->GetLiveInterval();
  LiveInterval* loop_update = phi->InputAt(1)->GetLiveInterval();
  ASSERT_TRUE(phi_interval->HasRegister());
  ASSERT_TRUE(loop_update->HasRegister());
  ASSERT_NE(phi_interval->GetRegister(), loop_update->GetRegister());

  HBasicBlock* return_block = graph->GetBlocks().Get(3);
  HReturn* ret = return_block->GetLastInstruction()->AsReturn();
  ASSERT_EQ(phi_interval->GetRegister(), ret->InputAt(0)->GetLiveInterval()->GetRegister());
}

TEST(RegisterAllocatorTest, FirstRegisterUse) {
  const uint16_t data[] = THREE_REGISTERS_CODE_ITEM(
    Instruction::CONST_4 | 0 | 0,
    Instruction::ADD_INT_LIT8 | 1 << 8, 1 << 8,
    Instruction::ADD_INT_LIT8 | 0 << 8, 1 << 8,
    Instruction::ADD_INT_LIT8 | 1 << 8, 1 << 8 | 1,
    Instruction::RETURN_VOID);

  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HGraph* graph = BuildSSAGraph(data, &allocator);
  x86::CodeGeneratorX86 codegen(graph);
  SsaLivenessAnalysis liveness(*graph, &codegen);
  liveness.Analyze();

  HAdd* first_add = graph->GetBlocks().Get(1)->GetFirstInstruction()->AsAdd();
  HAdd* last_add = graph->GetBlocks().Get(1)->GetLastInstruction()->GetPrevious()->AsAdd();
  ASSERT_EQ(last_add->InputAt(0), first_add);
  LiveInterval* interval = first_add->GetLiveInterval();
  ASSERT_EQ(interval->GetEnd(), last_add->GetLifetimePosition());
  ASSERT_TRUE(interval->GetNextSibling() == nullptr);

  // We need a register for the output of the instruction.
  ASSERT_EQ(interval->FirstRegisterUse(), first_add->GetLifetimePosition());

  // Split at the next instruction.
  interval = interval->SplitAt(first_add->GetLifetimePosition() + 2);
  // The user of the split is the last add.
  ASSERT_EQ(interval->FirstRegisterUse(), last_add->GetLifetimePosition());

  // Split before the last add.
  LiveInterval* new_interval = interval->SplitAt(last_add->GetLifetimePosition() - 1);
  // Ensure the current interval has no register use...
  ASSERT_EQ(interval->FirstRegisterUse(), kNoLifetime);
  // And the new interval has it for the last add.
  ASSERT_EQ(new_interval->FirstRegisterUse(), last_add->GetLifetimePosition());
}

TEST(RegisterAllocatorTest, DeadPhi) {
  /* Test for a dead loop phi taking as back-edge input a phi that also has
   * this loop phi as input. Walking backwards in SsaDeadPhiElimination
   * does not solve the problem because the loop phi will be visited last.
   *
   * Test the following snippet:
   *  int a = 0
   *  do {
   *    if (true) {
   *      a = 2;
   *    }
   *  } while (true);
   */

  const uint16_t data[] = TWO_REGISTERS_CODE_ITEM(
    Instruction::CONST_4 | 0 | 0,
    Instruction::CONST_4 | 1 << 8 | 0,
    Instruction::IF_NE | 1 << 8 | 1 << 12, 3,
    Instruction::CONST_4 | 2 << 12 | 0 << 8,
    Instruction::GOTO | 0xFD00,
    Instruction::RETURN_VOID);

  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HGraph* graph = BuildSSAGraph(data, &allocator);
  SsaDeadPhiElimination(graph).Run();
  x86::CodeGeneratorX86 codegen(graph);
  SsaLivenessAnalysis liveness(*graph, &codegen);
  liveness.Analyze();
  RegisterAllocator register_allocator(&allocator, &codegen, liveness);
  register_allocator.AllocateRegisters();
  ASSERT_TRUE(register_allocator.Validate(false));
}

/**
 * Test that the TryAllocateFreeReg method works in the presence of inactive intervals
 * that share the same register. It should split the interval it is currently
 * allocating for at the minimum lifetime position between the two inactive intervals.
 */
TEST(RegisterAllocatorTest, FreeUntil) {
  const uint16_t data[] = TWO_REGISTERS_CODE_ITEM(
    Instruction::CONST_4 | 0 | 0,
    Instruction::RETURN);

  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HGraph* graph = BuildSSAGraph(data, &allocator);
  SsaDeadPhiElimination(graph).Run();
  x86::CodeGeneratorX86 codegen(graph);
  SsaLivenessAnalysis liveness(*graph, &codegen);
  liveness.Analyze();
  RegisterAllocator register_allocator(&allocator, &codegen, liveness);

  // Add an artifical range to cover the temps that will be put in the unhandled list.
  LiveInterval* unhandled = graph->GetEntryBlock()->GetFirstInstruction()->GetLiveInterval();
  unhandled->AddLoopRange(0, 60);
  // For SSA value intervals, only an interval resulted from a split may intersect
  // with inactive intervals.
  unhandled = register_allocator.Split(unhandled, 5);

  // Add three temps holding the same register, and starting at different positions.
  // Put the one that should be picked in the middle of the inactive list to ensure
  // we do not depend on an order.
  LiveInterval* interval = LiveInterval::MakeInterval(&allocator, Primitive::kPrimInt);
  interval->SetRegister(0);
  interval->AddRange(40, 50);
  register_allocator.inactive_.Add(interval);

  interval = LiveInterval::MakeInterval(&allocator, Primitive::kPrimInt);
  interval->SetRegister(0);
  interval->AddRange(20, 30);
  register_allocator.inactive_.Add(interval);

  interval = LiveInterval::MakeInterval(&allocator, Primitive::kPrimInt);
  interval->SetRegister(0);
  interval->AddRange(60, 70);
  register_allocator.inactive_.Add(interval);

  register_allocator.number_of_registers_ = 1;
  register_allocator.registers_array_ = allocator.AllocArray<size_t>(1);
  register_allocator.processing_core_registers_ = true;
  register_allocator.unhandled_ = &register_allocator.unhandled_core_intervals_;

  ASSERT_TRUE(register_allocator.TryAllocateFreeReg(unhandled));

  // Check that we have split the interval.
  ASSERT_EQ(1u, register_allocator.unhandled_->Size());
  // Check that we know need to find a new register where the next interval
  // that uses the register starts.
  ASSERT_EQ(20u, register_allocator.unhandled_->Get(0)->GetStart());
}

static HGraph* BuildIfElseWithPhi(ArenaAllocator* allocator,
                                  HPhi** phi,
                                  HInstruction** input1,
                                  HInstruction** input2) {
  HGraph* graph = new (allocator) HGraph(allocator);
  HBasicBlock* entry = new (allocator) HBasicBlock(graph);
  graph->AddBlock(entry);
  graph->SetEntryBlock(entry);
  HInstruction* parameter = new (allocator) HParameterValue(0, Primitive::kPrimNot);
  entry->AddInstruction(parameter);

  HBasicBlock* block = new (allocator) HBasicBlock(graph);
  graph->AddBlock(block);
  entry->AddSuccessor(block);

  HInstruction* test = new (allocator) HInstanceFieldGet(
      parameter, Primitive::kPrimBoolean, MemberOffset(22), false);
  block->AddInstruction(test);
  block->AddInstruction(new (allocator) HIf(test));
  HBasicBlock* then = new (allocator) HBasicBlock(graph);
  HBasicBlock* else_ = new (allocator) HBasicBlock(graph);
  HBasicBlock* join = new (allocator) HBasicBlock(graph);
  graph->AddBlock(then);
  graph->AddBlock(else_);
  graph->AddBlock(join);

  block->AddSuccessor(then);
  block->AddSuccessor(else_);
  then->AddSuccessor(join);
  else_->AddSuccessor(join);
  then->AddInstruction(new (allocator) HGoto());
  else_->AddInstruction(new (allocator) HGoto());

  *phi = new (allocator) HPhi(allocator, 0, 0, Primitive::kPrimInt);
  join->AddPhi(*phi);
  *input1 = new (allocator) HInstanceFieldGet(parameter, Primitive::kPrimInt,
                                              MemberOffset(42), false);
  *input2 = new (allocator) HInstanceFieldGet(parameter, Primitive::kPrimInt,
                                              MemberOffset(42), false);
  then->AddInstruction(*input1);
  else_->AddInstruction(*input2);
  join->AddInstruction(new (allocator) HExit());
  (*phi)->AddInput(*input1);
  (*phi)->AddInput(*input2);

  graph->BuildDominatorTree();
  graph->AnalyzeNaturalLoops();
  return graph;
}

TEST(RegisterAllocatorTest, PhiHint) {
  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HPhi *phi;
  HInstruction *input1, *input2;

  {
    HGraph* graph = BuildIfElseWithPhi(&allocator, &phi, &input1, &input2);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    // Check that the register allocator is deterministic.
    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    ASSERT_EQ(input1->GetLiveInterval()->GetRegister(), 0);
    ASSERT_EQ(input2->GetLiveInterval()->GetRegister(), 0);
    ASSERT_EQ(phi->GetLiveInterval()->GetRegister(), 0);
  }

  {
    HGraph* graph = BuildIfElseWithPhi(&allocator, &phi, &input1, &input2);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    // Set the phi to a specific register, and check that the inputs get allocated
    // the same register.
    phi->GetLocations()->SetOut(Location::RegisterLocation(2));
    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    ASSERT_EQ(input1->GetLiveInterval()->GetRegister(), 2);
    ASSERT_EQ(input2->GetLiveInterval()->GetRegister(), 2);
    ASSERT_EQ(phi->GetLiveInterval()->GetRegister(), 2);
  }

  {
    HGraph* graph = BuildIfElseWithPhi(&allocator, &phi, &input1, &input2);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    // Set input1 to a specific register, and check that the phi and other input get allocated
    // the same register.
    input1->GetLocations()->SetOut(Location::RegisterLocation(2));
    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    ASSERT_EQ(input1->GetLiveInterval()->GetRegister(), 2);
    ASSERT_EQ(input2->GetLiveInterval()->GetRegister(), 2);
    ASSERT_EQ(phi->GetLiveInterval()->GetRegister(), 2);
  }

  {
    HGraph* graph = BuildIfElseWithPhi(&allocator, &phi, &input1, &input2);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    // Set input2 to a specific register, and check that the phi and other input get allocated
    // the same register.
    input2->GetLocations()->SetOut(Location::RegisterLocation(2));
    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    ASSERT_EQ(input1->GetLiveInterval()->GetRegister(), 2);
    ASSERT_EQ(input2->GetLiveInterval()->GetRegister(), 2);
    ASSERT_EQ(phi->GetLiveInterval()->GetRegister(), 2);
  }
}

static HGraph* BuildFieldReturn(ArenaAllocator* allocator,
                                HInstruction** field,
                                HInstruction** ret) {
  HGraph* graph = new (allocator) HGraph(allocator);
  HBasicBlock* entry = new (allocator) HBasicBlock(graph);
  graph->AddBlock(entry);
  graph->SetEntryBlock(entry);
  HInstruction* parameter = new (allocator) HParameterValue(0, Primitive::kPrimNot);
  entry->AddInstruction(parameter);

  HBasicBlock* block = new (allocator) HBasicBlock(graph);
  graph->AddBlock(block);
  entry->AddSuccessor(block);

  *field = new (allocator) HInstanceFieldGet(parameter, Primitive::kPrimInt,
                                             MemberOffset(42), false);
  block->AddInstruction(*field);
  *ret = new (allocator) HReturn(*field);
  block->AddInstruction(*ret);

  HBasicBlock* exit = new (allocator) HBasicBlock(graph);
  graph->AddBlock(exit);
  block->AddSuccessor(exit);
  exit->AddInstruction(new (allocator) HExit());
  return graph;
}

TEST(RegisterAllocatorTest, ExpectedInRegisterHint) {
  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HInstruction *field, *ret;

  {
    HGraph* graph = BuildFieldReturn(&allocator, &field, &ret);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    // Sanity check that in normal conditions, the register should be hinted to 0 (EAX).
    ASSERT_EQ(field->GetLiveInterval()->GetRegister(), 0);
  }

  {
    HGraph* graph = BuildFieldReturn(&allocator, &field, &ret);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    // Check that the field gets put in the register expected by its use.
    // Don't use SetInAt because we are overriding an already allocated location.
    ret->GetLocations()->inputs_.Put(0, Location::RegisterLocation(2));

    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    ASSERT_EQ(field->GetLiveInterval()->GetRegister(), 2);
  }
}

static HGraph* BuildTwoAdds(ArenaAllocator* allocator,
                            HInstruction** first_add,
                            HInstruction** second_add) {
  HGraph* graph = new (allocator) HGraph(allocator);
  HBasicBlock* entry = new (allocator) HBasicBlock(graph);
  graph->AddBlock(entry);
  graph->SetEntryBlock(entry);
  HInstruction* parameter = new (allocator) HParameterValue(0, Primitive::kPrimInt);
  HInstruction* constant1 = new (allocator) HIntConstant(0);
  HInstruction* constant2 = new (allocator) HIntConstant(0);
  entry->AddInstruction(parameter);
  entry->AddInstruction(constant1);
  entry->AddInstruction(constant2);

  HBasicBlock* block = new (allocator) HBasicBlock(graph);
  graph->AddBlock(block);
  entry->AddSuccessor(block);

  *first_add = new (allocator) HAdd(Primitive::kPrimInt, parameter, constant1);
  block->AddInstruction(*first_add);
  *second_add = new (allocator) HAdd(Primitive::kPrimInt, *first_add, constant2);
  block->AddInstruction(*second_add);

  block->AddInstruction(new (allocator) HExit());
  return graph;
}

TEST(RegisterAllocatorTest, SameAsFirstInputHint) {
  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HInstruction *first_add, *second_add;

  {
    HGraph* graph = BuildTwoAdds(&allocator, &first_add, &second_add);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    // Sanity check that in normal conditions, the registers are the same.
    ASSERT_EQ(first_add->GetLiveInterval()->GetRegister(), 1);
    ASSERT_EQ(second_add->GetLiveInterval()->GetRegister(), 1);
  }

  {
    HGraph* graph = BuildTwoAdds(&allocator, &first_add, &second_add);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    // check that both adds get the same register.
    // Don't use SetOutput because output is already allocated.
    first_add->InputAt(0)->GetLocations()->output_ = Location::RegisterLocation(2);
    ASSERT_EQ(first_add->GetLocations()->Out().GetPolicy(), Location::kSameAsFirstInput);
    ASSERT_EQ(second_add->GetLocations()->Out().GetPolicy(), Location::kSameAsFirstInput);

    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    ASSERT_EQ(first_add->GetLiveInterval()->GetRegister(), 2);
    ASSERT_EQ(second_add->GetLiveInterval()->GetRegister(), 2);
  }
}

static HGraph* BuildDiv(ArenaAllocator* allocator,
                        HInstruction** div) {
  HGraph* graph = new (allocator) HGraph(allocator);
  HBasicBlock* entry = new (allocator) HBasicBlock(graph);
  graph->AddBlock(entry);
  graph->SetEntryBlock(entry);
  HInstruction* first = new (allocator) HParameterValue(0, Primitive::kPrimInt);
  HInstruction* second = new (allocator) HParameterValue(0, Primitive::kPrimInt);
  entry->AddInstruction(first);
  entry->AddInstruction(second);

  HBasicBlock* block = new (allocator) HBasicBlock(graph);
  graph->AddBlock(block);
  entry->AddSuccessor(block);

  *div = new (allocator) HDiv(Primitive::kPrimInt, first, second, 0);  // don't care about dex_pc.
  block->AddInstruction(*div);

  block->AddInstruction(new (allocator) HExit());
  return graph;
}

TEST(RegisterAllocatorTest, ExpectedExactInRegisterAndSameOutputHint) {
  ArenaPool pool;
  ArenaAllocator allocator(&pool);
  HInstruction *div;

  {
    HGraph* graph = BuildDiv(&allocator, &div);
    x86::CodeGeneratorX86 codegen(graph);
    SsaLivenessAnalysis liveness(*graph, &codegen);
    liveness.Analyze();

    RegisterAllocator register_allocator(&allocator, &codegen, liveness);
    register_allocator.AllocateRegisters();

    // div on x86 requires its first input in eax and the output be the same as the first input.
    ASSERT_EQ(div->GetLiveInterval()->GetRegister(), 0);
  }
}

}  // namespace art