compiler/optimizing/induction_var_range.cc

/*
 * Copyright (C) 2015 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 "induction_var_range.h"

#include <limits>

namespace art {

/** Returns true if 64-bit constant fits in 32-bit constant. */
static bool CanLongValueFitIntoInt(int64_t c) {
  return std::numeric_limits<int32_t>::min() <= c && c <= std::numeric_limits<int32_t>::max();
}

/** Returns true if 32-bit addition can be done safely. */
static bool IsSafeAdd(int32_t c1, int32_t c2) {
  return CanLongValueFitIntoInt(static_cast<int64_t>(c1) + static_cast<int64_t>(c2));
}

/** Returns true if 32-bit subtraction can be done safely. */
static bool IsSafeSub(int32_t c1, int32_t c2) {
  return CanLongValueFitIntoInt(static_cast<int64_t>(c1) - static_cast<int64_t>(c2));
}

/** Returns true if 32-bit multiplication can be done safely. */
static bool IsSafeMul(int32_t c1, int32_t c2) {
  return CanLongValueFitIntoInt(static_cast<int64_t>(c1) * static_cast<int64_t>(c2));
}

/** Returns true if 32-bit division can be done safely. */
static bool IsSafeDiv(int32_t c1, int32_t c2) {
  return c2 != 0 && CanLongValueFitIntoInt(static_cast<int64_t>(c1) / static_cast<int64_t>(c2));
}

/** Returns true for 32/64-bit integral constant. */
static bool IsIntAndGet(HInstruction* instruction, int32_t* value) {
  if (instruction->IsIntConstant()) {
    *value = instruction->AsIntConstant()->GetValue();
    return true;
  } else if (instruction->IsLongConstant()) {
    const int64_t c = instruction->AsLongConstant()->GetValue();
    if (CanLongValueFitIntoInt(c)) {
      *value = static_cast<int32_t>(c);
      return true;
    }
  }
  return false;
}

/**
 * An upper bound a * (length / a) + b, where a > 0, can be conservatively rewritten as length + b
 * because length >= 0 is true. This makes it more likely the bound is useful to clients.
 */
static InductionVarRange::Value SimplifyMax(InductionVarRange::Value v) {
  int32_t value;
  if (v.a_constant > 1 &&
      v.instruction->IsDiv() &&
      v.instruction->InputAt(0)->IsArrayLength() &&
      IsIntAndGet(v.instruction->InputAt(1), &value) && v.a_constant == value) {
    return InductionVarRange::Value(v.instruction->InputAt(0), 1, v.b_constant);
  }
  return v;
}

/** Helper method to insert an instruction. */
static HInstruction* Insert(HBasicBlock* block, HInstruction* instruction) {
  DCHECK(block != nullptr);
  DCHECK(block->GetLastInstruction() != nullptr) << block->GetBlockId();
  DCHECK(instruction != nullptr);
  block->InsertInstructionBefore(instruction, block->GetLastInstruction());
  return instruction;
}

//
// Public class methods.
//

InductionVarRange::InductionVarRange(HInductionVarAnalysis* induction_analysis)
    : induction_analysis_(induction_analysis) {
  DCHECK(induction_analysis != nullptr);
}

void InductionVarRange::GetInductionRange(HInstruction* context,
                                          HInstruction* instruction,
                                          /*out*/Value* min_val,
                                          /*out*/Value* max_val,
                                          /*out*/bool* needs_finite_test) {
  HLoopInformation* loop = context->GetBlock()->GetLoopInformation();  // closest enveloping loop
  if (loop != nullptr) {
    // Set up loop information.
    HBasicBlock* header = loop->GetHeader();
    bool in_body = context->GetBlock() != header;
    HInductionVarAnalysis::InductionInfo* info =
        induction_analysis_->LookupInfo(loop, instruction);
    HInductionVarAnalysis::InductionInfo* trip =
        induction_analysis_->LookupInfo(loop, header->GetLastInstruction());
    // Find range.
    *min_val = GetVal(info, trip, in_body, /* is_min */ true);
    *max_val = SimplifyMax(GetVal(info, trip, in_body, /* is_min */ false));
    *needs_finite_test = NeedsTripCount(info) && IsUnsafeTripCount(trip);
  } else {
    // No loop to analyze.
    *min_val = Value();
    *max_val = Value();
    *needs_finite_test = false;
  }
}

bool InductionVarRange::CanGenerateCode(HInstruction* context,
                                        HInstruction* instruction,
                                        /*out*/bool* needs_finite_test,
                                        /*out*/bool* needs_taken_test) {
  return GenerateCode(context,
                      instruction,
                      nullptr, nullptr, nullptr, nullptr, nullptr,  // nothing generated yet
                      needs_finite_test,
                      needs_taken_test);
}

void InductionVarRange::GenerateRangeCode(HInstruction* context,
                                          HInstruction* instruction,
                                          HGraph* graph,
                                          HBasicBlock* block,
                                          /*out*/HInstruction** lower,
                                          /*out*/HInstruction** upper) {
  bool b1, b2;  // unused
  if (!GenerateCode(context, instruction, graph, block, lower, upper, nullptr, &b1, &b2)) {
    LOG(FATAL) << "Failed precondition: GenerateCode()";
  }
}

void InductionVarRange::GenerateTakenTest(HInstruction* context,
                                          HGraph* graph,
                                          HBasicBlock* block,
                                          /*out*/HInstruction** taken_test) {
  bool b1, b2;  // unused
  if (!GenerateCode(context, context, graph, block, nullptr, nullptr, taken_test, &b1, &b2)) {
    LOG(FATAL) << "Failed precondition: GenerateCode()";
  }
}

//
// Private class methods.
//

bool InductionVarRange::NeedsTripCount(HInductionVarAnalysis::InductionInfo* info) {
  if (info != nullptr) {
    if (info->induction_class == HInductionVarAnalysis::kLinear) {
      return true;
    } else if (info->induction_class == HInductionVarAnalysis::kWrapAround) {
      return NeedsTripCount(info->op_b);
    }
  }
  return false;
}

bool InductionVarRange::IsBodyTripCount(HInductionVarAnalysis::InductionInfo* trip) {
  if (trip != nullptr) {
    if (trip->induction_class == HInductionVarAnalysis::kInvariant) {
      return trip->operation == HInductionVarAnalysis::kTripCountInBody ||
             trip->operation == HInductionVarAnalysis::kTripCountInBodyUnsafe;
    }
  }
  return false;
}

bool InductionVarRange::IsUnsafeTripCount(HInductionVarAnalysis::InductionInfo* trip) {
  if (trip != nullptr) {
    if (trip->induction_class == HInductionVarAnalysis::kInvariant) {
      return trip->operation == HInductionVarAnalysis::kTripCountInBodyUnsafe ||
             trip->operation == HInductionVarAnalysis::kTripCountInLoopUnsafe;
    }
  }
  return false;
}

InductionVarRange::Value InductionVarRange::GetFetch(HInstruction* instruction,
                                                     HInductionVarAnalysis::InductionInfo* trip,
                                                     bool in_body,
                                                     bool is_min) {
  // Detect constants and chase the fetch a bit deeper into the HIR tree, so that it becomes
  // more likely range analysis will compare the same instructions as terminal nodes.
  int32_t value;
  if (IsIntAndGet(instruction, &value)) {
    return Value(value);
  } else if (instruction->IsAdd()) {
    if (IsIntAndGet(instruction->InputAt(0), &value)) {
      return AddValue(Value(value), GetFetch(instruction->InputAt(1), trip, in_body, is_min));
    } else if (IsIntAndGet(instruction->InputAt(1), &value)) {
      return AddValue(GetFetch(instruction->InputAt(0), trip, in_body, is_min), Value(value));
    }
  } else if (is_min) {
    // Special case for finding minimum: minimum of trip-count in loop-body is 1.
    if (trip != nullptr && in_body && instruction == trip->op_a->fetch) {
      return Value(1);
    }
  }
  return Value(instruction, 1, 0);
}

InductionVarRange::Value InductionVarRange::GetVal(HInductionVarAnalysis::InductionInfo* info,
                                                   HInductionVarAnalysis::InductionInfo* trip,
                                                   bool in_body,
                                                   bool is_min) {
  if (info != nullptr) {
    switch (info->induction_class) {
      case HInductionVarAnalysis::kInvariant:
        // Invariants.
        switch (info->operation) {
          case HInductionVarAnalysis::kAdd:
            return AddValue(GetVal(info->op_a, trip, in_body, is_min),
                            GetVal(info->op_b, trip, in_body, is_min));
          case HInductionVarAnalysis::kSub:  // second reversed!
            return SubValue(GetVal(info->op_a, trip, in_body, is_min),
                            GetVal(info->op_b, trip, in_body, !is_min));
          case HInductionVarAnalysis::kNeg:  // second reversed!
            return SubValue(Value(0),
                            GetVal(info->op_b, trip, in_body, !is_min));
          case HInductionVarAnalysis::kMul:
            return GetMul(info->op_a, info->op_b, trip, in_body, is_min);
          case HInductionVarAnalysis::kDiv:
            return GetDiv(info->op_a, info->op_b, trip, in_body, is_min);
          case HInductionVarAnalysis::kFetch:
            return GetFetch(info->fetch, trip, in_body, is_min);
          case HInductionVarAnalysis::kTripCountInLoop:
          case HInductionVarAnalysis::kTripCountInLoopUnsafe:
            if (!in_body && !is_min) {  // one extra!
              return GetVal(info->op_a, trip, in_body, is_min);
            }
            FALLTHROUGH_INTENDED;
          case HInductionVarAnalysis::kTripCountInBody:
          case HInductionVarAnalysis::kTripCountInBodyUnsafe:
            if (is_min) {
              return Value(0);
            } else if (in_body) {
              return SubValue(GetVal(info->op_a, trip, in_body, is_min), Value(1));
            }
            break;
          default:
            break;
        }
        break;
      case HInductionVarAnalysis::kLinear:
        // Linear induction a * i + b, for normalized 0 <= i < TC.
        return AddValue(GetMul(info->op_a, trip, trip, in_body, is_min),
                        GetVal(info->op_b, trip, in_body, is_min));
      case HInductionVarAnalysis::kWrapAround:
      case HInductionVarAnalysis::kPeriodic:
        // Merge values in the wrap-around/periodic.
        return MergeVal(GetVal(info->op_a, trip, in_body, is_min),
                        GetVal(info->op_b, trip, in_body, is_min), is_min);
    }
  }
  return Value();
}

InductionVarRange::Value InductionVarRange::GetMul(HInductionVarAnalysis::InductionInfo* info1,
                                                   HInductionVarAnalysis::InductionInfo* info2,
                                                   HInductionVarAnalysis::InductionInfo* trip,
                                                   bool in_body,
                                                   bool is_min) {
  Value v1_min = GetVal(info1, trip, in_body, /* is_min */ true);
  Value v1_max = GetVal(info1, trip, in_body, /* is_min */ false);
  Value v2_min = GetVal(info2, trip, in_body, /* is_min */ true);
  Value v2_max = GetVal(info2, trip, in_body, /* is_min */ false);
  if (v1_min.is_known && v1_min.a_constant == 0 && v1_min.b_constant >= 0) {
    // Positive range vs. positive or negative range.
    if (v2_min.is_known && v2_min.a_constant == 0 && v2_min.b_constant >= 0) {
      return is_min ? MulValue(v1_min, v2_min)
                    : MulValue(v1_max, v2_max);
    } else if (v2_max.is_known && v2_max.a_constant == 0 && v2_max.b_constant <= 0) {
      return is_min ? MulValue(v1_max, v2_min)
                    : MulValue(v1_min, v2_max);
    }
  } else if (v1_min.is_known && v1_min.a_constant == 0 && v1_min.b_constant <= 0) {
    // Negative range vs. positive or negative range.
    if (v2_min.is_known && v2_min.a_constant == 0 && v2_min.b_constant >= 0) {
      return is_min ? MulValue(v1_min, v2_max)
                    : MulValue(v1_max, v2_min);
    } else if (v2_max.is_known && v2_max.a_constant == 0 && v2_max.b_constant <= 0) {
      return is_min ? MulValue(v1_max, v2_max)
                    : MulValue(v1_min, v2_min);
    }
  }
  return Value();
}

InductionVarRange::Value InductionVarRange::GetDiv(HInductionVarAnalysis::InductionInfo* info1,
                                                   HInductionVarAnalysis::InductionInfo* info2,
                                                   HInductionVarAnalysis::InductionInfo* trip,
                                                   bool in_body,
                                                   bool is_min) {
  Value v1_min = GetVal(info1, trip, in_body, /* is_min */ true);
  Value v1_max = GetVal(info1, trip, in_body, /* is_min */ false);
  Value v2_min = GetVal(info2, trip, in_body, /* is_min */ true);
  Value v2_max = GetVal(info2, trip, in_body, /* is_min */ false);
  if (v1_min.is_known && v1_min.a_constant == 0 && v1_min.b_constant >= 0) {
    // Positive range vs. positive or negative range.
    if (v2_min.is_known && v2_min.a_constant == 0 && v2_min.b_constant >= 0) {
      return is_min ? DivValue(v1_min, v2_max)
                    : DivValue(v1_max, v2_min);
    } else if (v2_max.is_known && v2_max.a_constant == 0 && v2_max.b_constant <= 0) {
      return is_min ? DivValue(v1_max, v2_max)
                    : DivValue(v1_min, v2_min);
    }
  } else if (v1_min.is_known && v1_min.a_constant == 0 && v1_min.b_constant <= 0) {
    // Negative range vs. positive or negative range.
    if (v2_min.is_known && v2_min.a_constant == 0 && v2_min.b_constant >= 0) {
      return is_min ? DivValue(v1_min, v2_min)
                    : DivValue(v1_max, v2_max);
    } else if (v2_max.is_known && v2_max.a_constant == 0 && v2_max.b_constant <= 0) {
      return is_min ? DivValue(v1_max, v2_min)
                    : DivValue(v1_min, v2_max);
    }
  }
  return Value();
}

bool InductionVarRange::GetConstant(HInductionVarAnalysis::InductionInfo* info, int32_t *value) {
  Value v_min = GetVal(info, nullptr, false, /* is_min */ true);
  Value v_max = GetVal(info, nullptr, false, /* is_min */ false);
  if (v_min.is_known && v_max.is_known) {
    if (v_min.a_constant == 0 && v_max.a_constant == 0 && v_min.b_constant == v_max.b_constant) {
      *value = v_min.b_constant;
      return true;
    }
  }
  return false;
}

InductionVarRange::Value InductionVarRange::AddValue(Value v1, Value v2) {
  if (v1.is_known && v2.is_known && IsSafeAdd(v1.b_constant, v2.b_constant)) {
    const int32_t b = v1.b_constant + v2.b_constant;
    if (v1.a_constant == 0) {
      return Value(v2.instruction, v2.a_constant, b);
    } else if (v2.a_constant == 0) {
      return Value(v1.instruction, v1.a_constant, b);
    } else if (v1.instruction == v2.instruction && IsSafeAdd(v1.a_constant, v2.a_constant)) {
      return Value(v1.instruction, v1.a_constant + v2.a_constant, b);
    }
  }
  return Value();
}

InductionVarRange::Value InductionVarRange::SubValue(Value v1, Value v2) {
  if (v1.is_known && v2.is_known && IsSafeSub(v1.b_constant, v2.b_constant)) {
    const int32_t b = v1.b_constant - v2.b_constant;
    if (v1.a_constant == 0 && IsSafeSub(0, v2.a_constant)) {
      return Value(v2.instruction, -v2.a_constant, b);
    } else if (v2.a_constant == 0) {
      return Value(v1.instruction, v1.a_constant, b);
    } else if (v1.instruction == v2.instruction && IsSafeSub(v1.a_constant, v2.a_constant)) {
      return Value(v1.instruction, v1.a_constant - v2.a_constant, b);
    }
  }
  return Value();
}

InductionVarRange::Value InductionVarRange::MulValue(Value v1, Value v2) {
  if (v1.is_known && v2.is_known) {
    if (v1.a_constant == 0) {
      if (IsSafeMul(v1.b_constant, v2.a_constant) && IsSafeMul(v1.b_constant, v2.b_constant)) {
        return Value(v2.instruction, v1.b_constant * v2.a_constant, v1.b_constant * v2.b_constant);
      }
    } else if (v2.a_constant == 0) {
      if (IsSafeMul(v1.a_constant, v2.b_constant) && IsSafeMul(v1.b_constant, v2.b_constant)) {
        return Value(v1.instruction, v1.a_constant * v2.b_constant, v1.b_constant * v2.b_constant);
      }
    }
  }
  return Value();
}

InductionVarRange::Value InductionVarRange::DivValue(Value v1, Value v2) {
  if (v1.is_known && v2.is_known && v1.a_constant == 0 && v2.a_constant == 0) {
    if (IsSafeDiv(v1.b_constant, v2.b_constant)) {
      return Value(v1.b_constant / v2.b_constant);
    }
  }
  return Value();
}

InductionVarRange::Value InductionVarRange::MergeVal(Value v1, Value v2, bool is_min) {
  if (v1.is_known && v2.is_known) {
    if (v1.instruction == v2.instruction && v1.a_constant == v2.a_constant) {
      return Value(v1.instruction, v1.a_constant,
                   is_min ? std::min(v1.b_constant, v2.b_constant)
                          : std::max(v1.b_constant, v2.b_constant));
    }
  }
  return Value();
}

bool InductionVarRange::GenerateCode(HInstruction* context,
                                     HInstruction* instruction,
                                     HGraph* graph,
                                     HBasicBlock* block,
                                     /*out*/HInstruction** lower,
                                     /*out*/HInstruction** upper,
                                     /*out*/HInstruction** taken_test,
                                     /*out*/bool* needs_finite_test,
                                     /*out*/bool* needs_taken_test) {
  HLoopInformation* loop = context->GetBlock()->GetLoopInformation();  // closest enveloping loop
  if (loop != nullptr) {
    // Set up loop information.
    HBasicBlock* header = loop->GetHeader();
    bool in_body = context->GetBlock() != header;
    HInductionVarAnalysis::InductionInfo* info =
        induction_analysis_->LookupInfo(loop, instruction);
    if (info == nullptr) {
      return false;  // nothing to analyze
    }
    HInductionVarAnalysis::InductionInfo* trip =
        induction_analysis_->LookupInfo(loop, header->GetLastInstruction());
    // Determine what tests are needed.
    *needs_finite_test = NeedsTripCount(info) && IsUnsafeTripCount(trip);
    *needs_taken_test = NeedsTripCount(info) && IsBodyTripCount(trip);
    // Code generation for taken test: generate the code when requested or otherwise analyze
    // if code generation is feasible when taken test is needed.
    if (taken_test != nullptr) {
      return GenerateCode(
          trip->op_b, nullptr, graph, block, taken_test, in_body, /* is_min */ false);
    } else if (*needs_taken_test) {
      if (!GenerateCode(
          trip->op_b, nullptr, nullptr, nullptr, nullptr, in_body, /* is_min */ false)) {
        return false;
      }
    }
    // Code generation for lower and upper.
    return
        // Success on lower if invariant (not set), or code can be generated.
        ((info->induction_class == HInductionVarAnalysis::kInvariant) ||
            GenerateCode(info, trip, graph, block, lower, in_body, /* is_min */ true)) &&
        // And success on upper.
        GenerateCode(info, trip, graph, block, upper, in_body, /* is_min */ false);
  }
  return false;
}

bool InductionVarRange::GenerateCode(HInductionVarAnalysis::InductionInfo* info,
                                     HInductionVarAnalysis::InductionInfo* trip,
                                     HGraph* graph,  // when set, code is generated
                                     HBasicBlock* block,
                                     /*out*/HInstruction** result,
                                     bool in_body,
                                     bool is_min) {
  if (info != nullptr) {
    // Handle current operation.
    Primitive::Type type = Primitive::kPrimInt;
    HInstruction* opa = nullptr;
    HInstruction* opb = nullptr;
    switch (info->induction_class) {
      case HInductionVarAnalysis::kInvariant:
        // Invariants.
        switch (info->operation) {
          case HInductionVarAnalysis::kAdd:
          case HInductionVarAnalysis::kLT:
          case HInductionVarAnalysis::kLE:
          case HInductionVarAnalysis::kGT:
          case HInductionVarAnalysis::kGE:
            if (GenerateCode(info->op_a, trip, graph, block, &opa, in_body, is_min) &&
                GenerateCode(info->op_b, trip, graph, block, &opb, in_body, is_min)) {
              if (graph != nullptr) {
                HInstruction* operation = nullptr;
                switch (info->operation) {
                  case HInductionVarAnalysis::kAdd:
                    operation = new (graph->GetArena()) HAdd(type, opa, opb); break;
                  case HInductionVarAnalysis::kLT:
                    operation = new (graph->GetArena()) HLessThan(opa, opb); break;
                  case HInductionVarAnalysis::kLE:
                    operation = new (graph->GetArena()) HLessThanOrEqual(opa, opb); break;
                  case HInductionVarAnalysis::kGT:
                    operation = new (graph->GetArena()) HGreaterThan(opa, opb); break;
                  case HInductionVarAnalysis::kGE:
                    operation = new (graph->GetArena()) HGreaterThanOrEqual(opa, opb); break;
                  default:
                    LOG(FATAL) << "unknown operation";
                }
                *result = Insert(block, operation);
              }
              return true;
            }
            break;
          case HInductionVarAnalysis::kSub:  // second reversed!
            if (GenerateCode(info->op_a, trip, graph, block, &opa, in_body, is_min) &&
                GenerateCode(info->op_b, trip, graph, block, &opb, in_body, !is_min)) {
              if (graph != nullptr) {
                *result = Insert(block, new (graph->GetArena()) HSub(type, opa, opb));
              }
              return true;
            }
            break;
          case HInductionVarAnalysis::kNeg:  // reversed!
            if (GenerateCode(info->op_b, trip, graph, block, &opb, in_body, !is_min)) {
              if (graph != nullptr) {
                *result = Insert(block, new (graph->GetArena()) HNeg(type, opb));
              }
              return true;
            }
            break;
          case HInductionVarAnalysis::kFetch:
            if (graph != nullptr) {
              *result = info->fetch;  // already in HIR
            }
            return true;
          case HInductionVarAnalysis::kTripCountInLoop:
          case HInductionVarAnalysis::kTripCountInLoopUnsafe:
            if (!in_body && !is_min) {  // one extra!
              return GenerateCode(info->op_a, trip, graph, block, result, in_body, is_min);
            }
            FALLTHROUGH_INTENDED;
          case HInductionVarAnalysis::kTripCountInBody:
          case HInductionVarAnalysis::kTripCountInBodyUnsafe:
            if (is_min) {
              if (graph != nullptr) {
                *result = graph->GetIntConstant(0);
              }
              return true;
            } else if (in_body) {
              if (GenerateCode(info->op_a, trip, graph, block, &opb, in_body, is_min)) {
                if (graph != nullptr) {
                  *result = Insert(block,
                                   new (graph->GetArena())
                                       HSub(type, opb, graph->GetIntConstant(1)));
                }
                return true;
              }
            }
            break;
          default:
            break;
        }
        break;
      case HInductionVarAnalysis::kLinear: {
          // Linear induction a * i + b, for normalized 0 <= i < TC. Restrict to unit stride only
          // to avoid arithmetic wrap-around situations that are hard to guard against.
          int32_t stride_value = 0;
          if (GetConstant(info->op_a, &stride_value)) {
            if (stride_value == 1 || stride_value == -1) {
              const bool is_min_a = stride_value == 1 ? is_min : !is_min;
              if (GenerateCode(trip,       trip, graph, block, &opa, in_body, is_min_a) &&
                  GenerateCode(info->op_b, trip, graph, block, &opb, in_body, is_min)) {
                if (graph != nullptr) {
                  HInstruction* oper;
                  if (stride_value == 1) {
                    oper = new (graph->GetArena()) HAdd(type, opa, opb);
                  } else {
                    oper = new (graph->GetArena()) HSub(type, opb, opa);
                  }
                  *result = Insert(block, oper);
                }
                return true;
              }
            }
          }
        }
        break;
      default:
        break;
    }
  }
  return false;
}

}  // namespace art