swift-mirror/lib/SILOptimizer/Utils/LoadStoreOptUtils.cpp

//===--- LoadStoreOptUtils.cpp --------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sil-lsbase"
#include "swift/SILOptimizer/Utils/LoadStoreOptUtils.h"
#include "swift/SIL/InstructionUtils.h"
#include "swift/SILOptimizer/Utils/InstOptUtils.h"
#include "llvm/Support/Debug.h"

using namespace swift;

//===----------------------------------------------------------------------===//
//                              Utility Functions
//===----------------------------------------------------------------------===//
static void
removeLSLocations(LSLocationValueMap &Values, LSLocationList &NextLevel) {
  for (auto &X : NextLevel) {
    Values.erase(X);
  }
}

//===----------------------------------------------------------------------===//
//                                 LSValue
//===----------------------------------------------------------------------===//
void LSValue::expand(SILValue Base, SILModule *M, TypeExpansionContext context,
                     LSValueList &Vals, TypeExpansionAnalysis *TE) {
  for (const auto &P : TE->getTypeExpansion((*Base).getType(), M, context)) {
    Vals.push_back(LSValue(Base, P.value()));
  }
}

void LSValue::reduceInner(LSLocation &Base, SILModule *M,
                          LSLocationValueMap &Values, SILInstruction *InsertPt) {
  TypeExpansionContext context(*InsertPt->getFunction());

  // If this is a class reference type, we have reached end of the type tree.
  if (Base.getType(M, context).getClassOrBoundGenericClass())
    return;

  // This a don't expand node.
  if (!shouldExpand(*M, Base.getType(M, context))) {
    return;
  }

  // This is a leaf node, we must have a value for it.
  LSLocationList NextLevel;
  Base.getNextLevelLSLocations(NextLevel, M, context);
  if (NextLevel.empty())
    return;

  // This is not a leaf node, reduce the next level node one by one.
  for (auto &X : NextLevel) {
    LSValue::reduceInner(X, M, Values, InsertPt);
  }

  // This is NOT a leaf node, we need to construct a value for it.
  auto Iter = NextLevel.begin();

  // Don't make this a reference! It may be invalidated as soon as the Values
  // map is modified, e.g. later at Values[Base] = ...
  LSValue FirstVal = Values[*Iter];

  // There is only 1 children node and its value's projection path is not
  // empty, keep stripping it.
  if (NextLevel.size() == 1 && !FirstVal.hasEmptyProjectionPath()) {
    Values[Base] = FirstVal.stripLastLevelProjection();
    // We have a value for the parent, remove all the values for children.
    removeLSLocations(Values, NextLevel);
    return;
  }

  bool HasIdenticalBase = true;
  SILValue FirstBase = FirstVal.getBase();
  for (auto &X : NextLevel) {
    HasIdenticalBase &= (FirstBase == Values[X].getBase());
  }

  // This is NOT a leaf node and it has multiple children, but they have the
  // same value base.
  if (NextLevel.size() > 1 && HasIdenticalBase) {
    if (!FirstVal.hasEmptyProjectionPath()) {
      Values[Base] = FirstVal.stripLastLevelProjection();
      // We have a value for the parent, remove all the values for children.
      removeLSLocations(Values, NextLevel);
      return;
    }
  }

  // In 3 cases do we need aggregation.
  //
  // 1. If there is only 1 child and we cannot strip off any projections,
  //    that means we need to create an aggregation.
  // 
  // 2. There are multiple children and they have the same base, but empty
  //    projection paths.
  //
  // 3. Children have values from different bases, We need to create
  //    extractions and aggregation in this case.
  //
  llvm::SmallVector<SILValue, 8> Vals;
  for (auto &X : NextLevel) {
    Vals.push_back(Values[X].materialize(InsertPt));
  }
  SILBuilder Builder(InsertPt);
  Builder.setCurrentDebugScope(InsertPt->getFunction()->getDebugScope());
  
  // We use an auto-generated SILLocation for now.
  NullablePtr<swift::SingleValueInstruction> AI =
      Projection::createAggFromFirstLevelProjections(
          Builder, RegularLocation::getAutoGeneratedLocation(),
          Base.getType(M, context).getObjectType(), Vals);

  auto AvailVal = makeValueAvailable(AI.get(), InsertPt->getParent());

  // This is the Value for the current base.
  ProjectionPath P(Base.getType(M, context));
  Values[Base] = LSValue(AvailVal, P);
  removeLSLocations(Values, NextLevel);
}

SILValue LSValue::reduce(LSLocation &Base, SILModule *M,
                         LSLocationValueMap &Values, SILInstruction *InsertPt) {
  LSValue::reduceInner(Base, M, Values, InsertPt);
  // Finally materialize and return the forwarding SILValue.
  return Values.begin()->second.materialize(InsertPt);
}

//===----------------------------------------------------------------------===//
//                               LSLocation
//===----------------------------------------------------------------------===//
bool
LSLocation::isMustAliasLSLocation(const LSLocation &RHS, AliasAnalysis *AA) {
  // If the bases are not must-alias, the locations may not alias.
  if (!AA->isMustAlias(Base, RHS.getBase()))
    return false;
  // If projection paths are different, then the locations cannot alias.
  if (!hasIdenticalProjectionPath(RHS))
    return false;
  // Must-alias base and identical projection path. Same object!.
  return true;
}

bool
LSLocation::isMayAliasLSLocation(const LSLocation &RHS, AliasAnalysis *AA) {
  // If the bases do not alias, then the locations cannot alias.
  if (AA->isNoAlias(Base, RHS.getBase()))
    return false;
  // If one projection path is a prefix of another, then the locations
  // could alias.
  if (hasNonEmptySymmetricPathDifference(RHS))
    return false;
  // We can not prove the 2 locations do not alias.
  return true;
}

void LSLocation::getNextLevelLSLocations(LSLocationList &Locs, SILModule *Mod,
                                         TypeExpansionContext context) {
  SILType Ty = getType(Mod, context);
  llvm::SmallVector<Projection, 8> Out;
  Projection::getFirstLevelProjections(Ty, *Mod, context, Out);
  for (auto &X : Out) {
    ProjectionPath P((*Base).getType());
    P.append(Path.value());
    P.append(X);
    Locs.push_back(LSLocation(Base, P));
  }
}

void LSLocation::expand(LSLocation Base, SILModule *M,
                        TypeExpansionContext context, LSLocationList &Locs,
                        TypeExpansionAnalysis *TE) {
  const ProjectionPath &BasePath = Base.getPath().value();
  for (const auto &P :
       TE->getTypeExpansion(Base.getType(M, context), M, context)) {
    Locs.push_back(LSLocation(Base.getBase(), BasePath, P.value()));
  }
}

/// Gets the sub-locations of \p Base in \p SubLocations.
/// Returns false if this is not possible or too complex.
static bool getSubLocations(LSLocationList &SubLocations, LSLocation Base,
                            SILModule *M, TypeExpansionContext context,
                            const LSLocationList &Locs) {
  // If this is a class reference type, we have reached end of the type tree.
  if (Base.getType(M, context).getClassOrBoundGenericClass())
    return false;

  // Don't expand if it would be too complex. As Locs is a list (and not a set)
  // we want to avoid quadratic complexity in replaceInner().
  // Usually Locs is small anyway, because we limit expansion to 6 members.
  // But with deeply nested types we could run in a corner case where Locs is
  // large.
  if (!shouldExpand(*M, Base.getType(M, context)) || Locs.size() >= 8) {
    return false;
  }

  // This is a leaf node.
  Base.getNextLevelLSLocations(SubLocations, M, context);
  return !SubLocations.empty();
}

/// Replaces \p SubLocations with \p Base in \p Locs if all sub-locations are
/// alive, i.e. present in \p Locs.
static bool replaceSubLocations(LSLocation Base, SILModule *M,
                                TypeExpansionContext context,
                                LSLocationList &Locs,
                                const LSLocationList &SubLocations) {
  // Find whether all its children of Base are alive.
  bool Alive = true;
  for (auto &X : SubLocations) {
    // Recurse into the next level.
    LSLocationList NextInnerLevel;
    if (getSubLocations(NextInnerLevel, X, M, context, Locs)) {
      Alive &= replaceSubLocations(X, M, context, Locs, NextInnerLevel);
    } else {
      Alive &= is_contained(Locs, X);
    }
  }

  // All next level locations are alive, create the new aggregated location.
  if (!Alive)
    return false;

  auto newEnd = std::remove_if(Locs.begin(), Locs.end(), [&](const LSLocation &L) {
    return is_contained(SubLocations, L);
  });
  Locs.erase(newEnd, Locs.end());
  Locs.push_back(Base);
  return true;
}

void LSLocation::reduce(LSLocation Base, SILModule *M,
                        TypeExpansionContext context, LSLocationList &Locs) {
  LSLocationList SubLocations;
  if (getSubLocations(SubLocations, Base, M, context, Locs))
    replaceSubLocations(Base, M, context, Locs, SubLocations);
}

std::pair<SILValue, bool>
LSLocation::getBaseAddressOrObject(SILValue v, bool stopAtImmutable) {
  bool isImmutable = false;
  while (true) {
    if (auto *rea = dyn_cast<RefElementAddrInst>(v)) {
      if (rea->isImmutable()) {
        isImmutable = true;
        if (stopAtImmutable)
          return {v, true};
      }
    }
    if (auto *rta = dyn_cast<RefTailAddrInst>(v)) {
      if (rta->isImmutable()) {
        isImmutable = true;
        if (stopAtImmutable)
          return {v, true};
      }
    }
    SILValue v2 = stripCastsWithoutMarkDependence(v);
    v2 = stripSinglePredecessorArgs(v2);
    if (Projection::isAddressProjection(v2))
      v2 = cast<SingleValueInstruction>(v2)->getOperand(0);
    v2 = stripIndexingInsts(v2);
    v2 = lookThroughOwnershipInsts(v2);
    if (v2 == v)
      return {v2, isImmutable};
    v = v2;
  }
}

bool LSLocation::enumerateLSLocation(TypeExpansionContext context, SILModule *M,
                                     SILValue Mem,
                                     std::vector<LSLocation> &Locations,
                                     LSLocationIndexMap &IndexMap,
                                     LSLocationBaseMap &BaseMap,
                                     TypeExpansionAnalysis *TypeCache,
                                     bool stopAtImmutable) {
  // We have processed this SILValue before.
  if (BaseMap.find(Mem) != BaseMap.end())
    return false;

  // Construct a Location to represent the memory written by this instruction.
  // ProjectionPath currently does not handle mark_dependence so stop our
  // underlying object search at these instructions.
  // We still get a benefit if we cse mark_dependence instructions and then
  // merge loads from them.
  auto baseAndImmutable = getBaseAddressOrObject(Mem, stopAtImmutable);
  SILValue UO = baseAndImmutable.first;
  LSLocation L(UO, ProjectionPath::getProjectionPath(UO, Mem));

  // If we can't figure out the Base or Projection Path for the memory location,
  // simply ignore it for now.
  if (!L.isValid())
    return false;

  // Record the SILValue to location mapping.
  BaseMap[Mem] = L; 

  // Expand the given Mem into individual fields and add them to the
  // locationvault.
  LSLocationList Locs;
  LSLocation::expand(L, M, context, Locs, TypeCache);
  for (auto &Loc : Locs) {
    if (IndexMap.find(Loc) != IndexMap.end())
      continue;
    IndexMap[Loc] = Locations.size();
    Locations.push_back(Loc);
  }
  return baseAndImmutable.first;
}

void
LSLocation::enumerateLSLocations(SILFunction &F,
                                 std::vector<LSLocation> &Locations,
                                 LSLocationIndexMap &IndexMap,
                                 LSLocationBaseMap &BaseMap,
                                 TypeExpansionAnalysis *TypeCache,
                                 bool stopAtImmutable,
                                 int &numLoads, int &numStores,
                                 bool &immutableLoadsFound) {
  // Enumerate all locations accessed by the loads or stores.
  for (auto &B : F) {
    for (auto &I : B) {
      if (auto *LI = dyn_cast<LoadInst>(&I)) {
        if (enumerateLSLocation(F.getTypeExpansionContext(), &I.getModule(),
                            LI->getOperand(), Locations, IndexMap, BaseMap,
                            TypeCache, stopAtImmutable)) {
          immutableLoadsFound = true;
        }
        ++numLoads;
        continue;
      }
      if (auto *SI = dyn_cast<StoreInst>(&I)) {
        enumerateLSLocation(F.getTypeExpansionContext(), &I.getModule(),
                            SI->getDest(), Locations, IndexMap, BaseMap,
                            TypeCache, stopAtImmutable);
        ++numStores;
        continue;
      }
    }
  }
}