ExistentialSpecializer.cpp

//===--- ExistentialSpecializer.cpp - Specialization of functions -----===//
//===---                 with existential arguments               -----===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Specialize functions with existential parameters to generic ones.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sil-existential-specializer"
#include "ExistentialTransform.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SIL/SILInstruction.h"
#include "swift/SILOptimizer/Analysis/ProtocolConformanceAnalysis.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SILOptimizer/Utils/Existential.h"
#include "swift/SILOptimizer/Utils/InstOptUtils.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"

using namespace swift;

static llvm::cl::opt<bool>
EnableExistentialSpecializer("enable-existential-specializer",
                             llvm::cl::Hidden,
                             llvm::cl::init(true));

STATISTIC(NumFunctionsWithExistentialArgsSpecialized,
          "Number of functions with existential args specialized");

namespace {

/// ExistentialSpecializer class.
class ExistentialSpecializer : public SILFunctionTransform {

  /// Determine if the current function is a target for existential
  /// specialization of args.
  bool canSpecializeExistentialArgsInFunction(
      FullApplySite &Apply,
      llvm::SmallDenseMap<int, ExistentialTransformArgumentDescriptor>
          &ExistentialArgDescriptor);

  /// Can Callee be specialized?
  bool canSpecializeCalleeFunction(FullApplySite &Apply);

  /// Specialize existential args in function F.
  void specializeExistentialArgsInAppliesWithinFunction(SILFunction &F);

  /// Find concrete type using protocolconformance analysis.
  bool findConcreteTypeFromSoleConformingType(
    SILFunctionArgument *Arg, CanType &ConcreteType);

  /// CallerAnalysis information.
  CallerAnalysis *CA;

  // Determine the set of types a protocol conforms to in whole-module
  // compilation mode.
  ProtocolConformanceAnalysis *PCA;

  ClassHierarchyAnalysis *CHA;
public:
  void run() override {
    auto *F = getFunction();

    /// Don't optimize functions that should not be optimized.
    if (!F->shouldOptimize() || !EnableExistentialSpecializer) {
      return;
    }

    /// Get CallerAnalysis information handy.
    CA = PM->getAnalysis<CallerAnalysis>();

    /// Get ProtocolConformanceAnalysis.
    PCA = PM->getAnalysis<ProtocolConformanceAnalysis>();

    /// Get ClassHierarchyAnalysis.
    CHA = PM->getAnalysis<ClassHierarchyAnalysis>();
    /// Perform specialization.
    specializeExistentialArgsInAppliesWithinFunction(*F);
  }
};
} // namespace

/// Find concrete type from Sole Conforming Type.
bool ExistentialSpecializer::findConcreteTypeFromSoleConformingType(
    SILFunctionArgument *Arg, CanType &ConcreteType) {
  auto ArgType = Arg->getType();
  auto SwiftArgType = ArgType.getASTType();

  CanType constraint = SwiftArgType;
  if (auto existential = constraint->getAs<ExistentialType>())
    constraint = existential->getConstraintType()->getCanonicalType();

  /// Do not handle composition types yet.
  if (isa<ProtocolCompositionType>(constraint))
    return false;
  assert(ArgType.isExistentialType());
  /// Find the protocol decl.
  auto *PD = dyn_cast<ProtocolDecl>(constraint->getAnyNominal());
  if (!PD)
    return false;

  // Get SoleConformingType in ConcreteType using ProtocolConformanceAnalysis
  // and ClassHierarchyAnalysis.
  if (!PCA->getSoleConformingType(PD, CHA, ConcreteType))
    return false;
  return true;
}

/// Helper function to ensure that the argument is not InOut or InOut_Aliasable
static bool isNonInoutIndirectArgument(SILValue Arg,
                                       SILArgumentConvention ArgConvention) {
  return !Arg->getType().isObject() && ArgConvention.isIndirectConvention() &&
         ArgConvention != SILArgumentConvention::Indirect_Inout &&
         ArgConvention != SILArgumentConvention::Indirect_InoutAliasable;
}

/// Check if any apply argument meets the criteria for existential
/// specialization.
bool ExistentialSpecializer::canSpecializeExistentialArgsInFunction(
    FullApplySite &Apply,
    llvm::SmallDenseMap<int, ExistentialTransformArgumentDescriptor>
        &ExistentialArgDescriptor) {
  auto *F = Apply.getReferencedFunctionOrNull();
  auto CalleeArgs = F->begin()->getSILFunctionArguments();
  bool returnFlag = false;

  /// Analyze the argument for protocol conformance.  Iterator over the callee's
  /// function arguments.  The same SIL argument index is used for both caller
  /// and callee side arguments.
  auto origCalleeConv = Apply.getOrigCalleeConv();
  assert(Apply.getCalleeArgIndexOfFirstAppliedArg() == 0);
  for (unsigned Idx = 0, Num = CalleeArgs.size(); Idx < Num; ++Idx) {
    auto CalleeArg = CalleeArgs[Idx];
    auto ArgType = CalleeArg->getType();
    auto SwiftArgType = ArgType.getASTType();

    /// Checking for AnyObject and Any is added to ensure that we do not blow up
    /// the code size by specializing to every type that conforms to Any or
    /// AnyObject. In future, we may want to lift these two restrictions in a
    /// controlled way.
    if (!ArgType.isExistentialType() || ArgType.isAnyObject() ||
        SwiftArgType->isAny())
      continue;

    auto ExistentialRepr =
        CalleeArg->getType().getPreferredExistentialRepresentation();
    if (ExistentialRepr != ExistentialRepresentation::Opaque &&
          ExistentialRepr != ExistentialRepresentation::Class)
      continue;

    /// Find the concrete type.
    Operand &ArgOper = Apply.getArgumentRef(Idx);
    CanType ConcreteType =
        ConcreteExistentialInfo(ArgOper.get(), ArgOper.getUser()).ConcreteType;
    auto ArgConvention = F->getConventions().getSILArgumentConvention(Idx);
    /// Find the concrete type, either via sole type or via
    /// findInitExistential..
    CanType SoleConcreteType;
    if (!((F->getModule().isWholeModule() &&
           isNonInoutIndirectArgument(CalleeArg, ArgConvention) &&
           findConcreteTypeFromSoleConformingType(CalleeArg, SoleConcreteType)) ||
          ConcreteType)) {
      LLVM_DEBUG(
          llvm::dbgs()
              << "ExistentialSpecializer Pass: Bail! cannot find ConcreteType "
                 "for call argument to:"
              << F->getName() << " in caller:"
              << Apply.getInstruction()->getParent()->getParent()->getName()
              << "\n";);
      continue;
    }

    /// Determine attributes of the existential addr argument.
    ExistentialTransformArgumentDescriptor ETAD;
    auto paramInfo = origCalleeConv.getParamInfoForSILArg(Idx);
    // The ExistentialSpecializerCloner copies the incoming generic argument
    // into an existential. This won't work if the original argument is
    // mutated. Furthermore, SILCombine would not be able to replace a mutated
    // existential with a concrete value, so the specialization thunk could not
    // be optimized away.
    if (paramInfo.isIndirectMutating())
      continue;

    ETAD.AccessType = paramInfo.isConsumed()
                          ? OpenedExistentialAccess::Mutable
                          : OpenedExistentialAccess::Immutable;
    ETAD.isConsumed = paramInfo.isConsumed();

    /// Save the attributes
    ExistentialArgDescriptor[Idx] = ETAD;
    LLVM_DEBUG(llvm::dbgs()
               << "ExistentialSpecializer Pass:Function: " << F->getName()
               << " Arg:" << Idx << " has a concrete type.\n");
    returnFlag |= true;
  }
  return returnFlag;
}

/// Determine if this callee function can be specialized or not.
bool ExistentialSpecializer::canSpecializeCalleeFunction(FullApplySite &Apply) {
  /// Determine the caller of the apply.
  auto *Callee = Apply.getReferencedFunctionOrNull();
  if (!Callee)
    return false;

  /// Callee should be optimizable.
  if (!Callee->shouldOptimize())
    return false;

  /// External function definitions.
  if (!Callee->isDefinition())
    return false;

  // Ignore generic functions. Generic functions should be fully specialized
  // before attempting to introduce new generic parameters for existential
  // arguments. Otherwise, there's no guarantee that the generic specializer
  // will be able to specialize the new generic parameter created by this pass.
  //
  // Enabling this would require additional implementation work to correctly
  // substitute the original archetypes into the new generic signature.
  if (Callee->getLoweredFunctionType()->getSubstGenericSignature())
    return false;

  /// Ignore functions with indirect results.
  if (Callee->getConventions().hasIndirectSILResults())
    return false;

  /// Ignore error returning functions.
  if (Callee->getLoweredFunctionType()->hasErrorResult()) 
    return false;

  /// Do not optimize always_inlinable functions.
  if (Callee->getInlineStrategy() == Inline_t::AlwaysInline)
    return false;

  /// Ignore externally linked functions with public_external or higher
  /// linkage.
  if (isAvailableExternally(Callee->getLinkage())) {
    return false;
  }

  /// Only choose a select few function representations for specialization.
  switch (Callee->getRepresentation()) {
  case SILFunctionTypeRepresentation::ObjCMethod:
  case SILFunctionTypeRepresentation::Block:
    return false;
  default: break;
  }
  return true;
}

/// Specialize existential args passed as arguments to callees. Iterate over all
/// call sites of the caller F and check for legality to apply existential
/// specialization.
void ExistentialSpecializer::specializeExistentialArgsInAppliesWithinFunction(
    SILFunction &F) {
  bool Changed = false;
  for (auto &BB : F) {
    for (auto It = BB.begin(), End = BB.end(); It != End; ++It) {
      auto *I = &*It;

      /// Is it an apply site?
      FullApplySite Apply = FullApplySite::isa(I);
      if (!Apply)
        continue;

      /// Can the callee be specialized?
      if (!canSpecializeCalleeFunction(Apply)) {
        LLVM_DEBUG(llvm::dbgs() << "ExistentialSpecializer Pass: Bail! Due to "
                                   "canSpecializeCalleeFunction.\n";
                   I->dump(););
        continue;
      }

      auto *Callee = Apply.getReferencedFunctionOrNull();

      /// Handle recursion! Do not modify F right now.
      if (Callee == &F) {
        LLVM_DEBUG(llvm::dbgs() << "ExistentialSpecializer Pass: Bail! Due to "
                                   "recursion.\n";
                  I->dump(););
        continue;
      }

      /// Determine the arguments that can be specialized.
      llvm::SmallDenseMap<int, ExistentialTransformArgumentDescriptor>
          ExistentialArgDescriptor;
      if (!canSpecializeExistentialArgsInFunction(Apply,
                                                  ExistentialArgDescriptor)) {
        LLVM_DEBUG(llvm::dbgs()
                   << "ExistentialSpecializer Pass: Bail! Due to "
                      "canSpecializeExistentialArgsInFunction in function: "
                   << Callee->getName() << " -> abort\n");
        continue;
      }

      LLVM_DEBUG(llvm::dbgs()
                 << "ExistentialSpecializer Pass: Function::"
                 << Callee->getName()
                 << " has an existential argument and can be optimized "
                    "via ExistentialSpecializer\n");

      /// Name Mangler for naming the protocol constrained generic method.
      auto P = Demangle::SpecializationPass::FunctionSignatureOpts;
      Mangle::FunctionSignatureSpecializationMangler Mangler(
          P, Callee->isSerialized(), Callee);

      /// Save the arguments in a descriptor.
      llvm::SpecificBumpPtrAllocator<ProjectionTreeNode> Allocator;
      llvm::SmallVector<ArgumentDescriptor, 4> ArgumentDescList;
      auto Args = Callee->begin()->getSILFunctionArguments();
      for (unsigned i : indices(Args)) {
        ArgumentDescList.emplace_back(Args[i], Allocator);
      }

      /// This is the function to optimize for existential specilizer.
      LLVM_DEBUG(llvm::dbgs()
                 << "*** Running ExistentialSpecializer Pass on function: "
                 << Callee->getName() << " ***\n");

      /// Instantiate the ExistentialSpecializerTransform pass.
      SILOptFunctionBuilder FuncBuilder(*this);
      ExistentialTransform ET(FuncBuilder, Callee, Mangler, ArgumentDescList,
                              ExistentialArgDescriptor);

      /// Run the existential specializer pass.
      Changed = ET.run();

      if (Changed) {
        /// Update statistics on the number of functions specialized.
        ++NumFunctionsWithExistentialArgsSpecialized;

        /// Make sure the PM knows about the new specialized inner function.
        addFunctionToPassManagerWorklist(ET.getExistentialSpecializedFunction(),
                                         Callee);

        /// Invalidate analysis results of Callee.
        PM->invalidateAnalysis(Callee,
                               SILAnalysis::InvalidationKind::FunctionBody);
      }
    }
  }
  return;
}

SILTransform *swift::createExistentialSpecializer() {
  return new ExistentialSpecializer();
}