GenericSpecializer.cpp

//===--- GenericSpecializer.cpp - Specialization of generic functions -----===//
//
// 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 calls to generic functions by substituting static type
// information.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sil-generic-specializer"

#include "swift/SIL/OptimizationRemark.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SIL/SILInstruction.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SILOptimizer/Utils/Generics.h"
#include "swift/SILOptimizer/Utils/InstOptUtils.h"
#include "swift/SILOptimizer/Utils/SILOptFunctionBuilder.h"
#include "llvm/ADT/SmallVector.h"

using namespace swift;

// For testing during bring up.
static llvm::cl::opt<bool> EnableGenericSpecializerWithOwnership(
    "sil-generic-specializer-enable-ownership", llvm::cl::init(false));

namespace {

class GenericSpecializer : public SILFunctionTransform {

  bool specializeAppliesInFunction(SILFunction &F);

  /// The entry point to the transformation.
  void run() override {
    SILFunction &F = *getFunction();

    // TODO: We should be able to handle ownership.
    if (F.hasOwnership() && !EnableGenericSpecializerWithOwnership)
      return;

    LLVM_DEBUG(llvm::dbgs() << "***** GenericSpecializer on function:"
                            << F.getName() << " *****\n");

    if (specializeAppliesInFunction(F))
      invalidateAnalysis(SILAnalysis::InvalidationKind::Everything);
  }

};

} // end anonymous namespace

bool GenericSpecializer::specializeAppliesInFunction(SILFunction &F) {
  SILOptFunctionBuilder FunctionBuilder(*this);
  DeadInstructionSet DeadApplies;
  llvm::SmallSetVector<SILInstruction *, 8> Applies;
  OptRemark::Emitter ORE(DEBUG_TYPE, F);

  bool Changed = false;
  for (auto &BB : F) {
    // Collect the applies for this block in reverse order so that we
    // can pop them off the end of our vector and process them in
    // forward order.
    for (auto &I : llvm::reverse(BB)) {

      // Skip non-apply instructions, apply instructions with no
      // substitutions, apply instructions where we do not statically
      // know the called function, and apply instructions where we do
      // not have the body of the called function.
      ApplySite Apply = ApplySite::isa(&I);
      if (!Apply || !Apply.hasSubstitutions())
        continue;

      auto *Callee = Apply.getReferencedFunctionOrNull();
      if (!Callee)
        continue;
      if (!Callee->isDefinition()) {
        ORE.emit([&]() {
          using namespace OptRemark;
          return RemarkMissed("NoDef", I)
                 << "Unable to specialize generic function "
                 << NV("Callee", Callee) << " since definition is not visible";
        });
        continue;
      }

      Applies.insert(Apply.getInstruction());
    }

    // Attempt to specialize each apply we collected, deleting any
    // that we do specialize (along with other instructions we clone
    // in the process of doing so). We pop from the end of the list to
    // avoid tricky iterator invalidation issues.
    while (!Applies.empty()) {
      auto *I = Applies.pop_back_val();
      auto Apply = ApplySite::isa(I);
      assert(Apply && "Expected an apply!");
      SILFunction *Callee = Apply.getReferencedFunctionOrNull();
      assert(Callee && "Expected to have a known callee");

      if (!Apply.canOptimize() || !Callee->shouldOptimize())
        continue;

      // We have a call that can potentially be specialized, so
      // attempt to do so.
      llvm::SmallVector<SILFunction *, 2> NewFunctions;
      trySpecializeApplyOfGeneric(FunctionBuilder, Apply, DeadApplies,
                                  NewFunctions, ORE);

      // Remove all the now-dead applies. We must do this immediately
      // rather than defer it in order to avoid problems with cloning
      // dead instructions when doing recursive specialization.
      while (!DeadApplies.empty()) {
        auto *AI = DeadApplies.pop_back_val();

        // Remove any applies we are deleting so that we don't attempt
        // to specialize them.
        Applies.remove(AI);

        recursivelyDeleteTriviallyDeadInstructions(AI, true);
        Changed = true;
      }

      // If calling the specialization utility resulted in new functions
      // (as opposed to returning a previous specialization), we need to notify
      // the pass manager so that the new functions get optimized.
      for (SILFunction *NewF : reverse(NewFunctions)) {
        addFunctionToPassManagerWorklist(NewF, Callee);
      }
    }
  }

  return Changed;
}

SILTransform *swift::createGenericSpecializer() {
  return new GenericSpecializer();
}