lib/SILOptimizer/Utils/SILInliner.cpp

//===--- SILInliner.cpp - Inlines SIL 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
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sil-inliner"
#include "swift/SILOptimizer/Utils/SILInliner.h"
#include "swift/SIL/SILDebugScope.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
using namespace swift;

bool SILInliner::canInlineFunction(FullApplySite AI) {
  return AI.getFunction() != &Original;
}

/// \brief Inlines the callee of a given ApplyInst (which must be the value of a
/// FunctionRefInst referencing a function with a known body), into the caller
/// containing the ApplyInst, which must be the same function as provided to the
/// constructor of SILInliner. It only performs one step of inlining: it does
/// not recursively inline functions called by the callee.
///
/// It is the responsibility of the caller of this function to delete
/// the given ApplyInst when inlining is successful.
///
/// \returns true on success or false if it is unable to inline the function
/// (for any reason).
void SILInliner::inlineFunction(FullApplySite AI, ArrayRef<SILValue> Args) {
  assert(canInlineFunction(AI) &&
         "Asked to inline function that is unable to be inlined?!");

  // Setup the callee function.
  CalleeFunction = &Original;

  SILFunction &F = getBuilder().getFunction();
  assert(AI.getFunction() && AI.getFunction() == &F &&
         "Inliner called on apply instruction in wrong function?");
  assert(((CalleeFunction->getRepresentation()
             != SILFunctionTypeRepresentation::ObjCMethod &&
           CalleeFunction->getRepresentation()
             != SILFunctionTypeRepresentation::CFunctionPointer) ||
          IKind == InlineKind::PerformanceInline) &&
         "Cannot inline Objective-C methods or C functions in mandatory "
         "inlining");

  CalleeEntryBB = &*CalleeFunction->begin();

  // Compute the SILLocation which should be used by all the inlined
  // instructions.
  if (IKind == InlineKind::PerformanceInline) {
    Loc = InlinedLocation::getInlinedLocation(AI.getLoc());
  } else {
    assert(IKind == InlineKind::MandatoryInline && "Unknown InlineKind.");
    Loc = MandatoryInlinedLocation::getMandatoryInlinedLocation(AI.getLoc());
  }

  auto AIScope = AI.getDebugScope();
  // FIXME: Turn this into an assertion instead.
  if (!AIScope)
    AIScope = AI.getFunction()->getDebugScope();

  if (IKind == InlineKind::MandatoryInline) {
    // Mandatory inlining: every instruction inherits scope/location
    // from the call site.
    CallSiteScope = AIScope;
  } else {
    // Performance inlining. Construct a proper inline scope pointing
    // back to the call site.
    CallSiteScope = new (F.getModule())
        SILDebugScope(AI.getLoc(), nullptr, AIScope, AIScope->InlinedCallSite);
  }
  assert(CallSiteScope && "call site has no scope");
  assert(CallSiteScope->getParentFunction() == &F);

  // Increment the ref count for the inlined function, so it doesn't
  // get deleted before we can emit abstract debug info for it.
  CalleeFunction->setInlined();

  // If the caller's BB is not the last BB in the calling function, then keep
  // track of the next BB so we always insert new BBs before it; otherwise,
  // we just leave the new BBs at the end as they are by default.
  auto IBI = std::next(SILFunction::iterator(AI.getParent()));
  InsertBeforeBB = IBI != F.end() ? &*IBI : nullptr;

  // Clear argument map and map ApplyInst arguments to the arguments of the
  // callee's entry block.
  ValueMap.clear();
  assert(CalleeEntryBB->args_size() == Args.size() &&
         "Unexpected number of arguments to entry block of function?");
  auto BAI = CalleeEntryBB->args_begin();
  for (auto AI = Args.begin(), AE = Args.end(); AI != AE; ++AI, ++BAI)
    ValueMap.insert(std::make_pair(*BAI, *AI));

  BBMap.clear();
  // Do not allow the entry block to be cloned again
  SILBasicBlock::iterator InsertPoint =
    SILBasicBlock::iterator(AI.getInstruction());
  BBMap.insert(std::make_pair(CalleeEntryBB, AI.getParent()));
  getBuilder().setInsertionPoint(InsertPoint);
  // Recursively visit callee's BB in depth-first preorder, starting with the
  // entry block, cloning all instructions other than terminators.
  visitSILBasicBlock(CalleeEntryBB);

  // If we're inlining into a normal apply and the callee's entry
  // block ends in a return, then we can avoid a split.
  if (auto nonTryAI = dyn_cast<ApplyInst>(AI)) {
    if (auto *RI = dyn_cast<ReturnInst>(CalleeEntryBB->getTerminator())) {
      // Replace all uses of the apply instruction with the operands of the
      // return instruction, appropriately mapped.
      nonTryAI->replaceAllUsesWith(remapValue(RI->getOperand()));
      return;
    }
  }

  // If we're inlining into a try_apply, we already have a return-to BB.
  SILBasicBlock *ReturnToBB;
  if (auto tryAI = dyn_cast<TryApplyInst>(AI)) {
    ReturnToBB = tryAI->getNormalBB();

  // Otherwise, split the caller's basic block to create a return-to BB.
  } else {
    SILBasicBlock *CallerBB = AI.getParent();
    // Split the BB and do NOT create a branch between the old and new
    // BBs; we will create the appropriate terminator manually later.
    ReturnToBB = CallerBB->split(InsertPoint);
    // Place the return-to BB after all the other mapped BBs.
    if (InsertBeforeBB)
      F.getBlocks().splice(SILFunction::iterator(InsertBeforeBB), F.getBlocks(),
                           SILFunction::iterator(ReturnToBB));
    else
      F.getBlocks().splice(F.getBlocks().end(), F.getBlocks(),
                           SILFunction::iterator(ReturnToBB));

    // Create an argument on the return-to BB representing the returned value.
    auto apply = cast<ApplyInst>(AI.getInstruction());
    auto *RetArg = ReturnToBB->createPHIArgument(apply->getType(),
                                                 ValueOwnershipKind::Owned);
    // Replace all uses of the ApplyInst with the new argument.
    apply->replaceAllUsesWith(RetArg);
  }

  // Now iterate over the callee BBs and fix up the terminators.
  for (auto BI = BBMap.begin(), BE = BBMap.end(); BI != BE; ++BI) {
    getBuilder().setInsertionPoint(BI->second);

    // Modify return terminators to branch to the return-to BB, rather than
    // trying to clone the ReturnInst.
    if (auto *RI = dyn_cast<ReturnInst>(BI->first->getTerminator())) {
      auto thrownValue = remapValue(RI->getOperand());
      getBuilder().createBranch(Loc.getValue(), ReturnToBB,
                                thrownValue);
      continue;
    }

    // Modify throw terminators to branch to the error-return BB, rather than
    // trying to clone the ThrowInst.
    if (auto *TI = dyn_cast<ThrowInst>(BI->first->getTerminator())) {
      if (auto *A = dyn_cast<ApplyInst>(AI)) {
        (void)A;
        assert(A->isNonThrowing() &&
               "apply of a function with error result must be non-throwing");
        getBuilder().createUnreachable(Loc.getValue());
        continue;
      }
      auto tryAI = cast<TryApplyInst>(AI);
      auto returnedValue = remapValue(TI->getOperand());
      getBuilder().createBranch(Loc.getValue(), tryAI->getErrorBB(),
                                returnedValue);
      continue;
    }

    // Otherwise use normal visitor, which clones the existing instruction
    // but remaps basic blocks and values.
    visit(BI->first->getTerminator());
  }
}

void SILInliner::visitDebugValueInst(DebugValueInst *Inst) {
  // The mandatory inliner drops debug_value instructions when inlining, as if
  // it were a "nodebug" function in C.
  if (IKind == InlineKind::MandatoryInline) return;

  return SILCloner<SILInliner>::visitDebugValueInst(Inst);
}
void SILInliner::visitDebugValueAddrInst(DebugValueAddrInst *Inst) {
  // The mandatory inliner drops debug_value_addr instructions when inlining, as
  // if it were a "nodebug" function in C.
  if (IKind == InlineKind::MandatoryInline) return;

  return SILCloner<SILInliner>::visitDebugValueAddrInst(Inst);
}

const SILDebugScope *
SILInliner::getOrCreateInlineScope(const SILDebugScope *CalleeScope) {
  if (!CalleeScope)
    return CallSiteScope;
  auto it = InlinedScopeCache.find(CalleeScope);
  if (it != InlinedScopeCache.end())
    return it->second;

  auto &M = getBuilder().getFunction().getModule();
  auto InlinedAt =
      getOrCreateInlineScope(CalleeScope->InlinedCallSite);
  auto *InlinedScope = new (M) SILDebugScope(
      CalleeScope->Loc, CalleeScope->Parent.dyn_cast<SILFunction *>(),
      CalleeScope->Parent.dyn_cast<const SILDebugScope *>(), InlinedAt);
  InlinedScopeCache.insert({CalleeScope, InlinedScope});
  return InlinedScope;
}

//===----------------------------------------------------------------------===//
//                                 Cost Model
//===----------------------------------------------------------------------===//

static InlineCost getEnforcementCost(SILAccessEnforcement enforcement) {
  switch (enforcement) {
  case SILAccessEnforcement::Unknown:
    llvm_unreachable("evaluating cost of access with unknown enforcement?");
  case SILAccessEnforcement::Dynamic:
    return InlineCost::Expensive;
  case SILAccessEnforcement::Static:
  case SILAccessEnforcement::Unsafe:
    return InlineCost::Free;
  }
  llvm_unreachable("bad enforcement");
}

/// For now just assume that every SIL instruction is one to one with an LLVM
/// instruction. This is of course very much so not true.
InlineCost swift::instructionInlineCost(SILInstruction &I) {
  switch (I.getKind()) {
  case SILInstructionKind::IntegerLiteralInst:
  case SILInstructionKind::FloatLiteralInst:
  case SILInstructionKind::DebugValueInst:
  case SILInstructionKind::DebugValueAddrInst:
  case SILInstructionKind::StringLiteralInst:
  case SILInstructionKind::ConstStringLiteralInst:
  case SILInstructionKind::FixLifetimeInst:
  case SILInstructionKind::EndBorrowInst:
  case SILInstructionKind::EndBorrowArgumentInst:
  case SILInstructionKind::BeginBorrowInst:
  case SILInstructionKind::MarkDependenceInst:
  case SILInstructionKind::FunctionRefInst:
  case SILInstructionKind::AllocGlobalInst:
  case SILInstructionKind::GlobalAddrInst:
  case SILInstructionKind::EndLifetimeInst:
  case SILInstructionKind::UncheckedOwnershipConversionInst:
    return InlineCost::Free;

  // Typed GEPs are free.
  case SILInstructionKind::TupleElementAddrInst:
  case SILInstructionKind::StructElementAddrInst:
  case SILInstructionKind::ProjectBlockStorageInst:
    return InlineCost::Free;

  // Aggregates are exploded at the IR level; these are effectively no-ops.
  case SILInstructionKind::TupleInst:
  case SILInstructionKind::StructInst:
  case SILInstructionKind::StructExtractInst:
  case SILInstructionKind::TupleExtractInst:
    return InlineCost::Free;

  // Unchecked casts are free.
  case SILInstructionKind::AddressToPointerInst:
  case SILInstructionKind::PointerToAddressInst:

  case SILInstructionKind::UncheckedRefCastInst:
  case SILInstructionKind::UncheckedRefCastAddrInst:
  case SILInstructionKind::UncheckedAddrCastInst:
  case SILInstructionKind::UncheckedTrivialBitCastInst:
  case SILInstructionKind::UncheckedBitwiseCastInst:

  case SILInstructionKind::RawPointerToRefInst:
  case SILInstructionKind::RefToRawPointerInst:

  case SILInstructionKind::UpcastInst:

  case SILInstructionKind::ThinToThickFunctionInst:
  case SILInstructionKind::ThinFunctionToPointerInst:
  case SILInstructionKind::PointerToThinFunctionInst:
  case SILInstructionKind::ConvertFunctionInst:

  case SILInstructionKind::BridgeObjectToWordInst:
    return InlineCost::Free;

  // Access instructions are free unless we're dynamically enforcing them.
  case SILInstructionKind::BeginAccessInst:
    return getEnforcementCost(cast<BeginAccessInst>(I).getEnforcement());
  case SILInstructionKind::EndAccessInst:
    return getEnforcementCost(cast<EndAccessInst>(I).getBeginAccess()
                                                   ->getEnforcement());
  case SILInstructionKind::BeginUnpairedAccessInst:
    return getEnforcementCost(cast<BeginUnpairedAccessInst>(I)
                                .getEnforcement());
  case SILInstructionKind::EndUnpairedAccessInst:
    return getEnforcementCost(cast<EndUnpairedAccessInst>(I)
                                .getEnforcement());

  // TODO: These are free if the metatype is for a Swift class.
  case SILInstructionKind::ThickToObjCMetatypeInst:
  case SILInstructionKind::ObjCToThickMetatypeInst:
    return InlineCost::Expensive;
    
  // TODO: Bridge object conversions imply a masking operation that should be
  // "hella cheap" but not really expensive
  case SILInstructionKind::BridgeObjectToRefInst:
  case SILInstructionKind::RefToBridgeObjectInst:
    return InlineCost::Expensive;

  case SILInstructionKind::MetatypeInst:
    // Thin metatypes are always free.
    if (cast<MetatypeInst>(I).getType().castTo<MetatypeType>()
          ->getRepresentation() == MetatypeRepresentation::Thin)
      return InlineCost::Free;
    // TODO: Thick metatypes are free if they don't require generic or lazy
    // instantiation.
    return InlineCost::Expensive;

  // Protocol descriptor references are free.
  case SILInstructionKind::ObjCProtocolInst:
    return InlineCost::Free;

  // Metatype-to-object conversions are free.
  case SILInstructionKind::ObjCExistentialMetatypeToObjectInst:
  case SILInstructionKind::ObjCMetatypeToObjectInst:
    return InlineCost::Free;

  // Return and unreachable are free.
  case SILInstructionKind::UnreachableInst:
  case SILInstructionKind::ReturnInst:
  case SILInstructionKind::ThrowInst:
    return InlineCost::Free;

  case SILInstructionKind::ApplyInst:
  case SILInstructionKind::TryApplyInst:
  case SILInstructionKind::AllocBoxInst:
  case SILInstructionKind::AllocExistentialBoxInst:
  case SILInstructionKind::AllocRefInst:
  case SILInstructionKind::AllocRefDynamicInst:
  case SILInstructionKind::AllocStackInst:
  case SILInstructionKind::AllocValueBufferInst:
  case SILInstructionKind::BindMemoryInst:
  case SILInstructionKind::ValueMetatypeInst:
  case SILInstructionKind::WitnessMethodInst:
  case SILInstructionKind::AssignInst:
  case SILInstructionKind::BranchInst:
  case SILInstructionKind::CheckedCastBranchInst:
  case SILInstructionKind::CheckedCastValueBranchInst:
  case SILInstructionKind::CheckedCastAddrBranchInst:
  case SILInstructionKind::ClassMethodInst:
  case SILInstructionKind::CondBranchInst:
  case SILInstructionKind::CondFailInst:
  case SILInstructionKind::CopyBlockInst:
  case SILInstructionKind::CopyAddrInst:
  case SILInstructionKind::RetainValueInst:
  case SILInstructionKind::RetainValueAddrInst:
  case SILInstructionKind::UnmanagedRetainValueInst:
  case SILInstructionKind::CopyValueInst:
  case SILInstructionKind::CopyUnownedValueInst:
  case SILInstructionKind::DeallocBoxInst:
  case SILInstructionKind::DeallocExistentialBoxInst:
  case SILInstructionKind::DeallocRefInst:
  case SILInstructionKind::DeallocPartialRefInst:
  case SILInstructionKind::DeallocStackInst:
  case SILInstructionKind::DeallocValueBufferInst:
  case SILInstructionKind::DeinitExistentialAddrInst:
  case SILInstructionKind::DeinitExistentialValueInst:
  case SILInstructionKind::DestroyAddrInst:
  case SILInstructionKind::ProjectValueBufferInst:
  case SILInstructionKind::ProjectBoxInst:
  case SILInstructionKind::ProjectExistentialBoxInst:
  case SILInstructionKind::ReleaseValueInst:
  case SILInstructionKind::ReleaseValueAddrInst:
  case SILInstructionKind::UnmanagedReleaseValueInst:
  case SILInstructionKind::DestroyValueInst:
  case SILInstructionKind::AutoreleaseValueInst:
  case SILInstructionKind::UnmanagedAutoreleaseValueInst:
  case SILInstructionKind::DynamicMethodBranchInst:
  case SILInstructionKind::DynamicMethodInst:
  case SILInstructionKind::EnumInst:
  case SILInstructionKind::IndexAddrInst:
  case SILInstructionKind::TailAddrInst:
  case SILInstructionKind::IndexRawPointerInst:
  case SILInstructionKind::InitEnumDataAddrInst:
  case SILInstructionKind::InitExistentialAddrInst:
  case SILInstructionKind::InitExistentialValueInst:
  case SILInstructionKind::InitExistentialMetatypeInst:
  case SILInstructionKind::InitExistentialRefInst:
  case SILInstructionKind::InjectEnumAddrInst:
  case SILInstructionKind::IsNonnullInst:
  case SILInstructionKind::LoadInst:
  case SILInstructionKind::LoadBorrowInst:
  case SILInstructionKind::LoadUnownedInst:
  case SILInstructionKind::LoadWeakInst:
  case SILInstructionKind::OpenExistentialAddrInst:
  case SILInstructionKind::OpenExistentialBoxInst:
  case SILInstructionKind::OpenExistentialBoxValueInst:
  case SILInstructionKind::OpenExistentialMetatypeInst:
  case SILInstructionKind::OpenExistentialRefInst:
  case SILInstructionKind::OpenExistentialValueInst:
  case SILInstructionKind::PartialApplyInst:
  case SILInstructionKind::ExistentialMetatypeInst:
  case SILInstructionKind::RefElementAddrInst:
  case SILInstructionKind::RefTailAddrInst:
  case SILInstructionKind::RefToUnmanagedInst:
  case SILInstructionKind::RefToUnownedInst:
  case SILInstructionKind::StoreInst:
  case SILInstructionKind::StoreBorrowInst:
  case SILInstructionKind::StoreUnownedInst:
  case SILInstructionKind::StoreWeakInst:
  case SILInstructionKind::StrongPinInst:
  case SILInstructionKind::StrongReleaseInst:
  case SILInstructionKind::SetDeallocatingInst:
  case SILInstructionKind::StrongRetainInst:
  case SILInstructionKind::StrongRetainUnownedInst:
  case SILInstructionKind::StrongUnpinInst:
  case SILInstructionKind::SuperMethodInst:
  case SILInstructionKind::SwitchEnumAddrInst:
  case SILInstructionKind::SwitchEnumInst:
  case SILInstructionKind::SwitchValueInst:
  case SILInstructionKind::UncheckedEnumDataInst:
  case SILInstructionKind::UncheckedTakeEnumDataAddrInst:
  case SILInstructionKind::UnconditionalCheckedCastInst:
  case SILInstructionKind::UnconditionalCheckedCastAddrInst:
  case SILInstructionKind::UnconditionalCheckedCastValueInst:
  case SILInstructionKind::UnmanagedToRefInst:
  case SILInstructionKind::UnownedReleaseInst:
  case SILInstructionKind::UnownedRetainInst:
  case SILInstructionKind::IsUniqueInst:
  case SILInstructionKind::IsUniqueOrPinnedInst:
  case SILInstructionKind::UnownedToRefInst:
  case SILInstructionKind::InitBlockStorageHeaderInst:
  case SILInstructionKind::SelectEnumAddrInst:
  case SILInstructionKind::SelectEnumInst:
  case SILInstructionKind::SelectValueInst:
  case SILInstructionKind::KeyPathInst:
  case SILInstructionKind::GlobalValueInst:
    return InlineCost::Expensive;

  case SILInstructionKind::BuiltinInst: {
    auto *BI = cast<BuiltinInst>(&I);
    // Expect intrinsics are 'free' instructions.
    if (BI->getIntrinsicInfo().ID == llvm::Intrinsic::expect)
      return InlineCost::Free;
    if (BI->getBuiltinInfo().ID == BuiltinValueKind::OnFastPath)
      return InlineCost::Free;

    return InlineCost::Expensive;
  }
  case SILInstructionKind::MarkFunctionEscapeInst:
  case SILInstructionKind::MarkUninitializedInst:
  case SILInstructionKind::MarkUninitializedBehaviorInst:
    llvm_unreachable("not valid in canonical sil");
  case SILInstructionKind::ObjectInst:
    llvm_unreachable("not valid in a function");
  }

  llvm_unreachable("Unhandled ValueKind in switch.");
}