PerformanceDiagnostics.cpp

//==-------- PerformanceDiagnostics.cpp - Diagnose performance issues ------==//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2021 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 "performance-diagnostics"
#include "swift/AST/DiagnosticsSIL.h"
#include "swift/AST/SemanticAttrs.h"
#include "swift/SIL/BasicBlockDatastructures.h"
#include "swift/SIL/InstructionUtils.h"
#include "swift/SIL/ApplySite.h"
#include "swift/SILOptimizer/Analysis/ArraySemantic.h"
#include "swift/SILOptimizer/Analysis/BasicCalleeAnalysis.h"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SILOptimizer/Utils/BasicBlockOptUtils.h"
#include "llvm/Support/Debug.h"

using namespace swift;

namespace {

class PrettyStackTracePerformanceDiagnostics
  : public llvm::PrettyStackTraceEntry {
  const SILNode *node;
  const char *action;

public:
  PrettyStackTracePerformanceDiagnostics(const char *action, SILNodePointer node)
    : node(node), action(action) {}

  virtual void print(llvm::raw_ostream &OS) const override {
    OS << "While " << action << " -- visiting node ";
    node->print(OS);
    
    if (auto inst = dyn_cast<SILInstruction>(node)) {
      OS << "While visiting instruction in function ";
      inst->getFunction()->print(OS);
    }
  }
};

class PrettyStackTraceSILGlobal
  : public llvm::PrettyStackTraceEntry {
  const SILGlobalVariable *node;
  const char *action;

public:
    PrettyStackTraceSILGlobal(const char *action, SILGlobalVariable *node)
    : node(node), action(action) {}

  virtual void print(llvm::raw_ostream &OS) const override {
    OS << "While " << action << " -- visiting node ";
    node->print(OS);
  }
};

/// Issues performance diagnostics for functions which are annotated with
/// performance annotations, like @_noLocks, @_noAllocation.
///
/// This is done recursively for all functions which are called from
/// performance-annotated functions.
class PerformanceDiagnostics {

  /// A source location with a link to the location from the call-site.
  /// Used to print the whole back trace of a location.
  struct LocWithParent {
    SourceLoc loc;
    
    /// Null if this is the top-leve location.
    LocWithParent *parent;
    
    LocWithParent(SourceLoc loc, LocWithParent *parent) :
      loc(loc), parent(parent) {}
  };

  SILModule &module;
  BasicCalleeAnalysis *bca;
  llvm::DenseMap<SILFunction *, PerformanceConstraints> visitedFuncs;

public:
  PerformanceDiagnostics(SILModule &module, BasicCalleeAnalysis *bca) :
    module(module), bca(bca) {}

  /// Check a function with performance annotation(s) and all called functions
  /// recursively.
  bool visitFunction(SILFunction *function, PerformanceConstraints perfConstr) {
    return visitFunction(function, perfConstr, /*parentLoc*/ nullptr);
  }

  bool visitFunctionEmbeddedSwift(SILFunction *function) {
    return visitFunctionEmbeddedSwift(function, /*parentLoc*/ nullptr);
  }

  /// Check functions _without_ performance annotations.
  ///
  /// This is need to check closure arguments of called performance-annotated
  /// functions.
  void checkNonAnnotatedFunction(SILFunction *function);

private:
  bool visitFunction(SILFunction *function, PerformanceConstraints perfConstr,
                        LocWithParent *parentLoc);

  bool visitFunctionEmbeddedSwift(SILFunction *function,
                                  LocWithParent *parentLoc);

  bool visitInst(SILInstruction *inst, PerformanceConstraints perfConstr,
                    LocWithParent *parentLoc);

  /// Check if `as` has any non-escaping closure arguments and if all those
  /// passed closures meet the `perfConstr`.
  ///
  /// If `acceptFunctionArgs` is true it is assumed that calls to the function,
  /// which contains `as`, are already checked to have correct closure arguments.
  bool checkClosureArguments(ApplySite as,
                             bool acceptFunctionArgs,
                             PerformanceConstraints perfConstr,
                             LocWithParent *parentLoc);

  /// Check if `closure` meets the `perfConstr`.
  ///
  /// If `acceptFunctionArgs` is true it is assumed that calls to the function,
  /// which contains `callInst`, are already checked to have correct closure
  /// arguments.
  bool checkClosureValue(SILValue closure,
                         bool acceptFunctionArgs,
                         SILInstruction *callInst,
                         PerformanceConstraints perfConstr,
                         LocWithParent *parentLoc);

  bool visitCallee(SILInstruction *callInst, CalleeList callees,
                   PerformanceConstraints perfConstr, LocWithParent *parentLoc);
                      
  template<typename ...ArgTypes>
  void diagnose(LocWithParent loc, Diag<ArgTypes...> ID,
                typename detail::PassArgument<ArgTypes>::type... Args) {
    diagnose(loc, Diagnostic(ID, std::move(Args)...));
  }
  
  void diagnose(LocWithParent loc, Diagnostic &&D);
};

static bool isEffectFreeArraySemanticCall(SILInstruction *inst) {
  ArraySemanticsCall semCall(inst);
  switch (semCall.getKind()) {
  case ArrayCallKind::kGetElement:
    return cast<ApplyInst>(inst)->getType().isTrivial(*inst->getFunction());
  default:
    return false;
  }
}

static bool hasGenericValueDeinit(SILType ty, SILFunction *f) {
  if (!ty.isMoveOnly())
    return false;
  NominalTypeDecl *nominal = ty.getNominalOrBoundGenericNominal();
  if (!nominal)
    return false;

  if (nominal->getGenericSignature() && nominal->getValueTypeDestructor())
    return true;

  if (isa<StructDecl>(nominal)) {
    for (unsigned i = 0, n = ty.getNumNominalFields(); i < n; ++i) {
      if (hasGenericValueDeinit(ty.getFieldType(i, f), f))
        return true;
    }
  } else if (auto *en = dyn_cast<EnumDecl>(nominal)) {
    for (EnumElementDecl *element : en->getAllElements()) {
      if (element->hasAssociatedValues()) {
        if (hasGenericValueDeinit(ty.getEnumElementType(element, f), f))
          return true;
      }
    }
  }

  return false;
}

static bool allocsGenericValueTypeWithDeinit(AllocBoxInst *abi) {
  CanSILBoxType boxTy = abi->getBoxType();
  SILFunction *f = abi->getFunction();
  unsigned numFields = boxTy->getLayout()->getFields().size();
  for (unsigned fieldIdx = 0; fieldIdx < numFields; ++fieldIdx) {
    SILType fieldTy = getSILBoxFieldType(TypeExpansionContext(*f), boxTy,
                                         abi->getModule().Types, fieldIdx);
    if (hasGenericValueDeinit(fieldTy, f))
      return true;
  }
  return false;
}

/// Prints Embedded Swift specific performance diagnostics (no existentials,
/// no metatypes, optionally no allocations) for \p function.
bool PerformanceDiagnostics::visitFunctionEmbeddedSwift(
    SILFunction *function, LocWithParent *parentLoc) {
  // Don't check generic functions in embedded Swift, they're about to be
  // removed anyway.
  if (function->isGeneric())
    return false;

  if (!function->isDefinition())
    return false;

  if (visitedFuncs.contains(function))
    return false;
  visitedFuncs[function] = PerformanceConstraints::None;

  for (SILBasicBlock &block : *function) {
    for (SILInstruction &inst : block) {
      if (visitInst(&inst, PerformanceConstraints::None, parentLoc)) {
        if (inst.getLoc().getSourceLoc().isInvalid()) {
          auto demangledName = Demangle::demangleSymbolAsString(
              inst.getFunction()->getName(),
              Demangle::DemangleOptions::SimplifiedUIDemangleOptions());
          llvm::errs() << "in function " << demangledName << "\n";
        }
        LLVM_DEBUG(llvm::dbgs() << inst << *inst.getFunction());
        return true;
      }

      if (auto as = FullApplySite::isa(&inst)) {
        LocWithParent asLoc(inst.getLoc().getSourceLoc(), parentLoc);
        LocWithParent *loc = &asLoc;
        if (parentLoc &&
            asLoc.loc == inst.getFunction()->getLocation().getSourceLoc())
          loc = parentLoc;

        for (SILFunction *callee : bca->getCalleeList(as)) {
          if (visitFunctionEmbeddedSwift(callee, loc))
            return true;
        }
      } else if (auto *bi = dyn_cast<BuiltinInst>(&inst)) {
        PrettyStackTracePerformanceDiagnostics stackTrace(
            "visitFunction::BuiltinInst (once, once with context)", &inst);

        switch (bi->getBuiltinInfo().ID) {
        case BuiltinValueKind::Once:
        case BuiltinValueKind::OnceWithContext:
          if (auto *fri = dyn_cast<FunctionRefInst>(bi->getArguments()[1])) {
            LocWithParent asLoc(bi->getLoc().getSourceLoc(), parentLoc);
            LocWithParent *loc = &asLoc;
            if (parentLoc &&
                asLoc.loc == bi->getFunction()->getLocation().getSourceLoc())
              loc = parentLoc;

            if (visitFunctionEmbeddedSwift(fri->getReferencedFunction(), loc))
              return true;
          }
          break;
        default:
          break;
        }
      } else if (auto *abi = dyn_cast<AllocBoxInst>(&inst)) {
        // It needs a bit of work to support alloc_box of generic non-copyable
        // structs/enums with deinit, because we need to specialize the deinit
        // functions, though they are not explicitly referenced in SIL.
        // Until this is supported, give an error in such cases. Otherwise
        // IRGen would crash.
        if (allocsGenericValueTypeWithDeinit(abi)) {
          LocWithParent loc(abi->getLoc().getSourceLoc(), parentLoc);
          diagnose(loc, diag::embedded_capture_of_generic_value_with_deinit);
        }
      }
    }
  }
  return false;
}

/// Prints performance diagnostics for \p function.
bool PerformanceDiagnostics::visitFunction(SILFunction *function,
                                              PerformanceConstraints perfConstr,
                                              LocWithParent *parentLoc) {
  if (!function->isDefinition())
    return false;

  for (SILBasicBlock &block : *function) {
    // Exclude fatal-error blocks.
    if (isa<UnreachableInst>(block.getTerminator()))
      continue;

    for (SILInstruction &inst : block) {
      if (visitInst(&inst, perfConstr, parentLoc)) {
        if (inst.getLoc().getSourceLoc().isInvalid()) {
          auto demangledName = Demangle::demangleSymbolAsString(
              inst.getFunction()->getName(),
              Demangle::DemangleOptions::SimplifiedUIDemangleOptions());
          llvm::errs() << "in function " << demangledName << "\n";
        }
        LLVM_DEBUG(llvm::dbgs() << inst << *inst.getFunction());
        return true;
      }

      if (auto as = FullApplySite::isa(&inst)) {
        if (isEffectFreeArraySemanticCall(&inst))
          continue;

        // Check if closures, which are passed to `as` are okay.
        if (checkClosureArguments(as, /*acceptFunctionArgs=*/ true,
                                  perfConstr, parentLoc)) {
          return true;
        }

        if (as.getOrigCalleeType()->isNoEscape()) {
          // This is a call of a non-escaping closure. Check if the closure is
          // okay. In this case we don't need to `visitCallee`.
          if (checkClosureValue(as.getCallee(), /*acceptFunctionArgs=*/ true,
                                &inst, perfConstr, parentLoc)) {
            return true;
          }
          continue;
        }

        // Recursively walk into the callees.
        if (visitCallee(&inst, bca->getCalleeList(as), perfConstr, parentLoc))
          return true;
      } else if (auto *bi = dyn_cast<BuiltinInst>(&inst)) {
        PrettyStackTracePerformanceDiagnostics stackTrace(
            "visitFunction::BuiltinInst (once, once with context)", &inst);

        switch (bi->getBuiltinInfo().ID) {
          case BuiltinValueKind::Once:
          case BuiltinValueKind::OnceWithContext:
            if (auto *fri = dyn_cast<FunctionRefInst>(bi->getArguments()[1])) {
              if (visitCallee(bi, fri->getReferencedFunction(), perfConstr, parentLoc))
                return true;
            } else {
              LocWithParent loc(inst.getLoc().getSourceLoc(), parentLoc);
              diagnose(loc, diag::performance_unknown_callees);
              return true;
            }
            break;
          default:
            break;
        }
      }
    }
  }
  return false;
}

bool PerformanceDiagnostics::checkClosureArguments(ApplySite as,
                                            bool acceptFunctionArgs,
                                            PerformanceConstraints perfConstr,
                                            LocWithParent *parentLoc) {
  if (SILFunction *knownCallee = as.getReferencedFunctionOrNull()) {
    if (knownCallee->hasSemanticsAttr(semantics::NO_PERFORMANCE_ANALYSIS))
      return false;
  }

  for (SILValue arg : as.getArguments()) {
    auto fTy = arg->getType().getAs<SILFunctionType>();
    if (!fTy || !fTy->isNoEscape())
      continue;

    if (checkClosureValue(arg, acceptFunctionArgs, as.getInstruction(),
                          perfConstr, parentLoc)) {
      return true;
    }
  }
  return false;
}

bool PerformanceDiagnostics::checkClosureValue(SILValue closure,
                                            bool acceptFunctionArgs,
                                            SILInstruction *callInst,
                                            PerformanceConstraints perfConstr,
                                            LocWithParent *parentLoc) {
  // Walk through the definition of the closure until we find the "underlying"
  // function_ref instruction.
  while (!isa<FunctionRefInst>(closure)) {
    if (auto *pai = dyn_cast<PartialApplyInst>(closure)) {
      if (checkClosureArguments(ApplySite::isa(pai), acceptFunctionArgs,
                                perfConstr, parentLoc)) {
        return true;
      }
      closure = pai->getCallee();
    } else if (auto *tfi = dyn_cast<ThinToThickFunctionInst>(closure)) {
      closure = tfi->getOperand();
    } else if (auto *cp = dyn_cast<CopyValueInst>(closure)) {
      closure = cp->getOperand();
    } else if (auto *bb = dyn_cast<BeginBorrowInst>(closure)) {
      closure = bb->getOperand();
    } else if (auto *cv = dyn_cast<ConvertFunctionInst>(closure)) {
      closure = cv->getOperand();
    } else if (auto *md = dyn_cast<MarkDependenceInst>(closure)) {
      closure = md->getValue();
    } else if (acceptFunctionArgs && isa<SILFunctionArgument>(closure)) {
      // We can assume that a function closure argument is already checked at
      // the call site.
      return false;
    } else {
      PrettyStackTracePerformanceDiagnostics stackTrace(
          "validating closure (function ref, callee) - unknown callee", callInst);

      diagnose(LocWithParent(callInst->getLoc().getSourceLoc(), parentLoc), diag::performance_unknown_callees);
      return true;
    }
  }
  // Check what's happening inside the closure body.
  auto *fri = cast<FunctionRefInst>(closure);
  if (visitCallee(callInst, fri->getReferencedFunction(),
                  perfConstr, parentLoc)) {
    return true;
  }
  return false;
}

bool PerformanceDiagnostics::visitCallee(SILInstruction *callInst,
                                         CalleeList callees,
                                         PerformanceConstraints perfConstr,
                                         LocWithParent *parentLoc) {
  LocWithParent asLoc(callInst->getLoc().getSourceLoc(), parentLoc);
  LocWithParent *loc = &asLoc;
  if (parentLoc && asLoc.loc == callInst->getFunction()->getLocation().getSourceLoc())
    loc = parentLoc;

  if (callees.isIncomplete()) {
    PrettyStackTracePerformanceDiagnostics stackTrace("incomplete", callInst);

    diagnose(*loc, diag::performance_unknown_callees);
    return true;
  }
  for (SILFunction *callee : callees) {
    if (callee->hasSemanticsAttr(semantics::NO_PERFORMANCE_ANALYSIS))
      continue;
  
    // If the callee has a defined performance constraint which is at least as
    // strong as the required constraint, we are done.
    PerformanceConstraints calleeConstr = callee->getPerfConstraints();
    if (calleeConstr >= perfConstr)
      return false;

    if (!callee->isDefinition()) {
      PrettyStackTracePerformanceDiagnostics stackTrace("incomplete", callInst);

      diagnose(*loc, diag::performance_callee_unavailable);
      return true;
    }

    // Check if we already visited the callee while checking a constraint which
    // is at least as strong as  the required constraint.
    PerformanceConstraints &computedConstr = visitedFuncs[callee];
    if (computedConstr >= perfConstr)
      return false;
    computedConstr = perfConstr;
    
    if (visitFunction(callee, perfConstr, loc))
      return true;
  }
  return false;
}

static bool metatypeUsesAreNotRelevant(MetatypeInst *mt) {
  for (Operand *use : mt->getUses()) {
    if (auto  *bi = dyn_cast<BuiltinInst>(use->getUser())) {
      switch (bi->getBuiltinInfo().ID) {
        case BuiltinValueKind::Sizeof:
        case BuiltinValueKind::Strideof:
        case BuiltinValueKind::Alignof:
        case BuiltinValueKind::IsPOD:
        case BuiltinValueKind::IsConcrete:
        case BuiltinValueKind::IsBitwiseTakable:
          continue;
        default:
          break;
      }
    }
    if (auto *apply = dyn_cast<ApplyInst>(use->getUser())) {
      if (auto *callee = apply->getReferencedFunctionOrNull()) {
        // Exclude `Swift._diagnoseUnexpectedEnumCaseValue<A, B>(type: A.Type, rawValue: B) -> Swift.Never`
        // It's a fatal error function, used for imported C enums.
        if (callee->getName() == "$ss32_diagnoseUnexpectedEnumCaseValue4type03rawE0s5NeverOxm_q_tr0_lF" &&
            !mt->getModule().getOptions().EmbeddedSwift) {
          continue;
        }
      }
    }
    return false;
  }
  return true;
}

static bool allowedMetadataUseInEmbeddedSwift(SILInstruction *inst) {
  // Only diagnose metatype, value_metatype instructions, ...
  if ((isa<ValueMetatypeInst>(inst) || isa<MetatypeInst>(inst))) {
    auto metaTy = cast<SingleValueInstruction>(inst)->getType().castTo<MetatypeType>();
    if (metaTy->getRepresentation() == MetatypeRepresentation::Thick) {
      Type instTy = metaTy->getInstanceType();
      if (auto selfType = instTy->getAs<DynamicSelfType>())
        instTy = selfType->getSelfType();
      // Class metadata are supported in embedded Swift
      return instTy->getClassOrBoundGenericClass() ? true : false;
    }
  // ... and alloc_ref_dynamic, for now.
  } else if (isa<AllocRefDynamicInst>(inst)) {
    return false;
  }

  return true;
}

bool PerformanceDiagnostics::visitInst(SILInstruction *inst,
                                          PerformanceConstraints perfConstr,
                                          LocWithParent *parentLoc) {
  SILType impactType;
  RuntimeEffect impact = getRuntimeEffect(inst, impactType);
  LocWithParent loc(inst->getLoc().getSourceLoc(), parentLoc);

  if (perfConstr == PerformanceConstraints::NoExistentials &&
      ((impact & RuntimeEffect::Existential) ||
       (impact & RuntimeEffect::ExistentialClassBound))) {
    PrettyStackTracePerformanceDiagnostics stackTrace("existential", inst);
    if (impactType) {
      diagnose(loc, diag::perf_diag_existential_type, impactType.getASTType());
    } else {
      diagnose(loc, diag::perf_diag_existential);
    }
    return true;
  }

  if ((perfConstr == PerformanceConstraints::NoObjCBridging ||
       perfConstr == PerformanceConstraints::NoAllocation ||
       perfConstr == PerformanceConstraints::NoLocks) &&
      (impact & RuntimeEffect::ObjectiveC)) {
    PrettyStackTracePerformanceDiagnostics stackTrace(
        "found objc effect", inst);

    diagnose(loc, diag::performance_objectivec);
    return true;
  }

  if (module.getOptions().EmbeddedSwift) {
    // Explicitly don't detect RuntimeEffect::ExistentialClassBound - those are
    // allowed in Embedded Swift.
    if (impact & RuntimeEffect::Existential) {
      PrettyStackTracePerformanceDiagnostics stackTrace("existential", inst);
      if (impactType) {
        diagnose(loc, diag::embedded_swift_existential_type, impactType.getASTType());
      } else {
        diagnose(loc, diag::embedded_swift_existential);
      }
      return true;
    }

    if (impact & RuntimeEffect::MetaData) {
      if (isa<ReleaseValueInst>(inst)) {
        // Move-only value types for which the deinit is not de-virtualized.
        diagnose(loc, diag::embedded_swift_value_deinit, impactType.getASTType());
        return true;
      }
      if (isa<KeyPathInst>(inst)) {
        diagnose(loc, diag::embedded_swift_keypath);
        return true;
      }
      if (isa<CheckedCastAddrBranchInst>(inst) || isa<UnconditionalCheckedCastAddrInst>(inst)) {
        diagnose(loc, diag::embedded_swift_dynamic_cast);
        return true;
      }
      if (!allowedMetadataUseInEmbeddedSwift(inst)) {
        PrettyStackTracePerformanceDiagnostics stackTrace("metatype", inst);
        if (impactType) {
          diagnose(loc, diag::embedded_swift_metatype_type, impactType.getASTType());
        } else {
          diagnose(loc, diag::embedded_swift_metatype);
        }
        return true;
      }
    }

    if (module.getOptions().NoAllocations) {
      if (impact & RuntimeEffect::Allocating) {
        PrettyStackTracePerformanceDiagnostics stackTrace("allocation", inst);
        if (impactType) {
          diagnose(loc, diag::embedded_swift_allocating_type, impactType.getASTType());
        } else {
          diagnose(loc, diag::embedded_swift_allocating);
        }
        return true;
      }
    }
  }

  if (perfConstr == PerformanceConstraints::None ||
      perfConstr == PerformanceConstraints::NoExistentials ||
      perfConstr == PerformanceConstraints::NoObjCBridging)
    return false;

  if (impact & RuntimeEffect::Casting) {
    // TODO: be more specific on casting.
    // E.g. distinguish locking and allocating dynamic casts, etc.
    PrettyStackTracePerformanceDiagnostics stackTrace("bad cast", inst);

    diagnose(loc, diag::performance_dynamic_casting);
    return true;
  }
  if (impact & RuntimeEffect::MetaData) {
    // TODO: be more specific on metadata.
    // E.g. distinguish locking and allocating metadata operations, etc.
  
    // Try to give a good error message by looking which type of code it is.
    switch (inst->getKind()) {
    case SILInstructionKind::KeyPathInst: {
      PrettyStackTracePerformanceDiagnostics stackTrace("key path", inst);
      diagnose(loc, diag::performance_metadata, "using KeyPath");
      break;
    }
    case SILInstructionKind::AllocGlobalInst:
    case SILInstructionKind::GlobalValueInst: {
      PrettyStackTracePerformanceDiagnostics stackTrace(
            "AllocGlobalInst | GlobalValueInst", inst);
      diagnose(loc, diag::performance_metadata, "global or static variables");
      break;
    }
    case SILInstructionKind::PartialApplyInst: {
      PrettyStackTracePerformanceDiagnostics stackTrace(
          "PartialApplyInst", inst);
      diagnose(loc, diag::performance_metadata,
               "generic closures or local functions");
      break;
    }
    case SILInstructionKind::ApplyInst:
    case SILInstructionKind::TryApplyInst:
    case SILInstructionKind::BeginApplyInst: {
      PrettyStackTracePerformanceDiagnostics stackTrace(
          "ApplyInst | TryApplyInst | BeginApplyInst", inst);
      diagnose(loc, diag::performance_metadata, "generic function calls");
      break;
    }
    case SILInstructionKind::MetatypeInst:
      if (metatypeUsesAreNotRelevant(cast<MetatypeInst>(inst)))
        return false;
      LLVM_FALLTHROUGH;
    default:
      // We didn't recognize the instruction, so try to give an error message
      // based on the involved type.
      if (impactType) {
        PrettyStackTracePerformanceDiagnostics stackTrace(
            "impactType (unrecognized instruction)", inst);
        diagnose(loc, diag::performance_metadata_type, impactType.getASTType());
        break;
      }
      // The default error message.
      PrettyStackTracePerformanceDiagnostics stackTrace(
          "default error (fallthrough, unknown inst)", inst);
      diagnose(loc, diag::performance_metadata, "this code pattern");
      break;
    }
    return true;
  }
  
  if (perfConstr == PerformanceConstraints::NoRuntime)
    return false;
  
  if (impact & RuntimeEffect::Allocating) {
    PrettyStackTracePerformanceDiagnostics stackTrace(
        "found allocation effect", inst);

    switch (inst->getKind()) {
    case SILInstructionKind::BeginApplyInst:
      // Not all begin_applys necessarily allocate. But it's difficult to
      // estimate the effect on SIL level.
      diagnose(loc, diag::performance_allocating, "co-routine calls");
      break;
    case SILInstructionKind::PartialApplyInst:
      diagnose(loc, diag::performance_allocating, "closure captures");
      break;
    case SILInstructionKind::AllocRefInst:
    case SILInstructionKind::AllocRefDynamicInst:
      diagnose(loc, diag::performance_allocating, "class instance construction");
      break;
    default:
      diagnose(loc, diag::performance_allocating, "this code pattern");
      break;
    }
    return true;
  }
  if (impact & RuntimeEffect::Deallocating) {
    PrettyStackTracePerformanceDiagnostics stackTrace(
        "found deallocation effect", inst);

    if (impactType) {
      switch (inst->getKind()) {
      case SILInstructionKind::StoreInst:
      case SILInstructionKind::CopyAddrInst:
        diagnose(loc, diag::performance_deallocating_type,
                 "storing", impactType.getASTType());
        return true;
      case SILInstructionKind::DestroyAddrInst:
      case SILInstructionKind::DestroyValueInst:
        diagnose(loc, diag::performance_deallocating_type,
                 "ending the lifetime of", impactType.getASTType());
        return true;
      default:
        break;
      }
    }
    diagnose(loc, diag::performance_deallocating, "this code pattern");
    return true;
  }

  if (perfConstr == PerformanceConstraints::NoAllocation)
    return false;

  // Handle locking-only effects.
  
  PrettyStackTracePerformanceDiagnostics stackTrace(
      "found locking or ref counting effect", inst);

  if (impact & RuntimeEffect::Locking) {
    if (inst->getFunction()->isGlobalInit()) {
      diagnose(loc, diag::performance_locking,
               "global/static variable initialization");
    } else {
      diagnose(loc, diag::performance_locking, "this code pattern");
    }
    return true;
  }
  if (impact & RuntimeEffect::RefCounting) {
    diagnose(loc, diag::performance_arc);
    return true;
  }
  return false;
}

void PerformanceDiagnostics::checkNonAnnotatedFunction(SILFunction *function) {
  for (SILBasicBlock &block : *function) {
    for (SILInstruction &inst : block) {
      auto as = FullApplySite::isa(&inst);
      if (!as)
        continue;
        
      // We only consider direct calls.
      // TODO: this is a hole in the verification because we are not catching
      // cases where a "bad" closure is passed to a performance-annotated
      // v-table, witness table or closure function.
      SILFunction *callee = as.getReferencedFunctionOrNull();
      if (!callee)
        continue;

      if (callee->getPerfConstraints() == PerformanceConstraints::None)
        continue;

      if (checkClosureArguments(as, /*acceptFunctionArgs=*/ false,
                                callee->getPerfConstraints(),
                                /*LocWithParent*/ nullptr)) {
        return;
      }
    }
  }
}

void PerformanceDiagnostics::diagnose(LocWithParent loc, Diagnostic &&D) {  
  // Start with a valid location in the call tree.
  LocWithParent *validLoc = &loc;
  while (!validLoc->loc.isValid() && validLoc->parent) {
    validLoc = validLoc->parent;
  }
  module.getASTContext().Diags.diagnose(validLoc->loc, D);
  
  // Print the whole back trace. Otherwise it would be difficult for the user
  // to know which annotated function caused the error.
  LocWithParent *parentLoc = validLoc->parent;
  while (parentLoc) {
    if (parentLoc->loc.isValid()) {
      module.getASTContext().Diags.diagnose(parentLoc->loc,
                                            diag::performance_called_from);
    }
    parentLoc = parentLoc->parent;
  }
}

//===----------------------------------------------------------------------===//
//                            The function pass
//===----------------------------------------------------------------------===//

class PerformanceDiagnosticsPass : public SILModuleTransform {
public:
  PerformanceDiagnosticsPass() {}

private:
  void run() override {
    SILModule *module = getModule();

    // Skip all performance/embedded diagnostics if asked. This is used from
    // SourceKit to avoid reporting false positives when WMO is turned off for
    // indexing purposes.
    if (!module->getOptions().EnableWMORequiredDiagnostics) return;

    PerformanceDiagnostics diagnoser(*module, getAnalysis<BasicCalleeAnalysis>());

    // Check that @_section, @_silgen_name is only on constant globals
    for (SILGlobalVariable &g : module->getSILGlobals()) {
      if (!g.getStaticInitializerValue() && g.mustBeInitializedStatically()) {
        PrettyStackTraceSILGlobal stackTrace(
            "global inst", &g);

        auto *decl = g.getDecl();
        if (g.getSectionAttr()) {
          module->getASTContext().Diags.diagnose(
            g.getDecl()->getLoc(), diag::bad_attr_on_non_const_global,
            "@_section");
        } else if (decl && g.isDefinition() &&
                   decl->getAttrs().hasAttribute<SILGenNameAttr>()) {
          module->getASTContext().Diags.diagnose(
            g.getDecl()->getLoc(), diag::bad_attr_on_non_const_global,
            "@_silgen_name");
        } else {
          module->getASTContext().Diags.diagnose(
            g.getDecl()->getLoc(), diag::global_must_be_compile_time_const);
        }
      }
    }

    bool annotatedFunctionsFound = false;

    for (SILFunction &function : *module) {
      if (function.getPerfConstraints() != PerformanceConstraints::None) {
        annotatedFunctionsFound = true;
      
        // Don't rerun diagnostics on deserialized functions.
        if (function.wasDeserializedCanonical())
          continue;

        diagnoser.visitFunction(&function, function.getPerfConstraints());
      }
    }

    if (!annotatedFunctionsFound && !getModule()->getOptions().EmbeddedSwift)
      return;

    for (SILFunction &function : *module) {
      // Don't rerun diagnostics on deserialized functions.
      if (function.wasDeserializedCanonical())
        continue;

      if (function.getPerfConstraints() == PerformanceConstraints::None) {
        diagnoser.checkNonAnnotatedFunction(&function);
      }
    }

    if (getModule()->getOptions().EmbeddedSwift) {
      // Run embedded Swift SIL checks for metatype/existential use, and
      // allocation use (under -no-allocations mode). Try to start with public
      // and exported functions to get better call tree information.
      SmallVector<SILFunction *, 8> externallyVisibleFunctions;
      SmallVector<SILFunction *, 8> vtableMembers;
      SmallVector<SILFunction *, 8> others;
      SmallVector<SILFunction *, 8> constructorsAndDestructors;

      for (SILFunction &function : *module) {
        // There might be SILFunctions without a location, e.g.
        // swift_readAtKeyPath generated by SILGen for keypaths. It's okay to
        // skip the ctor/dtor/method detection logic for those, such functions
        // still end up in the "others" list and are still visited.
        if (function.hasLocation()) {
          auto func =
              function.getLocation().getAsASTNode<AbstractFunctionDecl>();
          if (func) {
            if (isa<DestructorDecl>(func) || isa<ConstructorDecl>(func)) {
              constructorsAndDestructors.push_back(&function);
              continue;
            }
            if (getMethodDispatch(func) == MethodDispatch::Class) {
              vtableMembers.push_back(&function);
              continue;
            }
          }
        }

        if (function.isPossiblyUsedExternally()) {
          externallyVisibleFunctions.push_back(&function);
          continue;
        }

        others.push_back(&function);
      }

      for (SILFunction *function : externallyVisibleFunctions) {
        diagnoser.visitFunctionEmbeddedSwift(function);
      }
      for (SILFunction *function : vtableMembers) {
        diagnoser.visitFunctionEmbeddedSwift(function);
      }
      for (SILFunction *function : others) {
        diagnoser.visitFunctionEmbeddedSwift(function);
      }
      for (SILFunction *function : constructorsAndDestructors) {
        diagnoser.visitFunctionEmbeddedSwift(function);
      }
    }
  }
};

} // end anonymous namespace

SILTransform *swift::createPerformanceDiagnostics() {
  return new PerformanceDiagnosticsPass();
}