clang/lib/AST/ByteCode/InterpState.h

//===--- InterpState.h - Interpreter state for the constexpr VM -*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Definition of the interpreter state and entry point.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_AST_INTERP_INTERPSTATE_H
#define LLVM_CLANG_AST_INTERP_INTERPSTATE_H

#include "Context.h"
#include "DynamicAllocator.h"
#include "Floating.h"
#include "FrameAllocator.h"
#include "Function.h"
#include "InterpFrame.h"
#include "InterpStack.h"
#include "State.h"
#include <limits>

namespace clang {
namespace interp {
class Context;
class SourceMapper;
struct EvalSettings;

struct StdAllocatorCaller {

  const Expr *Call = nullptr;
  QualType AllocType;
  explicit operator bool() { return Call; }
};

// FIXME: Create one for the "checking potential constant expression"
// evaluation.
enum class EvaluationKind : uint8_t {
  None,
  Dtor, /// We're checking for constant destruction of a global variable.
};

/// Interpreter context.
class InterpState final : public State {
public:
  InterpState(const EvalSettings &Settings, Program &P, InterpStack &Stk,
              FrameAllocator &FrameAlloc, Context &Ctx,
              SourceMapper *M = nullptr);

  InterpState(const EvalSettings &Settings, Program &P, InterpStack &Stk,
              FrameAllocator &FA, Context &Ctx, const Function *Func);

  InterpState(Expr::EvalStatus &Status, Program &P, InterpStack &Stk,
              FrameAllocator &FA, Context &Ctx, SourceMapper *M);

  ~InterpState();

  void cleanup();

  InterpState(const InterpState &) = delete;
  InterpState &operator=(const InterpState &) = delete;

  bool diagnosing() const { return getEvalStatus().Diag != nullptr; }

  // Stack frame accessors.
  const Frame *getCurrentFrame() override;
  unsigned getCallStackDepth() override {
    return Current ? (Current->getDepth() + 1) : 1;
  }
  bool stepsLeft() const override { return true; }
  bool inConstantContext() const;

  /// Deallocates a pointer.
  void deallocate(Block *B);

  /// Delegates source mapping to the mapper.
  SourceInfo getSource(CodePtr PC) const { return M->getSource(PC); }

  Context &getContext() const { return Ctx; }

  void setEvalLocation(SourceLocation SL) { this->EvalLocation = SL; }

  DynamicAllocator &getAllocator() {
    if (!Alloc) {
      if (!Allocator)
        Allocator.emplace();
      Alloc = std::make_unique<DynamicAllocator>(*Allocator);
    }

    return *Alloc;
  }

  /// Diagnose any dynamic allocations that haven't been freed yet.
  /// Will return \c false if there were any allocations to diagnose,
  /// \c true otherwise.
  bool maybeDiagnoseDanglingAllocations();

  StdAllocatorCaller getStdAllocatorCaller(StringRef Name) const;

  void *allocate(size_t Size, unsigned Align = 8) const {
    if (!Allocator)
      Allocator.emplace();
    return Allocator->Allocate(Size, Align);
  }
  template <typename T> T *allocate(size_t Num = 1) const {
    return static_cast<T *>(allocate(Num * sizeof(T), alignof(T)));
  }

  template <typename T> T allocAP(unsigned BitWidth) {
    unsigned NumWords = APInt::getNumWords(BitWidth);
    if (NumWords == 1)
      return T(BitWidth);
    uint64_t *Mem = (uint64_t *)this->allocate(NumWords * sizeof(uint64_t));
    // std::memset(Mem, 0, NumWords * sizeof(uint64_t)); // Debug
    return T(Mem, BitWidth);
  }

  Floating allocFloat(const llvm::fltSemantics &Sem) {
    if (Floating::singleWord(Sem))
      return Floating(llvm::APFloatBase::SemanticsToEnum(Sem));

    unsigned NumWords =
        APInt::getNumWords(llvm::APFloatBase::getSizeInBits(Sem));
    uint64_t *Mem = (uint64_t *)this->allocate(NumWords * sizeof(uint64_t));
    // std::memset(Mem, 0, NumWords * sizeof(uint64_t)); // Debug
    return Floating(Mem, llvm::APFloatBase::SemanticsToEnum(Sem));
  }
  const CXXRecordDecl **allocMemberPointerPath(unsigned Length) {
    return reinterpret_cast<const CXXRecordDecl **>(
        this->allocate(Length * sizeof(CXXRecordDecl *)));
  }
  PointerPathEntry *allocPointerPath(unsigned Length,
                                     const PointerPathEntry *OldPP) {
    assert(Length != 0);
    auto *PP = reinterpret_cast<PointerPathEntry *>(
        this->allocate(Length * sizeof(PointerPathEntry)));
    if (OldPP)
      std::memcpy(PP, OldPP, sizeof(PointerPathEntry) * Length);
    return PP;
  }
  /// Allocate a new pointer path of Length \c NewLength.
  /// NewLength - 1 elements are copied form \c OldPP.
  PointerPathEntry *extendPointerPath(unsigned NewLength,
                                      const PointerPathEntry *OldPP,
                                      PointerPathEntry NewEntry) {
    auto *PP = reinterpret_cast<PointerPathEntry *>(
        this->allocate(NewLength * sizeof(PointerPathEntry)));
    if (OldPP)
      std::memcpy(PP, OldPP, sizeof(PointerPathEntry) * (NewLength - 1));
    PP[NewLength - 1] = NewEntry;
    return PP;
  }

  /// Note that a step has been executed. If there are no more steps remaining,
  /// diagnoses and returns \c false.
  bool noteStep(CodePtr OpPC) {
    if (InfiniteSteps)
      return true;

    --StepsLeft;
    if (LLVM_LIKELY(StepsLeft != 0))
      return true;

    return diagnoseStepLimitExceeded(OpPC);
  }

  bool initializingBlock(const Block *B) const {
    for (PtrView V : InitializingPtrs)
      if (V.block() == B)
        return true;
    return false;
  }

  bool lifetimeStartedInEvaluation(const Block *B) const {
    if (EvalKind == EvaluationKind::None)
      return B->getEvalID() == EvalID;

    if (EvalKind == EvaluationKind::Dtor) {
      assert(EvaluatingDecl);
      if (B->getDescriptor()->asVarDecl() == EvaluatingDecl)
        return EvaluatingDecl->getType().isConstQualified();
    }
    return false;
  }

  /// Return if we're checking if a global variable has a constant destructor.
  bool checkingConstantDestruction() const {
    return EvalKind == EvaluationKind::Dtor;
  }
  /// Return if we're checking if a global variable has a constant destructor
  /// and the given pointer is pointing to the variable we're checking that for.
  bool checkingConstantDestruction(const Pointer &Ptr) const {
    return checkingConstantDestruction(Ptr.getRootVarDecl());
  }
  bool checkingConstantDestruction(const VarDecl *VD) const {
    return EvalKind == EvaluationKind::Dtor && VD == EvaluatingDecl;
  }

  unsigned newStringID() { return StringID++; }

  /// Allocate memory and create a new InterpFrame for the given function.
  template <typename... Ts>
  InterpFrame *allocFrame(const Function *F, Ts &&...Args) {
    size_t FrameSize = InterpFrame::allocSize(F);
    assert(FrameSize < std::numeric_limits<unsigned>::max());
    InterpFrame *NewFrame = new (FrameAlloc.reserve(FrameSize))
        InterpFrame(*this, F, std::forward<Ts>(Args)...);
    assert(NewFrame);
    return NewFrame;
  }

  /// Free resources associated with the current frame and set the caller to be
  /// the new current frame.
  void resetCurrentFrame() {
    assert(Current);
    unsigned CurrentSize = InterpFrame::allocSize(Current->getFunction());
    InterpFrame *Caller = Current->Caller;
    Current->~InterpFrame();
    FrameAlloc.pop(CurrentSize);
    Current = Caller;
  }

private:
  friend class EvaluationResult;
  friend class InterpStateCCOverride;
  /// Dead block chain.
  DeadBlock *DeadBlocks = nullptr;
  /// Reference to the offset-source mapping.
  SourceMapper *M;
  /// Allocator for everything else, e.g. floating-point values.
  mutable std::optional<llvm::BumpPtrAllocator> Allocator;
  /// Allocator used for dynamic allocations performed via the program.
  std::unique_ptr<DynamicAllocator> Alloc;
  /// Diagnose that we've reached the constexpr step limit.
  bool diagnoseStepLimitExceeded(CodePtr OpPC);

  FrameAllocator &FrameAlloc;

public:
  CodePtr PC;
  /// Reference to the module containing all bytecode.
  Program &P;
  /// Temporary stack.
  InterpStack &Stk;
  /// Interpreter Context.
  Context &Ctx;
  /// Bottom function frame.
  InterpFrame BottomFrame;
  /// The current frame.
  InterpFrame *Current = nullptr;
  /// Source location of the evaluating expression
  SourceLocation EvalLocation;
  /// Declaration we're initializing/evaluting, if any.
  const VarDecl *EvaluatingDecl = nullptr;
  /// Steps left during evaluation.
  unsigned StepsLeft = 1;
  /// Whether infinite evaluation steps have been requested. If this is false,
  /// we use the StepsLeft value above.
  const bool InfiniteSteps = false;
  /// ID identifying this evaluation.
  const unsigned EvalID;

  unsigned StringID = 0;

  EvaluationKind EvalKind = EvaluationKind::None;

  /// Things needed to do speculative execution.
  SmallVectorImpl<PartialDiagnosticAt> *PrevDiags = nullptr;
  bool PrevDiagsEmitted = false;
#ifndef NDEBUG
  unsigned SpeculationDepth = 0;
#endif
  unsigned DiagIgnoreDepth = 0;
  std::optional<bool> ConstantContextOverride;

  llvm::SmallVector<
      std::pair<const Expr *, const LifetimeExtendedTemporaryDecl *>>
      SeenGlobalTemporaries;

  /// List of blocks we're currently running either constructors or destructors
  /// for.
  llvm::SmallVector<PtrView> InitializingPtrs;
};

class InterpStateCCOverride final {
public:
  InterpStateCCOverride(InterpState &Ctx, bool Value)
      : Ctx(Ctx), OldCC(Ctx.ConstantContextOverride) {
    // We only override this if the new value is true.
    Enabled = Value;
    if (Enabled)
      Ctx.ConstantContextOverride = Value;
  }
  ~InterpStateCCOverride() {
    if (Enabled)
      Ctx.ConstantContextOverride = OldCC;
  }

private:
  bool Enabled;
  InterpState &Ctx;
  std::optional<bool> OldCC;
};

} // namespace interp
} // namespace clang

#endif