ByteCodeStmtGen.cpp

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//===--- ByteCodeStmtGen.cpp - Code generator for expressions ---*- 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
//
//===----------------------------------------------------------------------===//

#include "ByteCodeStmtGen.h"
#include "ByteCodeEmitter.h"
#include "ByteCodeGenError.h"
#include "Context.h"
#include "Function.h"
#include "PrimType.h"
#include "Program.h"
#include "State.h"

using namespace clang;
using namespace clang::interp;

template <typename T> using Expected = llvm::Expected<T>;
template <typename T> using Optional = llvm::Optional<T>;

namespace clang {
namespace interp {

/// Scope managing label targets.
template <class Emitter> class LabelScope {
public:
  virtual ~LabelScope() {  }

protected:
  LabelScope(ByteCodeStmtGen<Emitter> *Ctx) : Ctx(Ctx) {}
  /// ByteCodeStmtGen instance.
  ByteCodeStmtGen<Emitter> *Ctx;
};

/// Sets the context for break/continue statements.
template <class Emitter> class LoopScope final : public LabelScope<Emitter> {
public:
  using LabelTy = typename ByteCodeStmtGen<Emitter>::LabelTy;
  using OptLabelTy = typename ByteCodeStmtGen<Emitter>::OptLabelTy;

  LoopScope(ByteCodeStmtGen<Emitter> *Ctx, LabelTy BreakLabel,
            LabelTy ContinueLabel)
      : LabelScope<Emitter>(Ctx), OldBreakLabel(Ctx->BreakLabel),
        OldContinueLabel(Ctx->ContinueLabel) {
    this->Ctx->BreakLabel = BreakLabel;
    this->Ctx->ContinueLabel = ContinueLabel;
  }

  ~LoopScope() {
    this->Ctx->BreakLabel = OldBreakLabel;
    this->Ctx->ContinueLabel = OldContinueLabel;
  }

private:
  OptLabelTy OldBreakLabel;
  OptLabelTy OldContinueLabel;
};

// Sets the context for a switch scope, mapping labels.
template <class Emitter> class SwitchScope final : public LabelScope<Emitter> {
public:
  using LabelTy = typename ByteCodeStmtGen<Emitter>::LabelTy;
  using OptLabelTy = typename ByteCodeStmtGen<Emitter>::OptLabelTy;
  using CaseMap = typename ByteCodeStmtGen<Emitter>::CaseMap;

  SwitchScope(ByteCodeStmtGen<Emitter> *Ctx, CaseMap &&CaseLabels,
              LabelTy BreakLabel, OptLabelTy DefaultLabel)
      : LabelScope<Emitter>(Ctx), OldBreakLabel(Ctx->BreakLabel),
        OldDefaultLabel(this->Ctx->DefaultLabel),
        OldCaseLabels(std::move(this->Ctx->CaseLabels)) {
    this->Ctx->BreakLabel = BreakLabel;
    this->Ctx->DefaultLabel = DefaultLabel;
    this->Ctx->CaseLabels = std::move(CaseLabels);
  }

  ~SwitchScope() {
    this->Ctx->BreakLabel = OldBreakLabel;
    this->Ctx->DefaultLabel = OldDefaultLabel;
    this->Ctx->CaseLabels = std::move(OldCaseLabels);
  }

private:
  OptLabelTy OldBreakLabel;
  OptLabelTy OldDefaultLabel;
  CaseMap OldCaseLabels;
};

} // namespace interp
} // namespace clang

template <class Emitter>
bool ByteCodeStmtGen<Emitter>::visitFunc(const FunctionDecl *F) {
  // Classify the return type.
  ReturnType = this->classify(F->getReturnType());

  // Set up fields and context if a constructor.
  if (auto *MD = dyn_cast<CXXMethodDecl>(F))
    return this->bail(MD);

  if (auto *Body = F->getBody())
    if (!visitStmt(Body))
      return false;

  // Emit a guard return to protect against a code path missing one.
  if (F->getReturnType()->isVoidType())
    return this->emitRetVoid(SourceInfo{});
  else
    return this->emitNoRet(SourceInfo{});
}

template <class Emitter>
bool ByteCodeStmtGen<Emitter>::visitStmt(const Stmt *S) {
  switch (S->getStmtClass()) {
  case Stmt::CompoundStmtClass:
    return visitCompoundStmt(cast<CompoundStmt>(S));
  case Stmt::DeclStmtClass:
    return visitDeclStmt(cast<DeclStmt>(S));
  case Stmt::ReturnStmtClass:
    return visitReturnStmt(cast<ReturnStmt>(S));
  case Stmt::IfStmtClass:
    return visitIfStmt(cast<IfStmt>(S));
  case Stmt::NullStmtClass:
    return true;
  default: {
    if (auto *Exp = dyn_cast<Expr>(S))
      return this->discard(Exp);
    return this->bail(S);
  }
  }
}

template <class Emitter>
bool ByteCodeStmtGen<Emitter>::visitCompoundStmt(
    const CompoundStmt *CompoundStmt) {
  BlockScope<Emitter> Scope(this);
  for (auto *InnerStmt : CompoundStmt->body())
    if (!visitStmt(InnerStmt))
      return false;
  return true;
}

template <class Emitter>
bool ByteCodeStmtGen<Emitter>::visitDeclStmt(const DeclStmt *DS) {
  for (auto *D : DS->decls()) {
    // Variable declarator.
    if (auto *VD = dyn_cast<VarDecl>(D)) {
      if (!visitVarDecl(VD))
        return false;
      continue;
    }

    // Decomposition declarator.
    if (auto *DD = dyn_cast<DecompositionDecl>(D)) {
      return this->bail(DD);
    }
  }

  return true;
}

template <class Emitter>
bool ByteCodeStmtGen<Emitter>::visitReturnStmt(const ReturnStmt *RS) {
  if (const Expr *RE = RS->getRetValue()) {
    ExprScope<Emitter> RetScope(this);
    if (ReturnType) {
      // Primitive types are simply returned.
      if (!this->visit(RE))
        return false;
      this->emitCleanup();
      return this->emitRet(*ReturnType, RS);
    } else {
      // RVO - construct the value in the return location.
      auto ReturnLocation = [this, RE] { return this->emitGetParamPtr(0, RE); };
      if (!this->visitInitializer(RE, ReturnLocation))
        return false;
      this->emitCleanup();
      return this->emitRetVoid(RS);
    }
  } else {
    this->emitCleanup();
    if (!this->emitRetVoid(RS))
      return false;
    return true;
  }
}

template <class Emitter>
bool ByteCodeStmtGen<Emitter>::visitIfStmt(const IfStmt *IS) {
  BlockScope<Emitter> IfScope(this);
  if (auto *CondInit = IS->getInit())
    if (!visitStmt(IS->getInit()))
      return false;

  if (const DeclStmt *CondDecl = IS->getConditionVariableDeclStmt())
    if (!visitDeclStmt(CondDecl))
      return false;

  if (!this->visitBool(IS->getCond()))
    return false;

  if (const Stmt *Else = IS->getElse()) {
    LabelTy LabelElse = this->getLabel();
    LabelTy LabelEnd = this->getLabel();
    if (!this->jumpFalse(LabelElse))
      return false;
    if (!visitStmt(IS->getThen()))
      return false;
    if (!this->jump(LabelEnd))
      return false;
    this->emitLabel(LabelElse);
    if (!visitStmt(Else))
      return false;
    this->emitLabel(LabelEnd);
  } else {
    LabelTy LabelEnd = this->getLabel();
    if (!this->jumpFalse(LabelEnd))
      return false;
    if (!visitStmt(IS->getThen()))
      return false;
    this->emitLabel(LabelEnd);
  }

  return true;
}

template <class Emitter>
bool ByteCodeStmtGen<Emitter>::visitVarDecl(const VarDecl *VD) {
  auto DT = VD->getType();

  if (!VD->hasLocalStorage()) {
    // No code generation required.
    return true;
  }

  // Integers, pointers, primitives.
  if (Optional<PrimType> T = this->classify(DT)) {
    auto Off = this->allocateLocalPrimitive(VD, *T, DT.isConstQualified());
    // Compile the initialiser in its own scope.
    {
      ExprScope<Emitter> Scope(this);
      if (!this->visit(VD->getInit()))
        return false;
    }
    // Set the value.
    return this->emitSetLocal(*T, Off, VD);
  } else {
    // Composite types - allocate storage and initialize it.
    if (auto Off = this->allocateLocal(VD)) {
      return this->visitLocalInitializer(VD->getInit(), *Off);
    } else {
      return this->bail(VD);
    }
  }
}

namespace clang {
namespace interp {

template class ByteCodeStmtGen<ByteCodeEmitter>;

} // namespace interp
} // namespace clang