EvalEmitter.cpp

Go to the documentation of this file.

//===--- EvalEmitter.cpp - Instruction emitter for the 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
//
//===----------------------------------------------------------------------===//
 
#include "EvalEmitter.h"
#include "Context.h"
#include "IntegralAP.h"
#include "Interp.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/ExprCXX.h"
#include "llvm/ADT/ScopeExit.h"
 
using namespace clang;
using namespace clang::interp;
 
EvalEmitter::EvalEmitter(Context &Ctx, Program &P, State &Parent,
                         InterpStack &Stk)
    : Ctx(Ctx), P(P), S(Parent, P, Stk, Ctx, this), EvalResult(&Ctx) {}
 
/// Clean up all our resources. This needs to done in failed evaluations before
/// we call InterpStack::clear(), because there might be a Pointer on the stack
/// pointing into a Block in the EvalEmitter.
void EvalEmitter::cleanup() { S.cleanup(); }
 
EvaluationResult EvalEmitter::interpretExpr(const Expr *E,
                                            bool ConvertResultToRValue,
                                            bool DestroyToplevelScope) {
  S.setEvalLocation(E->getExprLoc());
  this->ConvertResultToRValue = ConvertResultToRValue && !isa<ConstantExpr>(E);
  this->CheckFullyInitialized = isa<ConstantExpr>(E) && !E->isGLValue();
  EvalResult.setSource(E);
 
  if (!this->visitExpr(E, DestroyToplevelScope)) {
    // EvalResult may already have a result set, but something failed
    // after that (e.g. evaluating destructors).
    EvalResult.setInvalid();
  }
 
  return std::move(this->EvalResult);
}
 
EvaluationResult EvalEmitter::interpretDecl(const VarDecl *VD, const Expr *Init,
                                            bool CheckFullyInitialized) {
  assert(VD);
  assert(Init);
  this->CheckFullyInitialized = CheckFullyInitialized;
  S.EvaluatingDecl = VD;
  S.setEvalLocation(VD->getLocation());
  EvalResult.setSource(VD);
 
  QualType T = VD->getType();
  this->ConvertResultToRValue = !Init->isGLValue() && !T->isPointerType() &&
                                !T->isObjCObjectPointerType();
 
  if (!this->visitDeclAndReturn(VD, Init, S.inConstantContext()))
    EvalResult.setInvalid();
 
  S.EvaluatingDecl = nullptr;
  updateGlobalTemporaries();
  return std::move(this->EvalResult);
}
 
EvaluationResult EvalEmitter::interpretDestructor(const VarDecl *VD,
                                                  const APValue &Value) {
  assert(VD);
  S.setEvalLocation(VD->getLocation());
  S.EvaluatingDecl = VD;
  S.EvalKind = EvaluationKind::Dtor;
  EvalResult.setSource(VD);
 
  if (!this->visitDtorCall(VD, Value))
    EvalResult.setInvalid();
 
  S.EvaluatingDecl = nullptr;
  return std::move(this->EvalResult);
}
 
EvaluationResult EvalEmitter::interpretAsPointer(const Expr *E,
                                                 PtrCallback PtrCB) {
  S.setEvalLocation(E->getExprLoc());
  this->ConvertResultToRValue = false;
  this->CheckFullyInitialized = false;
  this->PtrCB = PtrCB;
  EvalResult.setSource(E);
 
  if (!this->visitExpr(E, true)) {
    // EvalResult may already have a result set, but something failed
    // after that (e.g. evaluating destructors).
    EvalResult.setInvalid();
  }
 
  return std::move(this->EvalResult);
}
 
EvaluationResult EvalEmitter::interpretAsLValuePointer(const Expr *E,
                                                       PtrCallback PtrCB) {
  S.setEvalLocation(E->getExprLoc());
  this->ConvertResultToRValue = false;
  this->CheckFullyInitialized = false;
  this->PtrCB = PtrCB;
  EvalResult.setSource(E);
 
  if (!this->visitLValueExpr(E, true))
    EvalResult.setInvalid();
 
  return std::move(this->EvalResult);
}
 
bool EvalEmitter::interpretCall(const FunctionDecl *FD, const Expr *E) {
  // Add parameters to the parameter map. The values in the ParamOffset don't
  // matter in this case as reading from them can't ever work.
  for (const ParmVarDecl *PD : FD->parameters()) {
    this->Params.insert({PD, {0, false}});
  }
 
  return this->visitExpr(E, /*DestroyToplevelScope=*/false);
}
 
std::optional<bool> EvalEmitter::interpretWithSubstitutions(
    const FunctionDecl *Callee, ArrayRef<const Expr *> Args, const Expr *This,
    const Expr *Condition) {
 
  if (!this->visitWithSubstitutions(Callee, Args, This, Condition))
    return std::nullopt;
 
  if (EvalResult.empty() || EvalResult.isInvalid())
    return false;
 
  assert(!EvalResult.empty());
  APValue Result = EvalResult.stealAPValue();
 
  assert(Result.isInt());
  return Result.getInt().getBoolValue();
}
 
void EvalEmitter::emitLabel(LabelTy Label) { CurrentLabel = Label; }
 
EvalEmitter::LabelTy EvalEmitter::getLabel() { return NextLabel++; }
 
Scope::Local EvalEmitter::createLocal(const Descriptor *D) {
  // Allocate memory for a local.
  char *Memory = reinterpret_cast<char *>(
      S.allocate(sizeof(Block) + D->getAllocSize() + Block::InlineDescMD));
  auto *B = new (Memory) Block(Ctx.getEvalID(), D, Block::InlineDescMD,
                               /*IsStatic=*/false);
  B->invokeCtor();
 
  // Initialize local variable inline descriptor.
  auto &Desc = B->getBlockDesc<InlineDescriptor>();
  Desc.Desc = D;
  Desc.Offset = sizeof(InlineDescriptor);
  Desc.IsActive = false;
  Desc.IsBase = false;
  Desc.IsFieldMutable = false;
  Desc.IsConst = false;
  Desc.IsInitialized = false;
 
  // Register the local.
  unsigned Off = Locals.size();
  Locals.push_back(Memory);
  return {D, Off};
}
 
bool EvalEmitter::jumpTrue(const LabelTy &Label, SourceInfo SI) {
  if (isActive()) {
    CurrentSource = SI;
    if (S.Stk.pop<bool>())
      ActiveLabel = Label;
  }
  return true;
}
 
bool EvalEmitter::jumpFalse(const LabelTy &Label, SourceInfo SI) {
  if (isActive()) {
    CurrentSource = SI;
    if (!S.Stk.pop<bool>())
      ActiveLabel = Label;
  }
  return true;
}
 
bool EvalEmitter::jump(const LabelTy &Label, SourceInfo SI) {
  if (isActive()) {
    CurrentSource = SI;
    CurrentLabel = ActiveLabel = Label;
  }
  return true;
}
 
bool EvalEmitter::fallthrough(const LabelTy &Label) {
  if (isActive())
    ActiveLabel = Label;
  CurrentLabel = Label;
  return true;
}
 
bool EvalEmitter::speculate(const CallExpr *E, const LabelTy &EndLabel) {
  if (!isActive())
    return true;
 
  PushIgnoreDiags(S);
  auto _ = llvm::scope_exit([&]() { PopIgnoreDiags(S); });
 
  size_t StackSizeBefore = S.Stk.size();
  const Expr *Arg = E->getArg(0);
  if (!this->visit(Arg)) {
    S.Stk.clearTo(StackSizeBefore);
 
    if (S.inConstantContext() || Arg->HasSideEffects(S.getASTContext()))
      return this->emitBool(false, E);
    return Invalid(S, CodePtr());
  }
 
  PrimType T = Ctx.classify(Arg->getType()).value_or(PT_Ptr);
  if (T == PT_Ptr) {
    const auto &Ptr = S.Stk.pop<Pointer>();
    return this->emitBool(CheckBCPResult(S, Ptr), E);
  }
 
  // Otherwise, this is fine!
  if (!this->emitPop(T, E))
    return false;
  return this->emitBool(true, E);
}
 
template <PrimType OpType> bool EvalEmitter::emitRet(SourceInfo Info) {
  if (!isActive())
    return true;
 
  using T = typename PrimConv<OpType>::T;
  EvalResult.takeValue(S.Stk.pop<T>().toAPValue(Ctx.getASTContext()));
  return true;
}
 
template <> bool EvalEmitter::emitRet<PT_Ptr>(SourceInfo Info) {
  if (!isActive())
    return true;
 
  const Pointer &Ptr = S.Stk.pop<Pointer>();
  // If we're returning a raw pointer, call our callback.
  if (this->PtrCB)
    return (*this->PtrCB)(S, CodePtr(), Ptr);
 
  if (!EvalResult.checkDynamicAllocations(S, Ptr, Info))
    return false;
  if (CheckFullyInitialized && !EvalResult.checkFullyInitialized(S, Ptr))
    return false;
 
  // Function pointers are always returned as lvalues.
  if (Ptr.isFunctionPointer()) {
    if (ConvertResultToRValue && Ptr.asFunctionPointer().Func->getDecl())
      return false;
    EvalResult.takeValue(Ptr.toAPValue(Ctx.getASTContext()));
    return true;
  }
 
  // Implicitly convert lvalue to rvalue, if requested.
  if (ConvertResultToRValue) {
    if (Ptr.isPastEnd())
      return false;
 
    if (!Ptr.isZero() && !CheckFinalLoad(S, CodePtr(), Ptr))
      return false;
 
    // Never allow reading from a non-const pointer, unless the memory
    // has been created in this evaluation.
    if (!Ptr.isZero() && !Ptr.isConst() && Ptr.isBlockPointer() &&
        Ptr.block()->getEvalID() != Ctx.getEvalID())
      return false;
 
    if (std::optional<APValue> V =
            Ptr.toRValue(Ctx, EvalResult.getSourceType())) {
      EvalResult.takeValue(std::move(*V));
    } else {
      return false;
    }
  } else {
    // If this is pointing to a local variable, just return
    // the result, even if the pointer is dead.
    // This will later be diagnosed by CheckLValueConstantExpression.
    if (Ptr.isBlockPointer() && !Ptr.block()->isStatic()) {
      EvalResult.takeValue(Ptr.toAPValue(Ctx.getASTContext()));
      return true;
    }
 
    if (!Ptr.isLive() && !Ptr.isTemporary())
      return false;
 
    // If the variable of this pointer is being evaluated when returning
    // its value, mark it as constexpr-unknown.
    APValue V = Ptr.toAPValue(Ctx.getASTContext());
    if (const Descriptor *DeclDesc = Ptr.getDeclDesc();
        DeclDesc && S.EvaluatingDecl &&
        DeclDesc->asVarDecl() == S.EvaluatingDecl &&
        S.getLangOpts().CPlusPlus23 &&
        S.EvaluatingDecl->getType()->isReferenceType()) {
      V.setConstexprUnknown(true);
    }
    EvalResult.takeValue(std::move(V));
  }
 
  return true;
}
 
bool EvalEmitter::emitRetVoid(SourceInfo Info) {
  EvalResult.setValid();
  return true;
}
 
bool EvalEmitter::emitRetValue(SourceInfo Info) {
  const auto &Ptr = S.Stk.pop<Pointer>();
 
  if (!EvalResult.checkDynamicAllocations(S, Ptr, Info))
    return false;
  if (CheckFullyInitialized && !EvalResult.checkFullyInitialized(S, Ptr))
    return false;
 
  if (std::optional<APValue> APV =
          Ptr.toRValue(Ctx, EvalResult.getSourceType())) {
    EvalResult.takeValue(std::move(*APV));
    return true;
  }
 
  EvalResult.setInvalid();
  return false;
}
 
bool EvalEmitter::emitGetPtrLocal(uint32_t I, SourceInfo Info) {
  if (!isActive())
    return true;
 
  Block *B = getLocal(I);
  S.Stk.push<Pointer>(B, sizeof(InlineDescriptor));
  return true;
}
 
bool EvalEmitter::emitGetRefLocal(uint32_t I, SourceInfo Info) {
  if (!isActive())
    return true;
 
  Block *B = getLocal(I);
  return handleReference(S, CodePtr(), B);
}
 
template <PrimType OpType>
bool EvalEmitter::emitGetLocal(uint32_t I, SourceInfo Info) {
  if (!isActive())
    return true;
 
  using T = typename PrimConv<OpType>::T;
 
  Block *B = getLocal(I);
 
  if (!CheckLocalLoad(S, CodePtr(), B))
    return false;
 
  S.Stk.push<T>(B->deref<T>());
  return true;
}
 
template <PrimType OpType>
bool EvalEmitter::emitSetLocal(uint32_t I, SourceInfo Info) {
  if (!isActive())
    return true;
 
  using T = typename PrimConv<OpType>::T;
 
  Block *B = getLocal(I);
  B->deref<T>() = S.Stk.pop<T>();
  auto &Desc = B->getBlockDesc<InlineDescriptor>();
  Desc.IsInitialized = true;
  Desc.LifeState = Lifetime::Started;
 
  return true;
}
 
bool EvalEmitter::emitDestroy(uint32_t I, SourceInfo Info) {
  if (!isActive())
    return true;
 
  for (auto &Local : Descriptors[I]) {
    Block *B = getLocal(Local.Offset);
    S.deallocate(B);
  }
 
  return true;
}
 
bool EvalEmitter::emitGetLocalEnabled(uint32_t I, SourceInfo Info) {
  if (!isActive())
    return true;
 
  Block *B = getLocal(I);
  const auto &Desc = B->getBlockDesc<InlineDescriptor>();
 
  S.Stk.push<bool>(Desc.IsActive);
  return true;
}
 
bool EvalEmitter::emitEnableLocal(uint32_t I, SourceInfo Info) {
  if (!isActive())
    return true;
 
  // FIXME: This is a little dirty, but to avoid adding a flag to
  // InlineDescriptor that's only ever useful on the toplevel of local
  // variables, we reuse the IsActive flag for the enabled state. We should
  // probably use a different struct than InlineDescriptor for the block-level
  // inline descriptor of local varaibles.
  Block *B = getLocal(I);
  auto &Desc = B->getBlockDesc<InlineDescriptor>();
  Desc.IsActive = true;
  return true;
}
 
/// Global temporaries (LifetimeExtendedTemporary) carry their value
/// around as an APValue, which codegen accesses.
/// We set their value once when creating them, but we don't update it
/// afterwards when code changes it later.
/// This is what we do here.
void EvalEmitter::updateGlobalTemporaries() {
  for (const auto &[E, Temp] : S.SeenGlobalTemporaries) {
    UnsignedOrNone GlobalIndex = P.getGlobal(E);
    assert(GlobalIndex);
    const Pointer &Ptr = P.getPtrGlobal(*GlobalIndex);
    APValue *Cached = Temp->getOrCreateValue(true);
 
    QualType TempType = E->getType();
    if (const auto *MTE = dyn_cast<MaterializeTemporaryExpr>(E))
      TempType = MTE->getSubExpr()->skipRValueSubobjectAdjustments()->getType();
 
    if (OptPrimType T = Ctx.classify(TempType)) {
      TYPE_SWITCH(*T,
                  { *Cached = Ptr.deref<T>().toAPValue(Ctx.getASTContext()); });
    } else {
      if (std::optional<APValue> APV = Ptr.toRValue(Ctx, TempType))
        *Cached = *APV;
    }
  }
  S.SeenGlobalTemporaries.clear();
}
 
//===----------------------------------------------------------------------===//
// Opcode evaluators
//===----------------------------------------------------------------------===//
 
#define GET_EVAL_IMPL
#include "Opcodes.inc"
#undef GET_EVAL_IMPL