ByteCodeEmitter.cpp

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//===--- ByteCodeEmitter.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 "ByteCodeEmitter.h"
#include "Context.h"
#include "Floating.h"
#include "IntegralAP.h"
#include "Opcode.h"
#include "Program.h"
#include "clang/AST/ASTLambda.h"
#include "clang/AST/Attr.h"
#include "clang/AST/DeclCXX.h"
#include <type_traits>
 
using namespace clang;
using namespace clang::interp;
 
void ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl,
                                  Function *Func) {
  assert(FuncDecl);
  assert(Func);
  assert(FuncDecl->isThisDeclarationADefinition());
 
  // Set up lambda captures.
  if (Func->isLambdaCallOperator()) {
    // Set up lambda capture to closure record field mapping.
    const CXXRecordDecl *ParentDecl = Func->getParentDecl();
    const Record *R = P.getOrCreateRecord(ParentDecl);
    assert(R);
    llvm::DenseMap<const ValueDecl *, FieldDecl *> LC;
    FieldDecl *LTC;
 
    ParentDecl->getCaptureFields(LC, LTC);
 
    for (const auto &Cap : LC) {
      unsigned Offset = R->getField(Cap.second)->Offset;
      this->LambdaCaptures[Cap.first] = {
          Offset, Cap.second->getType()->isReferenceType()};
    }
    if (LTC) {
      QualType CaptureType = R->getField(LTC)->Decl->getType();
      this->LambdaThisCapture = {R->getField(LTC)->Offset,
                                 CaptureType->isPointerOrReferenceType()};
    }
  }
 
  bool IsValid = !FuncDecl->isInvalidDecl();
  // Register parameters and their index.
  for (unsigned ParamIndex = 0, N = Func->getNumWrittenParams();
       ParamIndex != N; ++ParamIndex) {
    const ParmVarDecl *PD = FuncDecl->getParamDecl(ParamIndex);
    if (PD->isInvalidDecl())
      IsValid = false;
    this->Params.insert({PD, {ParamIndex, Ctx.canClassify(PD->getType())}});
  }
 
  Func->setDefined(true);
 
  // Lambda static invokers are a special case that we emit custom code for.
  bool IsEligibleForCompilation = Func->isLambdaStaticInvoker() ||
                                  FuncDecl->isConstexpr() ||
                                  FuncDecl->hasAttr<MSConstexprAttr>();
 
  // Compile the function body.
  if (!IsEligibleForCompilation || !visitFunc(FuncDecl)) {
    Func->setIsFullyCompiled(true);
    return;
  }
 
  // Create scopes from descriptors.
  llvm::SmallVector<Scope, 2> Scopes;
  for (auto &DS : Descriptors) {
    Scopes.emplace_back(std::move(DS));
  }
 
  // Set the function's code.
  Func->setCode(FuncDecl, NextLocalOffset, std::move(Code), std::move(SrcMap),
                std::move(Scopes), FuncDecl->hasBody(), IsValid);
  Func->setIsFullyCompiled(true);
}
 
Scope::Local ByteCodeEmitter::createLocal(const Descriptor *D) {
  NextLocalOffset += sizeof(Block);
  unsigned Location = NextLocalOffset;
  NextLocalOffset += align(Block::InlineDescMD + D->getAllocSize());
  return {D, Location};
}
 
void ByteCodeEmitter::emitLabel(LabelTy Label) {
  const size_t Target = Code.size();
  LabelOffsets.insert({Label, Target});
 
  if (auto It = LabelRelocs.find(Label); It != LabelRelocs.end()) {
    for (unsigned Reloc : It->second) {
      using namespace llvm::support;
 
      // Rewrite the operand of all jumps to this label.
      void *Location = Code.data() + Reloc - align(sizeof(int32_t));
      assert(aligned(Location));
      const int32_t Offset = Target - static_cast<int64_t>(Reloc);
      endian::write<int32_t, llvm::endianness::native>(Location, Offset);
    }
    LabelRelocs.erase(It);
  }
}
 
int32_t ByteCodeEmitter::getOffset(LabelTy Label) {
  // Compute the PC offset which the jump is relative to.
  const int64_t Position =
      Code.size() + align(sizeof(Opcode)) + align(sizeof(int32_t));
  assert(aligned(Position));
 
  // If target is known, compute jump offset.
  if (auto It = LabelOffsets.find(Label); It != LabelOffsets.end())
    return It->second - Position;
 
  // Otherwise, record relocation and return dummy offset.
  LabelRelocs[Label].push_back(Position);
  return 0ull;
}
 
/// Helper to write bytecode and bail out if 32-bit offsets become invalid.
template <typename T>
static void emit(Program &P, llvm::SmallVectorImpl<std::byte> &Code,
                 const T &Val, bool &Success) {
  size_t ValPos = Code.size();
  size_t Size;
 
  if constexpr (std::is_pointer_v<T>)
    Size = align(sizeof(uintptr_t));
  else
    Size = align(sizeof(T));
 
  if (ValPos + Size > std::numeric_limits<unsigned>::max()) {
    Success = false;
    return;
  }
 
  // Access must be aligned!
  assert(aligned(ValPos));
  assert(aligned(ValPos + Size));
  Code.resize_for_overwrite(ValPos + Size);
 
  if constexpr (std::is_pointer_v<T>)
    new (Code.data() + ValPos) uintptr_t(reinterpret_cast<uintptr_t>(Val));
  else
    new (Code.data() + ValPos) T(Val);
}
 
/// Emits a serializable value. These usually (potentially) contain
/// heap-allocated memory and aren't trivially copyable.
template <typename T>
static void emitSerialized(llvm::SmallVectorImpl<std::byte> &Code, const T &Val,
                           bool &Success) {
  size_t ValPos = Code.size();
  size_t Size = align(Val.bytesToSerialize());
 
  if (ValPos + Size > std::numeric_limits<unsigned>::max()) {
    Success = false;
    return;
  }
 
  // Access must be aligned!
  assert(aligned(ValPos));
  assert(aligned(ValPos + Size));
  Code.resize_for_overwrite(ValPos + Size);
 
  Val.serialize(Code.data() + ValPos);
}
 
template <>
void emit(Program &P, llvm::SmallVectorImpl<std::byte> &Code,
          const Floating &Val, bool &Success) {
  emitSerialized(Code, Val, Success);
}
 
template <>
void emit(Program &P, llvm::SmallVectorImpl<std::byte> &Code,
          const IntegralAP<false> &Val, bool &Success) {
  emitSerialized(Code, Val, Success);
}
 
template <>
void emit(Program &P, llvm::SmallVectorImpl<std::byte> &Code,
          const IntegralAP<true> &Val, bool &Success) {
  emitSerialized(Code, Val, Success);
}
 
template <>
void emit(Program &P, llvm::SmallVectorImpl<std::byte> &Code,
          const FixedPoint &Val, bool &Success) {
  emitSerialized(Code, Val, Success);
}
 
template <typename... Tys>
bool ByteCodeEmitter::emitOp(Opcode Op, const Tys &...Args, SourceInfo SI) {
  bool Success = true;
 
  // The opcode is followed by arguments. The source info is
  // attached to the address after the opcode.
  emit(P, Code, Op, Success);
 
  SI = LocOverride.value_or(SI);
  if (SrcMap.empty() || SrcMap.back() != SI)
    SrcMap.push(Code.size(), SI);
 
  (..., emit(P, Code, Args, Success));
  return Success;
}
 
bool ByteCodeEmitter::jumpTrue(const LabelTy &Label, SourceInfo SI) {
  return emitJt(getOffset(Label), SI);
}
 
bool ByteCodeEmitter::jumpFalse(const LabelTy &Label, SourceInfo SI) {
  return emitJf(getOffset(Label), SI);
}
 
bool ByteCodeEmitter::jump(const LabelTy &Label, SourceInfo SI) {
  return emitJmp(getOffset(Label), SI);
}
 
bool ByteCodeEmitter::fallthrough(const LabelTy &Label) {
  emitLabel(Label);
  return true;
}
 
bool ByteCodeEmitter::speculate(const CallExpr *E, const LabelTy &EndLabel) {
  const Expr *Arg = E->getArg(0);
  PrimType T = Ctx.classify(Arg->getType()).value_or(PT_Ptr);
  if (!this->emitBCP(getOffset(EndLabel), T, E))
    return false;
  if (!this->visit(Arg))
    return false;
  return true;
}
 
//===----------------------------------------------------------------------===//
// Opcode emitters
//===----------------------------------------------------------------------===//
 
#define GET_LINK_IMPL
#include "Opcodes.inc"
#undef GET_LINK_IMPL