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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 "Opcode.h"
#include "Program.h"
#include "clang/AST/DeclCXX.h"
#include <type_traits>
using namespace clang;
using namespace clang::interp;
using APSInt = llvm::APSInt;
using Error = llvm::Error;
Expected<Function *>
ByteCodeEmitter::compileFunc(const FunctionDecl *FuncDecl) {
// Function is not defined at all or not yet. We will
// create a Function instance but not compile the body. That
// will (maybe) happen later.
bool HasBody = FuncDecl->hasBody(FuncDecl);
// Create a handle over the emitted code.
Function *Func = P.getFunction(FuncDecl);
if (!Func) {
// Set up argument indices.
unsigned ParamOffset = 0;
SmallVector<PrimType, 8> ParamTypes;
llvm::DenseMap<unsigned, Function::ParamDescriptor> ParamDescriptors;
// If the return is not a primitive, a pointer to the storage where the
// value is initialized in is passed as the first argument. See 'RVO'
// elsewhere in the code.
QualType Ty = FuncDecl->getReturnType();
bool HasRVO = false;
if (!Ty->isVoidType() && !Ctx.classify(Ty)) {
HasRVO = true;
ParamTypes.push_back(PT_Ptr);
ParamOffset += align(primSize(PT_Ptr));
}
// If the function decl is a member decl, the next parameter is
// the 'this' pointer. This parameter is pop()ed from the
// InterpStack when calling the function.
bool HasThisPointer = false;
if (const auto *MD = dyn_cast<CXXMethodDecl>(FuncDecl);
MD && MD->isInstance()) {
HasThisPointer = true;
ParamTypes.push_back(PT_Ptr);
ParamOffset += align(primSize(PT_Ptr));
}
// Assign descriptors to all parameters.
// Composite objects are lowered to pointers.
for (const ParmVarDecl *PD : FuncDecl->parameters()) {
PrimType Ty = Ctx.classify(PD->getType()).value_or(PT_Ptr);
Descriptor *Desc = P.createDescriptor(PD, Ty);
ParamDescriptors.insert({ParamOffset, {Ty, Desc}});
Params.insert({PD, ParamOffset});
ParamOffset += align(primSize(Ty));
ParamTypes.push_back(Ty);
}
Func =
P.createFunction(FuncDecl, ParamOffset, std::move(ParamTypes),
std::move(ParamDescriptors), HasThisPointer, HasRVO);
}
assert(Func);
if (!HasBody)
return Func;
// Compile the function body.
if (!FuncDecl->isConstexpr() || !visitFunc(FuncDecl)) {
// Return a dummy function if compilation failed.
if (BailLocation)
return llvm::make_error<ByteCodeGenError>(*BailLocation);
else {
Func->setIsFullyCompiled(true);
return Func;
}
} else {
// 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(NextLocalOffset, std::move(Code), std::move(SrcMap),
std::move(Scopes));
Func->setIsFullyCompiled(true);
return Func;
}
}
Scope::Local ByteCodeEmitter::createLocal(Descriptor *D) {
NextLocalOffset += sizeof(Block);
unsigned Location = NextLocalOffset;
NextLocalOffset += align(D->getAllocSize());
return {Location, D};
}
void ByteCodeEmitter::emitLabel(LabelTy Label) {
const size_t Target = Code.size();
LabelOffsets.insert({Label, Target});
auto It = LabelRelocs.find(Label);
if (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, endianness::native, 1>(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.
auto It = LabelOffsets.find(Label);
if (It != LabelOffsets.end()) {
return It->second - Position;
}
// Otherwise, record relocation and return dummy offset.
LabelRelocs[Label].push_back(Position);
return 0ull;
}
bool ByteCodeEmitter::bail(const SourceLocation &Loc) {
if (!BailLocation)
BailLocation = Loc;
return false;
}
/// Helper to write bytecode and bail out if 32-bit offsets become invalid.
/// Pointers will be automatically marshalled as 32-bit IDs.
template <typename T>
static void emit(Program &P, std::vector<char> &Code, const T &Val,
bool &Success) {
size_t Size;
if constexpr (std::is_pointer_v<T>)
Size = sizeof(uint32_t);
else
Size = sizeof(T);
if (Code.size() + Size > std::numeric_limits<unsigned>::max()) {
Success = false;
return;
}
// Access must be aligned!
size_t ValPos = align(Code.size());
Size = align(Size);
assert(aligned(ValPos + Size));
Code.resize(ValPos + Size);
if constexpr (!std::is_pointer_v<T>) {
new (Code.data() + ValPos) T(Val);
} else {
uint32_t ID = P.getOrCreateNativePointer(Val);
new (Code.data() + ValPos) uint32_t(ID);
}
}
template <typename... Tys>
bool ByteCodeEmitter::emitOp(Opcode Op, const Tys &... Args, const 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);
if (SI)
SrcMap.emplace_back(Code.size(), SI);
/// The initializer list forces the expression to be evaluated
/// for each argument in the variadic template, in order.
(void)std::initializer_list<int>{(emit(P, Code, Args, Success), 0)...};
return Success;
}
bool ByteCodeEmitter::jumpTrue(const LabelTy &Label) {
return emitJt(getOffset(Label), SourceInfo{});
}
bool ByteCodeEmitter::jumpFalse(const LabelTy &Label) {
return emitJf(getOffset(Label), SourceInfo{});
}
bool ByteCodeEmitter::jump(const LabelTy &Label) {
return emitJmp(getOffset(Label), SourceInfo{});
}
bool ByteCodeEmitter::fallthrough(const LabelTy &Label) {
emitLabel(Label);
return true;
}
//===----------------------------------------------------------------------===//
// Opcode emitters
//===----------------------------------------------------------------------===//
#define GET_LINK_IMPL
#include "Opcodes.inc"
#undef GET_LINK_IMPL
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