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// Copyright 2022 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#if !V8_ENABLE_WEBASSEMBLY
#error This header should only be included if WebAssembly is enabled.
#endif // !V8_ENABLE_WEBASSEMBLY
#ifndef V8_WASM_CONSTANT_EXPRESSION_H_
#define V8_WASM_CONSTANT_EXPRESSION_H_
#include <stdint.h>
#include <variant>
#include "src/base/bit-field.h"
#include "src/wasm/value-type.h"
#include "src/wasm/wasm-value.h"
namespace v8 {
namespace internal {
enum class MessageTemplate;
class WasmInstanceObject;
namespace wasm {
class WireBytesRef;
// A representation of a constant expression. The most common expression types
// are hard-coded, while the rest are represented as a {WireBytesRef}.
class ConstantExpression {
public:
enum Kind {
kEmpty,
kI32Const,
kRefNull,
kRefFunc,
kWireBytesRef,
kLastKind = kWireBytesRef
};
union Value {
int32_t i32_value;
uint32_t index_or_offset;
HeapType::Representation repr;
};
ConstantExpression() : bit_field_(KindField::encode(kEmpty)) {}
static ConstantExpression I32Const(int32_t value) {
return ConstantExpression(ValueField::encode(value) |
KindField::encode(kI32Const));
}
static ConstantExpression RefFunc(uint32_t index) {
return ConstantExpression(ValueField::encode(index) |
KindField::encode(kRefFunc));
}
static ConstantExpression RefNull(HeapType::Representation repr) {
return ConstantExpression(ValueField::encode(repr) |
KindField::encode(kRefNull));
}
static ConstantExpression WireBytes(uint32_t offset, uint32_t length) {
return ConstantExpression(OffsetField::encode(offset) |
LengthField::encode(length) |
KindField::encode(kWireBytesRef));
}
Kind kind() const { return KindField::decode(bit_field_); }
bool is_set() const { return kind() != kEmpty; }
uint32_t index() const {
DCHECK_EQ(kind(), kRefFunc);
return ValueField::decode(bit_field_);
}
HeapType::Representation repr() const {
DCHECK_EQ(kind(), kRefNull);
return static_cast<HeapType::Representation>(
ValueField::decode(bit_field_));
}
int32_t i32_value() const {
DCHECK_EQ(kind(), kI32Const);
return ValueField::decode(bit_field_);
}
V8_EXPORT_PRIVATE WireBytesRef wire_bytes_ref() const;
private:
static constexpr int kValueBits = 32;
static constexpr int kLengthBits = 30;
static constexpr int kOffsetBits = 30;
static constexpr int kKindBits = 3;
// There are two possible combinations of fields: offset + length + kind if
// kind = kWireBytesRef, or value + kind for anything else.
using ValueField = base::BitField<uint32_t, 0, kValueBits, uint64_t>;
using OffsetField = base::BitField<uint32_t, 0, kOffsetBits, uint64_t>;
using LengthField = OffsetField::Next<uint32_t, kLengthBits>;
using KindField = LengthField::Next<Kind, kKindBits>;
// Make sure we reserve enough bits for a {WireBytesRef}'s length and offset.
static_assert(kV8MaxWasmModuleSize <= LengthField::kMax + 1);
static_assert(kV8MaxWasmModuleSize <= OffsetField::kMax + 1);
// Make sure kind fits in kKindBits.
static_assert(kLastKind <= KindField::kMax + 1);
explicit ConstantExpression(uint64_t bit_field) : bit_field_(bit_field) {}
uint64_t bit_field_;
};
// We want to keep {ConstantExpression} small to reduce memory usage during
// compilation/instantiation.
static_assert(sizeof(ConstantExpression) <= 8);
using ValueOrError = std::variant<WasmValue, MessageTemplate>;
V8_INLINE bool is_error(ValueOrError result) {
return std::holds_alternative<MessageTemplate>(result);
}
V8_INLINE MessageTemplate to_error(ValueOrError result) {
return std::get<MessageTemplate>(result);
}
V8_INLINE WasmValue to_value(ValueOrError result) {
return std::get<WasmValue>(result);
}
// Evaluates a constant expression.
// Returns a {WasmValue} if the evaluation succeeds, or an error as a
// {MessageTemplate} if it fails.
ValueOrError EvaluateConstantExpression(Zone* zone, ConstantExpression expr,
ValueType expected, Isolate* isolate,
Handle<WasmInstanceObject> instance);
} // namespace wasm
} // namespace internal
} // namespace v8
#endif // V8_WASM_CONSTANT_EXPRESSION_H_
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