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/*
* Copyright 2019 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef WABT_DECOMPILER_LS_H_
#define WABT_DECOMPILER_LS_H_
#include "wabt/decompiler-ast.h"
#include "wabt/string-util.h"
#include <map>
namespace wabt {
// Names starting with "u" are unsigned, the rest are "signed or doesn't matter"
inline const char* GetDecompTypeName(Type t) {
switch (t) {
case Type::I8: return "byte";
case Type::I8U: return "ubyte";
case Type::I16: return "short";
case Type::I16U: return "ushort";
case Type::I32: return "int";
case Type::I32U: return "uint";
case Type::I64: return "long";
case Type::F32: return "float";
case Type::F64: return "double";
case Type::V128: return "simd";
case Type::Func: return "func";
case Type::FuncRef: return "funcref";
case Type::ExternRef: return "externref";
case Type::Void: return "void";
default: return "ILLEGAL";
}
}
inline Type GetMemoryType(Type operand_type, Opcode opc) {
// TODO: something something SIMD.
// TODO: this loses information of the type it is read into.
// That may well not be the biggest deal since that is usually obvious
// from context, if not, we should probably represent that as a cast around
// the access, since it should not be part of the field type.
if (operand_type == Type::I32 || operand_type == Type::I64) {
auto name = std::string_view(opc.GetName());
// FIXME: change into a new column in opcode.def instead?
auto is_unsigned = name.substr(name.size() - 2) == "_u";
switch (opc.GetMemorySize()) {
case 1: return is_unsigned ? Type::I8U : Type::I8;
case 2: return is_unsigned ? Type::I16U : Type::I16;
case 4: return is_unsigned ? Type::I32U : Type::I32;
}
}
return operand_type;
}
// Track all loads and stores inside a single function, to be able to detect
// struct layouts we can use to annotate variables with, to make code more
// readable.
struct LoadStoreTracking {
struct LSAccess {
Address byte_size = 0;
Type type = Type::Any;
Address align = 0;
uint32_t idx = 0;
bool is_uniform = true;
};
struct LSVar {
std::map<uint64_t, LSAccess> accesses;
bool struct_layout = true;
Type same_type = Type::Any;
Address same_align = kInvalidAddress;
Opcode last_opc;
};
void Track(const Node& n) {
for (auto& c : n.children) {
Track(c);
}
switch (n.etype) {
case ExprType::Load: {
auto& le = *cast<LoadExpr>(n.e);
LoadStore(le.offset, le.opcode, le.opcode.GetResultType(), le.align,
n.children[0]);
break;
}
case ExprType::Store: {
auto& se = *cast<StoreExpr>(n.e);
LoadStore(se.offset, se.opcode, se.opcode.GetParamType2(), se.align,
n.children[0]);
break;
}
default:
break;
}
}
const std::string AddrExpName(const Node& addr_exp) const {
// TODO: expand this to more kinds of address expressions.
switch (addr_exp.etype) {
case ExprType::LocalGet:
return cast<LocalGetExpr>(addr_exp.e)->var.name();
break;
case ExprType::LocalTee:
return cast<LocalTeeExpr>(addr_exp.e)->var.name();
break;
default:
return "";
}
}
void LoadStore(uint64_t offset,
Opcode opc,
Type type,
Address align,
const Node& addr_exp) {
auto byte_size = opc.GetMemorySize();
type = GetMemoryType(type, opc);
// We want to associate memory ops of a certain offset & size as being
// relative to a uniquely identifiable pointer, such as a local.
auto name = AddrExpName(addr_exp);
if (name.empty()) {
return;
}
auto& var = vars[name];
auto& access = var.accesses[offset];
// Check if previous access at this offset (if any) is of same size
// and type (see Checklayouts below).
if (access.byte_size && ((access.byte_size != byte_size) ||
(access.type != type) || (access.align != align)))
access.is_uniform = false;
// Also exclude weird alignment accesses from structs.
if (!opc.IsNaturallyAligned(align))
access.is_uniform = false;
access.byte_size = byte_size;
access.type = type;
access.align = align;
// Additionally, check if all accesses are to the same type, so
// if layout check fails, we can at least declare it as pointer to
// a type.
if ((var.same_type == type || var.same_type == Type::Any) &&
(var.same_align == align || var.same_align == kInvalidAddress)) {
var.same_type = type;
var.same_align = align;
var.last_opc = opc;
} else {
var.same_type = Type::Void;
var.same_align = kInvalidAddress;
}
}
void CheckLayouts() {
// Here we check if the set of accesses we have collected form a sequence
// we could declare as a struct, meaning they are properly aligned,
// contiguous, and have no overlaps between different types and sizes.
// We do this because an int access of size 2 at offset 0 followed by
// a float access of size 4 at offset 4 can compactly represented as a
// struct { short, float }, whereas something that reads from overlapping
// or discontinuous offsets would need a more complicated syntax that
// involves explicit offsets.
// We assume that the bulk of memory accesses are of this very regular kind,
// so we choose not to even emit struct layouts for irregular ones,
// given that they are rare and confusing, and thus do not benefit from
// being represented as if they were structs.
for (auto& var : vars) {
if (var.second.accesses.size() == 1) {
// If we have just one access, this is better represented as a pointer
// than a struct.
var.second.struct_layout = false;
continue;
}
uint64_t cur_offset = 0;
uint32_t idx = 0;
for (auto& access : var.second.accesses) {
access.second.idx = idx++;
if (!access.second.is_uniform) {
var.second.struct_layout = false;
break;
}
// Align to next access: all elements are expected to be aligned to
// a memory address thats a multiple of their own size.
auto mask = static_cast<uint64_t>(access.second.byte_size - 1);
cur_offset = (cur_offset + mask) & ~mask;
if (cur_offset != access.first) {
var.second.struct_layout = false;
break;
}
cur_offset += access.second.byte_size;
}
}
}
std::string IdxToName(uint32_t idx) const {
return IndexToAlphaName(idx); // TODO: more descriptive names?
}
std::string GenAlign(Address align, Opcode opc) const {
return opc.IsNaturallyAligned(align) ? "" : cat("@", std::to_string(align));
}
std::string GenTypeDecl(const std::string& name) const {
auto it = vars.find(name);
if (it == vars.end()) {
return "";
}
if (it->second.struct_layout) {
std::string s = "{ ";
for (auto& access : it->second.accesses) {
if (access.second.idx) {
s += ", ";
}
s += IdxToName(access.second.idx);
s += ':';
s += GetDecompTypeName(access.second.type);
}
s += " }";
return s;
}
// We don't have a struct layout, or the struct has just one field,
// so maybe we can just declare it as a pointer to one type?
if (it->second.same_type != Type::Void) {
return cat(GetDecompTypeName(it->second.same_type), "_ptr",
GenAlign(it->second.same_align, it->second.last_opc));
}
return "";
}
std::string GenAccess(uint64_t offset, const Node& addr_exp) const {
auto name = AddrExpName(addr_exp);
if (name.empty()) {
return "";
}
auto it = vars.find(name);
if (it == vars.end()) {
return "";
}
if (it->second.struct_layout) {
auto ait = it->second.accesses.find(offset);
assert(ait != it->second.accesses.end());
return IdxToName(ait->second.idx);
}
// Not a struct, see if it is a typed pointer.
if (it->second.same_type != Type::Void) {
return "*";
}
return "";
}
void Clear() { vars.clear(); }
std::map<std::string, LSVar> vars;
};
} // namespace wabt
#endif // WABT_DECOMPILER_LS_H_