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/*
* Copyright 2016 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
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
*/
//
// Removes module elements that are are never used: functions and globals,
// which may be imported or not, and function types (which we merge
// and remove if unneeded)
//
#include <memory>
#include "wasm.h"
#include "pass.h"
#include "ir/utils.h"
#include "asm_v_wasm.h"
namespace wasm {
enum class ModuleElementKind {
Function,
Global
};
typedef std::pair<ModuleElementKind, Name> ModuleElement;
// Finds reachabilities
struct ReachabilityAnalyzer : public PostWalker<ReachabilityAnalyzer> {
Module* module;
std::vector<ModuleElement> queue;
std::set<ModuleElement> reachable;
ReachabilityAnalyzer(Module* module, const std::vector<ModuleElement>& roots) : module(module) {
queue = roots;
// Globals used in memory/table init expressions are also roots
for (auto& segment : module->memory.segments) {
walk(segment.offset);
}
for (auto& segment : module->table.segments) {
walk(segment.offset);
}
// main loop
while (queue.size()) {
auto& curr = queue.back();
queue.pop_back();
if (reachable.count(curr) == 0) {
reachable.insert(curr);
if (curr.first == ModuleElementKind::Function) {
// if not an import, walk it
auto* func = module->getFunctionOrNull(curr.second);
if (func) {
walk(func->body);
}
} else {
// if not imported, it has an init expression we need to walk
auto* glob = module->getGlobalOrNull(curr.second);
if (glob) {
walk(glob->init);
}
}
}
}
}
void visitCall(Call* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Function, curr->target)) == 0) {
queue.emplace_back(ModuleElementKind::Function, curr->target);
}
}
void visitCallImport(CallImport* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Function, curr->target)) == 0) {
queue.emplace_back(ModuleElementKind::Function, curr->target);
}
}
void visitGetGlobal(GetGlobal* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0) {
queue.emplace_back(ModuleElementKind::Global, curr->name);
}
}
void visitSetGlobal(SetGlobal* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0) {
queue.emplace_back(ModuleElementKind::Global, curr->name);
}
}
};
// Finds function type usage
struct FunctionTypeAnalyzer : public PostWalker<FunctionTypeAnalyzer> {
std::vector<Import*> functionImports;
std::vector<Function*> functions;
std::vector<CallIndirect*> indirectCalls;
void visitImport(Import* curr) {
if (curr->kind == ExternalKind::Function && curr->functionType.is()) {
functionImports.push_back(curr);
}
}
void visitFunction(Function* curr) {
if (curr->type.is()) {
functions.push_back(curr);
}
}
void visitCallIndirect(CallIndirect* curr) {
indirectCalls.push_back(curr);
}
};
struct RemoveUnusedModuleElements : public Pass {
void run(PassRunner* runner, Module* module) override {
optimizeGlobalsAndFunctions(module);
optimizeFunctionTypes(module);
}
void optimizeGlobalsAndFunctions(Module* module) {
std::vector<ModuleElement> roots;
// Module start is a root.
if (module->start.is()) {
roots.emplace_back(ModuleElementKind::Function, module->start);
}
// Exports are roots.
for (auto& curr : module->exports) {
if (curr->kind == ExternalKind::Function) {
roots.emplace_back(ModuleElementKind::Function, curr->value);
} else if (curr->kind == ExternalKind::Global) {
roots.emplace_back(ModuleElementKind::Global, curr->value);
}
}
// For now, all functions that can be called indirectly are marked as roots.
for (auto& segment : module->table.segments) {
for (auto& curr : segment.data) {
roots.emplace_back(ModuleElementKind::Function, curr);
}
}
// Compute reachability starting from the root set.
ReachabilityAnalyzer analyzer(module, roots);
// Remove unreachable elements.
{
auto& v = module->functions;
v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Function>& curr) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Function, curr->name)) == 0;
}), v.end());
}
{
auto& v = module->globals;
v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Global>& curr) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0;
}), v.end());
}
{
auto& v = module->imports;
v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Import>& curr) {
if (curr->kind == ExternalKind::Function) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Function, curr->name)) == 0;
} else if (curr->kind == ExternalKind::Global) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0;
}
return false;
}), v.end());
}
module->updateMaps();
}
void optimizeFunctionTypes(Module* module) {
FunctionTypeAnalyzer analyzer;
analyzer.walkModule(module);
// maps each string signature to a single canonical function type
std::unordered_map<std::string, FunctionType*> canonicals;
std::unordered_set<FunctionType*> needed;
auto canonicalize = [&](Name name) {
if (!name.is()) return name;
FunctionType* type = module->getFunctionType(name);
auto sig = getSig(type);
auto iter = canonicals.find(sig);
if (iter == canonicals.end()) {
needed.insert(type);
canonicals[sig] = type;
return type->name;
} else {
return iter->second->name;
}
};
// canonicalize all uses of function types
for (auto* import : analyzer.functionImports) {
import->functionType = canonicalize(import->functionType);
}
for (auto* func : analyzer.functions) {
func->type = canonicalize(func->type);
}
for (auto* call : analyzer.indirectCalls) {
call->fullType = canonicalize(call->fullType);
}
// remove no-longer used types
module->functionTypes.erase(std::remove_if(module->functionTypes.begin(), module->functionTypes.end(), [&needed](std::unique_ptr<FunctionType>& type) {
return needed.count(type.get()) == 0;
}), module->functionTypes.end());
}
};
Pass* createRemoveUnusedModuleElementsPass() {
return new RemoveUnusedModuleElements();
}
} // namespace wasm
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