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/*
* Copyright 2017 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.
*/
// Avoids reinterprets by using more loads: if we load a value and
// reinterpret it, we could have loaded it with the other type
// anyhow. This uses more locals and loads, so it is not generally
// beneficial, unless reinterprets are very costly.
#include <ir/local-graph.h>
#include <ir/properties.h>
#include <pass.h>
#include <wasm-builder.h>
#include <wasm.h>
namespace wasm {
static Load* getSingleLoad(LocalGraph* localGraph, GetLocal* get) {
while (1) {
auto& sets = localGraph->getSetses[get];
if (sets.size() != 1) {
return nullptr;
}
auto* set = *sets.begin();
if (!set) {
return nullptr;
}
auto* value = Properties::getFallthrough(set->value);
if (auto* parentGet = value->dynCast<GetLocal>()) {
get = parentGet;
continue;
}
if (auto* load = value->dynCast<Load>()) {
return load;
}
return nullptr;
}
}
static bool isReinterpret(Unary* curr) {
return curr->op == ReinterpretInt32 || curr->op == ReinterpretInt64 ||
curr->op == ReinterpretFloat32 || curr->op == ReinterpretFloat64;
}
struct AvoidReinterprets : public WalkerPass<PostWalker<AvoidReinterprets>> {
bool isFunctionParallel() override { return true; }
Pass* create() override { return new AvoidReinterprets; }
struct Info {
// Info used when analyzing.
bool reinterpreted;
// Info used when optimizing.
Index ptrLocal;
Index reinterpretedLocal;
};
std::map<Load*, Info> infos;
LocalGraph* localGraph;
void doWalkFunction(Function* func) {
// prepare
LocalGraph localGraph_(func);
localGraph = &localGraph_;
// walk
PostWalker<AvoidReinterprets>::doWalkFunction(func);
// optimize
optimize(func);
}
void visitUnary(Unary* curr) {
if (isReinterpret(curr)) {
if (auto* get =
Properties::getFallthrough(curr->value)->dynCast<GetLocal>()) {
if (auto* load = getSingleLoad(localGraph, get)) {
auto& info = infos[load];
info.reinterpreted = true;
}
}
}
}
void optimize(Function* func) {
std::set<Load*> unoptimizables;
for (auto& pair : infos) {
auto* load = pair.first;
auto& info = pair.second;
if (info.reinterpreted && load->type != unreachable) {
// We should use another load here, to avoid reinterprets.
info.ptrLocal = Builder::addVar(func, i32);
info.reinterpretedLocal =
Builder::addVar(func, reinterpretType(load->type));
} else {
unoptimizables.insert(load);
}
}
for (auto* load : unoptimizables) {
infos.erase(load);
}
// We now know which we can optimize, and how.
struct FinalOptimizer : public PostWalker<FinalOptimizer> {
std::map<Load*, Info>& infos;
LocalGraph* localGraph;
Module* module;
FinalOptimizer(std::map<Load*, Info>& infos,
LocalGraph* localGraph,
Module* module)
: infos(infos), localGraph(localGraph), module(module) {}
void visitUnary(Unary* curr) {
if (isReinterpret(curr)) {
auto* value = Properties::getFallthrough(curr->value);
if (auto* load = value->dynCast<Load>()) {
// A reinterpret of a load - flip it right here.
replaceCurrent(makeReinterpretedLoad(load, load->ptr));
} else if (auto* get = value->dynCast<GetLocal>()) {
if (auto* load = getSingleLoad(localGraph, get)) {
auto iter = infos.find(load);
if (iter != infos.end()) {
auto& info = iter->second;
// A reinterpret of a get of a load - use the new local.
Builder builder(*module);
replaceCurrent(builder.makeGetLocal(
info.reinterpretedLocal, reinterpretType(load->type)));
}
}
}
}
}
void visitLoad(Load* curr) {
auto iter = infos.find(curr);
if (iter != infos.end()) {
auto& info = iter->second;
Builder builder(*module);
auto* ptr = curr->ptr;
curr->ptr = builder.makeGetLocal(info.ptrLocal, i32);
// Note that the other load can have its sign set to false - if the
// original were an integer, the other is a float anyhow; and if
// original were a float, we don't know what sign to use.
replaceCurrent(builder.makeBlock(
{builder.makeSetLocal(info.ptrLocal, ptr),
builder.makeSetLocal(
info.reinterpretedLocal,
makeReinterpretedLoad(curr,
builder.makeGetLocal(info.ptrLocal, i32))),
curr}));
}
}
Load* makeReinterpretedLoad(Load* load, Expression* ptr) {
Builder builder(*module);
return builder.makeLoad(load->bytes,
false,
load->offset,
load->align,
ptr,
reinterpretType(load->type));
}
} finalOptimizer(infos, localGraph, getModule());
finalOptimizer.walk(func->body);
}
};
Pass* createAvoidReinterpretsPass() { return new AvoidReinterprets(); }
} // namespace wasm
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