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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.
*/
//
// Sorts locals by access frequency.
//
// Secondarily, sort by first appearance. This canonicalizes the order.
//
// While sorting, we remove locals that have no uses at all.
//
#include <memory>
#include <wasm.h>
#include <pass.h>
namespace wasm {
struct ReorderLocals : public WalkerPass<PostWalker<ReorderLocals>> {
bool isFunctionParallel() override { return true; }
Pass* create() override { return new ReorderLocals; }
std::map<Index, Index> counts; // local => times it is used
std::map<Index, Index> firstUses; // local => index in the list of which local is first seen
void visitFunction(Function *curr) {
Index num = curr->getNumLocals();
std::vector<Index> newToOld;
for (size_t i = 0; i < num; i++) {
newToOld.push_back(i);
}
// sort, keeping params in front (where they will not be moved)
sort(newToOld.begin(), newToOld.end(), [this, curr](Index a, Index b) -> bool {
if (curr->isParam(a) && !curr->isParam(b)) return true;
if (curr->isParam(b) && !curr->isParam(a)) return false;
if (curr->isParam(b) && curr->isParam(a)) {
return a < b;
}
if (counts[a] == counts[b]) {
if (counts[a] == 0) return a < b;
return firstUses[a] < firstUses[b];
}
return counts[a] > counts[b];
});
// sorting left params in front, perhaps slightly reordered. verify and fix.
for (size_t i = 0; i < curr->params.size(); i++) {
assert(newToOld[i] < curr->params.size());
}
for (size_t i = 0; i < curr->params.size(); i++) {
newToOld[i] = i;
}
// sort vars, and drop unused ones
auto oldVars = curr->vars;
curr->vars.clear();
for (size_t i = curr->getVarIndexBase(); i < newToOld.size(); i++) {
Index index = newToOld[i];
if (counts[index] > 0) {
curr->vars.push_back(oldVars[index - curr->getVarIndexBase()]);
} else {
newToOld.resize(i);
break;
}
}
counts.clear();
std::vector<Index> oldToNew;
oldToNew.resize(num);
for (size_t i = 0; i < newToOld.size(); i++) {
if (curr->isParam(i)) {
oldToNew[i] = i;
} else {
oldToNew[newToOld[i]] = i;
}
}
// apply the renaming to AST nodes
struct ReIndexer : public PostWalker<ReIndexer> {
Function* func;
std::vector<Index>& oldToNew;
ReIndexer(Function* func, std::vector<Index>& oldToNew) : func(func), oldToNew(oldToNew) {}
void visitGetLocal(GetLocal *curr) {
if (func->isVar(curr->index)) {
curr->index = oldToNew[curr->index];
}
}
void visitSetLocal(SetLocal *curr) {
if (func->isVar(curr->index)) {
curr->index = oldToNew[curr->index];
}
}
};
ReIndexer reIndexer(curr, oldToNew);
reIndexer.walk(curr->body);
// apply to the names
auto oldLocalNames = curr->localNames;
auto oldLocalIndices = curr->localIndices;
curr->localNames.clear();
curr->localIndices.clear();
for (size_t i = 0; i < newToOld.size(); i++) {
if (newToOld[i] < oldLocalNames.size()) {
auto old = oldLocalNames[newToOld[i]];
curr->localNames[i] = old;
curr->localIndices[old] = i;
}
}
}
void visitGetLocal(GetLocal *curr) {
counts[curr->index]++;
if (firstUses.count(curr->index) == 0) {
firstUses[curr->index] = firstUses.size();
}
}
void visitSetLocal(SetLocal *curr) {
counts[curr->index]++;
if (firstUses.count(curr->index) == 0) {
firstUses[curr->index] = firstUses.size();
}
}
};
Pass *createReorderLocalsPass() {
return new ReorderLocals();
}
} // namespace wasm
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