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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 functions by their static use count. This helps reduce the size of wasm
// binaries because fewer bytes are needed to encode references to frequently
// used functions.
//
// This may incur a tradeoff, though, as while it reduces binary size, it may
// increase gzip size. This might be because the new order has the functions in
// a less beneficial position for compression, that is, mutually-compressible
// functions are no longer together (when they were before, in the original
// order, the has some natural tendency one way or the other). TODO: investigate
// similarity ordering here (see #4322)
//
#include <memory>
#include <ir/element-utils.h>
#include <pass.h>
#include <wasm.h>
namespace wasm {
using NameCountMap = std::unordered_map<Name, std::atomic<Index>>;
struct CallCountScanner : public WalkerPass<PostWalker<CallCountScanner>> {
bool isFunctionParallel() override { return true; }
bool modifiesBinaryenIR() override { return false; }
CallCountScanner(NameCountMap* counts) : counts(counts) {}
std::unique_ptr<Pass> create() override {
return std::make_unique<CallCountScanner>(counts);
}
void visitCall(Call* curr) {
// can't add a new element in parallel
assert(counts->count(curr->target) > 0);
(*counts)[curr->target]++;
}
private:
NameCountMap* counts;
};
struct ReorderFunctions : public Pass {
// Only reorders functions, does not change their contents.
bool requiresNonNullableLocalFixups() override { return false; }
void run(Module* module) override {
NameCountMap counts;
// fill in info, as we operate on it in parallel (each function to its own
// entry)
for (auto& func : module->functions) {
counts[func->name];
}
// find counts on function calls
CallCountScanner(&counts).run(getPassRunner(), module);
// find counts on global usages
if (module->start.is()) {
counts[module->start]++;
}
for (auto& curr : module->exports) {
counts[curr->value]++;
}
ElementUtils::iterAllElementFunctionNames(
module, [&](Name& name) { counts[name]++; });
// TODO: count all RefFunc as well
// TODO: count the declaration section as well, which adds another mention
// sort
std::sort(module->functions.begin(),
module->functions.end(),
[&counts](const std::unique_ptr<Function>& a,
const std::unique_ptr<Function>& b) -> bool {
if (counts[a->name] == counts[b->name]) {
return a->name > b->name;
}
return counts[a->name] > counts[b->name];
});
}
};
Pass* createReorderFunctionsPass() { return new ReorderFunctions(); }
struct ReorderFunctionsByName : public Pass {
// Only reorders functions, does not change their contents.
bool requiresNonNullableLocalFixups() override { return false; }
void run(Module* module) override {
std::sort(module->functions.begin(),
module->functions.end(),
[](const std::unique_ptr<Function>& a,
const std::unique_ptr<Function>& b) -> bool {
return a->name < b->name;
});
}
};
Pass* createReorderFunctionsByNamePass() {
return new ReorderFunctionsByName();
}
} // namespace wasm
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