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/*
* Copyright 2015 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.
*/
//
// Locals-related optimizations
//
// This "sinks" set_locals, pushing them to the next get_local where possible
#include <wasm.h>
#include <wasm-traversal.h>
#include <pass.h>
#include <ast_utils.h>
namespace wasm {
struct SimplifyLocals : public WalkerPass<LinearExecutionWalker<SimplifyLocals>> {
struct SinkableInfo {
Expression** item;
EffectAnalyzer effects;
SinkableInfo(Expression** item) : item(item) {
effects.walk(*item);
}
};
// locals in current linear execution trace, which we try to sink
std::map<Name, SinkableInfo> sinkables;
void noteNonLinear() {
sinkables.clear();
}
void visitGetLocal(GetLocal *curr) {
auto found = sinkables.find(curr->name);
if (found != sinkables.end()) {
// sink it, and nop the origin TODO: clean up nops
replaceCurrent(*found->second.item);
// reuse the getlocal that is dying
*found->second.item = curr;
ExpressionManipulator::nop(curr);
sinkables.erase(found);
}
}
void visitSetLocal(SetLocal *curr) {
// if we are a potentially-sinkable thing, forget it - this
// write overrides the last TODO: optimizable
// TODO: if no get_locals left, can remove the set as well (== expressionizer in emscripten optimizer)
auto found = sinkables.find(curr->name);
if (found != sinkables.end()) {
sinkables.erase(found);
}
}
void checkInvalidations(EffectAnalyzer& effects) {
// TODO: this is O(bad)
std::vector<Name> invalidated;
for (auto& sinkable : sinkables) {
if (effects.invalidates(sinkable.second.effects)) {
invalidated.push_back(sinkable.first);
}
}
for (auto name : invalidated) {
sinkables.erase(name);
}
}
static void visitPre(SimplifyLocals* self, Expression** currp) {
EffectAnalyzer effects;
if (effects.checkPre(*currp)) {
self->checkInvalidations(effects);
}
}
static void visitPost(SimplifyLocals* self, Expression** currp) {
EffectAnalyzer effects;
if (effects.checkPost(*currp)) {
self->checkInvalidations(effects);
}
}
static void tryMarkSinkable(SimplifyLocals* self, Expression** currp) {
auto* curr = (*currp)->dyn_cast<SetLocal>();
if (curr) {
Name name = curr->name;
assert(self->sinkables.count(name) == 0);
self->sinkables.emplace(std::make_pair(name, SinkableInfo(currp)));
}
}
// override scan to add a pre and a post check task to all nodes
static void scan(SimplifyLocals* self, Expression** currp) {
self->pushTask(visitPost, currp);
auto* curr = *currp;
if (curr->is<Block>()) {
// special-case blocks, by marking their children as locals.
// TODO sink from elsewhere? (need to make sure value is not used)
self->pushTask(SimplifyLocals::doNoteNonLinear, currp);
auto& list = curr->cast<Block>()->list;
int size = list.size();
// we can't sink the last element, as it might be a return value;
// and anyhow, control flow is nonlinear at the end of the block so
// it would be invalidated.
for (int i = size - 1; i >= 0; i--) {
if (i < size - 1) {
self->pushTask(tryMarkSinkable, &list[i]);
}
self->pushTask(scan, &list[i]);
}
} else {
WalkerPass<LinearExecutionWalker<SimplifyLocals>>::scan(self, currp);
}
self->pushTask(visitPre, currp);
}
};
static RegisterPass<SimplifyLocals> registerPass("simplify-locals", "miscellaneous locals-related optimizations");
} // namespace wasm
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