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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.
*/
#include <iterator>
#include <wasm-builder.h>
#include <wasm-printing.h>
#include <ir/find_all.h>
#include <ir/local-graph.h>
#include <cfg/cfg-traversal.h>
namespace wasm {
namespace LocalGraphInternal {
// A relevant action. Supports a get, a set, or an
// "other" which can be used for other purposes, to mark
// their position in a block
struct Action {
enum What {
Get = 0,
Set = 1
};
What what;
Index index; // the local index read or written
Expression* expr; // the expression itself
Action(What what, Index index, Expression* expr) : what(what), index(index), expr(expr) {
if (what == Get) assert(expr->is<GetLocal>());
if (what == Set) assert(expr->is<SetLocal>());
}
bool isGet() { return what == Get; }
bool isSet() { return what == Set; }
};
// information about a basic block
struct Info {
std::vector<Action> actions; // actions occurring in this block
std::vector<SetLocal*> lastSets; // for each index, the last set_local for it
void dump(Function* func) {
if (actions.empty()) return;
std::cout << " actions:\n";
for (auto& action : actions) {
std::cout << " " << (action.isGet() ? "get" : "set") << " " << func->getLocalName(action.index) << "\n";
}
}
};
// flow helper class. flows the gets to their sets
struct Flower : public CFGWalker<Flower, Visitor<Flower>, Info> {
LocalGraph::GetSetses& getSetses;
LocalGraph::Locations& locations;
Flower(LocalGraph::GetSetses& getSetses, LocalGraph::Locations& locations, Function* func) : getSetses(getSetses), locations(locations) {
setFunction(func);
// create the CFG by walking the IR
CFGWalker<Flower, Visitor<Flower>, Info>::doWalkFunction(func);
// flow gets across blocks
flow(func);
}
BasicBlock* makeBasicBlock() {
auto* ret = new BasicBlock();
auto& lastSets = ret->contents.lastSets;
lastSets.resize(getFunction()->getNumLocals());
std::fill(lastSets.begin(), lastSets.end(), nullptr);
return ret;
}
// cfg traversal work
static void doVisitGetLocal(Flower* self, Expression** currp) {
auto* curr = (*currp)->cast<GetLocal>();
// if in unreachable code, skip
if (!self->currBasicBlock) return;
self->currBasicBlock->contents.actions.emplace_back(Action::Get, curr->index, curr);
self->locations[curr] = currp;
}
static void doVisitSetLocal(Flower* self, Expression** currp) {
auto* curr = (*currp)->cast<SetLocal>();
// if in unreachable code, skip
if (!self->currBasicBlock) return;
self->currBasicBlock->contents.actions.emplace_back(Action::Set, curr->index, curr);
self->currBasicBlock->contents.lastSets[curr->index] = curr;
self->locations[curr] = currp;
}
void flow(Function* func) {
auto numLocals = func->getNumLocals();
std::vector<std::vector<GetLocal*>> allGets;
allGets.resize(numLocals);
std::unordered_set<BasicBlock*> seen;
std::vector<BasicBlock*> work;
for (auto& block : basicBlocks) {
#ifdef LOCAL_GRAPH_DEBUG
std::cout << "basic block " << block.get() << " :\n";
for (auto& action : block->contents.actions) {
std::cout << " action: " << action.expr << '\n';
}
for (auto* lastSet : block->contents.lastSets) {
std::cout << " last set " << lastSet << '\n';
}
#endif
// go through the block, finding each get and adding it to its index,
// and seeing how sets affect that
auto& actions = block->contents.actions;
// move towards the front, handling things as we go
for (int i = int(actions.size()) - 1; i >= 0; i--) {
auto& action = actions[i];
auto index = action.index;
if (action.isGet()) {
allGets[index].push_back(action.expr->cast<GetLocal>());
} else {
// this set is the only set for all those gets
auto* set = action.expr->cast<SetLocal>();
auto& gets = allGets[index];
for (auto* get : gets) {
getSetses[get].insert(set);
}
gets.clear();
}
}
// if anything is left, we must flow it back through other blocks. we
// can do that for all gets as a whole, they will get the same results
for (Index index = 0; index < numLocals; index++) {
auto& gets = allGets[index];
if (gets.empty()) continue;
work.push_back(block.get());
seen.clear();
// note that we may need to revisit the later parts of this initial
// block, if we are in a loop, so don't mark it as seen
while (!work.empty()) {
auto* curr = work.back();
work.pop_back();
// we have gone through this block; now we must handle flowing to
// the inputs
if (curr->in.empty()) {
if (curr == entry) {
// these receive a param or zero init value
for (auto* get : gets) {
getSetses[get].insert(nullptr);
}
}
} else {
for (auto* pred : curr->in) {
if (seen.count(pred)) continue;
seen.insert(pred);
auto* lastSet = pred->contents.lastSets[index];
if (lastSet) {
// there is a set here, apply it, and stop the flow
for (auto* get : gets) {
getSetses[get].insert(lastSet);
}
} else {
// keep on flowing
work.push_back(pred);
}
}
}
}
gets.clear();
}
}
}
};
} // namespace LocalGraphInternal
// LocalGraph implementation
LocalGraph::LocalGraph(Function* func) {
LocalGraphInternal::Flower flower(getSetses, locations, func);
#ifdef LOCAL_GRAPH_DEBUG
std::cout << "LocalGraph::dump\n";
for (auto& pair : getSetses) {
auto* get = pair.first;
auto& sets = pair.second;
std::cout << "GET\n" << get << " is influenced by\n";
for (auto* set : sets) {
std::cout << set << '\n';
}
}
std::cout << "total locations: " << locations.size() << '\n';
#endif
}
void LocalGraph::computeInfluences() {
for (auto& pair : locations) {
auto* curr = pair.first;
if (auto* set = curr->dynCast<SetLocal>()) {
FindAll<GetLocal> findAll(set->value);
for (auto* get : findAll.list) {
getInfluences[get].insert(set);
}
} else {
auto* get = curr->cast<GetLocal>();
for (auto* set : getSetses[get]) {
setInfluences[set].insert(get);
}
}
}
}
} // namespace wasm
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