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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.
*/
#ifndef wasm_ast_local_graph_h
#define wasm_ast_local_graph_h
namespace wasm {
//
// Finds the connections between get_locals and set_locals, creating
// a graph of those ties. This is useful for "ssa-style" optimization,
// in which you want to know exactly which sets are relevant for a
// a get, so it is as if each get has just one set, logically speaking
// (see the SSA pass for actually creating new local indexes based
// on this).
//
// TODO: the algorithm here is pretty simple, but also pretty slow,
// we should optimize it. e.g. we rely on set_interaction
// here, and worse we only use it to compute the size...
struct LocalGraph : public PostWalker<LocalGraph> {
// main API
// the constructor computes getSetses, the sets affecting each get
LocalGraph(Function* func, Module* module);
// the set_locals relevant for an index or a get.
typedef std::set<SetLocal*> Sets;
// externally useful information
std::map<GetLocal*, Sets> getSetses; // the sets affecting each get. a nullptr set means the initial
// value (0 for a var, the received value for a param)
std::map<Expression*, Expression**> locations; // where each get and set is (for easy replacing)
// optional computation: compute the influence graphs between sets and gets
// (useful for algorithms that propagate changes)
std::unordered_map<GetLocal*, std::unordered_set<SetLocal*>> getInfluences; // for each get, the sets whose values are influenced by that get
std::unordered_map<SetLocal*, std::unordered_set<GetLocal*>> setInfluences; // for each set, the gets whose values are influenced by that set
void computeInfluences();
private:
// we map local index => the set_locals for that index.
// a nullptr set means there is a virtual set, from a param
// initial value or the zero init initial value.
typedef std::vector<Sets> Mapping;
// internal state
Index numLocals;
Mapping currMapping;
std::vector<Mapping> mappingStack; // used in ifs, loops
std::map<Name, std::vector<Mapping>> breakMappings; // break target => infos that reach it
std::vector<std::vector<GetLocal*>> loopGetStack; // stack of loops, all the gets in each, so we can update them for back branches
public:
void doWalkFunction(Function* func);
// control flow
void visitBlock(Block* curr);
void finishIf();
static void afterIfCondition(LocalGraph* self, Expression** currp);
static void afterIfTrue(LocalGraph* self, Expression** currp);
static void afterIfFalse(LocalGraph* self, Expression** currp);
static void beforeLoop(LocalGraph* self, Expression** currp);
void visitLoop(Loop* curr);
void visitBreak(Break* curr);
void visitSwitch(Switch* curr);
void visitReturn(Return *curr);
void visitUnreachable(Unreachable *curr);
// local usage
void visitGetLocal(GetLocal* curr);
void visitSetLocal(SetLocal* curr);
// traversal
static void scan(LocalGraph* self, Expression** currp);
// helpers
void setUnreachable(Mapping& mapping);
bool isUnreachable(Mapping& mapping);
// merges a bunch of infos into one.
// if we need phis, writes them into the provided vector. the caller should
// ensure those are placed in the right location
Mapping& merge(std::vector<Mapping>& mappings);
};
} // namespace wasm
#endif // wasm_ast_local_graph_h
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