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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_ir_local_graph_h
#define wasm_ir_local_graph_h
namespace wasm {
//
// Finds the connections between local.gets and local.sets, 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).
//
struct LocalGraph {
// main API
// the constructor computes getSetses, the sets affecting each get
LocalGraph(Function* func);
// the local.sets relevant for an index or a get.
typedef std::set<SetLocal*> Sets;
typedef std::map<GetLocal*, Sets> GetSetses;
typedef std::map<Expression*, Expression**> Locations;
// externally useful information
GetSetses getSetses; // the sets affecting each get. a nullptr set means the initial
// value (0 for a var, the received value for a param)
Locations locations; // where each get and set is (for easy replacing)
// Optional: compute the influence graphs between sets and gets
// (useful for algorithms that propagate changes).
void computeInfluences();
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
// Optional: Compute the local indexes that are SSA, in the sense of
// * a single set for all the gets for that local index
// * the set dominates all the gets (logically implied by the former property)
// * no other set (aside from the zero-init)
// The third property is not exactly standard SSA, but is useful since we are not in
// SSA form in our IR. To see why it matters, consider these:
//
// x = 0 // zero init
// [..]
// x = 10
// y = x + 20
// x = 30 // !!!
// f(y)
//
// The !!! line violates that property - it is another set for x, and it may interfere
// say with replacing f(y) with f(x + 20). Instead, if we know the only other possible set for x
// is the zero init, then things like the !!! line cannot exist, and it is valid to replace
// f(y) with f(x + 20).
// (This could be simpler, but in wasm the zero init always exists.)
void computeSSAIndexes();
bool isSSA(Index x);
private:
std::set<Index> SSAIndexes;
};
} // namespace wasm
#endif // wasm_ir_local_graph_h
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