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/*
* Copyright 2021 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.
*/
//
// Apply more specific subtypes to signature/function types where possible.
//
// This differs from DeadArgumentElimination's refineArgumentTypes() etc. in
// that DAE will modify the type of a function. It can only do that if the
// function's type is not observable, which means it is not taken by reference.
// On the other hand, this pass will modify the signature types themselves,
// which means it can optimize functions whose reference is taken, and it does
// so while considering all users of the type (across all functions sharing that
// type, and all call_refs using it).
//
// TODO: optimize results too and not just params.
//
#include "ir/find_all.h"
#include "ir/lubs.h"
#include "ir/module-utils.h"
#include "ir/type-updating.h"
#include "pass.h"
#include "wasm-type.h"
#include "wasm.h"
using namespace std;
namespace wasm {
namespace {
struct SignatureRefining : public Pass {
// Maps each heap type to the possible refinement of the types in their
// signatures. We will fill this during analysis and then use it while doing
// an update of the types. If a type has no improvement that we can find, it
// will not appear in this map.
std::unordered_map<HeapType, Signature> newSignatures;
void run(PassRunner* runner, Module* module) override {
if (getTypeSystem() != TypeSystem::Nominal) {
Fatal() << "SignatureRefining requires nominal typing";
}
if (!module->tables.empty()) {
// When there are tables we must also take their types into account, which
// would require us to take call_indirect, element segments, etc. into
// account. For now, do nothing if there are tables.
// TODO
return;
}
// First, find all the calls and call_refs.
struct CallInfo {
std::vector<Call*> calls;
std::vector<CallRef*> callRefs;
};
ModuleUtils::ParallelFunctionAnalysis<CallInfo> analysis(
*module, [&](Function* func, CallInfo& info) {
if (func->imported()) {
return;
}
info.calls = std::move(FindAll<Call>(func->body).list);
info.callRefs = std::move(FindAll<CallRef>(func->body).list);
});
// A map of types to the calls and call_refs that use that type.
std::unordered_map<HeapType, CallInfo> allCallsTo;
// Combine all the information we gathered into that map.
for (auto& [func, info] : analysis.map) {
// For direct calls, add each call to the type of the function being
// called.
for (auto* call : info.calls) {
allCallsTo[module->getFunction(call->target)->type].calls.push_back(
call);
}
// For indirect calls, add each call_ref to the type the call_ref uses.
for (auto* callRef : info.callRefs) {
auto calledType = callRef->target->type;
if (calledType != Type::unreachable) {
allCallsTo[calledType.getHeapType()].callRefs.push_back(callRef);
}
}
}
// Compute optimal LUBs.
std::unordered_set<HeapType> seen;
for (auto& func : module->functions) {
auto type = func->type;
if (!seen.insert(type).second) {
continue;
}
auto sig = type.getSignature();
auto numParams = sig.params.size();
std::vector<LUBFinder> paramLUBs(numParams);
auto updateLUBs = [&](const ExpressionList& operands) {
for (Index i = 0; i < numParams; i++) {
paramLUBs[i].noteUpdatableExpression(operands[i]);
}
};
auto& callsTo = allCallsTo[type];
for (auto* call : callsTo.calls) {
updateLUBs(call->operands);
}
for (auto* callRef : callsTo.callRefs) {
updateLUBs(callRef->operands);
}
// Find the final LUBs, and see if we found an improvement.
std::vector<Type> newParamsTypes;
for (auto& lub : paramLUBs) {
if (!lub.noted()) {
break;
}
newParamsTypes.push_back(lub.getBestPossible());
}
if (newParamsTypes.size() < numParams) {
// We did not have type information to calculate a LUB (no calls, or
// some param is always unreachable), so there is nothing we can improve
// here. Other passes might remove the type entirely.
continue;
}
auto newParams = Type(newParamsTypes);
if (newParams != func->getParams()) {
// We found an improvement!
newSignatures[type] = Signature(newParams, Type::none);
for (auto& lub : paramLUBs) {
lub.updateNulls();
}
}
}
if (newSignatures.empty()) {
// We found nothing to optimize.
return;
}
// Update function contents for their new parameter types.
struct CodeUpdater : public WalkerPass<PostWalker<CodeUpdater>> {
bool isFunctionParallel() override { return true; }
SignatureRefining& parent;
Module& wasm;
CodeUpdater(SignatureRefining& parent, Module& wasm)
: parent(parent), wasm(wasm) {}
CodeUpdater* create() override { return new CodeUpdater(parent, wasm); }
void doWalkFunction(Function* func) {
auto iter = parent.newSignatures.find(func->type);
if (iter != parent.newSignatures.end()) {
std::vector<Type> newParamsTypes;
for (auto param : iter->second.params) {
newParamsTypes.push_back(param);
}
TypeUpdating::updateParamTypes(func, newParamsTypes, wasm);
}
}
};
CodeUpdater(*this, *module).run(runner, module);
// Rewrite the types.
class TypeRewriter : public GlobalTypeRewriter {
SignatureRefining& parent;
public:
TypeRewriter(Module& wasm, SignatureRefining& parent)
: GlobalTypeRewriter(wasm), parent(parent) {}
void modifySignature(HeapType oldSignatureType, Signature& sig) override {
auto iter = parent.newSignatures.find(oldSignatureType);
if (iter != parent.newSignatures.end()) {
sig.params = getTempType(iter->second.params);
}
}
};
TypeRewriter(*module, *this).update();
}
};
} // anonymous namespace
Pass* createSignatureRefiningPass() { return new SignatureRefining(); }
} // namespace wasm
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