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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.
*/
//
// Removes names from locations that are never branched to, and
// merge names when possible (by merging their blocks)
//
#include <ir/branch-utils.h>
#include <pass.h>
#include <shared-constants.h>
#include <wasm.h>
namespace wasm {
struct RemoveUnusedNames
: public WalkerPass<PostWalker<RemoveUnusedNames,
UnifiedExpressionVisitor<RemoveUnusedNames>>> {
bool isFunctionParallel() override { return true; }
// This pass only removes names, which can only help validation (as blocks
// without names are ignored, see the README section on non-nullable locals).
bool requiresNonNullableLocalFixups() override { return false; }
std::unique_ptr<Pass> create() override {
return std::make_unique<RemoveUnusedNames>();
}
// We maintain a list of branches that we saw in children, then when we reach
// a parent block, we know if it was branched to
std::map<Name, std::set<Expression*>> branchesSeen;
void visitExpression(Expression* curr) {
BranchUtils::operateOnScopeNameUses(curr, [&](Name& name) {
if (name.is()) {
branchesSeen[name].insert(curr);
}
});
}
void handleBreakTarget(Name& name) {
if (name.is()) {
if (branchesSeen.find(name) == branchesSeen.end()) {
name = Name();
} else {
branchesSeen.erase(name);
}
}
}
void visitBlock(Block* curr) {
if (curr->name.is() && curr->list.size() == 1) {
auto* child = curr->list[0]->dynCast<Block>();
if (child && child->name.is() && child->type == curr->type) {
// we have just one child, this block, so breaking out of it goes to the
// same place as breaking out of us, we just need one name (and block)
auto& branches = branchesSeen[curr->name];
for (auto* branch : branches) {
BranchUtils::replacePossibleTarget(branch, curr->name, child->name);
}
child->finalize(child->type);
replaceCurrent(child);
}
}
handleBreakTarget(curr->name);
}
void visitLoop(Loop* curr) {
handleBreakTarget(curr->name);
if (!curr->name.is() && curr->body->type == curr->type) {
replaceCurrent(curr->body);
}
}
void visitTry(Try* curr) {
handleBreakTarget(curr->name);
// Try has not just a break target but also an optional delegate with a
// target name, so call the generic visitor as well to handle that.
visitExpression(curr);
}
void visitFunction(Function* curr) {
// When we reach the function body we can erase delegations to the caller.
branchesSeen.erase(DELEGATE_CALLER_TARGET);
assert(branchesSeen.empty());
}
};
Pass* createRemoveUnusedNamesPass() { return new RemoveUnusedNames(); }
} // namespace wasm
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