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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 branches that go to where they go anyhow
//
#include <wasm.h>
#include <pass.h>
namespace wasm {
struct RemoveUnusedBrs : public Pass {
void visitBlock(Block *curr) override {
if (curr->name.isNull()) return;
if (curr->list.size() == 0) return;
Expression* last = curr->list.back();
if (Break* br = last->dyn_cast<Break>()) {
if (br->condition) return;
if (br->name == curr->name) {
if (!br->value) {
curr->list.pop_back();
} else {
curr->list[curr->list.size()-1] = br->value; // can replace with the value
}
}
} else if (If* ifelse = curr->list.back()->dyn_cast<If>()) {
if (!ifelse->ifFalse) return;
if (ifelse->type != none) return;
// an if_else that indirectly returns a value by breaking to this block can potentially remove both breaks
auto process = [&curr](Expression *side, bool doIt) {
Block* b = side->dyn_cast<Block>();
if (!b) return false;
Expression* last = b->list.back();
Break* br = last->dyn_cast<Break>();
if (!br) return false;
if (br->condition) return false;
if (!br->value) return false;
if (br->name != curr->name) return false;
if (doIt) {
b->list[b->list.size()-1] = br->value;
}
return true;
};
// do both, or none
if (process(ifelse->ifTrue, false) && process(ifelse->ifFalse, false)) {
process(ifelse->ifTrue, true);
process(ifelse->ifFalse, true);
ifelse->type = curr->type; // if_else now returns a value
}
}
}
};
static RegisterPass<RemoveUnusedBrs> registerPass("remove-unused-brs", "removes breaks from locations that are never branched to");
} // namespace wasm
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