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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.
*/
#ifndef wasm_ir_reorderer_h
#define wasm_ir_reorderer_h
#include <ir/effects.h>
#include <wasm-builder.h>
namespace wasm {
//
// Given two expressions that appear in a specific order - first and then
// second - this helper can create a sequence in which we return the value of
// the first. If the two expressions can be reordered, this simply returns
//
// (second, first)
//
// If side effects prevent that, it will use a local to save the value of the
// first, and return it at the end,
//
// (temp = first, second, temp)
//
// The first expression is assumed to not be unreachable (otherwise, there is no
// value to get the result of). If the second is unreachable, this returns
// something with type unreachable (that avoids returning something with a
// concrete type, which might replace something with unreachable type - we want
// to keep the type the same, in most cases).
inline Expression* getResultOfFirst(Expression* first,
Expression* second,
Function* func,
Module* wasm,
const PassOptions& passOptions) {
assert(first->type.isConcrete());
Builder builder(*wasm);
if (second->type == Type::unreachable) {
// No value is actually consumed here. Emit something with unreachable type.
// (Note that if we continued to the canReorder code after us, and emitted
// second followed by first, then the block would have a concrete type due
// to the last element having such a type - which would not have unreachable
// type.)
return builder.makeSequence(builder.makeDrop(first), second);
}
if (EffectAnalyzer::canReorder(passOptions, *wasm, first, second)) {
return builder.makeSequence(second, first);
}
auto type = first->type;
auto index = Builder::addVar(func, type);
return builder.makeBlock({builder.makeLocalSet(index, first),
second,
builder.makeLocalGet(index, type)});
}
} // namespace wasm
#endif // wasm_ir_reorderer_h
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