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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_ast_branch_h
#define wasm_ast_branch_h
#include "wasm.h"
#include "wasm-traversal.h"
namespace wasm {
namespace BranchUtils {
// branches not actually taken (e.g. (br $out (unreachable)))
// are trivially ignored in our type system
inline bool isBranchTaken(Break* br) {
return !(br->value && br->value->type == unreachable) &&
!(br->condition && br->condition->type == unreachable);
}
inline bool isBranchTaken(Switch* sw) {
return !(sw->value && sw->value->type == unreachable) &&
sw->condition->type != unreachable;
}
inline bool isBranchTaken(Expression* expr) {
if (auto* br = expr->dynCast<Break>()) {
return isBranchTaken(br);
} else if (auto* sw = expr->dynCast<Switch>()) {
return isBranchTaken(sw);
}
WASM_UNREACHABLE();
}
// returns the set of targets to which we branch that are
// outside of a node
inline std::set<Name> getExitingBranches(Expression* ast) {
struct Scanner : public PostWalker<Scanner> {
std::set<Name> targets;
void visitBreak(Break* curr) {
targets.insert(curr->name);
}
void visitSwitch(Switch* curr) {
for (auto target : targets) {
targets.insert(target);
}
targets.insert(curr->default_);
}
void visitBlock(Block* curr) {
if (curr->name.is()) {
targets.erase(curr->name);
}
}
void visitLoop(Loop* curr) {
if (curr->name.is()) {
targets.erase(curr->name);
}
}
};
Scanner scanner;
scanner.walk(ast);
// anything not erased is a branch out
return scanner.targets;
}
// returns the list of all branch targets in a node
inline std::set<Name> getBranchTargets(Expression* ast) {
struct Scanner : public PostWalker<Scanner> {
std::set<Name> targets;
void visitBlock(Block* curr) {
if (curr->name.is()) {
targets.insert(curr->name);
}
}
void visitLoop(Loop* curr) {
if (curr->name.is()) {
targets.insert(curr->name);
}
}
};
Scanner scanner;
scanner.walk(ast);
return scanner.targets;
}
// Finds if there are branches targeting a name. Note that since names are
// unique in our IR, we just need to look for the name, and do not need
// to analyze scoping.
// By default we consider untaken branches (so any named use). You can unset named to
// avoid that (and only note branches that are not obviously unreachable)
struct BranchSeeker : public PostWalker<BranchSeeker> {
Name target;
bool named = true;
Index found;
WasmType valueType;
BranchSeeker(Name target) : target(target), found(0) {}
void noteFound(Expression* value) {
found++;
if (found == 1) valueType = unreachable;
if (!value) valueType = none;
else if (value->type != unreachable) valueType = value->type;
}
void visitBreak(Break *curr) {
if (!named) {
// ignore an unreachable break
if (curr->condition && curr->condition->type == unreachable) return;
if (curr->value && curr->value->type == unreachable) return;
}
// check the break
if (curr->name == target) noteFound(curr->value);
}
void visitSwitch(Switch *curr) {
if (!named) {
// ignore an unreachable switch
if (curr->condition->type == unreachable) return;
if (curr->value && curr->value->type == unreachable) return;
}
// check the switch
for (auto name : curr->targets) {
if (name == target) noteFound(curr->value);
}
if (curr->default_ == target) noteFound(curr->value);
}
static bool hasTaken(Expression* tree, Name target) {
if (!target.is()) return false;
BranchSeeker seeker(target);
seeker.named = false;
seeker.walk(tree);
return seeker.found > 0;
}
static Index countTaken(Expression* tree, Name target) {
if (!target.is()) return 0;
BranchSeeker seeker(target);
seeker.named = false;
seeker.walk(tree);
return seeker.found;
}
static bool hasNamed(Expression* tree, Name target) {
if (!target.is()) return false;
BranchSeeker seeker(target);
seeker.walk(tree);
return seeker.found > 0;
}
static Index countNamed(Expression* tree, Name target) {
if (!target.is()) return 0;
BranchSeeker seeker(target);
seeker.walk(tree);
return seeker.found;
}
};
} // namespace BranchUtils
} // namespace wasm
#endif // wasm_ast_branch_h
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