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/*
* Copyright 2016 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_utils_h
#define wasm_ast_utils_h
#include "wasm.h"
#include "wasm-traversal.h"
namespace wasm {
struct BreakSeeker : public PostWalker<BreakSeeker, Visitor<BreakSeeker>> {
Name target; // look for this one XXX looking by name may fall prey to duplicate names
size_t found;
BreakSeeker(Name target) : target(target), found(false) {}
void visitBreak(Break *curr) {
if (curr->name == target) found++;
}
void visitSwitch(Switch *curr) {
for (auto name : curr->targets) {
if (name == target) found++;
}
if (curr->default_ == target) found++;
}
static bool has(Expression* tree, Name target) {
BreakSeeker breakSeeker(target);
breakSeeker.walk(tree);
return breakSeeker.found > 0;
}
};
// Look for side effects, including control flow
// TODO: optimize
struct EffectAnalyzer : public PostWalker<EffectAnalyzer, Visitor<EffectAnalyzer>> {
EffectAnalyzer() {}
EffectAnalyzer(Expression *ast) {
walk(ast);
}
bool branches = false;
bool calls = false;
std::set<Index> localsRead;
std::set<Index> localsWritten;
bool readsMemory = false;
bool writesMemory = false;
bool accessesLocal() { return localsRead.size() + localsWritten.size() > 0; }
bool accessesMemory() { return calls || readsMemory || writesMemory; }
bool hasSideEffects() { return calls || localsWritten.size() > 0 || writesMemory || branches; }
bool hasAnything() { return branches || calls || accessesLocal() || readsMemory || writesMemory; }
// checks if these effects would invalidate another set (e.g., if we write, we invalidate someone that reads, they can't be moved past us)
bool invalidates(EffectAnalyzer& other) {
if (branches || other.branches
|| ((writesMemory || calls) && other.accessesMemory())
|| (accessesMemory() && (other.writesMemory || other.calls))) {
return true;
}
assert(localsWritten.size() + localsRead.size() <= 1); // the code below is fast on that case, of one element vs many
for (auto local : localsWritten) {
if (other.localsWritten.count(local) || other.localsRead.count(local)) {
return true;
}
}
for (auto local : localsRead) {
if (other.localsWritten.count(local)) return true;
}
return false;
}
// the checks above happen after the node's children were processed, in the order of execution
// we must also check for control flow that happens before the children, i.e., loops
bool checkPre(Expression* curr) {
if (curr->is<Loop>()) {
branches = true;
return true;
}
return false;
}
bool checkPost(Expression* curr) {
visit(curr);
return hasAnything();
}
void visitIf(If *curr) { branches = true; }
void visitBreak(Break *curr) { branches = true; }
void visitSwitch(Switch *curr) { branches = true; }
void visitCall(Call *curr) { calls = true; }
void visitCallImport(CallImport *curr) { calls = true; }
void visitCallIndirect(CallIndirect *curr) { calls = true; }
void visitGetLocal(GetLocal *curr) {
localsRead.insert(curr->index);
}
void visitSetLocal(SetLocal *curr) {
localsWritten.insert(curr->index);
}
void visitLoad(Load *curr) { readsMemory = true; }
void visitStore(Store *curr) { writesMemory = true; }
void visitReturn(Return *curr) { branches = true; }
void visitHost(Host *curr) { calls = true; }
void visitUnreachable(Unreachable *curr) { branches = true; }
};
// Meausure the size of an AST
struct Measurer : public PostWalker<Measurer, UnifiedExpressionVisitor<Measurer>> {
size_t size = 0;
void visitExpression(Expression* curr) {
size++;
}
static bool measure(Expression* tree) {
Measurer measurer;
measurer.walk(tree);
return measurer.size;
}
};
// Manipulate expressions
struct ExpressionManipulator {
// Re-use a node's memory. This helps avoid allocation when optimizing.
template<typename InputType, typename OutputType>
static OutputType* convert(InputType *input) {
static_assert(sizeof(OutputType) <= sizeof(InputType),
"Can only convert to a smaller size Expression node");
input->~InputType(); // arena-allocaed, so no destructor, but avoid UB.
OutputType* output = (OutputType*)(input);
new (output) OutputType;
return output;
}
// Convenience method for nop, which is a common conversion
template<typename InputType>
static void nop(InputType* target) {
convert<InputType, Nop>(target);
}
// Convert a node that allocates
template<typename InputType, typename OutputType>
static OutputType* convert(InputType *input, MixedArena& allocator) {
assert(sizeof(OutputType) <= sizeof(InputType));
input->~InputType(); // arena-allocaed, so no destructor, but avoid UB.
OutputType* output = (OutputType*)(input);
new (output) OutputType(allocator);
return output;
}
};
struct ExpressionAnalyzer {
// Given a stack of expressions, checks if the topmost is used as a result.
// For example, if the parent is a block and the node is before the last position,
// it is not used.
static bool isResultUsed(std::vector<Expression*> stack, Function* func) {
for (int i = int(stack.size()) - 2; i >= 0; i--) {
auto* curr = stack[i];
auto* above = stack[i + 1];
// only if and block can drop values
if (curr->is<Block>()) {
auto* block = curr->cast<Block>();
for (size_t j = 0; j < block->list.size() - 1; j++) {
if (block->list[j] == above) return false;
}
assert(block->list.back() == above);
// continue down
} else if (curr->is<If>()) {
auto* iff = curr->cast<If>();
if (!iff->ifFalse) return false;
if (above == iff->condition) return true;
assert(above == iff->ifTrue || above == iff->ifFalse);
// continue down
} else {
return true; // all other node types use the result
}
}
// The value might be used, so it depends on if the function returns
return func->result != none;
}
};
} // namespace wasm
#endif // wasm_ast_utils_h
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