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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.
*/
// Optimize relooper-generated label variable usage: add blocks and turn
// a label-set/break/label-check into a break into the new block.
// This assumes the very specific output the fastcomp relooper emits,
// including the name of the 'label' variable.
#include "wasm.h"
#include "pass.h"
#include "ast_utils.h"
namespace wasm {
static Name LABEL("label");
// We need to use new label names, which we cannot create in parallel, so pre-create them
const Index MAX_NAME_INDEX = 1000;
std::vector<Name>* innerNames = nullptr;
std::vector<Name>* outerNames = nullptr;
struct NameEnsurer {
NameEnsurer() {
assert(!innerNames);
assert(!outerNames);
innerNames = new std::vector<Name>;
outerNames = new std::vector<Name>;
for (Index i = 0; i < MAX_NAME_INDEX; i++) {
innerNames->push_back(Name(std::string("jumpthreading$inner$") + std::to_string(i)));
outerNames->push_back(Name(std::string("jumpthreading$outer$") + std::to_string(i)));
}
}
};
struct RelooperJumpThreading : public WalkerPass<ExpressionStackWalker<RelooperJumpThreading, Visitor<RelooperJumpThreading>>> {
bool isFunctionParallel() override { return true; }
Pass* create() override { return new RelooperJumpThreading; }
void prepareToRun(PassRunner* runner, Module* module) override {
static NameEnsurer ensurer;
}
Index labelIndex;
Index newNameCounter = 0;
void visitBlock(Block* curr) {
// look for the if label == X pattern
auto& list = curr->list;
if (list.size() == 0) return;
for (Index i = 0; i < list.size() - 1; i++) {
Index origin = i;
for (Index j = i + 1; j < list.size(); j++) {
if (auto* iff = isLabelCheckingIf(list[j])) {
optimizeJumpsToLabelCheck(list[origin], iff);
ExpressionManipulator::nop(iff);
i++;
continue;
}
// if the next element is a block, it may be the holding block of label-checking ifs
if (auto* holder = list[j]->dynCast<Block>()) {
if (holder->list.size() > 0) {
if (If* iff = isLabelCheckingIf(holder->list[0])) {
// this is indeed a holder. we can process the ifs, and must also move
// the block to enclose the origin, so it is properly reachable
assert(holder->list.size() == 1); // must be size 1, a relooper multiple will have its own label, and is an if-else sequence and nothing more
optimizeJumpsToLabelCheck(list[origin], iff);
holder->list[0] = list[origin];
list[origin] = holder;
// reuse the if as a nop
list[j] = iff;
ExpressionManipulator::nop(iff);
i++;
continue;
}
}
}
break; // we didn't see something we like, so stop here
}
}
}
void doWalkFunction(Function* func) {
// if there isn't a label variable, nothing for us to do
if (func->localIndices.count(LABEL)) {
labelIndex = func->getLocalIndex(LABEL);
WalkerPass<ExpressionStackWalker<RelooperJumpThreading, Visitor<RelooperJumpThreading>>>::doWalkFunction(func);
}
}
private:
If* isLabelCheckingIf(Expression* curr) {
auto* iff = curr->dynCast<If>();
if (!iff) return nullptr;
auto* condition = iff->condition->dynCast<Binary>();
if (!(condition && condition->op == EqInt32)) return nullptr;
auto* left = condition->left->dynCast<GetLocal>();
if (!(left && left->index == labelIndex)) return nullptr;
return iff;
}
// optimizes jumps to a label check
// * origin is where the jumps originate, and also where we should write our output
// * iff is the if
void optimizeJumpsToLabelCheck(Expression*& origin, If* iff) {
Index nameCounter = newNameCounter++;
if (nameCounter >= MAX_NAME_INDEX) {
std::cerr << "too many names in RelooperJumpThreading :(\n";
return;
}
Index num = iff->condition->cast<Binary>()->right->cast<Const>()->value.geti32();
// create a new block for this jump target
Builder builder(*getModule());
// origin is where all jumps to this target must come from - the element right before this if
// we break out of inner to reach the target. instead of flowing out of normally, we break out of the outer, so we skip the target.
auto innerName = innerNames->at(nameCounter);
auto outerName = outerNames->at(nameCounter);
auto* ifFalse = iff->ifFalse;
// all assignments of label to the target can be replaced with breaks to the target, via innerName
struct JumpUpdater : public PostWalker<JumpUpdater, Visitor<JumpUpdater>> {
Index labelIndex;
Index targetNum;
Name targetName;
void visitSetLocal(SetLocal* curr) {
if (curr->index == labelIndex) {
if (Index(curr->value->cast<Const>()->value.geti32()) == targetNum) {
replaceCurrent(Builder(*getModule()).makeBreak(targetName));
}
}
}
};
JumpUpdater updater;
updater.labelIndex = labelIndex;
updater.targetNum = num;
updater.targetName = innerName;
updater.setModule(getModule());
updater.walk(origin);
// restructure code
auto* inner = builder.blockifyWithName(origin, innerName, builder.makeBreak(outerName));
auto* outer = builder.makeSequence(inner, iff->ifTrue);
outer->name = outerName;
origin = outer;
// if another label value is checked here, handle that too
if (ifFalse) {
optimizeJumpsToLabelCheck(origin, ifFalse->cast<If>());
}
}
};
// declare pass
Pass *createRelooperJumpThreadingPass() {
return new RelooperJumpThreading();
}
} // namespace wasm
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