/*
* Perform a DFS starting at block `bid', storing the post-order in
* `outVec'.
*/
void RegionDesc::postOrderSort(RegionDesc::BlockId bid,
RegionDesc::BlockIdSet& visited,
RegionDesc::BlockIdVec& outVec) {
if (visited.count(bid)) return;
visited.insert(bid);
if (auto nextRetr = nextRetrans(bid)) {
postOrderSort(nextRetr.value(), visited, outVec);
}
for (auto succ : succs(bid)) {
postOrderSort(succ, visited, outVec);
}
outVec.push_back(bid);
}
/**
* Sort the m_blocks vector in reverse post order. This enforces that
* m_blocks will be a topological order in case the region is acyclic.
* All region arcs are taken into account, including retranslation arcs.
*/
void RegionDesc::sortBlocks() {
RegionDesc::BlockIdSet visited;
RegionDesc::BlockIdVec reverse;
postOrderSort(entry()->id(), visited, reverse);
assertx(m_blocks.size() >= reverse.size());
// Remove unreachable blocks from `m_data'.
for (auto it = m_blocks.begin(); it != m_blocks.end();) {
auto bid = (*it)->id();
if (visited.count(bid) == 0) {
it = deleteBlock(it);
} else {
it++;
}
}
// Update `m_blocks' vector.
m_blocks.clear();
auto size = reverse.size();
for (size_t i = 0; i < size; i++) {
m_blocks.push_back(block(reverse[size - i - 1]));
}
}
/*
* Checks if the given region is well-formed, which entails the
* following properties:
*
* 1) The region has at least one block.
*
* 2) Each block in the region has a different id.
*
* 3) All arcs involve blocks within the region.
*
* 4) For each arc, the bytecode offset of the dst block must
* possibly follow the execution of the src block.
*
* 5) Each block contains at most one successor corresponding to a
* given SrcKey.
*
* 6) The region doesn't contain any loops, unless JitLoops is
* enabled.
*
* 7) All blocks are reachable from the entry block.
*
* 8) For each block, there must be a path from the entry to it that
* includes only earlier blocks in the region.
*
* 9) The region is topologically sorted unless loops are enabled.
*
* 10) The block-retranslation chains cannot have cycles.
*
*/
bool check(const RegionDesc& region, std::string& error) {
auto bad = [&](const std::string& errorMsg) {
error = errorMsg;
return false;
};
// 1) The region has at least one block.
if (region.empty()) return bad("empty region");
RegionDesc::BlockIdSet blockSet;
for (auto b : region.blocks()) {
auto bid = b->id();
// 2) Each block in the region has a different id.
if (blockSet.count(bid)) {
return bad(folly::sformat("many blocks with id {}", bid));
}
blockSet.insert(bid);
}
for (auto b : region.blocks()) {
auto bid = b->id();
SrcKey lastSk = region.block(bid)->last();
OffsetSet validSuccOffsets = lastSk.succOffsets();
OffsetSet succOffsets;
for (auto succ : region.succs(bid)) {
SrcKey succSk = region.block(succ)->start();
Offset succOffset = succSk.offset();
// 3) All arcs involve blocks within the region.
if (blockSet.count(succ) == 0) {
return bad(folly::sformat("arc with dst not in the region: {} -> {}",
bid, succ));
}
// Checks 4) and 5) below don't make sense for arcs corresponding
// to inlined calls and returns, so skip them in such cases.
// This won't be possible once task #4076399 is done.
if (lastSk.func() != succSk.func()) continue;
// 4) For each arc, the bytecode offset of the dst block must
// possibly follow the execution of the src block.
if (validSuccOffsets.count(succOffset) == 0) {
return bad(folly::sformat("arc with impossible control flow: {} -> {}",
bid, succ));
}
// 5) Each block contains at most one successor corresponding to a
// given SrcKey.
if (succOffsets.count(succOffset) > 0) {
return bad(folly::sformat("block {} has multiple successors with SK {}",
bid, show(succSk)));
}
succOffsets.insert(succOffset);
}
for (auto pred : region.preds(bid)) {
if (blockSet.count(pred) == 0) {
return bad(folly::sformat("arc with src not in the region: {} -> {}",
pred, bid));
}
}
}
// 6) is checked by dfsCheck.
DFSChecker dfsCheck(region);
if (!dfsCheck.check(region.entry()->id())) {
return bad("region is cyclic");
}
// 7) All blocks are reachable from the entry (first) block.
if (dfsCheck.numVisited() != blockSet.size()) {
return bad("region has unreachable blocks");
}
// 8) and 9) are checked below.
RegionDesc::BlockIdSet visited;
auto& blocks = region.blocks();
for (unsigned i = 0; i < blocks.size(); i++) {
auto bid = blocks[i]->id();
unsigned nVisited = 0;
for (auto pred : region.preds(bid)) {
nVisited += visited.count(pred);
}
// 8) For each block, there must be a path from the entry to it that
// includes only earlier blocks in the region.
if (nVisited == 0 && i != 0) {
return bad(folly::sformat("block {} appears before all its predecessors",
bid));
}
// 9) The region is topologically sorted unless loops are enabled.
if (!RuntimeOption::EvalJitLoops && nVisited != region.preds(bid).size()) {
return bad(folly::sformat("non-topological order (bid: {})", bid));
}
visited.insert(bid);
}
// 10) The block-retranslation chains cannot have cycles.
for (auto b : blocks) {
auto bid = b->id();
RegionDesc::BlockIdSet chainSet;
chainSet.insert(bid);
while (auto next = region.nextRetrans(bid)) {
auto nextId = next.value();
if (chainSet.count(nextId)) {
return bad(folly::sformat("cyclic retranslation chain for block {}",
bid));
}
chainSet.insert(nextId);
bid = nextId;
}
}
return true;
}