void region_prune_arcs(RegionDesc& region) {
FTRACE(4, "region_prune_arcs\n");
region.sortBlocks();
auto const sortedBlocks = region.blocks();
// Maps region block ids to their RPO ids.
auto blockToRPO = std::unordered_map<RegionDesc::BlockId,uint32_t>{};
auto blockInfos = std::vector<BlockInfo>(sortedBlocks.size());
auto workQ = dataflow_worklist<uint32_t>(sortedBlocks.size());
for (auto rpoID = uint32_t{0}; rpoID < sortedBlocks.size(); ++rpoID) {
auto const& b = sortedBlocks[rpoID];
auto& binfo = blockInfos[rpoID];
binfo.blockID = b->id();
blockToRPO[binfo.blockID] = rpoID;
}
workQ.push(0);
blockInfos[0].in = entry_state(region);
FTRACE(4, "Iterating:\n");
do {
auto const rpoID = workQ.pop();
auto& binfo = blockInfos[rpoID];
FTRACE(4, "B{}\n", binfo.blockID);
binfo.out = binfo.in;
apply_transfer_function(
binfo.out,
region.block(binfo.blockID)->postConds()
);
for (auto& succ : region.succs(binfo.blockID)) {
auto const succRPO = blockToRPO.find(succ);
assertx(succRPO != end(blockToRPO));
auto& succInfo = blockInfos[succRPO->second];
if (preconds_may_pass(*region.block(succInfo.blockID), binfo.out)) {
if (merge_into(succInfo.in, binfo.out)) {
FTRACE(5, " -> {}\n", succInfo.blockID);
workQ.push(succRPO->second);
}
}
}
} while (!workQ.empty());
FTRACE(2, "\nPostConds fixed point:\n{}\n",
[&] () -> std::string {
auto ret = std::string{};
for (auto& s : blockInfos) {
folly::format(&ret, "B{}:\n{}", s.blockID, show(s.in));
}
return ret;
}()
);
// Now remove any edge that looks like it will unconditionally fail type
// predictions, and completely remove any block that can't be reached.
using ArcIDs = std::pair<RegionDesc::BlockId,RegionDesc::BlockId>;
auto toRemove = std::vector<ArcIDs>{};
for (auto rpoID = uint32_t{0}; rpoID < sortedBlocks.size(); ++rpoID) {
auto const& binfo = blockInfos[rpoID];
for (auto& succ : region.succs(binfo.blockID)) {
auto const succRPO = blockToRPO.find(succ);
assertx(succRPO != end(blockToRPO));
auto const& succInfo = blockInfos[succRPO->second];
if (!binfo.in.initialized ||
!succInfo.in.initialized ||
!preconds_may_pass(*region.block(succInfo.blockID), binfo.out)) {
FTRACE(2, "Pruning arc: B{} -> B{}\n",
binfo.blockID,
succInfo.blockID);
toRemove.emplace_back(binfo.blockID, succInfo.blockID);
}
}
for (auto& r : toRemove) region.removeArc(r.first, r.second);
toRemove.clear();
}
// Get rid of the completely unreachable blocks, now that any arcs to/from
// them are gone.
for (auto rpoID = uint32_t{0}; rpoID < sortedBlocks.size(); ++rpoID) {
auto const& binfo = blockInfos[rpoID];
if (!binfo.in.initialized) {
FTRACE(2, "Pruning block: B{}\n", binfo.blockID);
region.deleteBlock(binfo.blockID);
}
}
FTRACE(2, "\n");
}
/*
* 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;
}
void region_prune_arcs(RegionDesc& region) {
FTRACE(4, "region_prune_arcs\n");
region.sortBlocks();
auto const sortedBlocks = region.blocks();
// Maps region block ids to their RPO ids.
auto blockToRPO = std::unordered_map<RegionDesc::BlockId,uint32_t>{};
auto blockInfos = std::vector<BlockInfo>(sortedBlocks.size());
auto workQ = dataflow_worklist<uint32_t>(sortedBlocks.size());
for (auto rpoID = uint32_t{0}; rpoID < sortedBlocks.size(); ++rpoID) {
auto const& b = sortedBlocks[rpoID];
auto& binfo = blockInfos[rpoID];
binfo.blockID = b->id();
blockToRPO[binfo.blockID] = rpoID;
}
workQ.push(0);
blockInfos[0].in = entry_state(region);
FTRACE(4, "Iterating:\n");
do {
auto const rpoID = workQ.pop();
auto& binfo = blockInfos[rpoID];
FTRACE(4, "B{}\n", binfo.blockID);
/*
* This code currently assumes inlined functions were entirely contained
* within a single profiling translation, and will need updates if we
* inline bigger things in a way visible to region selection.
*
* Note: inlined blocks /may/ have postConditions, if they are the last
* blocks from profiling translations. Currently any locations referred to
* in postconditions for these blocks are for the outermost caller, so this
* code handles that correctly.
*/
if (region.block(binfo.blockID)->inlineLevel() != 0) {
assertx(region.block(binfo.blockID)->typePreConditions().empty());
}
binfo.out = binfo.in;
apply_transfer_function(
binfo.out,
region.block(binfo.blockID)->postConds()
);
for (auto& succ : region.succs(binfo.blockID)) {
auto const succRPO = blockToRPO.find(succ);
assertx(succRPO != end(blockToRPO));
auto& succInfo = blockInfos[succRPO->second];
if (preconds_may_pass(*region.block(succInfo.blockID), binfo.out)) {
if (merge_into(succInfo.in, binfo.out)) {
FTRACE(5, " -> {}\n", succInfo.blockID);
workQ.push(succRPO->second);
}
}
}
} while (!workQ.empty());
FTRACE(2, "\nPostConds fixed point:\n{}\n",
[&] () -> std::string {
auto ret = std::string{};
for (auto& s : blockInfos) {
folly::format(&ret, "B{}:\n{}", s.blockID, show(s.in));
}
return ret;
}()
);
// Now remove any edge that looks like it will unconditionally fail type
// predictions, and completely remove any block that can't be reached.
using ArcIDs = std::pair<RegionDesc::BlockId,RegionDesc::BlockId>;
auto toRemove = std::vector<ArcIDs>{};
for (auto rpoID = uint32_t{0}; rpoID < sortedBlocks.size(); ++rpoID) {
auto const& binfo = blockInfos[rpoID];
for (auto& succ : region.succs(binfo.blockID)) {
auto const succRPO = blockToRPO.find(succ);
assertx(succRPO != end(blockToRPO));
auto const& succInfo = blockInfos[succRPO->second];
if (!binfo.in.initialized ||
!succInfo.in.initialized ||
!preconds_may_pass(*region.block(succInfo.blockID), binfo.out)) {
FTRACE(2, "Pruning arc: B{} -> B{}\n",
binfo.blockID,
succInfo.blockID);
toRemove.emplace_back(binfo.blockID, succInfo.blockID);
}
}
for (auto& r : toRemove) region.removeArc(r.first, r.second);
toRemove.clear();
}
// Get rid of the completely unreachable blocks, now that any arcs to/from
// them are gone.
for (auto rpoID = uint32_t{0}; rpoID < sortedBlocks.size(); ++rpoID) {
auto const& binfo = blockInfos[rpoID];
if (!binfo.in.initialized) {
FTRACE(2, "Pruning block: B{}\n", binfo.blockID);
region.deleteBlock(binfo.blockID);
}
}
FTRACE(2, "\n");
}