std::string show(const RegionDesc& region) {
return folly::format(
"Region ({} blocks):\n{}",
region.blocks().size(),
[&]{
std::string ret;
std::string arcs;
for (auto& b : region.blocks()) {
folly::toAppend(show(*b), &ret);
if (auto r = region.nextRetrans(b->id())) {
folly::toAppend(folly::format("{} -R-> {}\n", b->id(), r.value()),
&arcs);
}
for (auto s : region.succs(b->id())) {
folly::toAppend(folly::format("{} -> {}\n", b->id(), s), &arcs);
}
}
folly::toAppend("Arcs:\n" + arcs, &ret);
folly::toAppend("Side-exiting Blocks:\n",
folly::join(", ", region.sideExitingBlocks()),
"\n",
&ret);
return ret;
}()
).str();
}
void RegionDesc::copyBlocksFrom(const RegionDesc& other,
BlockVec::iterator where) {
auto otherBlocks = other.blocks();
m_blocks.insert(where, otherBlocks.begin(), otherBlocks.end());
for (auto b : otherBlocks) {
m_data[b->id()] = BlockData(b);
}
}
void RegionDesc::copyArcsFrom(const RegionDesc& srcRegion) {
for (auto const b : srcRegion.m_blocks) {
auto bid = b->id();
for (auto succId : srcRegion.succs(bid)) {
addArc(bid, succId);
}
}
}
std::string show(const RegionDesc& region) {
std::string ret{folly::sformat("Region ({} blocks):\n",
region.blocks().size())};
auto profData = mcg->tx().profData();
auto weight = [&] (RegionDesc::BlockPtr b) -> int64_t {
if (!profData) return 0;
auto tid = b->profTransID();
if (tid == kInvalidTransID) return 0;
return profData->transCounter(tid);
};
uint64_t maxBlockWgt = 1; // avoid div by 0
// Print contents of all blocks in pure text format.
for (auto& b : region.blocks()) {
folly::toAppend(show(*b), &ret);
auto w = weight(b);
if (w > maxBlockWgt) maxBlockWgt = w;
}
// Print CFG in dot format, coloring the blocks based on hotness.
// Print all the blocks first.
folly::toAppend("\ndigraph RegionCFG {\n node[shape=box,style=filled]\n",
&ret);
for (auto& b : region.blocks()) {
auto const id = b->id();
auto const& mergedSet = region.merged(id);
std::string mergedStr = mergedSet.empty() ? "" :
(" (" + folly::join(",", mergedSet) + ")");
uint32_t coldness = 255 - (255 * weight(b) / maxBlockWgt);
folly::format(&ret, " \"B{}\" [label=\"B {}{}\\np: {}\","
"fillcolor=\"#ff{:02x}{:02x}\"]\n",
id, id, mergedStr, weight(b), coldness, coldness);
}
// Print arcs in dot format.
for (auto& b : region.blocks()) {
if (auto r = region.nextRetrans(b->id())) {
folly::toAppend(folly::format(" \"B{}\" -> \"B{}\" [label=R,color=red]\n",
b->id(), r.value()), &ret);
}
for (auto s : region.succs(b->id())) {
folly::toAppend(folly::format(" \"B{}\" -> \"B{}\"\n", b->id(), s),
&ret);
}
}
ret += "}\n";
return ret;
}
/*
* 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;
}
bool InliningDecider::shouldInline(SrcKey callerSk,
const Func* callee,
const RegionDesc& region,
uint32_t maxTotalCost) {
auto sk = region.empty() ? SrcKey() : region.start();
assertx(callee);
assertx(sk.func() == callee);
// Tracing return lambdas.
auto refuse = [&] (const char* why) {
FTRACE(2, "shouldInline: rejecting callee region: {}", show(region));
return traceRefusal(m_topFunc, callee, why);
};
auto accept = [&, this] (const char* kind) {
FTRACE(2, "InliningDecider: inlining {}() <- {}()\t<reason: {}>\n",
m_topFunc->fullName()->data(), callee->fullName()->data(), kind);
return true;
};
if (m_stackDepth + callee->maxStackCells() >= kStackCheckLeafPadding) {
return refuse("inlining stack depth limit exceeded");
}
// Even if the func contains NativeImpl we may have broken the trace before
// we hit it.
auto containsNativeImpl = [&] {
for (auto block : region.blocks()) {
if (!block->empty() && block->last().op() == OpNativeImpl) return true;
}
return false;
};
// Try to inline CPP builtin functions.
// The NativeImpl opcode may appear later in the function because of Asserts
// generated in hhbbc
if (callee->isCPPBuiltin() && containsNativeImpl()) {
if (isInlinableCPPBuiltin(callee)) {
return accept("inlinable CPP builtin");
}
return refuse("non-inlinable CPP builtin");
}
// If the function may use a VarEnv (which is stored in the ActRec) or may be
// variadic, we restrict inlined callees to certain whitelisted instructions
// which we know won't actually require these features.
const bool needsCheckVVSafe = callee->attrs() & AttrMayUseVV;
bool hasRet = false;
// Iterate through the region, checking its suitability for inlining.
for (auto const& block : region.blocks()) {
sk = block->start();
for (auto i = 0, n = block->length(); i < n; ++i, sk.advance()) {
auto op = sk.op();
// We don't allow inlined functions in the region. The client is
// expected to disable inlining for the region it gives us to peek.
if (sk.func() != callee) {
return refuse("got region with inlined calls");
}
// Restrict to VV-safe opcodes if necessary.
if (needsCheckVVSafe && !isInliningVVSafe(op)) {
return refuse(folly::format("{} may use dynamic environment",
opcodeToName(op)).str().c_str());
}
// Count the returns.
if (isReturnish(op)) {
hasRet = true;
}
// We can't inline FCallArray. XXX: Why?
if (op == Op::FCallArray) {
return refuse("can't inline FCallArray");
}
}
}
if (!hasRet) {
return refuse("region has no returns");
}
// Refuse if the cost exceeds our thresholds.
// We measure the cost of inlining each callstack and stop when it exceeds a
// certain threshold. (Note that we do not measure the total cost of all the
// inlined calls for a given caller---just the cost of each nested stack.)
const int maxCost = maxTotalCost - m_cost;
const int cost = computeTranslationCost(callerSk, region);
if (cost > maxCost) {
return refuse("too expensive");
}
return accept("small region with return");
}
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");
}
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");
}
bool InliningDecider::shouldInline(const Func* callee,
const RegionDesc& region) {
auto sk = region.empty() ? SrcKey() : region.start();
assertx(callee);
assertx(sk.func() == callee);
int cost = 0;
// Tracing return lambdas.
auto refuse = [&] (const char* why) {
return traceRefusal(m_topFunc, callee, why);
};
auto accept = [&, this] (const char* kind) {
FTRACE(1, "InliningDecider: inlining {}() <- {}()\t<reason: {}>\n",
m_topFunc->fullName()->data(), callee->fullName()->data(), kind);
// Update our context.
m_costStack.push_back(cost);
m_cost += cost;
m_callDepth += 1;
m_stackDepth += callee->maxStackCells();
return true;
};
// Check inlining depths.
if (m_callDepth + 1 >= RuntimeOption::EvalHHIRInliningMaxDepth) {
return refuse("inlining call depth limit exceeded");
}
if (m_stackDepth + callee->maxStackCells() >= kStackCheckLeafPadding) {
return refuse("inlining stack depth limit exceeded");
}
// Even if the func contains NativeImpl we may have broken the trace before
// we hit it.
auto containsNativeImpl = [&] {
for (auto block : region.blocks()) {
if (!block->empty() && block->last().op() == OpNativeImpl) return true;
}
return false;
};
// Try to inline CPP builtin functions.
// The NativeImpl opcode may appear later in the function because of Asserts
// generated in hhbbc
if (callee->isCPPBuiltin() && containsNativeImpl()) {
if (isInlinableCPPBuiltin(callee)) {
return accept("inlinable CPP builtin");
}
return refuse("non-inlinable CPP builtin");
}
// If the function may use a VarEnv (which is stored in the ActRec) or may be
// variadic, we restrict inlined callees to certain whitelisted instructions
// which we know won't actually require these features.
const bool needsCheckVVSafe = callee->attrs() & AttrMayUseVV;
// We measure the cost of inlining each callstack and stop when it exceeds a
// certain threshold. (Note that we do not measure the total cost of all the
// inlined calls for a given caller---just the cost of each nested stack.)
const int maxCost = RuntimeOption::EvalHHIRInliningMaxCost - m_cost;
// We only inline callee regions that have exactly one return.
//
// NOTE: Currently, the tracelet selector uses the first Ret in the child's
// region to determine when to stop inlining. However, the safety of this
// behavior should not be considered guaranteed by InliningDecider; the
// "right" way to decide when inlining ends is to inline all of `region'.
int numRets = 0;
// Iterate through the region, checking its suitability for inlining.
for (auto const& block : region.blocks()) {
sk = block->start();
for (auto i = 0, n = block->length(); i < n; ++i, sk.advance()) {
auto op = sk.op();
// We don't allow inlined functions in the region. The client is
// expected to disable inlining for the region it gives us to peek.
if (sk.func() != callee) {
return refuse("got region with inlined calls");
}
// Restrict to VV-safe opcodes if necessary.
if (needsCheckVVSafe && !isInliningVVSafe(op)) {
return refuse(folly::format("{} may use dynamic environment",
opcodeToName(op)).str().c_str());
}
// Count the returns.
if (isRet(op) || op == Op::NativeImpl) {
if (++numRets > 1) {
return refuse("region has too many returns");
}
continue;
}
// We can't inline FCallArray. XXX: Why?
if (op == Op::FCallArray) {
return refuse("can't inline FCallArray");
}
// Assert opcodes don't contribute to the inlining cost.
if (op == Op::AssertRATL || op == Op::AssertRATStk) continue;
cost += 1;
// Add the size of immediate vectors to the cost.
auto const pc = reinterpret_cast<const Op*>(sk.pc());
if (hasMVector(op)) {
cost += getMVector(pc).size();
} else if (hasImmVector(op)) {
cost += getImmVector(pc).size();
}
// Refuse if the cost exceeds our thresholds.
if (cost > maxCost) {
return refuse("too expensive");
}
}
}
if (numRets != 1) {
return refuse("region has no returns");
}
return accept("small region with single return");
}
