--- /dev/null
+//===- PlaceSafepoints.cpp - Place GC Safepoints --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Place garbage collection safepoints at appropriate locations in the IR. This
+// does not make relocation semantics or variable liveness explicit. That's
+// done by RewriteStatepointsForGC.
+//
+// Terminology:
+// - A call is said to be "parseable" if there is a stack map generated for the
+// return PC of the call. A runtime can determine where values listed in the
+// deopt arguments and (after RewriteStatepointsForGC) gc arguments are located
+// on the stack when the code is suspended inside such a call. Every parse
+// point is represented by a call wrapped in an gc.statepoint intrinsic.
+// - A "poll" is an explicit check in the generated code to determine if the
+// runtime needs the generated code to cooperate by calling a helper routine
+// and thus suspending its execution at a known state. The call to the helper
+// routine will be parseable. The (gc & runtime specific) logic of a poll is
+// assumed to be provided in a function of the name "gc.safepoint_poll".
+//
+// We aim to insert polls such that running code can quickly be brought to a
+// well defined state for inspection by the collector. In the current
+// implementation, this is done via the insertion of poll sites at method entry
+// and the backedge of most loops. We try to avoid inserting more polls than
+// are necessary to ensure a finite period between poll sites. This is not
+// because the poll itself is expensive in the generated code; it's not. Polls
+// do tend to impact the optimizer itself in negative ways; we'd like to avoid
+// perturbing the optimization of the method as much as we can.
+//
+// We also need to make most call sites parseable. The callee might execute a
+// poll (or otherwise be inspected by the GC). If so, the entire stack
+// (including the suspended frame of the current method) must be parseable.
+//
+// This pass will insert:
+// - Call parse points ("call safepoints") for any call which may need to
+// reach a safepoint during the execution of the callee function.
+// - Backedge safepoint polls and entry safepoint polls to ensure that
+// executing code reaches a safepoint poll in a finite amount of time.
+//
+// We do not currently support return statepoints, but adding them would not
+// be hard. They are not required for correctness - entry safepoints are an
+// alternative - but some GCs may prefer them. Patches welcome.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/Statepoint.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/Local.h"
+
+#define DEBUG_TYPE "safepoint-placement"
+
+STATISTIC(NumEntrySafepoints, "Number of entry safepoints inserted");
+STATISTIC(NumBackedgeSafepoints, "Number of backedge safepoints inserted");
+
+STATISTIC(CallInLoop,
+ "Number of loops without safepoints due to calls in loop");
+STATISTIC(FiniteExecution,
+ "Number of loops without safepoints finite execution");
+
+using namespace llvm;
+
+// Ignore opportunities to avoid placing safepoints on backedges, useful for
+// validation
+static cl::opt<bool> AllBackedges("spp-all-backedges", cl::Hidden,
+ cl::init(false));
+
+/// How narrow does the trip count of a loop have to be to have to be considered
+/// "counted"? Counted loops do not get safepoints at backedges.
+static cl::opt<int> CountedLoopTripWidth("spp-counted-loop-trip-width",
+ cl::Hidden, cl::init(32));
+
+// If true, split the backedge of a loop when placing the safepoint, otherwise
+// split the latch block itself. Both are useful to support for
+// experimentation, but in practice, it looks like splitting the backedge
+// optimizes better.
+static cl::opt<bool> SplitBackedge("spp-split-backedge", cl::Hidden,
+ cl::init(false));
+
+namespace {
+
+/// An analysis pass whose purpose is to identify each of the backedges in
+/// the function which require a safepoint poll to be inserted.
+struct PlaceBackedgeSafepointsImpl : public FunctionPass {
+ static char ID;
+
+ /// The output of the pass - gives a list of each backedge (described by
+ /// pointing at the branch) which need a poll inserted.
+ std::vector<Instruction *> PollLocations;
+
+ /// True unless we're running spp-no-calls in which case we need to disable
+ /// the call-dependent placement opts.
+ bool CallSafepointsEnabled;
+
+ ScalarEvolution *SE = nullptr;
+ DominatorTree *DT = nullptr;
+ LoopInfo *LI = nullptr;
+ TargetLibraryInfo *TLI = nullptr;
+
+ PlaceBackedgeSafepointsImpl(bool CallSafepoints = false)
+ : FunctionPass(ID), CallSafepointsEnabled(CallSafepoints) {
+ initializePlaceBackedgeSafepointsImplPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnLoop(Loop *);
+ void runOnLoopAndSubLoops(Loop *L) {
+ // Visit all the subloops
+ for (Loop *I : *L)
+ runOnLoopAndSubLoops(I);
+ runOnLoop(L);
+ }
+
+ bool runOnFunction(Function &F) override {
+ SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
+ for (Loop *I : *LI) {
+ runOnLoopAndSubLoops(I);
+ }
+ return false;
+ }
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<ScalarEvolutionWrapperPass>();
+ AU.addRequired<LoopInfoWrapperPass>();
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
+ // We no longer modify the IR at all in this pass. Thus all
+ // analysis are preserved.
+ AU.setPreservesAll();
+ }
+};
+}
+
+static cl::opt<bool> NoEntry("spp-no-entry", cl::Hidden, cl::init(false));
+static cl::opt<bool> NoCall("spp-no-call", cl::Hidden, cl::init(false));
+static cl::opt<bool> NoBackedge("spp-no-backedge", cl::Hidden, cl::init(false));
+
+namespace {
+struct PlaceSafepoints : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+
+ PlaceSafepoints() : FunctionPass(ID) {
+ initializePlaceSafepointsPass(*PassRegistry::getPassRegistry());
+ }
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ // We modify the graph wholesale (inlining, block insertion, etc). We
+ // preserve nothing at the moment. We could potentially preserve dom tree
+ // if that was worth doing
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
+ }
+};
+}
+
+// Insert a safepoint poll immediately before the given instruction. Does
+// not handle the parsability of state at the runtime call, that's the
+// callers job.
+static void
+InsertSafepointPoll(Instruction *InsertBefore,
+ std::vector<CallBase *> &ParsePointsNeeded /*rval*/,
+ const TargetLibraryInfo &TLI);
+
+static bool needsStatepoint(CallBase *Call, const TargetLibraryInfo &TLI) {
+ if (callsGCLeafFunction(Call, TLI))
+ return false;
+ if (auto *CI = dyn_cast<CallInst>(Call)) {
+ if (CI->isInlineAsm())
+ return false;
+ }
+
+ return !(isa<GCStatepointInst>(Call) || isa<GCRelocateInst>(Call) ||
+ isa<GCResultInst>(Call));
+}
+
+/// Returns true if this loop is known to contain a call safepoint which
+/// must unconditionally execute on any iteration of the loop which returns
+/// to the loop header via an edge from Pred. Returns a conservative correct
+/// answer; i.e. false is always valid.
+static bool containsUnconditionalCallSafepoint(Loop *L, BasicBlock *Header,
+ BasicBlock *Pred,
+ DominatorTree &DT,
+ const TargetLibraryInfo &TLI) {
+ // In general, we're looking for any cut of the graph which ensures
+ // there's a call safepoint along every edge between Header and Pred.
+ // For the moment, we look only for the 'cuts' that consist of a single call
+ // instruction in a block which is dominated by the Header and dominates the
+ // loop latch (Pred) block. Somewhat surprisingly, walking the entire chain
+ // of such dominating blocks gets substantially more occurrences than just
+ // checking the Pred and Header blocks themselves. This may be due to the
+ // density of loop exit conditions caused by range and null checks.
+ // TODO: structure this as an analysis pass, cache the result for subloops,
+ // avoid dom tree recalculations
+ assert(DT.dominates(Header, Pred) && "loop latch not dominated by header?");
+
+ BasicBlock *Current = Pred;
+ while (true) {
+ for (Instruction &I : *Current) {
+ if (auto *Call = dyn_cast<CallBase>(&I))
+ // Note: Technically, needing a safepoint isn't quite the right
+ // condition here. We should instead be checking if the target method
+ // has an
+ // unconditional poll. In practice, this is only a theoretical concern
+ // since we don't have any methods with conditional-only safepoint
+ // polls.
+ if (needsStatepoint(Call, TLI))
+ return true;
+ }
+
+ if (Current == Header)
+ break;
+ Current = DT.getNode(Current)->getIDom()->getBlock();
+ }
+
+ return false;
+}
+
+/// Returns true if this loop is known to terminate in a finite number of
+/// iterations. Note that this function may return false for a loop which
+/// does actual terminate in a finite constant number of iterations due to
+/// conservatism in the analysis.
+static bool mustBeFiniteCountedLoop(Loop *L, ScalarEvolution *SE,
+ BasicBlock *Pred) {
+ // A conservative bound on the loop as a whole.
+ const SCEV *MaxTrips = SE->getConstantMaxBackedgeTakenCount(L);
+ if (!isa<SCEVCouldNotCompute>(MaxTrips) &&
+ SE->getUnsignedRange(MaxTrips).getUnsignedMax().isIntN(
+ CountedLoopTripWidth))
+ return true;
+
+ // If this is a conditional branch to the header with the alternate path
+ // being outside the loop, we can ask questions about the execution frequency
+ // of the exit block.
+ if (L->isLoopExiting(Pred)) {
+ // This returns an exact expression only. TODO: We really only need an
+ // upper bound here, but SE doesn't expose that.
+ const SCEV *MaxExec = SE->getExitCount(L, Pred);
+ if (!isa<SCEVCouldNotCompute>(MaxExec) &&
+ SE->getUnsignedRange(MaxExec).getUnsignedMax().isIntN(
+ CountedLoopTripWidth))
+ return true;
+ }
+
+ return /* not finite */ false;
+}
+
+static void scanOneBB(Instruction *Start, Instruction *End,
+ std::vector<CallInst *> &Calls,
+ DenseSet<BasicBlock *> &Seen,
+ std::vector<BasicBlock *> &Worklist) {
+ for (BasicBlock::iterator BBI(Start), BBE0 = Start->getParent()->end(),
+ BBE1 = BasicBlock::iterator(End);
+ BBI != BBE0 && BBI != BBE1; BBI++) {
+ if (CallInst *CI = dyn_cast<CallInst>(&*BBI))
+ Calls.push_back(CI);
+
+ // FIXME: This code does not handle invokes
+ assert(!isa<InvokeInst>(&*BBI) &&
+ "support for invokes in poll code needed");
+
+ // Only add the successor blocks if we reach the terminator instruction
+ // without encountering end first
+ if (BBI->isTerminator()) {
+ BasicBlock *BB = BBI->getParent();
+ for (BasicBlock *Succ : successors(BB)) {
+ if (Seen.insert(Succ).second) {
+ Worklist.push_back(Succ);
+ }
+ }
+ }
+ }
+}
+
+static void scanInlinedCode(Instruction *Start, Instruction *End,
+ std::vector<CallInst *> &Calls,
+ DenseSet<BasicBlock *> &Seen) {
+ Calls.clear();
+ std::vector<BasicBlock *> Worklist;
+ Seen.insert(Start->getParent());
+ scanOneBB(Start, End, Calls, Seen, Worklist);
+ while (!Worklist.empty()) {
+ BasicBlock *BB = Worklist.back();
+ Worklist.pop_back();
+ scanOneBB(&*BB->begin(), End, Calls, Seen, Worklist);
+ }
+}
+
+bool PlaceBackedgeSafepointsImpl::runOnLoop(Loop *L) {
+ // Loop through all loop latches (branches controlling backedges). We need
+ // to place a safepoint on every backedge (potentially).
+ // Note: In common usage, there will be only one edge due to LoopSimplify
+ // having run sometime earlier in the pipeline, but this code must be correct
+ // w.r.t. loops with multiple backedges.
+ BasicBlock *Header = L->getHeader();
+ SmallVector<BasicBlock*, 16> LoopLatches;
+ L->getLoopLatches(LoopLatches);
+ for (BasicBlock *Pred : LoopLatches) {
+ assert(L->contains(Pred));
+
+ // Make a policy decision about whether this loop needs a safepoint or
+ // not. Note that this is about unburdening the optimizer in loops, not
+ // avoiding the runtime cost of the actual safepoint.
+ if (!AllBackedges) {
+ if (mustBeFiniteCountedLoop(L, SE, Pred)) {
+ LLVM_DEBUG(dbgs() << "skipping safepoint placement in finite loop\n");
+ FiniteExecution++;
+ continue;
+ }
+ if (CallSafepointsEnabled &&
+ containsUnconditionalCallSafepoint(L, Header, Pred, *DT, *TLI)) {
+ // Note: This is only semantically legal since we won't do any further
+ // IPO or inlining before the actual call insertion.. If we hadn't, we
+ // might latter loose this call safepoint.
+ LLVM_DEBUG(
+ dbgs()
+ << "skipping safepoint placement due to unconditional call\n");
+ CallInLoop++;
+ continue;
+ }
+ }
+
+ // TODO: We can create an inner loop which runs a finite number of
+ // iterations with an outer loop which contains a safepoint. This would
+ // not help runtime performance that much, but it might help our ability to
+ // optimize the inner loop.
+
+ // Safepoint insertion would involve creating a new basic block (as the
+ // target of the current backedge) which does the safepoint (of all live
+ // variables) and branches to the true header
+ Instruction *Term = Pred->getTerminator();
+
+ LLVM_DEBUG(dbgs() << "[LSP] terminator instruction: " << *Term);
+
+ PollLocations.push_back(Term);
+ }
+
+ return false;
+}
+
+/// Returns true if an entry safepoint is not required before this callsite in
+/// the caller function.
+static bool doesNotRequireEntrySafepointBefore(CallBase *Call) {
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Call)) {
+ switch (II->getIntrinsicID()) {
+ case Intrinsic::experimental_gc_statepoint:
+ case Intrinsic::experimental_patchpoint_void:
+ case Intrinsic::experimental_patchpoint_i64:
+ // The can wrap an actual call which may grow the stack by an unbounded
+ // amount or run forever.
+ return false;
+ default:
+ // Most LLVM intrinsics are things which do not expand to actual calls, or
+ // at least if they do, are leaf functions that cause only finite stack
+ // growth. In particular, the optimizer likes to form things like memsets
+ // out of stores in the original IR. Another important example is
+ // llvm.localescape which must occur in the entry block. Inserting a
+ // safepoint before it is not legal since it could push the localescape
+ // out of the entry block.
+ return true;
+ }
+ }
+ return false;
+}
+
+static Instruction *findLocationForEntrySafepoint(Function &F,
+ DominatorTree &DT) {
+
+ // Conceptually, this poll needs to be on method entry, but in
+ // practice, we place it as late in the entry block as possible. We
+ // can place it as late as we want as long as it dominates all calls
+ // that can grow the stack. This, combined with backedge polls,
+ // give us all the progress guarantees we need.
+
+ // hasNextInstruction and nextInstruction are used to iterate
+ // through a "straight line" execution sequence.
+
+ auto HasNextInstruction = [](Instruction *I) {
+ if (!I->isTerminator())
+ return true;
+
+ BasicBlock *nextBB = I->getParent()->getUniqueSuccessor();
+ return nextBB && (nextBB->getUniquePredecessor() != nullptr);
+ };
+
+ auto NextInstruction = [&](Instruction *I) {
+ assert(HasNextInstruction(I) &&
+ "first check if there is a next instruction!");
+
+ if (I->isTerminator())
+ return &I->getParent()->getUniqueSuccessor()->front();
+ return &*++I->getIterator();
+ };
+
+ Instruction *Cursor = nullptr;
+ for (Cursor = &F.getEntryBlock().front(); HasNextInstruction(Cursor);
+ Cursor = NextInstruction(Cursor)) {
+
+ // We need to ensure a safepoint poll occurs before any 'real' call. The
+ // easiest way to ensure finite execution between safepoints in the face of
+ // recursive and mutually recursive functions is to enforce that each take
+ // a safepoint. Additionally, we need to ensure a poll before any call
+ // which can grow the stack by an unbounded amount. This isn't required
+ // for GC semantics per se, but is a common requirement for languages
+ // which detect stack overflow via guard pages and then throw exceptions.
+ if (auto *Call = dyn_cast<CallBase>(Cursor)) {
+ if (doesNotRequireEntrySafepointBefore(Call))
+ continue;
+ break;
+ }
+ }
+
+ assert((HasNextInstruction(Cursor) || Cursor->isTerminator()) &&
+ "either we stopped because of a call, or because of terminator");
+
+ return Cursor;
+}
+
+const char GCSafepointPollName[] = "gc.safepoint_poll";
+
+static bool isGCSafepointPoll(Function &F) {
+ return F.getName().equals(GCSafepointPollName);
+}
+
+/// Returns true if this function should be rewritten to include safepoint
+/// polls and parseable call sites. The main point of this function is to be
+/// an extension point for custom logic.
+static bool shouldRewriteFunction(Function &F) {
+ // TODO: This should check the GCStrategy
+ if (F.hasGC()) {
+ const auto &FunctionGCName = F.getGC();
+ const StringRef StatepointExampleName("statepoint-example");
+ const StringRef CoreCLRName("coreclr");
+ return (StatepointExampleName == FunctionGCName) ||
+ (CoreCLRName == FunctionGCName);
+ } else
+ return false;
+}
+
+// TODO: These should become properties of the GCStrategy, possibly with
+// command line overrides.
+static bool enableEntrySafepoints(Function &F) { return !NoEntry; }
+static bool enableBackedgeSafepoints(Function &F) { return !NoBackedge; }
+static bool enableCallSafepoints(Function &F) { return !NoCall; }
+
+bool PlaceSafepoints::runOnFunction(Function &F) {
+ if (F.isDeclaration() || F.empty()) {
+ // This is a declaration, nothing to do. Must exit early to avoid crash in
+ // dom tree calculation
+ return false;
+ }
+
+ if (isGCSafepointPoll(F)) {
+ // Given we're inlining this inside of safepoint poll insertion, this
+ // doesn't make any sense. Note that we do make any contained calls
+ // parseable after we inline a poll.
+ return false;
+ }
+
+ if (!shouldRewriteFunction(F))
+ return false;
+
+ const TargetLibraryInfo &TLI =
+ getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
+
+ bool Modified = false;
+
+ // In various bits below, we rely on the fact that uses are reachable from
+ // defs. When there are basic blocks unreachable from the entry, dominance
+ // and reachablity queries return non-sensical results. Thus, we preprocess
+ // the function to ensure these properties hold.
+ Modified |= removeUnreachableBlocks(F);
+
+ // STEP 1 - Insert the safepoint polling locations. We do not need to
+ // actually insert parse points yet. That will be done for all polls and
+ // calls in a single pass.
+
+ DominatorTree DT;
+ DT.recalculate(F);
+
+ SmallVector<Instruction *, 16> PollsNeeded;
+ std::vector<CallBase *> ParsePointNeeded;
+
+ if (enableBackedgeSafepoints(F)) {
+ // Construct a pass manager to run the LoopPass backedge logic. We
+ // need the pass manager to handle scheduling all the loop passes
+ // appropriately. Doing this by hand is painful and just not worth messing
+ // with for the moment.
+ legacy::FunctionPassManager FPM(F.getParent());
+ bool CanAssumeCallSafepoints = enableCallSafepoints(F);
+ auto *PBS = new PlaceBackedgeSafepointsImpl(CanAssumeCallSafepoints);
+ FPM.add(PBS);
+ FPM.run(F);
+
+ // We preserve dominance information when inserting the poll, otherwise
+ // we'd have to recalculate this on every insert
+ DT.recalculate(F);
+
+ auto &PollLocations = PBS->PollLocations;
+
+ auto OrderByBBName = [](Instruction *a, Instruction *b) {
+ return a->getParent()->getName() < b->getParent()->getName();
+ };
+ // We need the order of list to be stable so that naming ends up stable
+ // when we split edges. This makes test cases much easier to write.
+ llvm::sort(PollLocations, OrderByBBName);
+
+ // We can sometimes end up with duplicate poll locations. This happens if
+ // a single loop is visited more than once. The fact this happens seems
+ // wrong, but it does happen for the split-backedge.ll test case.
+ PollLocations.erase(std::unique(PollLocations.begin(),
+ PollLocations.end()),
+ PollLocations.end());
+
+ // Insert a poll at each point the analysis pass identified
+ // The poll location must be the terminator of a loop latch block.
+ for (Instruction *Term : PollLocations) {
+ // We are inserting a poll, the function is modified
+ Modified = true;
+
+ if (SplitBackedge) {
+ // Split the backedge of the loop and insert the poll within that new
+ // basic block. This creates a loop with two latches per original
+ // latch (which is non-ideal), but this appears to be easier to
+ // optimize in practice than inserting the poll immediately before the
+ // latch test.
+
+ // Since this is a latch, at least one of the successors must dominate
+ // it. Its possible that we have a) duplicate edges to the same header
+ // and b) edges to distinct loop headers. We need to insert pools on
+ // each.
+ SetVector<BasicBlock *> Headers;
+ for (unsigned i = 0; i < Term->getNumSuccessors(); i++) {
+ BasicBlock *Succ = Term->getSuccessor(i);
+ if (DT.dominates(Succ, Term->getParent())) {
+ Headers.insert(Succ);
+ }
+ }
+ assert(!Headers.empty() && "poll location is not a loop latch?");
+
+ // The split loop structure here is so that we only need to recalculate
+ // the dominator tree once. Alternatively, we could just keep it up to
+ // date and use a more natural merged loop.
+ SetVector<BasicBlock *> SplitBackedges;
+ for (BasicBlock *Header : Headers) {
+ BasicBlock *NewBB = SplitEdge(Term->getParent(), Header, &DT);
+ PollsNeeded.push_back(NewBB->getTerminator());
+ NumBackedgeSafepoints++;
+ }
+ } else {
+ // Split the latch block itself, right before the terminator.
+ PollsNeeded.push_back(Term);
+ NumBackedgeSafepoints++;
+ }
+ }
+ }
+
+ if (enableEntrySafepoints(F)) {
+ if (Instruction *Location = findLocationForEntrySafepoint(F, DT)) {
+ PollsNeeded.push_back(Location);
+ Modified = true;
+ NumEntrySafepoints++;
+ }
+ // TODO: else we should assert that there was, in fact, a policy choice to
+ // not insert a entry safepoint poll.
+ }
+
+ // Now that we've identified all the needed safepoint poll locations, insert
+ // safepoint polls themselves.
+ for (Instruction *PollLocation : PollsNeeded) {
+ std::vector<CallBase *> RuntimeCalls;
+ InsertSafepointPoll(PollLocation, RuntimeCalls, TLI);
+ llvm::append_range(ParsePointNeeded, RuntimeCalls);
+ }
+
+ return Modified;
+}
+
+char PlaceBackedgeSafepointsImpl::ID = 0;
+char PlaceSafepoints::ID = 0;
+
+FunctionPass *llvm::createPlaceSafepointsPass() {
+ return new PlaceSafepoints();
+}
+
+INITIALIZE_PASS_BEGIN(PlaceBackedgeSafepointsImpl,
+ "place-backedge-safepoints-impl",
+ "Place Backedge Safepoints", false, false)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_END(PlaceBackedgeSafepointsImpl,
+ "place-backedge-safepoints-impl",
+ "Place Backedge Safepoints", false, false)
+
+INITIALIZE_PASS_BEGIN(PlaceSafepoints, "place-safepoints", "Place Safepoints",
+ false, false)
+INITIALIZE_PASS_END(PlaceSafepoints, "place-safepoints", "Place Safepoints",
+ false, false)
+
+static void
+InsertSafepointPoll(Instruction *InsertBefore,
+ std::vector<CallBase *> &ParsePointsNeeded /*rval*/,
+ const TargetLibraryInfo &TLI) {
+ BasicBlock *OrigBB = InsertBefore->getParent();
+ Module *M = InsertBefore->getModule();
+ assert(M && "must be part of a module");
+
+ // Inline the safepoint poll implementation - this will get all the branch,
+ // control flow, etc.. Most importantly, it will introduce the actual slow
+ // path call - where we need to insert a safepoint (parsepoint).
+
+ auto *F = M->getFunction(GCSafepointPollName);
+ assert(F && "gc.safepoint_poll function is missing");
+ assert(F->getValueType() ==
+ FunctionType::get(Type::getVoidTy(M->getContext()), false) &&
+ "gc.safepoint_poll declared with wrong type");
+ assert(!F->empty() && "gc.safepoint_poll must be a non-empty function");
+ CallInst *PollCall = CallInst::Create(F, "", InsertBefore);
+
+ // Record some information about the call site we're replacing
+ BasicBlock::iterator Before(PollCall), After(PollCall);
+ bool IsBegin = false;
+ if (Before == OrigBB->begin())
+ IsBegin = true;
+ else
+ Before--;
+
+ After++;
+ assert(After != OrigBB->end() && "must have successor");
+
+ // Do the actual inlining
+ InlineFunctionInfo IFI;
+ bool InlineStatus = InlineFunction(*PollCall, IFI).isSuccess();
+ assert(InlineStatus && "inline must succeed");
+ (void)InlineStatus; // suppress warning in release-asserts
+
+ // Check post-conditions
+ assert(IFI.StaticAllocas.empty() && "can't have allocs");
+
+ std::vector<CallInst *> Calls; // new calls
+ DenseSet<BasicBlock *> BBs; // new BBs + insertee
+
+ // Include only the newly inserted instructions, Note: begin may not be valid
+ // if we inserted to the beginning of the basic block
+ BasicBlock::iterator Start = IsBegin ? OrigBB->begin() : std::next(Before);
+
+ // If your poll function includes an unreachable at the end, that's not
+ // valid. Bugpoint likes to create this, so check for it.
+ assert(isPotentiallyReachable(&*Start, &*After) &&
+ "malformed poll function");
+
+ scanInlinedCode(&*Start, &*After, Calls, BBs);
+ assert(!Calls.empty() && "slow path not found for safepoint poll");
+
+ // Record the fact we need a parsable state at the runtime call contained in
+ // the poll function. This is required so that the runtime knows how to
+ // parse the last frame when we actually take the safepoint (i.e. execute
+ // the slow path)
+ assert(ParsePointsNeeded.empty());
+ for (auto *CI : Calls) {
+ // No safepoint needed or wanted
+ if (!needsStatepoint(CI, TLI))
+ continue;
+
+ // These are likely runtime calls. Should we assert that via calling
+ // convention or something?
+ ParsePointsNeeded.push_back(CI);
+ }
+ assert(ParsePointsNeeded.size() <= Calls.size());
+}