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Diffstat (limited to 'lib/Transforms/Scalar/PlaceSafepoints.cpp')
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diff --git a/lib/Transforms/Scalar/PlaceSafepoints.cpp b/lib/Transforms/Scalar/PlaceSafepoints.cpp new file mode 100644 index 0000000..944725a --- /dev/null +++ b/lib/Transforms/Scalar/PlaceSafepoints.cpp @@ -0,0 +1,989 @@ +//===- PlaceSafepoints.cpp - Place GC Safepoints --------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// 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 neccessary 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/Pass.h" +#include "llvm/IR/LegacyPassManager.h" +#include "llvm/ADT/SetOperations.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/LoopPass.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/Analysis/ScalarEvolutionExpressions.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Statepoint.h" +#include "llvm/IR/Value.h" +#include "llvm/IR/Verifier.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/raw_ostream.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(NumCallSafepoints, "Number of call safepoints inserted"); +STATISTIC(NumBackedgeSafepoints, "Number of backedge safepoints inserted"); + +STATISTIC(CallInLoop, "Number of loops w/o safepoints due to calls in loop"); +STATISTIC(FiniteExecution, "Number of loops w/o safepoints finite execution"); + +using namespace llvm; + +// Ignore oppurtunities to avoid placing safepoints on backedges, useful for +// validation +static cl::opt<bool> AllBackedges("spp-all-backedges", cl::Hidden, + cl::init(false)); + +/// If true, do not place backedge safepoints in counted loops. +static cl::opt<bool> SkipCounted("spp-counted", cl::Hidden, cl::init(true)); + +// 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)); + +// Print tracing output +static cl::opt<bool> TraceLSP("spp-trace", 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 LoopPass { + 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<TerminatorInst *> PollLocations; + + /// True unless we're running spp-no-calls in which case we need to disable + /// the call dependend placement opts. + bool CallSafepointsEnabled; + PlaceBackedgeSafepointsImpl(bool CallSafepoints = false) + : LoopPass(ID), CallSafepointsEnabled(CallSafepoints) { + initializePlaceBackedgeSafepointsImplPass(*PassRegistry::getPassRegistry()); + } + + bool runOnLoop(Loop *, LPPassManager &LPM) override; + + void getAnalysisUsage(AnalysisUsage &AU) const override { + // needed for determining if the loop is finite + AU.addRequired<ScalarEvolution>(); + // to ensure each edge has a single backedge + // TODO: is this still required? + AU.addRequiredID(LoopSimplifyID); + + // 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 ModulePass { + static char ID; // Pass identification, replacement for typeid + + PlaceSafepoints() : ModulePass(ID) { + initializePlaceSafepointsPass(*PassRegistry::getPassRegistry()); + } + bool runOnModule(Module &M) override { + bool modified = false; + for (Function &F : M) { + modified |= runOnFunction(F); + } + return modified; + } + bool runOnFunction(Function &F); + + 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 + } +}; +} + +// 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(DominatorTree &DT, Instruction *after, + std::vector<CallSite> &ParsePointsNeeded /*rval*/); + +static bool isGCLeafFunction(const CallSite &CS); + +static bool needsStatepoint(const CallSite &CS) { + if (isGCLeafFunction(CS)) + return false; + if (CS.isCall()) { + CallInst *call = cast<CallInst>(CS.getInstruction()); + if (call->isInlineAsm()) + return false; + } + if (isStatepoint(CS) || isGCRelocate(CS) || isGCResult(CS)) { + return false; + } + return true; +} + +static Value *ReplaceWithStatepoint(const CallSite &CS, Pass *P); + +/// 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) { + // 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 substaintially more occurences 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 (CallSite CS = &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(CS)) + 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) { + // Only used when SkipCounted is off + const unsigned upperTripBound = 8192; + + // A conservative bound on the loop as a whole. + const SCEV *MaxTrips = SE->getMaxBackedgeTakenCount(L); + if (MaxTrips != SE->getCouldNotCompute()) { + if (SE->getUnsignedRange(MaxTrips).getUnsignedMax().ult(upperTripBound)) + return true; + if (SkipCounted && + SE->getUnsignedRange(MaxTrips).getUnsignedMax().isIntN(32)) + 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 (MaxExec != SE->getCouldNotCompute()) { + if (SE->getUnsignedRange(MaxExec).getUnsignedMax().ult(upperTripBound)) + return true; + if (SkipCounted && + SE->getUnsignedRange(MaxExec).getUnsignedMax().isIntN(32)) + return true; + } + } + + return /* not finite */ false; +} + +static void scanOneBB(Instruction *start, Instruction *end, + std::vector<CallInst *> &calls, + std::set<BasicBlock *> &seen, + std::vector<BasicBlock *> &worklist) { + for (BasicBlock::iterator itr(start); + itr != start->getParent()->end() && itr != BasicBlock::iterator(end); + itr++) { + if (CallInst *CI = dyn_cast<CallInst>(&*itr)) { + calls.push_back(CI); + } + // FIXME: This code does not handle invokes + assert(!dyn_cast<InvokeInst>(&*itr) && + "support for invokes in poll code needed"); + // Only add the successor blocks if we reach the terminator instruction + // without encountering end first + if (itr->isTerminator()) { + BasicBlock *BB = itr->getParent(); + for (BasicBlock *Succ : successors(BB)) { + if (seen.count(Succ) == 0) { + worklist.push_back(Succ); + seen.insert(Succ); + } + } + } + } +} +static void scanInlinedCode(Instruction *start, Instruction *end, + std::vector<CallInst *> &calls, + std::set<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, LPPassManager &LPM) { + ScalarEvolution *SE = &getAnalysis<ScalarEvolution>(); + + // Loop through all predecessors of the loop header and identify all + // backedges. We need to place a safepoint on every backedge (potentially). + // Note: Due to LoopSimplify there should only be one. Assert? Or can we + // relax this? + BasicBlock *header = L->getHeader(); + + // TODO: Use the analysis pass infrastructure for this. There is no reason + // to recalculate this here. + DominatorTree DT; + DT.recalculate(*header->getParent()); + + bool modified = false; + for (BasicBlock *pred : predecessors(header)) { + if (!L->contains(pred)) { + // This is not a backedge, it's coming from outside the loop + continue; + } + + // 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)) { + if (TraceLSP) + errs() << "skipping safepoint placement in finite loop\n"; + FiniteExecution++; + continue; + } + if (CallSafepointsEnabled && + containsUnconditionalCallSafepoint(L, header, pred, DT)) { + // 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. + if (TraceLSP) + errs() << "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. + + // We're unconditionally going to modify this loop. + modified = true; + + // 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 + TerminatorInst *term = pred->getTerminator(); + + if (TraceLSP) { + errs() << "[LSP] terminator instruction: "; + term->dump(); + } + + PollLocations.push_back(term); + } + + return modified; +} + +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. + + // Due to the way the frontend generates IR, we may have a couple of initial + // basic blocks before the first bytecode. These will be single-entry + // single-exit blocks which conceptually are just part of the first 'real + // basic block'. Since we don't have deopt state until the first bytecode, + // walk forward until we've found the first unconditional branch or merge. + + // 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 = [&hasNextInstruction](Instruction *I) { + assert(hasNextInstruction(I) && + "first check if there is a next instruction!"); + if (I->isTerminator()) { + return I->getParent()->getUniqueSuccessor()->begin(); + } else { + return std::next(BasicBlock::iterator(I)); + } + }; + + Instruction *cursor = nullptr; + for (cursor = F.getEntryBlock().begin(); hasNextInstruction(cursor); + cursor = nextInstruction(cursor)) { + + // We need to stop going forward as soon as we see a call that can + // grow the stack (i.e. the call target has a non-zero frame + // size). + if (CallSite CS = cursor) { + (void)CS; // Silence an unused variable warning by gcc 4.8.2 + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(cursor)) { + // llvm.assume(...) are not really calls. + if (II->getIntrinsicID() == Intrinsic::assume) { + continue; + } + } + break; + } + } + + assert((hasNextInstruction(cursor) || cursor->isTerminator()) && + "either we stopped because of a call, or because of terminator"); + + if (cursor->isTerminator()) { + return cursor; + } + + BasicBlock *BB = cursor->getParent(); + SplitBlock(BB, cursor, nullptr); + + // Note: SplitBlock modifies the DT. Simply passing a Pass (which is a + // module pass) is not enough. + DT.recalculate(F); +#ifndef NDEBUG + // SplitBlock updates the DT + DT.verifyDomTree(); +#endif + + return BB->getTerminator(); +} + +/// Identify the list of call sites which need to be have parseable state +static void findCallSafepoints(Function &F, + std::vector<CallSite> &Found /*rval*/) { + assert(Found.empty() && "must be empty!"); + for (Instruction &I : inst_range(F)) { + Instruction *inst = &I; + if (isa<CallInst>(inst) || isa<InvokeInst>(inst)) { + CallSite CS(inst); + + // No safepoint needed or wanted + if (!needsStatepoint(CS)) { + continue; + } + + Found.push_back(CS); + } + } +} + +/// Implement a unique function which doesn't require we sort the input +/// vector. Doing so has the effect of changing the output of a couple of +/// tests in ways which make them less useful in testing fused safepoints. +template <typename T> static void unique_unsorted(std::vector<T> &vec) { + std::set<T> seen; + std::vector<T> tmp; + vec.reserve(vec.size()); + std::swap(tmp, vec); + for (auto V : tmp) { + if (seen.insert(V).second) { + vec.push_back(V); + } + } +} + +static std::string 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 std::string StatepointExampleName("statepoint-example"); + return StatepointExampleName == F.getGC(); + } 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; + + 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. + + // Note: With the migration, we need to recompute this for each 'pass'. Once + // we merge these, we'll do it once before the analysis + DominatorTree DT; + + std::vector<CallSite> 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); + PlaceBackedgeSafepointsImpl *PBS = + new PlaceBackedgeSafepointsImpl(CanAssumeCallSafepoints); + FPM.add(PBS); + // Note: While the analysis pass itself won't modify the IR, LoopSimplify + // (which it depends on) may. i.e. analysis must be recalculated after run + FPM.run(F); + + // We preserve dominance information when inserting the poll, otherwise + // we'd have to recalculate this on every insert + DT.recalculate(F); + + // Insert a poll at each point the analysis pass identified + for (size_t i = 0; i < PBS->PollLocations.size(); i++) { + // We are inserting a poll, the function is modified + modified = true; + + // The poll location must be the terminator of a loop latch block. + TerminatorInst *Term = PBS->PollLocations[i]; + + std::vector<CallSite> ParsePoints; + 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. (Note: This still relies on LoopSimplify.) + DenseSet<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. + DenseSet<BasicBlock *> SplitBackedges; + for (BasicBlock *Header : Headers) { + BasicBlock *NewBB = SplitEdge(Term->getParent(), Header, nullptr); + SplitBackedges.insert(NewBB); + } + DT.recalculate(F); + for (BasicBlock *NewBB : SplitBackedges) { + InsertSafepointPoll(DT, NewBB->getTerminator(), ParsePoints); + NumBackedgeSafepoints++; + } + + } else { + // Split the latch block itself, right before the terminator. + InsertSafepointPoll(DT, Term, ParsePoints); + NumBackedgeSafepoints++; + } + + // Record the parse points for later use + ParsePointNeeded.insert(ParsePointNeeded.end(), ParsePoints.begin(), + ParsePoints.end()); + } + } + + if (enableEntrySafepoints(F)) { + DT.recalculate(F); + Instruction *term = findLocationForEntrySafepoint(F, DT); + if (!term) { + // policy choice not to insert? + } else { + std::vector<CallSite> RuntimeCalls; + InsertSafepointPoll(DT, term, RuntimeCalls); + modified = true; + NumEntrySafepoints++; + ParsePointNeeded.insert(ParsePointNeeded.end(), RuntimeCalls.begin(), + RuntimeCalls.end()); + } + } + + if (enableCallSafepoints(F)) { + DT.recalculate(F); + std::vector<CallSite> Calls; + findCallSafepoints(F, Calls); + NumCallSafepoints += Calls.size(); + ParsePointNeeded.insert(ParsePointNeeded.end(), Calls.begin(), Calls.end()); + } + + // Unique the vectors since we can end up with duplicates if we scan the call + // site for call safepoints after we add it for entry or backedge. The + // only reason we need tracking at all is that some functions might have + // polls but not call safepoints and thus we might miss marking the runtime + // calls for the polls. (This is useful in test cases!) + unique_unsorted(ParsePointNeeded); + + // Any parse point (no matter what source) will be handled here + DT.recalculate(F); // Needed? + + // We're about to start modifying the function + if (!ParsePointNeeded.empty()) + modified = true; + + // Now run through and insert the safepoints, but do _NOT_ update or remove + // any existing uses. We have references to live variables that need to + // survive to the last iteration of this loop. + std::vector<Value *> Results; + Results.reserve(ParsePointNeeded.size()); + for (size_t i = 0; i < ParsePointNeeded.size(); i++) { + CallSite &CS = ParsePointNeeded[i]; + Value *GCResult = ReplaceWithStatepoint(CS, nullptr); + Results.push_back(GCResult); + } + assert(Results.size() == ParsePointNeeded.size()); + + // Adjust all users of the old call sites to use the new ones instead + for (size_t i = 0; i < ParsePointNeeded.size(); i++) { + CallSite &CS = ParsePointNeeded[i]; + Value *GCResult = Results[i]; + if (GCResult) { + // In case if we inserted result in a different basic block than the + // original safepoint (this can happen for invokes). We need to be sure + // that + // original result value was not used in any of the phi nodes at the + // beginning of basic block with gc result. Because we know that all such + // blocks will have single predecessor we can safely assume that all phi + // nodes have single entry (because of normalizeBBForInvokeSafepoint). + // Just remove them all here. + if (CS.isInvoke()) { + FoldSingleEntryPHINodes(cast<Instruction>(GCResult)->getParent(), + nullptr); + assert( + !isa<PHINode>(cast<Instruction>(GCResult)->getParent()->begin())); + } + + // Replace all uses with the new call + CS.getInstruction()->replaceAllUsesWith(GCResult); + } + + // Now that we've handled all uses, remove the original call itself + // Note: The insert point can't be the deleted instruction! + CS.getInstruction()->eraseFromParent(); + } + return modified; +} + +char PlaceBackedgeSafepointsImpl::ID = 0; +char PlaceSafepoints::ID = 0; + +ModulePass *llvm::createPlaceSafepointsPass() { return new PlaceSafepoints(); } + +INITIALIZE_PASS_BEGIN(PlaceBackedgeSafepointsImpl, + "place-backedge-safepoints-impl", + "Place Backedge Safepoints", false, false) +INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) +INITIALIZE_PASS_DEPENDENCY(LoopSimplify) +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 bool isGCLeafFunction(const CallSite &CS) { + Instruction *inst = CS.getInstruction(); + if (isa<IntrinsicInst>(inst)) { + // Most LLVM intrinsics are things which can never take a safepoint. + // As a result, we don't need to have the stack parsable at the + // callsite. This is a highly useful optimization since intrinsic + // calls are fairly prevelent, particularly in debug builds. + return true; + } + + // If this function is marked explicitly as a leaf call, we don't need to + // place a safepoint of it. In fact, for correctness we *can't* in many + // cases. Note: Indirect calls return Null for the called function, + // these obviously aren't runtime functions with attributes + // TODO: Support attributes on the call site as well. + const Function *F = CS.getCalledFunction(); + bool isLeaf = + F && + F->getFnAttribute("gc-leaf-function").getValueAsString().equals("true"); + if (isLeaf) { + return true; + } + return false; +} + +static void +InsertSafepointPoll(DominatorTree &DT, Instruction *term, + std::vector<CallSite> &ParsePointsNeeded /*rval*/) { + Module *M = term->getParent()->getParent()->getParent(); + assert(M); + + // 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). + FunctionType *ftype = + FunctionType::get(Type::getVoidTy(M->getContext()), false); + assert(ftype && "null?"); + // Note: This cast can fail if there's a function of the same name with a + // different type inserted previously + Function *F = + dyn_cast<Function>(M->getOrInsertFunction("gc.safepoint_poll", ftype)); + assert(F && "void @gc.safepoint_poll() must be defined"); + assert(!F->empty() && "gc.safepoint_poll must be a non-empty function"); + CallInst *poll = CallInst::Create(F, "", term); + + // Record some information about the call site we're replacing + BasicBlock *OrigBB = term->getParent(); + BasicBlock::iterator before(poll), after(poll); + bool isBegin(false); + if (before == term->getParent()->begin()) { + isBegin = true; + } else { + before--; + } + after++; + assert(after != poll->getParent()->end() && "must have successor"); + assert(DT.dominates(before, after) && "trivially true"); + + // do the actual inlining + InlineFunctionInfo IFI; + bool inlineStatus = InlineFunction(poll, IFI); + 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 + std::set<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; + if (isBegin) { + start = OrigBB->begin(); + } else { + start = before; + start++; + } + + // 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, nullptr, nullptr) && + "malformed poll function"); + + scanInlinedCode(&*(start), &*(after), calls, BBs); + + // Recompute since we've invalidated cached data. Conceptually we + // shouldn't need to do this, but implementation wise we appear to. Needed + // so we can insert safepoints correctly. + // TODO: update more cheaply + DT.recalculate(*after->getParent()->getParent()); + + 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 (size_t i = 0; i < calls.size(); i++) { + + // No safepoint needed or wanted + if (!needsStatepoint(calls[i])) { + continue; + } + + // These are likely runtime calls. Should we assert that via calling + // convention or something? + ParsePointsNeeded.push_back(CallSite(calls[i])); + } + assert(ParsePointsNeeded.size() <= calls.size()); +} + +// Normalize basic block to make it ready to be target of invoke statepoint. +// It means spliting it to have single predecessor. Return newly created BB +// ready to be successor of invoke statepoint. +static BasicBlock *normalizeBBForInvokeSafepoint(BasicBlock *BB, + BasicBlock *InvokeParent) { + BasicBlock *ret = BB; + + if (!BB->getUniquePredecessor()) { + ret = SplitBlockPredecessors(BB, InvokeParent, ""); + } + + // Another requirement for such basic blocks is to not have any phi nodes. + // Since we just ensured that new BB will have single predecessor, + // all phi nodes in it will have one value. Here it would be naturall place + // to + // remove them all. But we can not do this because we are risking to remove + // one of the values stored in liveset of another statepoint. We will do it + // later after placing all safepoints. + + return ret; +} + +/// Replaces the given call site (Call or Invoke) with a gc.statepoint +/// intrinsic with an empty deoptimization arguments list. This does +/// NOT do explicit relocation for GC support. +static Value *ReplaceWithStatepoint(const CallSite &CS, /* to replace */ + Pass *P) { + BasicBlock *BB = CS.getInstruction()->getParent(); + Function *F = BB->getParent(); + Module *M = F->getParent(); + assert(M && "must be set"); + + // TODO: technically, a pass is not allowed to get functions from within a + // function pass since it might trigger a new function addition. Refactor + // this logic out to the initialization of the pass. Doesn't appear to + // matter in practice. + + // Then go ahead and use the builder do actually do the inserts. We insert + // immediately before the previous instruction under the assumption that all + // arguments will be available here. We can't insert afterwards since we may + // be replacing a terminator. + Instruction *insertBefore = CS.getInstruction(); + IRBuilder<> Builder(insertBefore); + + // Note: The gc args are not filled in at this time, that's handled by + // RewriteStatepointsForGC (which is currently under review). + + // Create the statepoint given all the arguments + Instruction *token = nullptr; + AttributeSet return_attributes; + if (CS.isCall()) { + CallInst *toReplace = cast<CallInst>(CS.getInstruction()); + CallInst *Call = Builder.CreateGCStatepoint( + CS.getCalledValue(), makeArrayRef(CS.arg_begin(), CS.arg_end()), None, + None, "safepoint_token"); + Call->setTailCall(toReplace->isTailCall()); + Call->setCallingConv(toReplace->getCallingConv()); + + // Before we have to worry about GC semantics, all attributes are legal + AttributeSet new_attrs = toReplace->getAttributes(); + // In case if we can handle this set of sttributes - set up function attrs + // directly on statepoint and return attrs later for gc_result intrinsic. + Call->setAttributes(new_attrs.getFnAttributes()); + return_attributes = new_attrs.getRetAttributes(); + // TODO: handle param attributes + + token = Call; + + // Put the following gc_result and gc_relocate calls immediately after the + // the old call (which we're about to delete) + BasicBlock::iterator next(toReplace); + assert(BB->end() != next && "not a terminator, must have next"); + next++; + Instruction *IP = &*(next); + Builder.SetInsertPoint(IP); + Builder.SetCurrentDebugLocation(IP->getDebugLoc()); + + } else if (CS.isInvoke()) { + // TODO: make CreateGCStatepoint return an Instruction that we can cast to a + // Call or Invoke, instead of doing this junk here. + + // Fill in the one generic type'd argument (the function is also + // vararg) + std::vector<Type *> argTypes; + argTypes.push_back(CS.getCalledValue()->getType()); + + Function *gc_statepoint_decl = Intrinsic::getDeclaration( + M, Intrinsic::experimental_gc_statepoint, argTypes); + + // First, create the statepoint (with all live ptrs as arguments). + std::vector<llvm::Value *> args; + // target, #call args, unused, ... call parameters, #deopt args, ... deopt + // parameters, ... gc parameters + Value *Target = CS.getCalledValue(); + args.push_back(Target); + int callArgSize = CS.arg_size(); + // #call args + args.push_back(Builder.getInt32(callArgSize)); + // unused + args.push_back(Builder.getInt32(0)); + // call parameters + args.insert(args.end(), CS.arg_begin(), CS.arg_end()); + // #deopt args: 0 + args.push_back(Builder.getInt32(0)); + + InvokeInst *toReplace = cast<InvokeInst>(CS.getInstruction()); + + // Insert the new invoke into the old block. We'll remove the old one in a + // moment at which point this will become the new terminator for the + // original block. + InvokeInst *invoke = InvokeInst::Create( + gc_statepoint_decl, toReplace->getNormalDest(), + toReplace->getUnwindDest(), args, "", toReplace->getParent()); + invoke->setCallingConv(toReplace->getCallingConv()); + + // Currently we will fail on parameter attributes and on certain + // function attributes. + AttributeSet new_attrs = toReplace->getAttributes(); + // In case if we can handle this set of sttributes - set up function attrs + // directly on statepoint and return attrs later for gc_result intrinsic. + invoke->setAttributes(new_attrs.getFnAttributes()); + return_attributes = new_attrs.getRetAttributes(); + + token = invoke; + + // We'll insert the gc.result into the normal block + BasicBlock *normalDest = normalizeBBForInvokeSafepoint( + toReplace->getNormalDest(), invoke->getParent()); + Instruction *IP = &*(normalDest->getFirstInsertionPt()); + Builder.SetInsertPoint(IP); + } else { + llvm_unreachable("unexpect type of CallSite"); + } + assert(token); + + // Handle the return value of the original call - update all uses to use a + // gc_result hanging off the statepoint node we just inserted + + // Only add the gc_result iff there is actually a used result + if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) { + std::string takenName = + CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : ""; + CallInst *gc_result = + Builder.CreateGCResult(token, CS.getType(), takenName); + gc_result->setAttributes(return_attributes); + return gc_result; + } else { + // No return value for the call. + return nullptr; + } +} |