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e10581ac39
Use the IRBuilder helpers for gc.statepoint and gc.result, instead of coding the construction by hand. Note that the gc.statepoint IRBuilder handles only CallInst, not InvokeInst; retain that part of hand-coding. Differential Revision: http://reviews.llvm.org/D7518 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230591 91177308-0d34-0410-b5e6-96231b3b80d8
990 lines
38 KiB
C++
990 lines
38 KiB
C++
//===- PlaceSafepoints.cpp - Place GC Safepoints --------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Place garbage collection safepoints at appropriate locations in the IR. This
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// does not make relocation semantics or variable liveness explicit. That's
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// done by RewriteStatepointsForGC.
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//
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// Terminology:
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// - A call is said to be "parseable" if there is a stack map generated for the
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// return PC of the call. A runtime can determine where values listed in the
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// deopt arguments and (after RewriteStatepointsForGC) gc arguments are located
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// on the stack when the code is suspended inside such a call. Every parse
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// point is represented by a call wrapped in an gc.statepoint intrinsic.
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// - A "poll" is an explicit check in the generated code to determine if the
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// runtime needs the generated code to cooperate by calling a helper routine
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// and thus suspending its execution at a known state. The call to the helper
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// routine will be parseable. The (gc & runtime specific) logic of a poll is
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// assumed to be provided in a function of the name "gc.safepoint_poll".
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//
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// We aim to insert polls such that running code can quickly be brought to a
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// well defined state for inspection by the collector. In the current
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// implementation, this is done via the insertion of poll sites at method entry
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// and the backedge of most loops. We try to avoid inserting more polls than
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// are neccessary to ensure a finite period between poll sites. This is not
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// because the poll itself is expensive in the generated code; it's not. Polls
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// do tend to impact the optimizer itself in negative ways; we'd like to avoid
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// perturbing the optimization of the method as much as we can.
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//
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// We also need to make most call sites parseable. The callee might execute a
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// poll (or otherwise be inspected by the GC). If so, the entire stack
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// (including the suspended frame of the current method) must be parseable.
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//
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// This pass will insert:
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// - Call parse points ("call safepoints") for any call which may need to
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// reach a safepoint during the execution of the callee function.
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// - Backedge safepoint polls and entry safepoint polls to ensure that
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// executing code reaches a safepoint poll in a finite amount of time.
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//
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// We do not currently support return statepoints, but adding them would not
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// be hard. They are not required for correctness - entry safepoints are an
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// alternative - but some GCs may prefer them. Patches welcome.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Pass.h"
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#include "llvm/IR/LegacyPassManager.h"
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#include "llvm/ADT/SetOperations.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/CFG.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/CallSite.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Statepoint.h"
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#include "llvm/IR/Value.h"
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#include "llvm/IR/Verifier.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Transforms/Utils/Local.h"
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#define DEBUG_TYPE "safepoint-placement"
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STATISTIC(NumEntrySafepoints, "Number of entry safepoints inserted");
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STATISTIC(NumCallSafepoints, "Number of call safepoints inserted");
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STATISTIC(NumBackedgeSafepoints, "Number of backedge safepoints inserted");
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STATISTIC(CallInLoop, "Number of loops w/o safepoints due to calls in loop");
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STATISTIC(FiniteExecution, "Number of loops w/o safepoints finite execution");
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using namespace llvm;
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// Ignore oppurtunities to avoid placing safepoints on backedges, useful for
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// validation
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static cl::opt<bool> AllBackedges("spp-all-backedges", cl::Hidden,
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cl::init(false));
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/// If true, do not place backedge safepoints in counted loops.
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static cl::opt<bool> SkipCounted("spp-counted", cl::Hidden, cl::init(true));
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// If true, split the backedge of a loop when placing the safepoint, otherwise
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// split the latch block itself. Both are useful to support for
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// experimentation, but in practice, it looks like splitting the backedge
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// optimizes better.
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static cl::opt<bool> SplitBackedge("spp-split-backedge", cl::Hidden,
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cl::init(false));
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// Print tracing output
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static cl::opt<bool> TraceLSP("spp-trace", cl::Hidden, cl::init(false));
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namespace {
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/** An analysis pass whose purpose is to identify each of the backedges in
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the function which require a safepoint poll to be inserted. */
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struct PlaceBackedgeSafepointsImpl : public LoopPass {
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static char ID;
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/// The output of the pass - gives a list of each backedge (described by
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/// pointing at the branch) which need a poll inserted.
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std::vector<TerminatorInst *> PollLocations;
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/// True unless we're running spp-no-calls in which case we need to disable
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/// the call dependend placement opts.
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bool CallSafepointsEnabled;
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PlaceBackedgeSafepointsImpl(bool CallSafepoints = false)
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: LoopPass(ID), CallSafepointsEnabled(CallSafepoints) {
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initializePlaceBackedgeSafepointsImplPass(*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop *, LPPassManager &LPM) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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// needed for determining if the loop is finite
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AU.addRequired<ScalarEvolution>();
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// to ensure each edge has a single backedge
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// TODO: is this still required?
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AU.addRequiredID(LoopSimplifyID);
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// We no longer modify the IR at all in this pass. Thus all
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// analysis are preserved.
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AU.setPreservesAll();
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}
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};
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}
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static cl::opt<bool> NoEntry("spp-no-entry", cl::Hidden, cl::init(false));
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static cl::opt<bool> NoCall("spp-no-call", cl::Hidden, cl::init(false));
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static cl::opt<bool> NoBackedge("spp-no-backedge", cl::Hidden, cl::init(false));
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namespace {
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struct PlaceSafepoints : public ModulePass {
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static char ID; // Pass identification, replacement for typeid
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PlaceSafepoints() : ModulePass(ID) {
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initializePlaceSafepointsPass(*PassRegistry::getPassRegistry());
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}
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bool runOnModule(Module &M) override {
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bool modified = false;
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for (Function &F : M) {
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modified |= runOnFunction(F);
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}
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return modified;
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}
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bool runOnFunction(Function &F);
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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// We modify the graph wholesale (inlining, block insertion, etc). We
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// preserve nothing at the moment. We could potentially preserve dom tree
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// if that was worth doing
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}
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};
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}
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// Insert a safepoint poll immediately before the given instruction. Does
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// not handle the parsability of state at the runtime call, that's the
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// callers job.
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static void
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InsertSafepointPoll(DominatorTree &DT, Instruction *after,
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std::vector<CallSite> &ParsePointsNeeded /*rval*/);
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static bool isGCLeafFunction(const CallSite &CS);
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static bool needsStatepoint(const CallSite &CS) {
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if (isGCLeafFunction(CS))
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return false;
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if (CS.isCall()) {
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CallInst *call = cast<CallInst>(CS.getInstruction());
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if (call->isInlineAsm())
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return false;
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}
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if (isStatepoint(CS) || isGCRelocate(CS) || isGCResult(CS)) {
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return false;
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}
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return true;
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}
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static Value *ReplaceWithStatepoint(const CallSite &CS, Pass *P);
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/// Returns true if this loop is known to contain a call safepoint which
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/// must unconditionally execute on any iteration of the loop which returns
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/// to the loop header via an edge from Pred. Returns a conservative correct
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/// answer; i.e. false is always valid.
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static bool containsUnconditionalCallSafepoint(Loop *L, BasicBlock *Header,
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BasicBlock *Pred,
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DominatorTree &DT) {
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// In general, we're looking for any cut of the graph which ensures
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// there's a call safepoint along every edge between Header and Pred.
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// For the moment, we look only for the 'cuts' that consist of a single call
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// instruction in a block which is dominated by the Header and dominates the
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// loop latch (Pred) block. Somewhat surprisingly, walking the entire chain
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// of such dominating blocks gets substaintially more occurences than just
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// checking the Pred and Header blocks themselves. This may be due to the
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// density of loop exit conditions caused by range and null checks.
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// TODO: structure this as an analysis pass, cache the result for subloops,
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// avoid dom tree recalculations
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assert(DT.dominates(Header, Pred) && "loop latch not dominated by header?");
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BasicBlock *Current = Pred;
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while (true) {
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for (Instruction &I : *Current) {
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if (CallSite CS = &I)
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// Note: Technically, needing a safepoint isn't quite the right
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// condition here. We should instead be checking if the target method
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// has an
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// unconditional poll. In practice, this is only a theoretical concern
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// since we don't have any methods with conditional-only safepoint
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// polls.
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if (needsStatepoint(CS))
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return true;
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}
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if (Current == Header)
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break;
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Current = DT.getNode(Current)->getIDom()->getBlock();
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}
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return false;
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}
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/// Returns true if this loop is known to terminate in a finite number of
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/// iterations. Note that this function may return false for a loop which
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/// does actual terminate in a finite constant number of iterations due to
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/// conservatism in the analysis.
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static bool mustBeFiniteCountedLoop(Loop *L, ScalarEvolution *SE,
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BasicBlock *Pred) {
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// Only used when SkipCounted is off
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const unsigned upperTripBound = 8192;
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// A conservative bound on the loop as a whole.
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const SCEV *MaxTrips = SE->getMaxBackedgeTakenCount(L);
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if (MaxTrips != SE->getCouldNotCompute()) {
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if (SE->getUnsignedRange(MaxTrips).getUnsignedMax().ult(upperTripBound))
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return true;
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if (SkipCounted &&
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SE->getUnsignedRange(MaxTrips).getUnsignedMax().isIntN(32))
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return true;
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}
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// If this is a conditional branch to the header with the alternate path
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// being outside the loop, we can ask questions about the execution frequency
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// of the exit block.
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if (L->isLoopExiting(Pred)) {
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// This returns an exact expression only. TODO: We really only need an
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// upper bound here, but SE doesn't expose that.
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const SCEV *MaxExec = SE->getExitCount(L, Pred);
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if (MaxExec != SE->getCouldNotCompute()) {
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if (SE->getUnsignedRange(MaxExec).getUnsignedMax().ult(upperTripBound))
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return true;
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if (SkipCounted &&
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SE->getUnsignedRange(MaxExec).getUnsignedMax().isIntN(32))
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return true;
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}
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}
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return /* not finite */ false;
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}
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static void scanOneBB(Instruction *start, Instruction *end,
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std::vector<CallInst *> &calls,
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std::set<BasicBlock *> &seen,
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std::vector<BasicBlock *> &worklist) {
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for (BasicBlock::iterator itr(start);
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itr != start->getParent()->end() && itr != BasicBlock::iterator(end);
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itr++) {
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if (CallInst *CI = dyn_cast<CallInst>(&*itr)) {
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calls.push_back(CI);
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}
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// FIXME: This code does not handle invokes
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assert(!dyn_cast<InvokeInst>(&*itr) &&
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"support for invokes in poll code needed");
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// Only add the successor blocks if we reach the terminator instruction
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// without encountering end first
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if (itr->isTerminator()) {
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BasicBlock *BB = itr->getParent();
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for (BasicBlock *Succ : successors(BB)) {
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if (seen.count(Succ) == 0) {
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worklist.push_back(Succ);
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seen.insert(Succ);
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}
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}
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}
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}
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}
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static void scanInlinedCode(Instruction *start, Instruction *end,
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std::vector<CallInst *> &calls,
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std::set<BasicBlock *> &seen) {
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calls.clear();
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std::vector<BasicBlock *> worklist;
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seen.insert(start->getParent());
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scanOneBB(start, end, calls, seen, worklist);
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while (!worklist.empty()) {
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BasicBlock *BB = worklist.back();
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worklist.pop_back();
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scanOneBB(&*BB->begin(), end, calls, seen, worklist);
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}
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}
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bool PlaceBackedgeSafepointsImpl::runOnLoop(Loop *L, LPPassManager &LPM) {
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ScalarEvolution *SE = &getAnalysis<ScalarEvolution>();
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// Loop through all predecessors of the loop header and identify all
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// backedges. We need to place a safepoint on every backedge (potentially).
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// Note: Due to LoopSimplify there should only be one. Assert? Or can we
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// relax this?
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BasicBlock *header = L->getHeader();
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// TODO: Use the analysis pass infrastructure for this. There is no reason
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// to recalculate this here.
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DominatorTree DT;
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DT.recalculate(*header->getParent());
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bool modified = false;
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for (BasicBlock *pred : predecessors(header)) {
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if (!L->contains(pred)) {
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// This is not a backedge, it's coming from outside the loop
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continue;
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}
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// Make a policy decision about whether this loop needs a safepoint or
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// not. Note that this is about unburdening the optimizer in loops, not
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// avoiding the runtime cost of the actual safepoint.
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if (!AllBackedges) {
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if (mustBeFiniteCountedLoop(L, SE, pred)) {
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if (TraceLSP)
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errs() << "skipping safepoint placement in finite loop\n";
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FiniteExecution++;
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continue;
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}
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if (CallSafepointsEnabled &&
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containsUnconditionalCallSafepoint(L, header, pred, DT)) {
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// Note: This is only semantically legal since we won't do any further
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// IPO or inlining before the actual call insertion.. If we hadn't, we
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// might latter loose this call safepoint.
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if (TraceLSP)
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errs() << "skipping safepoint placement due to unconditional call\n";
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CallInLoop++;
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continue;
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}
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}
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// TODO: We can create an inner loop which runs a finite number of
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// iterations with an outer loop which contains a safepoint. This would
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// not help runtime performance that much, but it might help our ability to
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// optimize the inner loop.
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// We're unconditionally going to modify this loop.
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modified = true;
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// Safepoint insertion would involve creating a new basic block (as the
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// target of the current backedge) which does the safepoint (of all live
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// variables) and branches to the true header
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TerminatorInst *term = pred->getTerminator();
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if (TraceLSP) {
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errs() << "[LSP] terminator instruction: ";
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term->dump();
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}
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PollLocations.push_back(term);
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}
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return modified;
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}
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static Instruction *findLocationForEntrySafepoint(Function &F,
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DominatorTree &DT) {
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// Conceptually, this poll needs to be on method entry, but in
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// practice, we place it as late in the entry block as possible. We
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// can place it as late as we want as long as it dominates all calls
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// that can grow the stack. This, combined with backedge polls,
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// give us all the progress guarantees we need.
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// Due to the way the frontend generates IR, we may have a couple of initial
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// basic blocks before the first bytecode. These will be single-entry
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// single-exit blocks which conceptually are just part of the first 'real
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// basic block'. Since we don't have deopt state until the first bytecode,
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// walk forward until we've found the first unconditional branch or merge.
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// hasNextInstruction and nextInstruction are used to iterate
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// through a "straight line" execution sequence.
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auto hasNextInstruction = [](Instruction *I) {
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if (!I->isTerminator()) {
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return true;
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}
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BasicBlock *nextBB = I->getParent()->getUniqueSuccessor();
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return nextBB && (nextBB->getUniquePredecessor() != nullptr);
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};
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auto nextInstruction = [&hasNextInstruction](Instruction *I) {
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assert(hasNextInstruction(I) &&
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"first check if there is a next instruction!");
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if (I->isTerminator()) {
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return I->getParent()->getUniqueSuccessor()->begin();
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} else {
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return std::next(BasicBlock::iterator(I));
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}
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};
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Instruction *cursor = nullptr;
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for (cursor = F.getEntryBlock().begin(); hasNextInstruction(cursor);
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cursor = nextInstruction(cursor)) {
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// We need to stop going forward as soon as we see a call that can
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// grow the stack (i.e. the call target has a non-zero frame
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// size).
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if (CallSite CS = cursor) {
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(void)CS; // Silence an unused variable warning by gcc 4.8.2
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if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(cursor)) {
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// llvm.assume(...) are not really calls.
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if (II->getIntrinsicID() == Intrinsic::assume) {
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continue;
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}
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}
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break;
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}
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}
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assert((hasNextInstruction(cursor) || cursor->isTerminator()) &&
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"either we stopped because of a call, or because of terminator");
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if (cursor->isTerminator()) {
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return cursor;
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}
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BasicBlock *BB = cursor->getParent();
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SplitBlock(BB, cursor, nullptr);
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// Note: SplitBlock modifies the DT. Simply passing a Pass (which is a
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// module pass) is not enough.
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DT.recalculate(F);
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#ifndef NDEBUG
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// SplitBlock updates the DT
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DT.verifyDomTree();
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#endif
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return BB->getTerminator();
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}
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/// Identify the list of call sites which need to be have parseable state
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static void findCallSafepoints(Function &F,
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std::vector<CallSite> &Found /*rval*/) {
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assert(Found.empty() && "must be empty!");
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for (Instruction &I : inst_range(F)) {
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Instruction *inst = &I;
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if (isa<CallInst>(inst) || isa<InvokeInst>(inst)) {
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CallSite CS(inst);
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// 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;
|
|
}
|
|
}
|