// 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.
+// 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
// 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
+// are necessary to ensure a finite period between poll sites. This is not
// because the poll itself is expensive in the generated code; it's not. Polls
// do tend to impact the optimizer itself in negative ways; we'd like to avoid
// perturbing the optimization of the method as much as we can.
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
using namespace llvm;
-// Ignore oppurtunities to avoid placing safepoints on backedges, useful for
+// Ignore opportunities 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));
+/// How narrow does the trip count of a loop have to be to have to be considered
+/// "counted"? Counted loops do not get safepoints at backedges.
+static cl::opt<int> CountedLoopTripWidth("spp-counted-loop-trip-width",
+ cl::Hidden, cl::init(32));
// If true, split the backedge of a loop when placing the safepoint, otherwise
// split the latch block itself. Both are useful to support for
std::vector<TerminatorInst *> PollLocations;
/// True unless we're running spp-no-calls in which case we need to disable
- /// the call dependend placement opts.
+ /// the call-dependent placement opts.
bool CallSafepointsEnabled;
ScalarEvolution *SE = nullptr;
DominatorTree *DT = nullptr;
LoopInfo *LI = nullptr;
-
+
PlaceBackedgeSafepointsImpl(bool CallSafepoints = false)
: FunctionPass(ID), CallSafepointsEnabled(CallSafepoints) {
initializePlaceBackedgeSafepointsImplPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
- SE = &getAnalysis<ScalarEvolution>();
+ SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
for (auto I = LI->begin(), E = LI->end(); I != E; I++) {
}
return false;
}
-
+
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<DominatorTreeWrapperPass>();
- AU.addRequired<ScalarEvolution>();
+ AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
// We no longer modify the IR at all in this pass. Thus all
// analysis are preserved.
// Insert a safepoint poll immediately before the given instruction. Does
// not handle the parsability of state at the runtime call, that's the
// callers job.
-static void
-InsertSafepointPoll(Instruction *after,
+static void
+InsertSafepointPoll(Instruction *InsertBefore,
std::vector<CallSite> &ParsePointsNeeded /*rval*/);
-static bool isGCLeafFunction(const CallSite &CS);
-
static bool needsStatepoint(const CallSite &CS) {
- if (isGCLeafFunction(CS))
+ if (callsGCLeafFunction(CS))
return false;
if (CS.isCall()) {
CallInst *call = cast<CallInst>(CS.getInstruction());
return true;
}
-static Value *ReplaceWithStatepoint(const CallSite &CS, Pass *P);
+static Value *ReplaceWithStatepoint(const CallSite &CS);
/// Returns true if this loop is known to contain a call safepoint which
/// must unconditionally execute on any iteration of the loop which returns
// 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
+ // of such dominating blocks gets substantially more occurrences than just
// checking the Pred and Header blocks themselves. This may be due to the
// density of loop exit conditions caused by range and null checks.
// TODO: structure this as an analysis pass, cache the result for subloops,
/// 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 (MaxTrips != SE->getCouldNotCompute() &&
+ SE->getUnsignedRange(MaxTrips).getUnsignedMax().isIntN(
+ CountedLoopTripWidth))
+ return true;
// If this is a conditional branch to the header with the alternate path
// being outside the loop, we can ask questions about the execution frequency
// 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))
+ if (MaxExec != SE->getCouldNotCompute() &&
+ SE->getUnsignedRange(MaxExec).getUnsignedMax().isIntN(
+ CountedLoopTripWidth))
return true;
- }
}
return /* not finite */ false;
bool PlaceBackedgeSafepointsImpl::runOnLoop(Loop *L) {
// Loop through all loop latches (branches controlling backedges). We need
- // to place a safepoint on every backedge (potentially).
+ // to place a safepoint on every backedge (potentially).
// Note: In common usage, there will be only one edge due to LoopSimplify
// having run sometime earlier in the pipeline, but this code must be correct
// w.r.t. loops with multiple backedges.
return false;
}
+/// Returns true if an entry safepoint is not required before this callsite in
+/// the caller function.
+static bool doesNotRequireEntrySafepointBefore(const CallSite &CS) {
+ Instruction *Inst = CS.getInstruction();
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
+ switch (II->getIntrinsicID()) {
+ case Intrinsic::experimental_gc_statepoint:
+ case Intrinsic::experimental_patchpoint_void:
+ case Intrinsic::experimental_patchpoint_i64:
+ // The can wrap an actual call which may grow the stack by an unbounded
+ // amount or run forever.
+ return false;
+ default:
+ // Most LLVM intrinsics are things which do not expand to actual calls, or
+ // at least if they do, are leaf functions that cause only finite stack
+ // growth. In particular, the optimizer likes to form things like memsets
+ // out of stores in the original IR. Another important example is
+ // llvm.localescape which must occur in the entry block. Inserting a
+ // safepoint before it is not legal since it could push the localescape
+ // out of the entry block.
+ return true;
+ }
+ }
+ return false;
+}
+
static Instruction *findLocationForEntrySafepoint(Function &F,
DominatorTree &DT) {
// 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.
assert(hasNextInstruction(I) &&
"first check if there is a next instruction!");
if (I->isTerminator()) {
- return I->getParent()->getUniqueSuccessor()->begin();
+ return &I->getParent()->getUniqueSuccessor()->front();
} else {
- return std::next(BasicBlock::iterator(I));
+ return &*++I->getIterator();
}
};
Instruction *cursor = nullptr;
- for (cursor = F.getEntryBlock().begin(); hasNextInstruction(cursor);
+ for (cursor = &F.getEntryBlock().front(); 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(cursor)) {
- if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(cursor)) {
- // llvm.assume(...) are not really calls.
- if (II->getIntrinsicID() == Intrinsic::assume) {
- continue;
- }
- // llvm.frameescape() intrinsic is not a real call. The intrinsic can
- // exist only in the entry block.
- // Inserting a statepoint before llvm.frameescape() may split the
- // entry block, and push the intrinsic out of the entry block.
- if (II->getIntrinsicID() == Intrinsic::frameescape) {
- continue;
- }
- }
+ // We need to ensure a safepoint poll occurs before any 'real' call. The
+ // easiest way to ensure finite execution between safepoints in the face of
+ // recursive and mutually recursive functions is to enforce that each take
+ // a safepoint. Additionally, we need to ensure a poll before any call
+ // which can grow the stack by an unbounded amount. This isn't required
+ // for GC semantics per se, but is a common requirement for languages
+ // which detect stack overflow via guard pages and then throw exceptions.
+ if (auto CS = CallSite(cursor)) {
+ if (doesNotRequireEntrySafepointBefore(CS))
+ 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, &DT);
-
- // SplitBlock updates the DT
- DEBUG(DT.verifyDomTree());
-
- return BB->getTerminator();
+ return cursor;
}
/// 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)) {
+ for (Instruction &I : instructions(F)) {
Instruction *inst = &I;
if (isa<CallInst>(inst) || isa<InvokeInst>(inst)) {
CallSite CS(inst);
}
}
-static std::string GCSafepointPollName("gc.safepoint_poll");
+static const char *const 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.
+/// 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();
+ const auto &FunctionGCName = F.getGC();
+ const StringRef StatepointExampleName("statepoint-example");
+ const StringRef CoreCLRName("coreclr");
+ return (StatepointExampleName == FunctionGCName) ||
+ (CoreCLRName == FunctionGCName);
} else
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.
+ // parseable after we inline a poll.
return false;
}
for (TerminatorInst *Term : PollLocations) {
// We are inserting a poll, the function is modified
modified = true;
-
+
if (SplitBackedge) {
// Split the backedge of the loop and insert the poll within that new
// basic block. This creates a loop with two latches per original
// The dominator tree has been invalidated by the inlining performed in the
// above loop. TODO: Teach the inliner how to update the dom tree?
DT.recalculate(F);
-
+
if (enableCallSafepoints(F)) {
std::vector<CallSite> Calls;
findCallSafepoints(F, Calls);
Invoke->getParent());
}
- Value *GCResult = ReplaceWithStatepoint(CS, nullptr);
+ Value *GCResult = ReplaceWithStatepoint(CS);
Results.push_back(GCResult);
}
assert(Results.size() == ParsePointNeeded.size());
CallSite &CS = ParsePointNeeded[i];
Value *GCResult = Results[i];
if (GCResult) {
- // Can not RAUW for the gc result in case of phi nodes preset.
- assert(!isa<PHINode>(cast<Instruction>(GCResult)->getParent()->begin()));
+ // Can not RAUW for the invoke gc result in case of phi nodes preset.
+ assert(
CS.isCall() || !isa<PHINode>(cast<Instruction>(GCResult)->getParent()->begin()));
// Replace all uses with the new call
CS.getInstruction()->replaceAllUsesWith(GCResult);
INITIALIZE_PASS_BEGIN(PlaceBackedgeSafepointsImpl,
"place-backedge-safepoints-impl",
"Place Backedge Safepoints", false, false)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_END(PlaceBackedgeSafepointsImpl,
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(Instruction *term,
+InsertSafepointPoll(Instruction *InsertBefore,
std::vector<CallSite> &ParsePointsNeeded /*rval*/) {
- Module *M = term->getParent()->getParent()->getParent();
- assert(M);
+ BasicBlock *OrigBB = InsertBefore->getParent();
+ Module *M = InsertBefore->getModule();
+ assert(M && "must be part of a module");
// Inline the safepoint poll implementation - this will get all the branch,
// control flow, etc.. Most importantly, it will introduce the actual slow
// path call - where we need to insert a safepoint (parsepoint).
- 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");
+
+ auto *F = M->getFunction(GCSafepointPollName);
+ assert(F && "gc.safepoint_poll function is missing");
+ assert(F->getType()->getElementType() ==
+ FunctionType::get(Type::getVoidTy(M->getContext()), false) &&
+ "gc.safepoint_poll declared with wrong type");
assert(!F->empty() && "gc.safepoint_poll must be a non-empty function");
- CallInst *poll = CallInst::Create(F, "", term);
+ CallInst *PollCall = CallInst::Create(F, "", InsertBefore);
// Record some information about the call site we're replacing
- BasicBlock *OrigBB = term->getParent();
- BasicBlock::iterator before(poll), after(poll);
+ BasicBlock::iterator before(PollCall), after(PollCall);
bool isBegin(false);
- if (before == term->getParent()->begin()) {
+ if (before == OrigBB->begin()) {
isBegin = true;
} else {
before--;
}
after++;
- assert(after != poll->getParent()->end() && "must have successor");
+ assert(after != OrigBB->end() && "must have successor");
// do the actual inlining
InlineFunctionInfo IFI;
- bool inlineStatus = InlineFunction(poll, IFI);
- assert(inlineStatus && "inline must succeed");
- (void)inlineStatus; // suppress warning in release-asserts
+ bool InlineStatus = InlineFunction(PollCall, IFI);
+ assert(InlineStatus && "inline must succeed");
+ (void)InlineStatus; // suppress warning in release-asserts
// Check post conditions
assert(IFI.StaticAllocas.empty() && "can't have allocs");
/// 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) {
- assert(CS.getInstruction()->getParent()->getParent()->getParent() &&
- "must be set");
+static Value *ReplaceWithStatepoint(const CallSite &CS /* to replace */) {
+ assert(CS.getInstruction()->getModule() && "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
CS.getInstruction()->getContext(), AttributeSet::FunctionIndex,
AttrsToRemove);
- Value *StatepointTarget = NumPatchBytes == 0
- ? CS.getCalledValue()
- : ConstantPointerNull::get(cast<PointerType>(
- CS.getCalledValue()->getType()));
-
if (CS.isCall()) {
CallInst *ToReplace = cast<CallInst>(CS.getInstruction());
CallInst *Call = Builder.CreateGCStatepointCall(
- ID, NumPatchBytes, StatepointTarget,
+ ID, NumPatchBytes, CS.getCalledValue(),
makeArrayRef(CS.arg_begin(), CS.arg_end()), None, None,
"safepoint_token");
Call->setTailCall(ToReplace->isTailCall());
Token = Call;
- // Put the following gc_result and gc_relocate calls immediately after the
+ // Put the following gc_result and gc_relocate calls immediately after
// the old call (which we're about to delete).
assert(ToReplace->getNextNode() && "not a terminator, must have next");
Builder.SetInsertPoint(ToReplace->getNextNode());
// original block.
Builder.SetInsertPoint(ToReplace->getParent());
InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
- ID, NumPatchBytes, StatepointTarget, ToReplace->getNormalDest(),
+ ID, NumPatchBytes, CS.getCalledValue(), ToReplace->getNormalDest(),
ToReplace->getUnwindDest(), makeArrayRef(CS.arg_begin(), CS.arg_end()),
None, None, "safepoint_token");
+ Invoke->setCallingConv(ToReplace->getCallingConv());
+
// In case if we can handle this set of attributes - set up function
// attributes directly on statepoint and return attributes later for
// gc_result intrinsic.
// We'll insert the gc.result into the normal block
BasicBlock *NormalDest = ToReplace->getNormalDest();
// Can not insert gc.result in case of phi nodes preset.
- // Should have removed this cases prior to runnning this function
+ // Should have removed this cases prior to running this function
assert(!isa<PHINode>(NormalDest->begin()));
Instruction *IP = &*(NormalDest->getFirstInsertionPt());
Builder.SetInsertPoint(IP);
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