1 //===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Rewrite an existing set of gc.statepoints such that they make potential
11 // relocations performed by the garbage collector explicit in the IR.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Pass.h"
16 #include "llvm/Analysis/CFG.h"
17 #include "llvm/Analysis/TargetTransformInfo.h"
18 #include "llvm/ADT/SetOperations.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/ADT/DenseSet.h"
21 #include "llvm/ADT/SetVector.h"
22 #include "llvm/ADT/StringRef.h"
23 #include "llvm/IR/BasicBlock.h"
24 #include "llvm/IR/CallSite.h"
25 #include "llvm/IR/Dominators.h"
26 #include "llvm/IR/Function.h"
27 #include "llvm/IR/IRBuilder.h"
28 #include "llvm/IR/InstIterator.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/Intrinsics.h"
31 #include "llvm/IR/IntrinsicInst.h"
32 #include "llvm/IR/Module.h"
33 #include "llvm/IR/MDBuilder.h"
34 #include "llvm/IR/Statepoint.h"
35 #include "llvm/IR/Value.h"
36 #include "llvm/IR/Verifier.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Support/CommandLine.h"
39 #include "llvm/Transforms/Scalar.h"
40 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
41 #include "llvm/Transforms/Utils/Cloning.h"
42 #include "llvm/Transforms/Utils/Local.h"
43 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
45 #define DEBUG_TYPE "rewrite-statepoints-for-gc"
49 // Print tracing output
50 static cl::opt<bool> TraceLSP("trace-rewrite-statepoints", cl::Hidden,
53 // Print the liveset found at the insert location
54 static cl::opt<bool> PrintLiveSet("spp-print-liveset", cl::Hidden,
56 static cl::opt<bool> PrintLiveSetSize("spp-print-liveset-size", cl::Hidden,
58 // Print out the base pointers for debugging
59 static cl::opt<bool> PrintBasePointers("spp-print-base-pointers", cl::Hidden,
62 // Cost threshold measuring when it is profitable to rematerialize value instead
64 static cl::opt<unsigned>
65 RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden,
69 static bool ClobberNonLive = true;
71 static bool ClobberNonLive = false;
73 static cl::opt<bool, true> ClobberNonLiveOverride("rs4gc-clobber-non-live",
74 cl::location(ClobberNonLive),
78 struct RewriteStatepointsForGC : public ModulePass {
79 static char ID; // Pass identification, replacement for typeid
81 RewriteStatepointsForGC() : ModulePass(ID) {
82 initializeRewriteStatepointsForGCPass(*PassRegistry::getPassRegistry());
84 bool runOnFunction(Function &F);
85 bool runOnModule(Module &M) override {
88 Changed |= runOnFunction(F);
91 // stripDereferenceabilityInfo asserts that shouldRewriteStatepointsIn
92 // returns true for at least one function in the module. Since at least
93 // one function changed, we know that the precondition is satisfied.
94 stripDereferenceabilityInfo(M);
100 void getAnalysisUsage(AnalysisUsage &AU) const override {
101 // We add and rewrite a bunch of instructions, but don't really do much
102 // else. We could in theory preserve a lot more analyses here.
103 AU.addRequired<DominatorTreeWrapperPass>();
104 AU.addRequired<TargetTransformInfoWrapperPass>();
107 /// The IR fed into RewriteStatepointsForGC may have had attributes implying
108 /// dereferenceability that are no longer valid/correct after
109 /// RewriteStatepointsForGC has run. This is because semantically, after
110 /// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire
111 /// heap. stripDereferenceabilityInfo (conservatively) restores correctness
112 /// by erasing all attributes in the module that externally imply
113 /// dereferenceability.
115 void stripDereferenceabilityInfo(Module &M);
117 // Helpers for stripDereferenceabilityInfo
118 void stripDereferenceabilityInfoFromBody(Function &F);
119 void stripDereferenceabilityInfoFromPrototype(Function &F);
123 char RewriteStatepointsForGC::ID = 0;
125 ModulePass *llvm::createRewriteStatepointsForGCPass() {
126 return new RewriteStatepointsForGC();
129 INITIALIZE_PASS_BEGIN(RewriteStatepointsForGC, "rewrite-statepoints-for-gc",
130 "Make relocations explicit at statepoints", false, false)
131 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
132 INITIALIZE_PASS_END(RewriteStatepointsForGC, "rewrite-statepoints-for-gc",
133 "Make relocations explicit at statepoints", false, false)
136 struct GCPtrLivenessData {
137 /// Values defined in this block.
138 DenseMap<BasicBlock *, DenseSet<Value *>> KillSet;
139 /// Values used in this block (and thus live); does not included values
140 /// killed within this block.
141 DenseMap<BasicBlock *, DenseSet<Value *>> LiveSet;
143 /// Values live into this basic block (i.e. used by any
144 /// instruction in this basic block or ones reachable from here)
145 DenseMap<BasicBlock *, DenseSet<Value *>> LiveIn;
147 /// Values live out of this basic block (i.e. live into
148 /// any successor block)
149 DenseMap<BasicBlock *, DenseSet<Value *>> LiveOut;
152 // The type of the internal cache used inside the findBasePointers family
153 // of functions. From the callers perspective, this is an opaque type and
154 // should not be inspected.
156 // In the actual implementation this caches two relations:
157 // - The base relation itself (i.e. this pointer is based on that one)
158 // - The base defining value relation (i.e. before base_phi insertion)
159 // Generally, after the execution of a full findBasePointer call, only the
160 // base relation will remain. Internally, we add a mixture of the two
161 // types, then update all the second type to the first type
162 typedef DenseMap<Value *, Value *> DefiningValueMapTy;
163 typedef DenseSet<llvm::Value *> StatepointLiveSetTy;
164 typedef DenseMap<Instruction *, Value *> RematerializedValueMapTy;
166 struct PartiallyConstructedSafepointRecord {
167 /// The set of values known to be live accross this safepoint
168 StatepointLiveSetTy liveset;
170 /// Mapping from live pointers to a base-defining-value
171 DenseMap<llvm::Value *, llvm::Value *> PointerToBase;
173 /// The *new* gc.statepoint instruction itself. This produces the token
174 /// that normal path gc.relocates and the gc.result are tied to.
175 Instruction *StatepointToken;
177 /// Instruction to which exceptional gc relocates are attached
178 /// Makes it easier to iterate through them during relocationViaAlloca.
179 Instruction *UnwindToken;
181 /// Record live values we are rematerialized instead of relocating.
182 /// They are not included into 'liveset' field.
183 /// Maps rematerialized copy to it's original value.
184 RematerializedValueMapTy RematerializedValues;
188 /// Compute the live-in set for every basic block in the function
189 static void computeLiveInValues(DominatorTree &DT, Function &F,
190 GCPtrLivenessData &Data);
192 /// Given results from the dataflow liveness computation, find the set of live
193 /// Values at a particular instruction.
194 static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data,
195 StatepointLiveSetTy &out);
197 // TODO: Once we can get to the GCStrategy, this becomes
198 // Optional<bool> isGCManagedPointer(const Value *V) const override {
200 static bool isGCPointerType(const Type *T) {
201 if (const PointerType *PT = dyn_cast<PointerType>(T))
202 // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
203 // GC managed heap. We know that a pointer into this heap needs to be
204 // updated and that no other pointer does.
205 return (1 == PT->getAddressSpace());
209 // Return true if this type is one which a) is a gc pointer or contains a GC
210 // pointer and b) is of a type this code expects to encounter as a live value.
211 // (The insertion code will assert that a type which matches (a) and not (b)
212 // is not encountered.)
213 static bool isHandledGCPointerType(Type *T) {
214 // We fully support gc pointers
215 if (isGCPointerType(T))
217 // We partially support vectors of gc pointers. The code will assert if it
218 // can't handle something.
219 if (auto VT = dyn_cast<VectorType>(T))
220 if (isGCPointerType(VT->getElementType()))
226 /// Returns true if this type contains a gc pointer whether we know how to
227 /// handle that type or not.
228 static bool containsGCPtrType(Type *Ty) {
229 if (isGCPointerType(Ty))
231 if (VectorType *VT = dyn_cast<VectorType>(Ty))
232 return isGCPointerType(VT->getScalarType());
233 if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
234 return containsGCPtrType(AT->getElementType());
235 if (StructType *ST = dyn_cast<StructType>(Ty))
237 ST->subtypes().begin(), ST->subtypes().end(),
238 [](Type *SubType) { return containsGCPtrType(SubType); });
242 // Returns true if this is a type which a) is a gc pointer or contains a GC
243 // pointer and b) is of a type which the code doesn't expect (i.e. first class
244 // aggregates). Used to trip assertions.
245 static bool isUnhandledGCPointerType(Type *Ty) {
246 return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty);
250 static bool order_by_name(llvm::Value *a, llvm::Value *b) {
251 if (a->hasName() && b->hasName()) {
252 return -1 == a->getName().compare(b->getName());
253 } else if (a->hasName() && !b->hasName()) {
255 } else if (!a->hasName() && b->hasName()) {
258 // Better than nothing, but not stable
263 // Conservatively identifies any definitions which might be live at the
264 // given instruction. The analysis is performed immediately before the
265 // given instruction. Values defined by that instruction are not considered
266 // live. Values used by that instruction are considered live.
267 static void analyzeParsePointLiveness(
268 DominatorTree &DT, GCPtrLivenessData &OriginalLivenessData,
269 const CallSite &CS, PartiallyConstructedSafepointRecord &result) {
270 Instruction *inst = CS.getInstruction();
272 StatepointLiveSetTy liveset;
273 findLiveSetAtInst(inst, OriginalLivenessData, liveset);
276 // Note: This output is used by several of the test cases
277 // The order of elemtns in a set is not stable, put them in a vec and sort
279 SmallVector<Value *, 64> temp;
280 temp.insert(temp.end(), liveset.begin(), liveset.end());
281 std::sort(temp.begin(), temp.end(), order_by_name);
282 errs() << "Live Variables:\n";
283 for (Value *V : temp) {
284 errs() << " " << V->getName(); // no newline
288 if (PrintLiveSetSize) {
289 errs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n";
290 errs() << "Number live values: " << liveset.size() << "\n";
292 result.liveset = liveset;
295 static Value *findBaseDefiningValue(Value *I);
297 /// Return a base defining value for the 'Index' element of the given vector
298 /// instruction 'I'. If Index is null, returns a BDV for the entire vector
299 /// 'I'. As an optimization, this method will try to determine when the
300 /// element is known to already be a base pointer. If this can be established,
301 /// the second value in the returned pair will be true. Note that either a
302 /// vector or a pointer typed value can be returned. For the former, the
303 /// vector returned is a BDV (and possibly a base) of the entire vector 'I'.
304 /// If the later, the return pointer is a BDV (or possibly a base) for the
305 /// particular element in 'I'.
306 static std::pair<Value *, bool>
307 findBaseDefiningValueOfVector(Value *I, Value *Index = nullptr) {
308 assert(I->getType()->isVectorTy() &&
309 cast<VectorType>(I->getType())->getElementType()->isPointerTy() &&
310 "Illegal to ask for the base pointer of a non-pointer type");
312 // Each case parallels findBaseDefiningValue below, see that code for
313 // detailed motivation.
315 if (isa<Argument>(I))
316 // An incoming argument to the function is a base pointer
317 return std::make_pair(I, true);
319 // We shouldn't see the address of a global as a vector value?
320 assert(!isa<GlobalVariable>(I) &&
321 "unexpected global variable found in base of vector");
323 // inlining could possibly introduce phi node that contains
324 // undef if callee has multiple returns
325 if (isa<UndefValue>(I))
326 // utterly meaningless, but useful for dealing with partially optimized
328 return std::make_pair(I, true);
330 // Due to inheritance, this must be _after_ the global variable and undef
332 if (Constant *Con = dyn_cast<Constant>(I)) {
333 assert(!isa<GlobalVariable>(I) && !isa<UndefValue>(I) &&
334 "order of checks wrong!");
335 assert(Con->isNullValue() && "null is the only case which makes sense");
336 return std::make_pair(Con, true);
339 if (isa<LoadInst>(I))
340 return std::make_pair(I, true);
342 // For an insert element, we might be able to look through it if we know
343 // something about the indexes.
344 if (InsertElementInst *IEI = dyn_cast<InsertElementInst>(I)) {
346 Value *InsertIndex = IEI->getOperand(2);
347 // This index is inserting the value, look for its BDV
348 if (InsertIndex == Index)
349 return std::make_pair(findBaseDefiningValue(IEI->getOperand(1)), false);
350 // Both constant, and can't be equal per above. This insert is definitely
351 // not relevant, look back at the rest of the vector and keep trying.
352 if (isa<ConstantInt>(Index) && isa<ConstantInt>(InsertIndex))
353 return findBaseDefiningValueOfVector(IEI->getOperand(0), Index);
356 // We don't know whether this vector contains entirely base pointers or
357 // not. To be conservatively correct, we treat it as a BDV and will
358 // duplicate code as needed to construct a parallel vector of bases.
359 return std::make_pair(IEI, false);
362 if (isa<ShuffleVectorInst>(I))
363 // We don't know whether this vector contains entirely base pointers or
364 // not. To be conservatively correct, we treat it as a BDV and will
365 // duplicate code as needed to construct a parallel vector of bases.
366 // TODO: There a number of local optimizations which could be applied here
367 // for particular sufflevector patterns.
368 return std::make_pair(I, false);
370 // A PHI or Select is a base defining value. The outer findBasePointer
371 // algorithm is responsible for constructing a base value for this BDV.
372 assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
373 "unknown vector instruction - no base found for vector element");
374 return std::make_pair(I, false);
377 static bool isKnownBaseResult(Value *V);
379 /// Helper function for findBasePointer - Will return a value which either a)
380 /// defines the base pointer for the input or b) blocks the simple search
381 /// (i.e. a PHI or Select of two derived pointers)
382 static Value *findBaseDefiningValue(Value *I) {
383 if (I->getType()->isVectorTy())
384 return findBaseDefiningValueOfVector(I).first;
386 assert(I->getType()->isPointerTy() &&
387 "Illegal to ask for the base pointer of a non-pointer type");
389 // This case is a bit of a hack - it only handles extracts from vectors which
390 // trivially contain only base pointers or cases where we can directly match
391 // the index of the original extract element to an insertion into the vector.
392 // See note inside the function for how to improve this.
393 if (auto *EEI = dyn_cast<ExtractElementInst>(I)) {
394 Value *VectorOperand = EEI->getVectorOperand();
395 Value *Index = EEI->getIndexOperand();
396 std::pair<Value *, bool> pair =
397 findBaseDefiningValueOfVector(VectorOperand, Index);
398 Value *VectorBase = pair.first;
399 if (VectorBase->getType()->isPointerTy())
400 // We found a BDV for this specific element with the vector. This is an
401 // optimization, but in practice it covers most of the useful cases
402 // created via scalarization.
405 assert(VectorBase->getType()->isVectorTy());
407 // If the entire vector returned is known to be entirely base pointers,
408 // then the extractelement is valid base for this value.
411 // Otherwise, we have an instruction which potentially produces a
412 // derived pointer and we need findBasePointers to clone code for us
413 // such that we can create an instruction which produces the
414 // accompanying base pointer.
415 // Note: This code is currently rather incomplete. We don't currently
416 // support the general form of shufflevector of insertelement.
417 // Conceptually, these are just 'base defining values' of the same
418 // variety as phi or select instructions. We need to update the
419 // findBasePointers algorithm to insert new 'base-only' versions of the
420 // original instructions. This is relative straight forward to do, but
421 // the case which would motivate the work hasn't shown up in real
423 assert((isa<PHINode>(VectorBase) || isa<SelectInst>(VectorBase)) &&
424 "need to extend findBasePointers for generic vector"
425 "instruction cases");
431 if (isa<Argument>(I))
432 // An incoming argument to the function is a base pointer
433 // We should have never reached here if this argument isn't an gc value
436 if (isa<GlobalVariable>(I))
440 // inlining could possibly introduce phi node that contains
441 // undef if callee has multiple returns
442 if (isa<UndefValue>(I))
443 // utterly meaningless, but useful for dealing with
444 // partially optimized code.
447 // Due to inheritance, this must be _after_ the global variable and undef
449 if (Constant *Con = dyn_cast<Constant>(I)) {
450 assert(!isa<GlobalVariable>(I) && !isa<UndefValue>(I) &&
451 "order of checks wrong!");
452 // Note: Finding a constant base for something marked for relocation
453 // doesn't really make sense. The most likely case is either a) some
454 // screwed up the address space usage or b) your validating against
455 // compiled C++ code w/o the proper separation. The only real exception
456 // is a null pointer. You could have generic code written to index of
457 // off a potentially null value and have proven it null. We also use
458 // null pointers in dead paths of relocation phis (which we might later
459 // want to find a base pointer for).
460 assert(isa<ConstantPointerNull>(Con) &&
461 "null is the only case which makes sense");
465 if (CastInst *CI = dyn_cast<CastInst>(I)) {
466 Value *Def = CI->stripPointerCasts();
467 // If we find a cast instruction here, it means we've found a cast which is
468 // not simply a pointer cast (i.e. an inttoptr). We don't know how to
469 // handle int->ptr conversion.
470 assert(!isa<CastInst>(Def) && "shouldn't find another cast here");
471 return findBaseDefiningValue(Def);
474 if (isa<LoadInst>(I))
475 return I; // The value loaded is an gc base itself
477 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
478 // The base of this GEP is the base
479 return findBaseDefiningValue(GEP->getPointerOperand());
481 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
482 switch (II->getIntrinsicID()) {
483 case Intrinsic::experimental_gc_result_ptr:
485 // fall through to general call handling
487 case Intrinsic::experimental_gc_statepoint:
488 case Intrinsic::experimental_gc_result_float:
489 case Intrinsic::experimental_gc_result_int:
490 llvm_unreachable("these don't produce pointers");
491 case Intrinsic::experimental_gc_relocate: {
492 // Rerunning safepoint insertion after safepoints are already
493 // inserted is not supported. It could probably be made to work,
494 // but why are you doing this? There's no good reason.
495 llvm_unreachable("repeat safepoint insertion is not supported");
497 case Intrinsic::gcroot:
498 // Currently, this mechanism hasn't been extended to work with gcroot.
499 // There's no reason it couldn't be, but I haven't thought about the
500 // implications much.
502 "interaction with the gcroot mechanism is not supported");
505 // We assume that functions in the source language only return base
506 // pointers. This should probably be generalized via attributes to support
507 // both source language and internal functions.
508 if (isa<CallInst>(I) || isa<InvokeInst>(I))
511 // I have absolutely no idea how to implement this part yet. It's not
512 // neccessarily hard, I just haven't really looked at it yet.
513 assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented");
515 if (isa<AtomicCmpXchgInst>(I))
516 // A CAS is effectively a atomic store and load combined under a
517 // predicate. From the perspective of base pointers, we just treat it
521 assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are "
522 "binary ops which don't apply to pointers");
524 // The aggregate ops. Aggregates can either be in the heap or on the
525 // stack, but in either case, this is simply a field load. As a result,
526 // this is a defining definition of the base just like a load is.
527 if (isa<ExtractValueInst>(I))
530 // We should never see an insert vector since that would require we be
531 // tracing back a struct value not a pointer value.
532 assert(!isa<InsertValueInst>(I) &&
533 "Base pointer for a struct is meaningless");
535 // The last two cases here don't return a base pointer. Instead, they
536 // return a value which dynamically selects from amoung several base
537 // derived pointers (each with it's own base potentially). It's the job of
538 // the caller to resolve these.
539 assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
540 "missing instruction case in findBaseDefiningValing");
544 /// Returns the base defining value for this value.
545 static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) {
546 Value *&Cached = Cache[I];
548 Cached = findBaseDefiningValue(I);
549 DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> "
550 << Cached->getName() << "\n");
552 assert(Cache[I] != nullptr);
556 /// Return a base pointer for this value if known. Otherwise, return it's
557 /// base defining value.
558 static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) {
559 Value *Def = findBaseDefiningValueCached(I, Cache);
560 auto Found = Cache.find(Def);
561 if (Found != Cache.end()) {
562 // Either a base-of relation, or a self reference. Caller must check.
563 return Found->second;
565 // Only a BDV available
569 /// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV,
570 /// is it known to be a base pointer? Or do we need to continue searching.
571 static bool isKnownBaseResult(Value *V) {
572 if (!isa<PHINode>(V) && !isa<SelectInst>(V)) {
573 // no recursion possible
576 if (isa<Instruction>(V) &&
577 cast<Instruction>(V)->getMetadata("is_base_value")) {
578 // This is a previously inserted base phi or select. We know
579 // that this is a base value.
583 // We need to keep searching
588 /// Models the state of a single base defining value in the findBasePointer
589 /// algorithm for determining where a new instruction is needed to propagate
590 /// the base of this BDV.
593 enum Status { Unknown, Base, Conflict };
595 BDVState(Status s, Value *b = nullptr) : status(s), base(b) {
596 assert(status != Base || b);
598 explicit BDVState(Value *b) : status(Base), base(b) {}
599 BDVState() : status(Unknown), base(nullptr) {}
601 Status getStatus() const { return status; }
602 Value *getBase() const { return base; }
604 bool isBase() const { return getStatus() == Base; }
605 bool isUnknown() const { return getStatus() == Unknown; }
606 bool isConflict() const { return getStatus() == Conflict; }
608 bool operator==(const BDVState &other) const {
609 return base == other.base && status == other.status;
612 bool operator!=(const BDVState &other) const { return !(*this == other); }
615 void dump() const { print(dbgs()); dbgs() << '\n'; }
617 void print(raw_ostream &OS) const {
618 OS << status << " (" << base << " - "
619 << (base ? base->getName() : "nullptr") << "): ";
624 Value *base; // non null only if status == base
627 inline raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) {
633 typedef DenseMap<Value *, BDVState> ConflictStateMapTy;
634 // Values of type BDVState form a lattice, and this is a helper
635 // class that implementes the meet operation. The meat of the meet
636 // operation is implemented in MeetBDVStates::pureMeet
637 class MeetBDVStates {
639 /// Initializes the currentResult to the TOP state so that if can be met with
640 /// any other state to produce that state.
643 // Destructively meet the current result with the given BDVState
644 void meetWith(BDVState otherState) {
645 currentResult = meet(otherState, currentResult);
648 BDVState getResult() const { return currentResult; }
651 BDVState currentResult;
653 /// Perform a meet operation on two elements of the BDVState lattice.
654 static BDVState meet(BDVState LHS, BDVState RHS) {
655 assert((pureMeet(LHS, RHS) == pureMeet(RHS, LHS)) &&
656 "math is wrong: meet does not commute!");
657 BDVState Result = pureMeet(LHS, RHS);
658 DEBUG(dbgs() << "meet of " << LHS << " with " << RHS
659 << " produced " << Result << "\n");
663 static BDVState pureMeet(const BDVState &stateA, const BDVState &stateB) {
664 switch (stateA.getStatus()) {
665 case BDVState::Unknown:
669 assert(stateA.getBase() && "can't be null");
670 if (stateB.isUnknown())
673 if (stateB.isBase()) {
674 if (stateA.getBase() == stateB.getBase()) {
675 assert(stateA == stateB && "equality broken!");
678 return BDVState(BDVState::Conflict);
680 assert(stateB.isConflict() && "only three states!");
681 return BDVState(BDVState::Conflict);
683 case BDVState::Conflict:
686 llvm_unreachable("only three states!");
690 /// For a given value or instruction, figure out what base ptr it's derived
691 /// from. For gc objects, this is simply itself. On success, returns a value
692 /// which is the base pointer. (This is reliable and can be used for
693 /// relocation.) On failure, returns nullptr.
694 static Value *findBasePointer(Value *I, DefiningValueMapTy &cache) {
695 Value *def = findBaseOrBDV(I, cache);
697 if (isKnownBaseResult(def)) {
701 // Here's the rough algorithm:
702 // - For every SSA value, construct a mapping to either an actual base
703 // pointer or a PHI which obscures the base pointer.
704 // - Construct a mapping from PHI to unknown TOP state. Use an
705 // optimistic algorithm to propagate base pointer information. Lattice
710 // When algorithm terminates, all PHIs will either have a single concrete
711 // base or be in a conflict state.
712 // - For every conflict, insert a dummy PHI node without arguments. Add
713 // these to the base[Instruction] = BasePtr mapping. For every
714 // non-conflict, add the actual base.
715 // - For every conflict, add arguments for the base[a] of each input
718 // Note: A simpler form of this would be to add the conflict form of all
719 // PHIs without running the optimistic algorithm. This would be
720 // analougous to pessimistic data flow and would likely lead to an
721 // overall worse solution.
723 auto isExpectedBDVType = [](Value *BDV) {
724 return isa<PHINode>(BDV) || isa<SelectInst>(BDV);
727 // Once populated, will contain a mapping from each potentially non-base BDV
728 // to a lattice value (described above) which corresponds to that BDV.
729 ConflictStateMapTy states;
730 // Recursively fill in all phis & selects reachable from the initial one
731 // for which we don't already know a definite base value for
733 DenseSet<Value *> Visited;
734 SmallVector<Value*, 16> Worklist;
735 Worklist.push_back(def);
737 while (!Worklist.empty()) {
738 Value *Current = Worklist.pop_back_val();
739 assert(!isKnownBaseResult(Current) && "why did it get added?");
741 auto visitIncomingValue = [&](Value *InVal) {
742 Value *Base = findBaseOrBDV(InVal, cache);
743 if (isKnownBaseResult(Base))
744 // Known bases won't need new instructions introduced and can be
747 assert(isExpectedBDVType(Base) && "the only non-base values "
748 "we see should be base defining values");
749 if (Visited.insert(Base).second)
750 Worklist.push_back(Base);
752 if (PHINode *Phi = dyn_cast<PHINode>(Current)) {
753 for (Value *InVal : Phi->incoming_values())
754 visitIncomingValue(InVal);
756 SelectInst *Sel = cast<SelectInst>(Current);
757 visitIncomingValue(Sel->getTrueValue());
758 visitIncomingValue(Sel->getFalseValue());
761 // The frontier of visited instructions are the ones we might need to
762 // duplicate, so fill in the starting state for the optimistic algorithm
764 for (Value *BDV : Visited) {
765 states[BDV] = BDVState();
770 errs() << "States after initialization:\n";
771 for (auto Pair : states)
772 dbgs() << " " << Pair.second << " for " << Pair.first << "\n";
775 // TODO: come back and revisit the state transitions around inputs which
776 // have reached conflict state. The current version seems too conservative.
778 // Return a phi state for a base defining value. We'll generate a new
779 // base state for known bases and expect to find a cached state otherwise.
780 auto getStateForBDV = [&](Value *baseValue) {
781 if (isKnownBaseResult(baseValue))
782 return BDVState(baseValue);
783 auto I = states.find(baseValue);
784 assert(I != states.end() && "lookup failed!");
788 bool progress = true;
791 size_t oldSize = states.size();
794 // We're only changing keys in this loop, thus safe to keep iterators
795 for (auto Pair : states) {
796 Value *v = Pair.first;
797 assert(!isKnownBaseResult(v) && "why did it get added?");
799 // Given an input value for the current instruction, return a BDVState
800 // instance which represents the BDV of that value.
801 auto getStateForInput = [&](Value *V) mutable {
802 Value *BDV = findBaseOrBDV(V, cache);
803 return getStateForBDV(BDV);
806 MeetBDVStates calculateMeet;
807 if (SelectInst *select = dyn_cast<SelectInst>(v)) {
808 calculateMeet.meetWith(getStateForInput(select->getTrueValue()));
809 calculateMeet.meetWith(getStateForInput(select->getFalseValue()));
811 for (Value *Val : cast<PHINode>(v)->incoming_values())
812 calculateMeet.meetWith(getStateForInput(Val));
814 BDVState oldState = states[v];
815 BDVState newState = calculateMeet.getResult();
816 if (oldState != newState) {
818 states[v] = newState;
822 assert(oldSize <= states.size());
823 assert(oldSize == states.size() || progress);
827 errs() << "States after meet iteration:\n";
828 for (auto Pair : states)
829 dbgs() << " " << Pair.second << " for " << Pair.first << "\n";
832 // Insert Phis for all conflicts
833 // We want to keep naming deterministic in the loop that follows, so
834 // sort the keys before iteration. This is useful in allowing us to
835 // write stable tests. Note that there is no invalidation issue here.
836 SmallVector<Value *, 16> Keys;
837 Keys.reserve(states.size());
838 for (auto Pair : states) {
839 Value *V = Pair.first;
842 std::sort(Keys.begin(), Keys.end(), order_by_name);
843 // TODO: adjust naming patterns to avoid this order of iteration dependency
844 for (Value *V : Keys) {
845 Instruction *I = cast<Instruction>(V);
846 BDVState State = states[I];
847 assert(!isKnownBaseResult(I) && "why did it get added?");
848 assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
849 if (!State.isConflict())
852 /// Create and insert a new instruction which will represent the base of
853 /// the given instruction 'I'.
854 auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* {
855 if (isa<PHINode>(I)) {
856 BasicBlock *BB = I->getParent();
857 int NumPreds = std::distance(pred_begin(BB), pred_end(BB));
858 assert(NumPreds > 0 && "how did we reach here");
859 return PHINode::Create(I->getType(), NumPreds, "base_phi", I);
861 SelectInst *Sel = cast<SelectInst>(I);
862 // The undef will be replaced later
863 UndefValue *Undef = UndefValue::get(Sel->getType());
864 return SelectInst::Create(Sel->getCondition(), Undef,
865 Undef, "base_select", Sel);
867 Instruction *BaseInst = MakeBaseInstPlaceholder(I);
868 // Add metadata marking this as a base value
869 BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
870 states[I] = BDVState(BDVState::Conflict, BaseInst);
873 // Fixup all the inputs of the new PHIs
874 for (auto Pair : states) {
875 Instruction *v = cast<Instruction>(Pair.first);
876 BDVState state = Pair.second;
878 assert(!isKnownBaseResult(v) && "why did it get added?");
879 assert(!state.isUnknown() && "Optimistic algorithm didn't complete!");
880 if (!state.isConflict())
883 if (PHINode *basephi = dyn_cast<PHINode>(state.getBase())) {
884 PHINode *phi = cast<PHINode>(v);
885 unsigned NumPHIValues = phi->getNumIncomingValues();
886 for (unsigned i = 0; i < NumPHIValues; i++) {
887 Value *InVal = phi->getIncomingValue(i);
888 BasicBlock *InBB = phi->getIncomingBlock(i);
890 // If we've already seen InBB, add the same incoming value
891 // we added for it earlier. The IR verifier requires phi
892 // nodes with multiple entries from the same basic block
893 // to have the same incoming value for each of those
894 // entries. If we don't do this check here and basephi
895 // has a different type than base, we'll end up adding two
896 // bitcasts (and hence two distinct values) as incoming
897 // values for the same basic block.
899 int blockIndex = basephi->getBasicBlockIndex(InBB);
900 if (blockIndex != -1) {
901 Value *oldBase = basephi->getIncomingValue(blockIndex);
902 basephi->addIncoming(oldBase, InBB);
904 Value *base = findBaseOrBDV(InVal, cache);
905 if (!isKnownBaseResult(base)) {
906 // Either conflict or base.
907 assert(states.count(base));
908 base = states[base].getBase();
909 assert(base != nullptr && "unknown BDVState!");
912 // In essense this assert states: the only way two
913 // values incoming from the same basic block may be
914 // different is by being different bitcasts of the same
915 // value. A cleanup that remains TODO is changing
916 // findBaseOrBDV to return an llvm::Value of the correct
917 // type (and still remain pure). This will remove the
918 // need to add bitcasts.
919 assert(base->stripPointerCasts() == oldBase->stripPointerCasts() &&
920 "sanity -- findBaseOrBDV should be pure!");
925 // Find either the defining value for the PHI or the normal base for
927 Value *base = findBaseOrBDV(InVal, cache);
928 if (!isKnownBaseResult(base)) {
929 // Either conflict or base.
930 assert(states.count(base));
931 base = states[base].getBase();
932 assert(base != nullptr && "unknown BDVState!");
934 assert(base && "can't be null");
935 // Must use original input BB since base may not be Instruction
936 // The cast is needed since base traversal may strip away bitcasts
937 if (base->getType() != basephi->getType()) {
938 base = new BitCastInst(base, basephi->getType(), "cast",
939 InBB->getTerminator());
941 basephi->addIncoming(base, InBB);
943 assert(basephi->getNumIncomingValues() == NumPHIValues);
945 SelectInst *basesel = cast<SelectInst>(state.getBase());
946 SelectInst *sel = cast<SelectInst>(v);
947 // Operand 1 & 2 are true, false path respectively. TODO: refactor to
948 // something more safe and less hacky.
949 for (int i = 1; i <= 2; i++) {
950 Value *InVal = sel->getOperand(i);
951 // Find either the defining value for the PHI or the normal base for
953 Value *base = findBaseOrBDV(InVal, cache);
954 if (!isKnownBaseResult(base)) {
955 // Either conflict or base.
956 assert(states.count(base));
957 base = states[base].getBase();
958 assert(base != nullptr && "unknown BDVState!");
960 assert(base && "can't be null");
961 // Must use original input BB since base may not be Instruction
962 // The cast is needed since base traversal may strip away bitcasts
963 if (base->getType() != basesel->getType()) {
964 base = new BitCastInst(base, basesel->getType(), "cast", basesel);
966 basesel->setOperand(i, base);
971 // Cache all of our results so we can cheaply reuse them
972 // NOTE: This is actually two caches: one of the base defining value
973 // relation and one of the base pointer relation! FIXME
974 for (auto item : states) {
975 Value *v = item.first;
976 Value *base = item.second.getBase();
978 assert(!isKnownBaseResult(v) && "why did it get added?");
981 std::string fromstr =
982 cache.count(v) ? (cache[v]->hasName() ? cache[v]->getName() : "")
984 errs() << "Updating base value cache"
985 << " for: " << (v->hasName() ? v->getName() : "")
986 << " from: " << fromstr
987 << " to: " << (base->hasName() ? base->getName() : "") << "\n";
990 assert(isKnownBaseResult(base) &&
991 "must be something we 'know' is a base pointer");
992 if (cache.count(v)) {
993 // Once we transition from the BDV relation being store in the cache to
994 // the base relation being stored, it must be stable
995 assert((!isKnownBaseResult(cache[v]) || cache[v] == base) &&
996 "base relation should be stable");
1000 assert(cache.find(def) != cache.end());
1004 // For a set of live pointers (base and/or derived), identify the base
1005 // pointer of the object which they are derived from. This routine will
1006 // mutate the IR graph as needed to make the 'base' pointer live at the
1007 // definition site of 'derived'. This ensures that any use of 'derived' can
1008 // also use 'base'. This may involve the insertion of a number of
1009 // additional PHI nodes.
1011 // preconditions: live is a set of pointer type Values
1013 // side effects: may insert PHI nodes into the existing CFG, will preserve
1014 // CFG, will not remove or mutate any existing nodes
1016 // post condition: PointerToBase contains one (derived, base) pair for every
1017 // pointer in live. Note that derived can be equal to base if the original
1018 // pointer was a base pointer.
1020 findBasePointers(const StatepointLiveSetTy &live,
1021 DenseMap<llvm::Value *, llvm::Value *> &PointerToBase,
1022 DominatorTree *DT, DefiningValueMapTy &DVCache) {
1023 // For the naming of values inserted to be deterministic - which makes for
1024 // much cleaner and more stable tests - we need to assign an order to the
1025 // live values. DenseSets do not provide a deterministic order across runs.
1026 SmallVector<Value *, 64> Temp;
1027 Temp.insert(Temp.end(), live.begin(), live.end());
1028 std::sort(Temp.begin(), Temp.end(), order_by_name);
1029 for (Value *ptr : Temp) {
1030 Value *base = findBasePointer(ptr, DVCache);
1031 assert(base && "failed to find base pointer");
1032 PointerToBase[ptr] = base;
1033 assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) ||
1034 DT->dominates(cast<Instruction>(base)->getParent(),
1035 cast<Instruction>(ptr)->getParent())) &&
1036 "The base we found better dominate the derived pointer");
1038 // If you see this trip and like to live really dangerously, the code should
1039 // be correct, just with idioms the verifier can't handle. You can try
1040 // disabling the verifier at your own substaintial risk.
1041 assert(!isa<ConstantPointerNull>(base) &&
1042 "the relocation code needs adjustment to handle the relocation of "
1043 "a null pointer constant without causing false positives in the "
1044 "safepoint ir verifier.");
1048 /// Find the required based pointers (and adjust the live set) for the given
1050 static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache,
1052 PartiallyConstructedSafepointRecord &result) {
1053 DenseMap<llvm::Value *, llvm::Value *> PointerToBase;
1054 findBasePointers(result.liveset, PointerToBase, &DT, DVCache);
1056 if (PrintBasePointers) {
1057 // Note: Need to print these in a stable order since this is checked in
1059 errs() << "Base Pairs (w/o Relocation):\n";
1060 SmallVector<Value *, 64> Temp;
1061 Temp.reserve(PointerToBase.size());
1062 for (auto Pair : PointerToBase) {
1063 Temp.push_back(Pair.first);
1065 std::sort(Temp.begin(), Temp.end(), order_by_name);
1066 for (Value *Ptr : Temp) {
1067 Value *Base = PointerToBase[Ptr];
1068 errs() << " derived %" << Ptr->getName() << " base %" << Base->getName()
1073 result.PointerToBase = PointerToBase;
1076 /// Given an updated version of the dataflow liveness results, update the
1077 /// liveset and base pointer maps for the call site CS.
1078 static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
1080 PartiallyConstructedSafepointRecord &result);
1082 static void recomputeLiveInValues(
1083 Function &F, DominatorTree &DT, Pass *P, ArrayRef<CallSite> toUpdate,
1084 MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
1085 // TODO-PERF: reuse the original liveness, then simply run the dataflow
1086 // again. The old values are still live and will help it stablize quickly.
1087 GCPtrLivenessData RevisedLivenessData;
1088 computeLiveInValues(DT, F, RevisedLivenessData);
1089 for (size_t i = 0; i < records.size(); i++) {
1090 struct PartiallyConstructedSafepointRecord &info = records[i];
1091 const CallSite &CS = toUpdate[i];
1092 recomputeLiveInValues(RevisedLivenessData, CS, info);
1096 // When inserting gc.relocate calls, we need to ensure there are no uses
1097 // of the original value between the gc.statepoint and the gc.relocate call.
1098 // One case which can arise is a phi node starting one of the successor blocks.
1099 // We also need to be able to insert the gc.relocates only on the path which
1100 // goes through the statepoint. We might need to split an edge to make this
1103 normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent,
1104 DominatorTree &DT) {
1105 BasicBlock *Ret = BB;
1106 if (!BB->getUniquePredecessor()) {
1107 Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT);
1110 // Now that 'ret' has unique predecessor we can safely remove all phi nodes
1112 FoldSingleEntryPHINodes(Ret);
1113 assert(!isa<PHINode>(Ret->begin()));
1115 // At this point, we can safely insert a gc.relocate as the first instruction
1116 // in Ret if needed.
1120 static int find_index(ArrayRef<Value *> livevec, Value *val) {
1121 auto itr = std::find(livevec.begin(), livevec.end(), val);
1122 assert(livevec.end() != itr);
1123 size_t index = std::distance(livevec.begin(), itr);
1124 assert(index < livevec.size());
1128 // Create new attribute set containing only attributes which can be transfered
1129 // from original call to the safepoint.
1130 static AttributeSet legalizeCallAttributes(AttributeSet AS) {
1133 for (unsigned Slot = 0; Slot < AS.getNumSlots(); Slot++) {
1134 unsigned index = AS.getSlotIndex(Slot);
1136 if (index == AttributeSet::ReturnIndex ||
1137 index == AttributeSet::FunctionIndex) {
1139 for (auto it = AS.begin(Slot), it_end = AS.end(Slot); it != it_end;
1141 Attribute attr = *it;
1143 // Do not allow certain attributes - just skip them
1144 // Safepoint can not be read only or read none.
1145 if (attr.hasAttribute(Attribute::ReadNone) ||
1146 attr.hasAttribute(Attribute::ReadOnly))
1149 ret = ret.addAttributes(
1150 AS.getContext(), index,
1151 AttributeSet::get(AS.getContext(), index, AttrBuilder(attr)));
1155 // Just skip parameter attributes for now
1161 /// Helper function to place all gc relocates necessary for the given
1164 /// liveVariables - list of variables to be relocated.
1165 /// liveStart - index of the first live variable.
1166 /// basePtrs - base pointers.
1167 /// statepointToken - statepoint instruction to which relocates should be
1169 /// Builder - Llvm IR builder to be used to construct new calls.
1170 static void CreateGCRelocates(ArrayRef<llvm::Value *> LiveVariables,
1171 const int LiveStart,
1172 ArrayRef<llvm::Value *> BasePtrs,
1173 Instruction *StatepointToken,
1174 IRBuilder<> Builder) {
1175 if (LiveVariables.empty())
1178 // All gc_relocate are set to i8 addrspace(1)* type. We originally generated
1179 // unique declarations for each pointer type, but this proved problematic
1180 // because the intrinsic mangling code is incomplete and fragile. Since
1181 // we're moving towards a single unified pointer type anyways, we can just
1182 // cast everything to an i8* of the right address space. A bitcast is added
1183 // later to convert gc_relocate to the actual value's type.
1184 Module *M = StatepointToken->getModule();
1185 auto AS = cast<PointerType>(LiveVariables[0]->getType())->getAddressSpace();
1186 Type *Types[] = {Type::getInt8PtrTy(M->getContext(), AS)};
1187 Value *GCRelocateDecl =
1188 Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate, Types);
1190 for (unsigned i = 0; i < LiveVariables.size(); i++) {
1191 // Generate the gc.relocate call and save the result
1193 Builder.getInt32(LiveStart + find_index(LiveVariables, BasePtrs[i]));
1195 Builder.getInt32(LiveStart + find_index(LiveVariables, LiveVariables[i]));
1197 // only specify a debug name if we can give a useful one
1198 CallInst *Reloc = Builder.CreateCall(
1199 GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx},
1200 LiveVariables[i]->hasName() ? LiveVariables[i]->getName() + ".relocated"
1202 // Trick CodeGen into thinking there are lots of free registers at this
1204 Reloc->setCallingConv(CallingConv::Cold);
1209 makeStatepointExplicitImpl(const CallSite &CS, /* to replace */
1210 const SmallVectorImpl<llvm::Value *> &basePtrs,
1211 const SmallVectorImpl<llvm::Value *> &liveVariables,
1213 PartiallyConstructedSafepointRecord &result) {
1214 assert(basePtrs.size() == liveVariables.size());
1215 assert(isStatepoint(CS) &&
1216 "This method expects to be rewriting a statepoint");
1218 BasicBlock *BB = CS.getInstruction()->getParent();
1220 Function *F = BB->getParent();
1221 assert(F && "must be set");
1222 Module *M = F->getParent();
1224 assert(M && "must be set");
1226 // We're not changing the function signature of the statepoint since the gc
1227 // arguments go into the var args section.
1228 Function *gc_statepoint_decl = CS.getCalledFunction();
1230 // Then go ahead and use the builder do actually do the inserts. We insert
1231 // immediately before the previous instruction under the assumption that all
1232 // arguments will be available here. We can't insert afterwards since we may
1233 // be replacing a terminator.
1234 Instruction *insertBefore = CS.getInstruction();
1235 IRBuilder<> Builder(insertBefore);
1236 // Copy all of the arguments from the original statepoint - this includes the
1237 // target, call args, and deopt args
1238 SmallVector<llvm::Value *, 64> args;
1239 args.insert(args.end(), CS.arg_begin(), CS.arg_end());
1240 // TODO: Clear the 'needs rewrite' flag
1242 // add all the pointers to be relocated (gc arguments)
1243 // Capture the start of the live variable list for use in the gc_relocates
1244 const int live_start = args.size();
1245 args.insert(args.end(), liveVariables.begin(), liveVariables.end());
1247 // Create the statepoint given all the arguments
1248 Instruction *token = nullptr;
1249 AttributeSet return_attributes;
1251 CallInst *toReplace = cast<CallInst>(CS.getInstruction());
1253 Builder.CreateCall(gc_statepoint_decl, args, "safepoint_token");
1254 call->setTailCall(toReplace->isTailCall());
1255 call->setCallingConv(toReplace->getCallingConv());
1257 // Currently we will fail on parameter attributes and on certain
1258 // function attributes.
1259 AttributeSet new_attrs = legalizeCallAttributes(toReplace->getAttributes());
1260 // In case if we can handle this set of sttributes - set up function attrs
1261 // directly on statepoint and return attrs later for gc_result intrinsic.
1262 call->setAttributes(new_attrs.getFnAttributes());
1263 return_attributes = new_attrs.getRetAttributes();
1267 // Put the following gc_result and gc_relocate calls immediately after the
1268 // the old call (which we're about to delete)
1269 BasicBlock::iterator next(toReplace);
1270 assert(BB->end() != next && "not a terminator, must have next");
1272 Instruction *IP = &*(next);
1273 Builder.SetInsertPoint(IP);
1274 Builder.SetCurrentDebugLocation(IP->getDebugLoc());
1277 InvokeInst *toReplace = cast<InvokeInst>(CS.getInstruction());
1279 // Insert the new invoke into the old block. We'll remove the old one in a
1280 // moment at which point this will become the new terminator for the
1282 InvokeInst *invoke = InvokeInst::Create(
1283 gc_statepoint_decl, toReplace->getNormalDest(),
1284 toReplace->getUnwindDest(), args, "", toReplace->getParent());
1285 invoke->setCallingConv(toReplace->getCallingConv());
1287 // Currently we will fail on parameter attributes and on certain
1288 // function attributes.
1289 AttributeSet new_attrs = legalizeCallAttributes(toReplace->getAttributes());
1290 // In case if we can handle this set of sttributes - set up function attrs
1291 // directly on statepoint and return attrs later for gc_result intrinsic.
1292 invoke->setAttributes(new_attrs.getFnAttributes());
1293 return_attributes = new_attrs.getRetAttributes();
1297 // Generate gc relocates in exceptional path
1298 BasicBlock *unwindBlock = toReplace->getUnwindDest();
1299 assert(!isa<PHINode>(unwindBlock->begin()) &&
1300 unwindBlock->getUniquePredecessor() &&
1301 "can't safely insert in this block!");
1303 Instruction *IP = &*(unwindBlock->getFirstInsertionPt());
1304 Builder.SetInsertPoint(IP);
1305 Builder.SetCurrentDebugLocation(toReplace->getDebugLoc());
1307 // Extract second element from landingpad return value. We will attach
1308 // exceptional gc relocates to it.
1309 const unsigned idx = 1;
1310 Instruction *exceptional_token =
1311 cast<Instruction>(Builder.CreateExtractValue(
1312 unwindBlock->getLandingPadInst(), idx, "relocate_token"));
1313 result.UnwindToken = exceptional_token;
1315 CreateGCRelocates(liveVariables, live_start, basePtrs,
1316 exceptional_token, Builder);
1318 // Generate gc relocates and returns for normal block
1319 BasicBlock *normalDest = toReplace->getNormalDest();
1320 assert(!isa<PHINode>(normalDest->begin()) &&
1321 normalDest->getUniquePredecessor() &&
1322 "can't safely insert in this block!");
1324 IP = &*(normalDest->getFirstInsertionPt());
1325 Builder.SetInsertPoint(IP);
1327 // gc relocates will be generated later as if it were regular call
1332 // Take the name of the original value call if it had one.
1333 token->takeName(CS.getInstruction());
1335 // The GCResult is already inserted, we just need to find it
1337 Instruction *toReplace = CS.getInstruction();
1338 assert((toReplace->hasNUses(0) || toReplace->hasNUses(1)) &&
1339 "only valid use before rewrite is gc.result");
1340 assert(!toReplace->hasOneUse() ||
1341 isGCResult(cast<Instruction>(*toReplace->user_begin())));
1344 // Update the gc.result of the original statepoint (if any) to use the newly
1345 // inserted statepoint. This is safe to do here since the token can't be
1346 // considered a live reference.
1347 CS.getInstruction()->replaceAllUsesWith(token);
1349 result.StatepointToken = token;
1351 // Second, create a gc.relocate for every live variable
1352 CreateGCRelocates(liveVariables, live_start, basePtrs, token, Builder);
1356 struct name_ordering {
1359 bool operator()(name_ordering const &a, name_ordering const &b) {
1360 return -1 == a.derived->getName().compare(b.derived->getName());
1364 static void stablize_order(SmallVectorImpl<Value *> &basevec,
1365 SmallVectorImpl<Value *> &livevec) {
1366 assert(basevec.size() == livevec.size());
1368 SmallVector<name_ordering, 64> temp;
1369 for (size_t i = 0; i < basevec.size(); i++) {
1371 v.base = basevec[i];
1372 v.derived = livevec[i];
1375 std::sort(temp.begin(), temp.end(), name_ordering());
1376 for (size_t i = 0; i < basevec.size(); i++) {
1377 basevec[i] = temp[i].base;
1378 livevec[i] = temp[i].derived;
1382 // Replace an existing gc.statepoint with a new one and a set of gc.relocates
1383 // which make the relocations happening at this safepoint explicit.
1385 // WARNING: Does not do any fixup to adjust users of the original live
1386 // values. That's the callers responsibility.
1388 makeStatepointExplicit(DominatorTree &DT, const CallSite &CS, Pass *P,
1389 PartiallyConstructedSafepointRecord &result) {
1390 auto liveset = result.liveset;
1391 auto PointerToBase = result.PointerToBase;
1393 // Convert to vector for efficient cross referencing.
1394 SmallVector<Value *, 64> basevec, livevec;
1395 livevec.reserve(liveset.size());
1396 basevec.reserve(liveset.size());
1397 for (Value *L : liveset) {
1398 livevec.push_back(L);
1399 assert(PointerToBase.count(L));
1400 Value *base = PointerToBase[L];
1401 basevec.push_back(base);
1403 assert(livevec.size() == basevec.size());
1405 // To make the output IR slightly more stable (for use in diffs), ensure a
1406 // fixed order of the values in the safepoint (by sorting the value name).
1407 // The order is otherwise meaningless.
1408 stablize_order(basevec, livevec);
1410 // Do the actual rewriting and delete the old statepoint
1411 makeStatepointExplicitImpl(CS, basevec, livevec, P, result);
1412 CS.getInstruction()->eraseFromParent();
1415 // Helper function for the relocationViaAlloca.
1416 // It receives iterator to the statepoint gc relocates and emits store to the
1418 // location (via allocaMap) for the each one of them.
1419 // Add visited values into the visitedLiveValues set we will later use them
1420 // for sanity check.
1422 insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs,
1423 DenseMap<Value *, Value *> &AllocaMap,
1424 DenseSet<Value *> &VisitedLiveValues) {
1426 for (User *U : GCRelocs) {
1427 if (!isa<IntrinsicInst>(U))
1430 IntrinsicInst *RelocatedValue = cast<IntrinsicInst>(U);
1432 // We only care about relocates
1433 if (RelocatedValue->getIntrinsicID() !=
1434 Intrinsic::experimental_gc_relocate) {
1438 GCRelocateOperands RelocateOperands(RelocatedValue);
1439 Value *OriginalValue =
1440 const_cast<Value *>(RelocateOperands.getDerivedPtr());
1441 assert(AllocaMap.count(OriginalValue));
1442 Value *Alloca = AllocaMap[OriginalValue];
1444 // Emit store into the related alloca
1445 // All gc_relocate are i8 addrspace(1)* typed, and it must be bitcasted to
1446 // the correct type according to alloca.
1447 assert(RelocatedValue->getNextNode() && "Should always have one since it's not a terminator");
1448 IRBuilder<> Builder(RelocatedValue->getNextNode());
1449 Value *CastedRelocatedValue =
1450 Builder.CreateBitCast(RelocatedValue, cast<AllocaInst>(Alloca)->getAllocatedType(),
1451 RelocatedValue->hasName() ? RelocatedValue->getName() + ".casted" : "");
1453 StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca);
1454 Store->insertAfter(cast<Instruction>(CastedRelocatedValue));
1457 VisitedLiveValues.insert(OriginalValue);
1462 // Helper function for the "relocationViaAlloca". Similar to the
1463 // "insertRelocationStores" but works for rematerialized values.
1465 insertRematerializationStores(
1466 RematerializedValueMapTy RematerializedValues,
1467 DenseMap<Value *, Value *> &AllocaMap,
1468 DenseSet<Value *> &VisitedLiveValues) {
1470 for (auto RematerializedValuePair: RematerializedValues) {
1471 Instruction *RematerializedValue = RematerializedValuePair.first;
1472 Value *OriginalValue = RematerializedValuePair.second;
1474 assert(AllocaMap.count(OriginalValue) &&
1475 "Can not find alloca for rematerialized value");
1476 Value *Alloca = AllocaMap[OriginalValue];
1478 StoreInst *Store = new StoreInst(RematerializedValue, Alloca);
1479 Store->insertAfter(RematerializedValue);
1482 VisitedLiveValues.insert(OriginalValue);
1487 /// do all the relocation update via allocas and mem2reg
1488 static void relocationViaAlloca(
1489 Function &F, DominatorTree &DT, ArrayRef<Value *> Live,
1490 ArrayRef<struct PartiallyConstructedSafepointRecord> Records) {
1492 // record initial number of (static) allocas; we'll check we have the same
1493 // number when we get done.
1494 int InitialAllocaNum = 0;
1495 for (auto I = F.getEntryBlock().begin(), E = F.getEntryBlock().end(); I != E;
1497 if (isa<AllocaInst>(*I))
1501 // TODO-PERF: change data structures, reserve
1502 DenseMap<Value *, Value *> AllocaMap;
1503 SmallVector<AllocaInst *, 200> PromotableAllocas;
1504 // Used later to chack that we have enough allocas to store all values
1505 std::size_t NumRematerializedValues = 0;
1506 PromotableAllocas.reserve(Live.size());
1508 // Emit alloca for "LiveValue" and record it in "allocaMap" and
1509 // "PromotableAllocas"
1510 auto emitAllocaFor = [&](Value *LiveValue) {
1511 AllocaInst *Alloca = new AllocaInst(LiveValue->getType(), "",
1512 F.getEntryBlock().getFirstNonPHI());
1513 AllocaMap[LiveValue] = Alloca;
1514 PromotableAllocas.push_back(Alloca);
1517 // emit alloca for each live gc pointer
1518 for (unsigned i = 0; i < Live.size(); i++) {
1519 emitAllocaFor(Live[i]);
1522 // emit allocas for rematerialized values
1523 for (size_t i = 0; i < Records.size(); i++) {
1524 const struct PartiallyConstructedSafepointRecord &Info = Records[i];
1526 for (auto RematerializedValuePair : Info.RematerializedValues) {
1527 Value *OriginalValue = RematerializedValuePair.second;
1528 if (AllocaMap.count(OriginalValue) != 0)
1531 emitAllocaFor(OriginalValue);
1532 ++NumRematerializedValues;
1536 // The next two loops are part of the same conceptual operation. We need to
1537 // insert a store to the alloca after the original def and at each
1538 // redefinition. We need to insert a load before each use. These are split
1539 // into distinct loops for performance reasons.
1541 // update gc pointer after each statepoint
1542 // either store a relocated value or null (if no relocated value found for
1543 // this gc pointer and it is not a gc_result)
1544 // this must happen before we update the statepoint with load of alloca
1545 // otherwise we lose the link between statepoint and old def
1546 for (size_t i = 0; i < Records.size(); i++) {
1547 const struct PartiallyConstructedSafepointRecord &Info = Records[i];
1548 Value *Statepoint = Info.StatepointToken;
1550 // This will be used for consistency check
1551 DenseSet<Value *> VisitedLiveValues;
1553 // Insert stores for normal statepoint gc relocates
1554 insertRelocationStores(Statepoint->users(), AllocaMap, VisitedLiveValues);
1556 // In case if it was invoke statepoint
1557 // we will insert stores for exceptional path gc relocates.
1558 if (isa<InvokeInst>(Statepoint)) {
1559 insertRelocationStores(Info.UnwindToken->users(), AllocaMap,
1563 // Do similar thing with rematerialized values
1564 insertRematerializationStores(Info.RematerializedValues, AllocaMap,
1567 if (ClobberNonLive) {
1568 // As a debuging aid, pretend that an unrelocated pointer becomes null at
1569 // the gc.statepoint. This will turn some subtle GC problems into
1570 // slightly easier to debug SEGVs. Note that on large IR files with
1571 // lots of gc.statepoints this is extremely costly both memory and time
1573 SmallVector<AllocaInst *, 64> ToClobber;
1574 for (auto Pair : AllocaMap) {
1575 Value *Def = Pair.first;
1576 AllocaInst *Alloca = cast<AllocaInst>(Pair.second);
1578 // This value was relocated
1579 if (VisitedLiveValues.count(Def)) {
1582 ToClobber.push_back(Alloca);
1585 auto InsertClobbersAt = [&](Instruction *IP) {
1586 for (auto *AI : ToClobber) {
1587 auto AIType = cast<PointerType>(AI->getType());
1588 auto PT = cast<PointerType>(AIType->getElementType());
1589 Constant *CPN = ConstantPointerNull::get(PT);
1590 StoreInst *Store = new StoreInst(CPN, AI);
1591 Store->insertBefore(IP);
1595 // Insert the clobbering stores. These may get intermixed with the
1596 // gc.results and gc.relocates, but that's fine.
1597 if (auto II = dyn_cast<InvokeInst>(Statepoint)) {
1598 InsertClobbersAt(II->getNormalDest()->getFirstInsertionPt());
1599 InsertClobbersAt(II->getUnwindDest()->getFirstInsertionPt());
1601 BasicBlock::iterator Next(cast<CallInst>(Statepoint));
1603 InsertClobbersAt(Next);
1607 // update use with load allocas and add store for gc_relocated
1608 for (auto Pair : AllocaMap) {
1609 Value *Def = Pair.first;
1610 Value *Alloca = Pair.second;
1612 // we pre-record the uses of allocas so that we dont have to worry about
1614 // that change the user information.
1615 SmallVector<Instruction *, 20> Uses;
1616 // PERF: trade a linear scan for repeated reallocation
1617 Uses.reserve(std::distance(Def->user_begin(), Def->user_end()));
1618 for (User *U : Def->users()) {
1619 if (!isa<ConstantExpr>(U)) {
1620 // If the def has a ConstantExpr use, then the def is either a
1621 // ConstantExpr use itself or null. In either case
1622 // (recursively in the first, directly in the second), the oop
1623 // it is ultimately dependent on is null and this particular
1624 // use does not need to be fixed up.
1625 Uses.push_back(cast<Instruction>(U));
1629 std::sort(Uses.begin(), Uses.end());
1630 auto Last = std::unique(Uses.begin(), Uses.end());
1631 Uses.erase(Last, Uses.end());
1633 for (Instruction *Use : Uses) {
1634 if (isa<PHINode>(Use)) {
1635 PHINode *Phi = cast<PHINode>(Use);
1636 for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) {
1637 if (Def == Phi->getIncomingValue(i)) {
1638 LoadInst *Load = new LoadInst(
1639 Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
1640 Phi->setIncomingValue(i, Load);
1644 LoadInst *Load = new LoadInst(Alloca, "", Use);
1645 Use->replaceUsesOfWith(Def, Load);
1649 // emit store for the initial gc value
1650 // store must be inserted after load, otherwise store will be in alloca's
1651 // use list and an extra load will be inserted before it
1652 StoreInst *Store = new StoreInst(Def, Alloca);
1653 if (Instruction *Inst = dyn_cast<Instruction>(Def)) {
1654 if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) {
1655 // InvokeInst is a TerminatorInst so the store need to be inserted
1656 // into its normal destination block.
1657 BasicBlock *NormalDest = Invoke->getNormalDest();
1658 Store->insertBefore(NormalDest->getFirstNonPHI());
1660 assert(!Inst->isTerminator() &&
1661 "The only TerminatorInst that can produce a value is "
1662 "InvokeInst which is handled above.");
1663 Store->insertAfter(Inst);
1666 assert(isa<Argument>(Def));
1667 Store->insertAfter(cast<Instruction>(Alloca));
1671 assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues &&
1672 "we must have the same allocas with lives");
1673 if (!PromotableAllocas.empty()) {
1674 // apply mem2reg to promote alloca to SSA
1675 PromoteMemToReg(PromotableAllocas, DT);
1679 for (auto I = F.getEntryBlock().begin(), E = F.getEntryBlock().end(); I != E;
1681 if (isa<AllocaInst>(*I))
1683 assert(InitialAllocaNum == 0 && "We must not introduce any extra allocas");
1687 /// Implement a unique function which doesn't require we sort the input
1688 /// vector. Doing so has the effect of changing the output of a couple of
1689 /// tests in ways which make them less useful in testing fused safepoints.
1690 template <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) {
1691 SmallSet<T, 8> Seen;
1692 Vec.erase(std::remove_if(Vec.begin(), Vec.end(), [&](const T &V) {
1693 return !Seen.insert(V).second;
1697 /// Insert holders so that each Value is obviously live through the entire
1698 /// lifetime of the call.
1699 static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values,
1700 SmallVectorImpl<CallInst *> &Holders) {
1702 // No values to hold live, might as well not insert the empty holder
1705 Module *M = CS.getInstruction()->getParent()->getParent()->getParent();
1706 // Use a dummy vararg function to actually hold the values live
1707 Function *Func = cast<Function>(M->getOrInsertFunction(
1708 "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true)));
1710 // For call safepoints insert dummy calls right after safepoint
1711 BasicBlock::iterator Next(CS.getInstruction());
1713 Holders.push_back(CallInst::Create(Func, Values, "", Next));
1716 // For invoke safepooints insert dummy calls both in normal and
1717 // exceptional destination blocks
1718 auto *II = cast<InvokeInst>(CS.getInstruction());
1719 Holders.push_back(CallInst::Create(
1720 Func, Values, "", II->getNormalDest()->getFirstInsertionPt()));
1721 Holders.push_back(CallInst::Create(
1722 Func, Values, "", II->getUnwindDest()->getFirstInsertionPt()));
1725 static void findLiveReferences(
1726 Function &F, DominatorTree &DT, Pass *P, ArrayRef<CallSite> toUpdate,
1727 MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
1728 GCPtrLivenessData OriginalLivenessData;
1729 computeLiveInValues(DT, F, OriginalLivenessData);
1730 for (size_t i = 0; i < records.size(); i++) {
1731 struct PartiallyConstructedSafepointRecord &info = records[i];
1732 const CallSite &CS = toUpdate[i];
1733 analyzeParsePointLiveness(DT, OriginalLivenessData, CS, info);
1737 /// Remove any vector of pointers from the liveset by scalarizing them over the
1738 /// statepoint instruction. Adds the scalarized pieces to the liveset. It
1739 /// would be preferrable to include the vector in the statepoint itself, but
1740 /// the lowering code currently does not handle that. Extending it would be
1741 /// slightly non-trivial since it requires a format change. Given how rare
1742 /// such cases are (for the moment?) scalarizing is an acceptable comprimise.
1743 static void splitVectorValues(Instruction *StatepointInst,
1744 StatepointLiveSetTy &LiveSet,
1745 DenseMap<Value *, Value *>& PointerToBase,
1746 DominatorTree &DT) {
1747 SmallVector<Value *, 16> ToSplit;
1748 for (Value *V : LiveSet)
1749 if (isa<VectorType>(V->getType()))
1750 ToSplit.push_back(V);
1752 if (ToSplit.empty())
1755 DenseMap<Value *, SmallVector<Value *, 16>> ElementMapping;
1757 Function &F = *(StatepointInst->getParent()->getParent());
1759 DenseMap<Value *, AllocaInst *> AllocaMap;
1760 // First is normal return, second is exceptional return (invoke only)
1761 DenseMap<Value *, std::pair<Value *, Value *>> Replacements;
1762 for (Value *V : ToSplit) {
1763 AllocaInst *Alloca =
1764 new AllocaInst(V->getType(), "", F.getEntryBlock().getFirstNonPHI());
1765 AllocaMap[V] = Alloca;
1767 VectorType *VT = cast<VectorType>(V->getType());
1768 IRBuilder<> Builder(StatepointInst);
1769 SmallVector<Value *, 16> Elements;
1770 for (unsigned i = 0; i < VT->getNumElements(); i++)
1771 Elements.push_back(Builder.CreateExtractElement(V, Builder.getInt32(i)));
1772 ElementMapping[V] = Elements;
1774 auto InsertVectorReform = [&](Instruction *IP) {
1775 Builder.SetInsertPoint(IP);
1776 Builder.SetCurrentDebugLocation(IP->getDebugLoc());
1777 Value *ResultVec = UndefValue::get(VT);
1778 for (unsigned i = 0; i < VT->getNumElements(); i++)
1779 ResultVec = Builder.CreateInsertElement(ResultVec, Elements[i],
1780 Builder.getInt32(i));
1784 if (isa<CallInst>(StatepointInst)) {
1785 BasicBlock::iterator Next(StatepointInst);
1787 Instruction *IP = &*(Next);
1788 Replacements[V].first = InsertVectorReform(IP);
1789 Replacements[V].second = nullptr;
1791 InvokeInst *Invoke = cast<InvokeInst>(StatepointInst);
1792 // We've already normalized - check that we don't have shared destination
1794 BasicBlock *NormalDest = Invoke->getNormalDest();
1795 assert(!isa<PHINode>(NormalDest->begin()));
1796 BasicBlock *UnwindDest = Invoke->getUnwindDest();
1797 assert(!isa<PHINode>(UnwindDest->begin()));
1798 // Insert insert element sequences in both successors
1799 Instruction *IP = &*(NormalDest->getFirstInsertionPt());
1800 Replacements[V].first = InsertVectorReform(IP);
1801 IP = &*(UnwindDest->getFirstInsertionPt());
1802 Replacements[V].second = InsertVectorReform(IP);
1806 for (Value *V : ToSplit) {
1807 AllocaInst *Alloca = AllocaMap[V];
1809 // Capture all users before we start mutating use lists
1810 SmallVector<Instruction *, 16> Users;
1811 for (User *U : V->users())
1812 Users.push_back(cast<Instruction>(U));
1814 for (Instruction *I : Users) {
1815 if (auto Phi = dyn_cast<PHINode>(I)) {
1816 for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++)
1817 if (V == Phi->getIncomingValue(i)) {
1818 LoadInst *Load = new LoadInst(
1819 Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
1820 Phi->setIncomingValue(i, Load);
1823 LoadInst *Load = new LoadInst(Alloca, "", I);
1824 I->replaceUsesOfWith(V, Load);
1828 // Store the original value and the replacement value into the alloca
1829 StoreInst *Store = new StoreInst(V, Alloca);
1830 if (auto I = dyn_cast<Instruction>(V))
1831 Store->insertAfter(I);
1833 Store->insertAfter(Alloca);
1835 // Normal return for invoke, or call return
1836 Instruction *Replacement = cast<Instruction>(Replacements[V].first);
1837 (new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
1838 // Unwind return for invoke only
1839 Replacement = cast_or_null<Instruction>(Replacements[V].second);
1841 (new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
1844 // apply mem2reg to promote alloca to SSA
1845 SmallVector<AllocaInst *, 16> Allocas;
1846 for (Value *V : ToSplit)
1847 Allocas.push_back(AllocaMap[V]);
1848 PromoteMemToReg(Allocas, DT);
1850 // Update our tracking of live pointers and base mappings to account for the
1851 // changes we just made.
1852 for (Value *V : ToSplit) {
1853 auto &Elements = ElementMapping[V];
1856 LiveSet.insert(Elements.begin(), Elements.end());
1857 // We need to update the base mapping as well.
1858 assert(PointerToBase.count(V));
1859 Value *OldBase = PointerToBase[V];
1860 auto &BaseElements = ElementMapping[OldBase];
1861 PointerToBase.erase(V);
1862 assert(Elements.size() == BaseElements.size());
1863 for (unsigned i = 0; i < Elements.size(); i++) {
1864 Value *Elem = Elements[i];
1865 PointerToBase[Elem] = BaseElements[i];
1870 // Helper function for the "rematerializeLiveValues". It walks use chain
1871 // starting from the "CurrentValue" until it meets "BaseValue". Only "simple"
1872 // values are visited (currently it is GEP's and casts). Returns true if it
1873 // sucessfully reached "BaseValue" and false otherwise.
1874 // Fills "ChainToBase" array with all visited values. "BaseValue" is not
1876 static bool findRematerializableChainToBasePointer(
1877 SmallVectorImpl<Instruction*> &ChainToBase,
1878 Value *CurrentValue, Value *BaseValue) {
1880 // We have found a base value
1881 if (CurrentValue == BaseValue) {
1885 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) {
1886 ChainToBase.push_back(GEP);
1887 return findRematerializableChainToBasePointer(ChainToBase,
1888 GEP->getPointerOperand(),
1892 if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) {
1893 Value *Def = CI->stripPointerCasts();
1895 // This two checks are basically similar. First one is here for the
1896 // consistency with findBasePointers logic.
1897 assert(!isa<CastInst>(Def) && "not a pointer cast found");
1898 if (!CI->isNoopCast(CI->getModule()->getDataLayout()))
1901 ChainToBase.push_back(CI);
1902 return findRematerializableChainToBasePointer(ChainToBase, Def, BaseValue);
1905 // Not supported instruction in the chain
1909 // Helper function for the "rematerializeLiveValues". Compute cost of the use
1910 // chain we are going to rematerialize.
1912 chainToBasePointerCost(SmallVectorImpl<Instruction*> &Chain,
1913 TargetTransformInfo &TTI) {
1916 for (Instruction *Instr : Chain) {
1917 if (CastInst *CI = dyn_cast<CastInst>(Instr)) {
1918 assert(CI->isNoopCast(CI->getModule()->getDataLayout()) &&
1919 "non noop cast is found during rematerialization");
1921 Type *SrcTy = CI->getOperand(0)->getType();
1922 Cost += TTI.getCastInstrCost(CI->getOpcode(), CI->getType(), SrcTy);
1924 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Instr)) {
1925 // Cost of the address calculation
1926 Type *ValTy = GEP->getPointerOperandType()->getPointerElementType();
1927 Cost += TTI.getAddressComputationCost(ValTy);
1929 // And cost of the GEP itself
1930 // TODO: Use TTI->getGEPCost here (it exists, but appears to be not
1931 // allowed for the external usage)
1932 if (!GEP->hasAllConstantIndices())
1936 llvm_unreachable("unsupported instruciton type during rematerialization");
1943 // From the statepoint liveset pick values that are cheaper to recompute then to
1944 // relocate. Remove this values from the liveset, rematerialize them after
1945 // statepoint and record them in "Info" structure. Note that similar to
1946 // relocated values we don't do any user adjustments here.
1947 static void rematerializeLiveValues(CallSite CS,
1948 PartiallyConstructedSafepointRecord &Info,
1949 TargetTransformInfo &TTI) {
1950 const unsigned int ChainLengthThreshold = 10;
1952 // Record values we are going to delete from this statepoint live set.
1953 // We can not di this in following loop due to iterator invalidation.
1954 SmallVector<Value *, 32> LiveValuesToBeDeleted;
1956 for (Value *LiveValue: Info.liveset) {
1957 // For each live pointer find it's defining chain
1958 SmallVector<Instruction *, 3> ChainToBase;
1959 assert(Info.PointerToBase.count(LiveValue));
1961 findRematerializableChainToBasePointer(ChainToBase,
1963 Info.PointerToBase[LiveValue]);
1964 // Nothing to do, or chain is too long
1966 ChainToBase.size() == 0 ||
1967 ChainToBase.size() > ChainLengthThreshold)
1970 // Compute cost of this chain
1971 unsigned Cost = chainToBasePointerCost(ChainToBase, TTI);
1972 // TODO: We can also account for cases when we will be able to remove some
1973 // of the rematerialized values by later optimization passes. I.e if
1974 // we rematerialized several intersecting chains. Or if original values
1975 // don't have any uses besides this statepoint.
1977 // For invokes we need to rematerialize each chain twice - for normal and
1978 // for unwind basic blocks. Model this by multiplying cost by two.
1979 if (CS.isInvoke()) {
1982 // If it's too expensive - skip it
1983 if (Cost >= RematerializationThreshold)
1986 // Remove value from the live set
1987 LiveValuesToBeDeleted.push_back(LiveValue);
1989 // Clone instructions and record them inside "Info" structure
1991 // Walk backwards to visit top-most instructions first
1992 std::reverse(ChainToBase.begin(), ChainToBase.end());
1994 // Utility function which clones all instructions from "ChainToBase"
1995 // and inserts them before "InsertBefore". Returns rematerialized value
1996 // which should be used after statepoint.
1997 auto rematerializeChain = [&ChainToBase](Instruction *InsertBefore) {
1998 Instruction *LastClonedValue = nullptr;
1999 Instruction *LastValue = nullptr;
2000 for (Instruction *Instr: ChainToBase) {
2001 // Only GEP's and casts are suported as we need to be careful to not
2002 // introduce any new uses of pointers not in the liveset.
2003 // Note that it's fine to introduce new uses of pointers which were
2004 // otherwise not used after this statepoint.
2005 assert(isa<GetElementPtrInst>(Instr) || isa<CastInst>(Instr));
2007 Instruction *ClonedValue = Instr->clone();
2008 ClonedValue->insertBefore(InsertBefore);
2009 ClonedValue->setName(Instr->getName() + ".remat");
2011 // If it is not first instruction in the chain then it uses previously
2012 // cloned value. We should update it to use cloned value.
2013 if (LastClonedValue) {
2015 ClonedValue->replaceUsesOfWith(LastValue, LastClonedValue);
2017 // Assert that cloned instruction does not use any instructions from
2018 // this chain other than LastClonedValue
2019 for (auto OpValue : ClonedValue->operand_values()) {
2020 assert(std::find(ChainToBase.begin(), ChainToBase.end(), OpValue) ==
2021 ChainToBase.end() &&
2022 "incorrect use in rematerialization chain");
2027 LastClonedValue = ClonedValue;
2030 assert(LastClonedValue);
2031 return LastClonedValue;
2034 // Different cases for calls and invokes. For invokes we need to clone
2035 // instructions both on normal and unwind path.
2037 Instruction *InsertBefore = CS.getInstruction()->getNextNode();
2038 assert(InsertBefore);
2039 Instruction *RematerializedValue = rematerializeChain(InsertBefore);
2040 Info.RematerializedValues[RematerializedValue] = LiveValue;
2042 InvokeInst *Invoke = cast<InvokeInst>(CS.getInstruction());
2044 Instruction *NormalInsertBefore =
2045 Invoke->getNormalDest()->getFirstInsertionPt();
2046 Instruction *UnwindInsertBefore =
2047 Invoke->getUnwindDest()->getFirstInsertionPt();
2049 Instruction *NormalRematerializedValue =
2050 rematerializeChain(NormalInsertBefore);
2051 Instruction *UnwindRematerializedValue =
2052 rematerializeChain(UnwindInsertBefore);
2054 Info.RematerializedValues[NormalRematerializedValue] = LiveValue;
2055 Info.RematerializedValues[UnwindRematerializedValue] = LiveValue;
2059 // Remove rematerializaed values from the live set
2060 for (auto LiveValue: LiveValuesToBeDeleted) {
2061 Info.liveset.erase(LiveValue);
2065 static bool insertParsePoints(Function &F, DominatorTree &DT, Pass *P,
2066 SmallVectorImpl<CallSite> &toUpdate) {
2068 // sanity check the input
2069 std::set<CallSite> uniqued;
2070 uniqued.insert(toUpdate.begin(), toUpdate.end());
2071 assert(uniqued.size() == toUpdate.size() && "no duplicates please!");
2073 for (size_t i = 0; i < toUpdate.size(); i++) {
2074 CallSite &CS = toUpdate[i];
2075 assert(CS.getInstruction()->getParent()->getParent() == &F);
2076 assert(isStatepoint(CS) && "expected to already be a deopt statepoint");
2080 // When inserting gc.relocates for invokes, we need to be able to insert at
2081 // the top of the successor blocks. See the comment on
2082 // normalForInvokeSafepoint on exactly what is needed. Note that this step
2083 // may restructure the CFG.
2084 for (CallSite CS : toUpdate) {
2087 InvokeInst *invoke = cast<InvokeInst>(CS.getInstruction());
2088 normalizeForInvokeSafepoint(invoke->getNormalDest(), invoke->getParent(),
2090 normalizeForInvokeSafepoint(invoke->getUnwindDest(), invoke->getParent(),
2094 // A list of dummy calls added to the IR to keep various values obviously
2095 // live in the IR. We'll remove all of these when done.
2096 SmallVector<CallInst *, 64> holders;
2098 // Insert a dummy call with all of the arguments to the vm_state we'll need
2099 // for the actual safepoint insertion. This ensures reference arguments in
2100 // the deopt argument list are considered live through the safepoint (and
2101 // thus makes sure they get relocated.)
2102 for (size_t i = 0; i < toUpdate.size(); i++) {
2103 CallSite &CS = toUpdate[i];
2104 Statepoint StatepointCS(CS);
2106 SmallVector<Value *, 64> DeoptValues;
2107 for (Use &U : StatepointCS.vm_state_args()) {
2108 Value *Arg = cast<Value>(&U);
2109 assert(!isUnhandledGCPointerType(Arg->getType()) &&
2110 "support for FCA unimplemented");
2111 if (isHandledGCPointerType(Arg->getType()))
2112 DeoptValues.push_back(Arg);
2114 insertUseHolderAfter(CS, DeoptValues, holders);
2117 SmallVector<struct PartiallyConstructedSafepointRecord, 64> records;
2118 records.reserve(toUpdate.size());
2119 for (size_t i = 0; i < toUpdate.size(); i++) {
2120 struct PartiallyConstructedSafepointRecord info;
2121 records.push_back(info);
2123 assert(records.size() == toUpdate.size());
2125 // A) Identify all gc pointers which are staticly live at the given call
2127 findLiveReferences(F, DT, P, toUpdate, records);
2129 // B) Find the base pointers for each live pointer
2130 /* scope for caching */ {
2131 // Cache the 'defining value' relation used in the computation and
2132 // insertion of base phis and selects. This ensures that we don't insert
2133 // large numbers of duplicate base_phis.
2134 DefiningValueMapTy DVCache;
2136 for (size_t i = 0; i < records.size(); i++) {
2137 struct PartiallyConstructedSafepointRecord &info = records[i];
2138 CallSite &CS = toUpdate[i];
2139 findBasePointers(DT, DVCache, CS, info);
2141 } // end of cache scope
2143 // The base phi insertion logic (for any safepoint) may have inserted new
2144 // instructions which are now live at some safepoint. The simplest such
2147 // phi a <-- will be a new base_phi here
2148 // safepoint 1 <-- that needs to be live here
2152 // We insert some dummy calls after each safepoint to definitely hold live
2153 // the base pointers which were identified for that safepoint. We'll then
2154 // ask liveness for _every_ base inserted to see what is now live. Then we
2155 // remove the dummy calls.
2156 holders.reserve(holders.size() + records.size());
2157 for (size_t i = 0; i < records.size(); i++) {
2158 struct PartiallyConstructedSafepointRecord &info = records[i];
2159 CallSite &CS = toUpdate[i];
2161 SmallVector<Value *, 128> Bases;
2162 for (auto Pair : info.PointerToBase) {
2163 Bases.push_back(Pair.second);
2165 insertUseHolderAfter(CS, Bases, holders);
2168 // By selecting base pointers, we've effectively inserted new uses. Thus, we
2169 // need to rerun liveness. We may *also* have inserted new defs, but that's
2170 // not the key issue.
2171 recomputeLiveInValues(F, DT, P, toUpdate, records);
2173 if (PrintBasePointers) {
2174 for (size_t i = 0; i < records.size(); i++) {
2175 struct PartiallyConstructedSafepointRecord &info = records[i];
2176 errs() << "Base Pairs: (w/Relocation)\n";
2177 for (auto Pair : info.PointerToBase) {
2178 errs() << " derived %" << Pair.first->getName() << " base %"
2179 << Pair.second->getName() << "\n";
2183 for (size_t i = 0; i < holders.size(); i++) {
2184 holders[i]->eraseFromParent();
2185 holders[i] = nullptr;
2189 // Do a limited scalarization of any live at safepoint vector values which
2190 // contain pointers. This enables this pass to run after vectorization at
2191 // the cost of some possible performance loss. TODO: it would be nice to
2192 // natively support vectors all the way through the backend so we don't need
2193 // to scalarize here.
2194 for (size_t i = 0; i < records.size(); i++) {
2195 struct PartiallyConstructedSafepointRecord &info = records[i];
2196 Instruction *statepoint = toUpdate[i].getInstruction();
2197 splitVectorValues(cast<Instruction>(statepoint), info.liveset,
2198 info.PointerToBase, DT);
2201 // In order to reduce live set of statepoint we might choose to rematerialize
2202 // some values instead of relocating them. This is purelly an optimization and
2203 // does not influence correctness.
2204 TargetTransformInfo &TTI =
2205 P->getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
2207 for (size_t i = 0; i < records.size(); i++) {
2208 struct PartiallyConstructedSafepointRecord &info = records[i];
2209 CallSite &CS = toUpdate[i];
2211 rematerializeLiveValues(CS, info, TTI);
2214 // Now run through and replace the existing statepoints with new ones with
2215 // the live variables listed. We do not yet update uses of the values being
2216 // relocated. We have references to live variables that need to
2217 // survive to the last iteration of this loop. (By construction, the
2218 // previous statepoint can not be a live variable, thus we can and remove
2219 // the old statepoint calls as we go.)
2220 for (size_t i = 0; i < records.size(); i++) {
2221 struct PartiallyConstructedSafepointRecord &info = records[i];
2222 CallSite &CS = toUpdate[i];
2223 makeStatepointExplicit(DT, CS, P, info);
2225 toUpdate.clear(); // prevent accident use of invalid CallSites
2227 // Do all the fixups of the original live variables to their relocated selves
2228 SmallVector<Value *, 128> live;
2229 for (size_t i = 0; i < records.size(); i++) {
2230 struct PartiallyConstructedSafepointRecord &info = records[i];
2231 // We can't simply save the live set from the original insertion. One of
2232 // the live values might be the result of a call which needs a safepoint.
2233 // That Value* no longer exists and we need to use the new gc_result.
2234 // Thankfully, the liveset is embedded in the statepoint (and updated), so
2235 // we just grab that.
2236 Statepoint statepoint(info.StatepointToken);
2237 live.insert(live.end(), statepoint.gc_args_begin(),
2238 statepoint.gc_args_end());
2240 // Do some basic sanity checks on our liveness results before performing
2241 // relocation. Relocation can and will turn mistakes in liveness results
2242 // into non-sensical code which is must harder to debug.
2243 // TODO: It would be nice to test consistency as well
2244 assert(DT.isReachableFromEntry(info.StatepointToken->getParent()) &&
2245 "statepoint must be reachable or liveness is meaningless");
2246 for (Value *V : statepoint.gc_args()) {
2247 if (!isa<Instruction>(V))
2248 // Non-instruction values trivial dominate all possible uses
2250 auto LiveInst = cast<Instruction>(V);
2251 assert(DT.isReachableFromEntry(LiveInst->getParent()) &&
2252 "unreachable values should never be live");
2253 assert(DT.dominates(LiveInst, info.StatepointToken) &&
2254 "basic SSA liveness expectation violated by liveness analysis");
2258 unique_unsorted(live);
2262 for (auto ptr : live) {
2263 assert(isGCPointerType(ptr->getType()) && "must be a gc pointer type");
2267 relocationViaAlloca(F, DT, live, records);
2268 return !records.empty();
2271 // Handles both return values and arguments for Functions and CallSites.
2272 template <typename AttrHolder>
2273 static void RemoveDerefAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH,
2276 if (AH.getDereferenceableBytes(Index))
2277 R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable,
2278 AH.getDereferenceableBytes(Index)));
2279 if (AH.getDereferenceableOrNullBytes(Index))
2280 R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull,
2281 AH.getDereferenceableOrNullBytes(Index)));
2284 AH.setAttributes(AH.getAttributes().removeAttributes(
2285 Ctx, Index, AttributeSet::get(Ctx, Index, R)));
2289 RewriteStatepointsForGC::stripDereferenceabilityInfoFromPrototype(Function &F) {
2290 LLVMContext &Ctx = F.getContext();
2292 for (Argument &A : F.args())
2293 if (isa<PointerType>(A.getType()))
2294 RemoveDerefAttrAtIndex(Ctx, F, A.getArgNo() + 1);
2296 if (isa<PointerType>(F.getReturnType()))
2297 RemoveDerefAttrAtIndex(Ctx, F, AttributeSet::ReturnIndex);
2300 void RewriteStatepointsForGC::stripDereferenceabilityInfoFromBody(Function &F) {
2304 LLVMContext &Ctx = F.getContext();
2305 MDBuilder Builder(Ctx);
2307 for (Instruction &I : inst_range(F)) {
2308 if (const MDNode *MD = I.getMetadata(LLVMContext::MD_tbaa)) {
2309 assert(MD->getNumOperands() < 5 && "unrecognized metadata shape!");
2310 bool IsImmutableTBAA =
2311 MD->getNumOperands() == 4 &&
2312 mdconst::extract<ConstantInt>(MD->getOperand(3))->getValue() == 1;
2314 if (!IsImmutableTBAA)
2315 continue; // no work to do, MD_tbaa is already marked mutable
2317 MDNode *Base = cast<MDNode>(MD->getOperand(0));
2318 MDNode *Access = cast<MDNode>(MD->getOperand(1));
2320 mdconst::extract<ConstantInt>(MD->getOperand(2))->getZExtValue();
2322 MDNode *MutableTBAA =
2323 Builder.createTBAAStructTagNode(Base, Access, Offset);
2324 I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA);
2327 if (CallSite CS = CallSite(&I)) {
2328 for (int i = 0, e = CS.arg_size(); i != e; i++)
2329 if (isa<PointerType>(CS.getArgument(i)->getType()))
2330 RemoveDerefAttrAtIndex(Ctx, CS, i + 1);
2331 if (isa<PointerType>(CS.getType()))
2332 RemoveDerefAttrAtIndex(Ctx, CS, AttributeSet::ReturnIndex);
2337 /// Returns true if this function should be rewritten by this pass. The main
2338 /// point of this function is as an extension point for custom logic.
2339 static bool shouldRewriteStatepointsIn(Function &F) {
2340 // TODO: This should check the GCStrategy
2342 const char *FunctionGCName = F.getGC();
2343 const StringRef StatepointExampleName("statepoint-example");
2344 const StringRef CoreCLRName("coreclr");
2345 return (StatepointExampleName == FunctionGCName) ||
2346 (CoreCLRName == FunctionGCName);
2351 void RewriteStatepointsForGC::stripDereferenceabilityInfo(Module &M) {
2353 assert(std::any_of(M.begin(), M.end(), shouldRewriteStatepointsIn) &&
2357 for (Function &F : M)
2358 stripDereferenceabilityInfoFromPrototype(F);
2360 for (Function &F : M)
2361 stripDereferenceabilityInfoFromBody(F);
2364 bool RewriteStatepointsForGC::runOnFunction(Function &F) {
2365 // Nothing to do for declarations.
2366 if (F.isDeclaration() || F.empty())
2369 // Policy choice says not to rewrite - the most common reason is that we're
2370 // compiling code without a GCStrategy.
2371 if (!shouldRewriteStatepointsIn(F))
2374 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
2376 // Gather all the statepoints which need rewritten. Be careful to only
2377 // consider those in reachable code since we need to ask dominance queries
2378 // when rewriting. We'll delete the unreachable ones in a moment.
2379 SmallVector<CallSite, 64> ParsePointNeeded;
2380 bool HasUnreachableStatepoint = false;
2381 for (Instruction &I : inst_range(F)) {
2382 // TODO: only the ones with the flag set!
2383 if (isStatepoint(I)) {
2384 if (DT.isReachableFromEntry(I.getParent()))
2385 ParsePointNeeded.push_back(CallSite(&I));
2387 HasUnreachableStatepoint = true;
2391 bool MadeChange = false;
2393 // Delete any unreachable statepoints so that we don't have unrewritten
2394 // statepoints surviving this pass. This makes testing easier and the
2395 // resulting IR less confusing to human readers. Rather than be fancy, we
2396 // just reuse a utility function which removes the unreachable blocks.
2397 if (HasUnreachableStatepoint)
2398 MadeChange |= removeUnreachableBlocks(F);
2400 // Return early if no work to do.
2401 if (ParsePointNeeded.empty())
2404 // As a prepass, go ahead and aggressively destroy single entry phi nodes.
2405 // These are created by LCSSA. They have the effect of increasing the size
2406 // of liveness sets for no good reason. It may be harder to do this post
2407 // insertion since relocations and base phis can confuse things.
2408 for (BasicBlock &BB : F)
2409 if (BB.getUniquePredecessor()) {
2411 FoldSingleEntryPHINodes(&BB);
2414 MadeChange |= insertParsePoints(F, DT, this, ParsePointNeeded);
2418 // liveness computation via standard dataflow
2419 // -------------------------------------------------------------------
2421 // TODO: Consider using bitvectors for liveness, the set of potentially
2422 // interesting values should be small and easy to pre-compute.
2424 /// Compute the live-in set for the location rbegin starting from
2425 /// the live-out set of the basic block
2426 static void computeLiveInValues(BasicBlock::reverse_iterator rbegin,
2427 BasicBlock::reverse_iterator rend,
2428 DenseSet<Value *> &LiveTmp) {
2430 for (BasicBlock::reverse_iterator ritr = rbegin; ritr != rend; ritr++) {
2431 Instruction *I = &*ritr;
2433 // KILL/Def - Remove this definition from LiveIn
2436 // Don't consider *uses* in PHI nodes, we handle their contribution to
2437 // predecessor blocks when we seed the LiveOut sets
2438 if (isa<PHINode>(I))
2441 // USE - Add to the LiveIn set for this instruction
2442 for (Value *V : I->operands()) {
2443 assert(!isUnhandledGCPointerType(V->getType()) &&
2444 "support for FCA unimplemented");
2445 if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
2446 // The choice to exclude all things constant here is slightly subtle.
2447 // There are two idependent reasons:
2448 // - We assume that things which are constant (from LLVM's definition)
2449 // do not move at runtime. For example, the address of a global
2450 // variable is fixed, even though it's contents may not be.
2451 // - Second, we can't disallow arbitrary inttoptr constants even
2452 // if the language frontend does. Optimization passes are free to
2453 // locally exploit facts without respect to global reachability. This
2454 // can create sections of code which are dynamically unreachable and
2455 // contain just about anything. (see constants.ll in tests)
2462 static void computeLiveOutSeed(BasicBlock *BB, DenseSet<Value *> &LiveTmp) {
2464 for (BasicBlock *Succ : successors(BB)) {
2465 const BasicBlock::iterator E(Succ->getFirstNonPHI());
2466 for (BasicBlock::iterator I = Succ->begin(); I != E; I++) {
2467 PHINode *Phi = cast<PHINode>(&*I);
2468 Value *V = Phi->getIncomingValueForBlock(BB);
2469 assert(!isUnhandledGCPointerType(V->getType()) &&
2470 "support for FCA unimplemented");
2471 if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
2478 static DenseSet<Value *> computeKillSet(BasicBlock *BB) {
2479 DenseSet<Value *> KillSet;
2480 for (Instruction &I : *BB)
2481 if (isHandledGCPointerType(I.getType()))
2487 /// Check that the items in 'Live' dominate 'TI'. This is used as a basic
2488 /// sanity check for the liveness computation.
2489 static void checkBasicSSA(DominatorTree &DT, DenseSet<Value *> &Live,
2490 TerminatorInst *TI, bool TermOkay = false) {
2491 for (Value *V : Live) {
2492 if (auto *I = dyn_cast<Instruction>(V)) {
2493 // The terminator can be a member of the LiveOut set. LLVM's definition
2494 // of instruction dominance states that V does not dominate itself. As
2495 // such, we need to special case this to allow it.
2496 if (TermOkay && TI == I)
2498 assert(DT.dominates(I, TI) &&
2499 "basic SSA liveness expectation violated by liveness analysis");
2504 /// Check that all the liveness sets used during the computation of liveness
2505 /// obey basic SSA properties. This is useful for finding cases where we miss
2507 static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data,
2509 checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator());
2510 checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true);
2511 checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator());
2515 static void computeLiveInValues(DominatorTree &DT, Function &F,
2516 GCPtrLivenessData &Data) {
2518 SmallSetVector<BasicBlock *, 200> Worklist;
2519 auto AddPredsToWorklist = [&](BasicBlock *BB) {
2520 // We use a SetVector so that we don't have duplicates in the worklist.
2521 Worklist.insert(pred_begin(BB), pred_end(BB));
2523 auto NextItem = [&]() {
2524 BasicBlock *BB = Worklist.back();
2525 Worklist.pop_back();
2529 // Seed the liveness for each individual block
2530 for (BasicBlock &BB : F) {
2531 Data.KillSet[&BB] = computeKillSet(&BB);
2532 Data.LiveSet[&BB].clear();
2533 computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB]);
2536 for (Value *Kill : Data.KillSet[&BB])
2537 assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill");
2540 Data.LiveOut[&BB] = DenseSet<Value *>();
2541 computeLiveOutSeed(&BB, Data.LiveOut[&BB]);
2542 Data.LiveIn[&BB] = Data.LiveSet[&BB];
2543 set_union(Data.LiveIn[&BB], Data.LiveOut[&BB]);
2544 set_subtract(Data.LiveIn[&BB], Data.KillSet[&BB]);
2545 if (!Data.LiveIn[&BB].empty())
2546 AddPredsToWorklist(&BB);
2549 // Propagate that liveness until stable
2550 while (!Worklist.empty()) {
2551 BasicBlock *BB = NextItem();
2553 // Compute our new liveout set, then exit early if it hasn't changed
2554 // despite the contribution of our successor.
2555 DenseSet<Value *> LiveOut = Data.LiveOut[BB];
2556 const auto OldLiveOutSize = LiveOut.size();
2557 for (BasicBlock *Succ : successors(BB)) {
2558 assert(Data.LiveIn.count(Succ));
2559 set_union(LiveOut, Data.LiveIn[Succ]);
2561 // assert OutLiveOut is a subset of LiveOut
2562 if (OldLiveOutSize == LiveOut.size()) {
2563 // If the sets are the same size, then we didn't actually add anything
2564 // when unioning our successors LiveIn Thus, the LiveIn of this block
2568 Data.LiveOut[BB] = LiveOut;
2570 // Apply the effects of this basic block
2571 DenseSet<Value *> LiveTmp = LiveOut;
2572 set_union(LiveTmp, Data.LiveSet[BB]);
2573 set_subtract(LiveTmp, Data.KillSet[BB]);
2575 assert(Data.LiveIn.count(BB));
2576 const DenseSet<Value *> &OldLiveIn = Data.LiveIn[BB];
2577 // assert: OldLiveIn is a subset of LiveTmp
2578 if (OldLiveIn.size() != LiveTmp.size()) {
2579 Data.LiveIn[BB] = LiveTmp;
2580 AddPredsToWorklist(BB);
2582 } // while( !worklist.empty() )
2585 // Sanity check our ouput against SSA properties. This helps catch any
2586 // missing kills during the above iteration.
2587 for (BasicBlock &BB : F) {
2588 checkBasicSSA(DT, Data, BB);
2593 static void findLiveSetAtInst(Instruction *Inst, GCPtrLivenessData &Data,
2594 StatepointLiveSetTy &Out) {
2596 BasicBlock *BB = Inst->getParent();
2598 // Note: The copy is intentional and required
2599 assert(Data.LiveOut.count(BB));
2600 DenseSet<Value *> LiveOut = Data.LiveOut[BB];
2602 // We want to handle the statepoint itself oddly. It's
2603 // call result is not live (normal), nor are it's arguments
2604 // (unless they're used again later). This adjustment is
2605 // specifically what we need to relocate
2606 BasicBlock::reverse_iterator rend(Inst);
2607 computeLiveInValues(BB->rbegin(), rend, LiveOut);
2608 LiveOut.erase(Inst);
2609 Out.insert(LiveOut.begin(), LiveOut.end());
2612 static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
2614 PartiallyConstructedSafepointRecord &Info) {
2615 Instruction *Inst = CS.getInstruction();
2616 StatepointLiveSetTy Updated;
2617 findLiveSetAtInst(Inst, RevisedLivenessData, Updated);
2620 DenseSet<Value *> Bases;
2621 for (auto KVPair : Info.PointerToBase) {
2622 Bases.insert(KVPair.second);
2625 // We may have base pointers which are now live that weren't before. We need
2626 // to update the PointerToBase structure to reflect this.
2627 for (auto V : Updated)
2628 if (!Info.PointerToBase.count(V)) {
2629 assert(Bases.count(V) && "can't find base for unexpected live value");
2630 Info.PointerToBase[V] = V;
2635 for (auto V : Updated) {
2636 assert(Info.PointerToBase.count(V) &&
2637 "must be able to find base for live value");
2641 // Remove any stale base mappings - this can happen since our liveness is
2642 // more precise then the one inherent in the base pointer analysis
2643 DenseSet<Value *> ToErase;
2644 for (auto KVPair : Info.PointerToBase)
2645 if (!Updated.count(KVPair.first))
2646 ToErase.insert(KVPair.first);
2647 for (auto V : ToErase)
2648 Info.PointerToBase.erase(V);
2651 for (auto KVPair : Info.PointerToBase)
2652 assert(Updated.count(KVPair.first) && "record for non-live value");
2655 Info.liveset = Updated;