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 call/invoke instructions so as to make potential relocations
11 // performed by the garbage collector explicit in the IR.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Scalar/RewriteStatepointsForGC.h"
17 #include "llvm/ADT/ArrayRef.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/DenseSet.h"
20 #include "llvm/ADT/MapVector.h"
21 #include "llvm/ADT/None.h"
22 #include "llvm/ADT/Optional.h"
23 #include "llvm/ADT/STLExtras.h"
24 #include "llvm/ADT/SetVector.h"
25 #include "llvm/ADT/SmallSet.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/StringRef.h"
28 #include "llvm/ADT/iterator_range.h"
29 #include "llvm/Analysis/TargetLibraryInfo.h"
30 #include "llvm/Analysis/TargetTransformInfo.h"
31 #include "llvm/Transforms/Utils/Local.h"
32 #include "llvm/IR/Argument.h"
33 #include "llvm/IR/Attributes.h"
34 #include "llvm/IR/BasicBlock.h"
35 #include "llvm/IR/CallSite.h"
36 #include "llvm/IR/CallingConv.h"
37 #include "llvm/IR/Constant.h"
38 #include "llvm/IR/Constants.h"
39 #include "llvm/IR/DataLayout.h"
40 #include "llvm/IR/DerivedTypes.h"
41 #include "llvm/IR/Dominators.h"
42 #include "llvm/IR/Function.h"
43 #include "llvm/IR/IRBuilder.h"
44 #include "llvm/IR/InstIterator.h"
45 #include "llvm/IR/InstrTypes.h"
46 #include "llvm/IR/Instruction.h"
47 #include "llvm/IR/Instructions.h"
48 #include "llvm/IR/IntrinsicInst.h"
49 #include "llvm/IR/Intrinsics.h"
50 #include "llvm/IR/LLVMContext.h"
51 #include "llvm/IR/MDBuilder.h"
52 #include "llvm/IR/Metadata.h"
53 #include "llvm/IR/Module.h"
54 #include "llvm/IR/Statepoint.h"
55 #include "llvm/IR/Type.h"
56 #include "llvm/IR/User.h"
57 #include "llvm/IR/Value.h"
58 #include "llvm/IR/ValueHandle.h"
59 #include "llvm/Pass.h"
60 #include "llvm/Support/Casting.h"
61 #include "llvm/Support/CommandLine.h"
62 #include "llvm/Support/Compiler.h"
63 #include "llvm/Support/Debug.h"
64 #include "llvm/Support/ErrorHandling.h"
65 #include "llvm/Support/raw_ostream.h"
66 #include "llvm/Transforms/Scalar.h"
67 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
68 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
79 #define DEBUG_TYPE "rewrite-statepoints-for-gc"
83 // Print the liveset found at the insert location
84 static cl::opt<bool> PrintLiveSet("spp-print-liveset", cl::Hidden,
86 static cl::opt<bool> PrintLiveSetSize("spp-print-liveset-size", cl::Hidden,
89 // Print out the base pointers for debugging
90 static cl::opt<bool> PrintBasePointers("spp-print-base-pointers", cl::Hidden,
93 // Cost threshold measuring when it is profitable to rematerialize value instead
95 static cl::opt<unsigned>
96 RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden,
99 #ifdef EXPENSIVE_CHECKS
100 static bool ClobberNonLive = true;
102 static bool ClobberNonLive = false;
105 static cl::opt<bool, true> ClobberNonLiveOverride("rs4gc-clobber-non-live",
106 cl::location(ClobberNonLive),
110 AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info",
111 cl::Hidden, cl::init(true));
113 /// The IR fed into RewriteStatepointsForGC may have had attributes and
114 /// metadata implying dereferenceability that are no longer valid/correct after
115 /// RewriteStatepointsForGC has run. This is because semantically, after
116 /// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire
117 /// heap. stripNonValidData (conservatively) restores
118 /// correctness by erasing all attributes in the module that externally imply
119 /// dereferenceability. Similar reasoning also applies to the noalias
120 /// attributes and metadata. gc.statepoint can touch the entire heap including
122 /// Apart from attributes and metadata, we also remove instructions that imply
123 /// constant physical memory: llvm.invariant.start.
124 static void stripNonValidData(Module &M);
126 static bool shouldRewriteStatepointsIn(Function &F);
128 PreservedAnalyses RewriteStatepointsForGC::run(Module &M,
129 ModuleAnalysisManager &AM) {
130 bool Changed = false;
131 auto &FAM = AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
132 for (Function &F : M) {
133 // Nothing to do for declarations.
134 if (F.isDeclaration() || F.empty())
137 // Policy choice says not to rewrite - the most common reason is that we're
138 // compiling code without a GCStrategy.
139 if (!shouldRewriteStatepointsIn(F))
142 auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
143 auto &TTI = FAM.getResult<TargetIRAnalysis>(F);
144 auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F);
145 Changed |= runOnFunction(F, DT, TTI, TLI);
148 return PreservedAnalyses::all();
150 // stripNonValidData asserts that shouldRewriteStatepointsIn
151 // returns true for at least one function in the module. Since at least
152 // one function changed, we know that the precondition is satisfied.
153 stripNonValidData(M);
155 PreservedAnalyses PA;
156 PA.preserve<TargetIRAnalysis>();
157 PA.preserve<TargetLibraryAnalysis>();
163 class RewriteStatepointsForGCLegacyPass : public ModulePass {
164 RewriteStatepointsForGC Impl;
167 static char ID; // Pass identification, replacement for typeid
169 RewriteStatepointsForGCLegacyPass() : ModulePass(ID), Impl() {
170 initializeRewriteStatepointsForGCLegacyPassPass(
171 *PassRegistry::getPassRegistry());
174 bool runOnModule(Module &M) override {
175 bool Changed = false;
176 const TargetLibraryInfo &TLI =
177 getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
178 for (Function &F : M) {
179 // Nothing to do for declarations.
180 if (F.isDeclaration() || F.empty())
183 // Policy choice says not to rewrite - the most common reason is that
184 // we're compiling code without a GCStrategy.
185 if (!shouldRewriteStatepointsIn(F))
188 TargetTransformInfo &TTI =
189 getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
190 auto &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
192 Changed |= Impl.runOnFunction(F, DT, TTI, TLI);
198 // stripNonValidData asserts that shouldRewriteStatepointsIn
199 // returns true for at least one function in the module. Since at least
200 // one function changed, we know that the precondition is satisfied.
201 stripNonValidData(M);
205 void getAnalysisUsage(AnalysisUsage &AU) const override {
206 // We add and rewrite a bunch of instructions, but don't really do much
207 // else. We could in theory preserve a lot more analyses here.
208 AU.addRequired<DominatorTreeWrapperPass>();
209 AU.addRequired<TargetTransformInfoWrapperPass>();
210 AU.addRequired<TargetLibraryInfoWrapperPass>();
214 } // end anonymous namespace
216 char RewriteStatepointsForGCLegacyPass::ID = 0;
218 ModulePass *llvm::createRewriteStatepointsForGCLegacyPass() {
219 return new RewriteStatepointsForGCLegacyPass();
222 INITIALIZE_PASS_BEGIN(RewriteStatepointsForGCLegacyPass,
223 "rewrite-statepoints-for-gc",
224 "Make relocations explicit at statepoints", false, false)
225 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
226 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
227 INITIALIZE_PASS_END(RewriteStatepointsForGCLegacyPass,
228 "rewrite-statepoints-for-gc",
229 "Make relocations explicit at statepoints", false, false)
233 struct GCPtrLivenessData {
234 /// Values defined in this block.
235 MapVector<BasicBlock *, SetVector<Value *>> KillSet;
237 /// Values used in this block (and thus live); does not included values
238 /// killed within this block.
239 MapVector<BasicBlock *, SetVector<Value *>> LiveSet;
241 /// Values live into this basic block (i.e. used by any
242 /// instruction in this basic block or ones reachable from here)
243 MapVector<BasicBlock *, SetVector<Value *>> LiveIn;
245 /// Values live out of this basic block (i.e. live into
246 /// any successor block)
247 MapVector<BasicBlock *, SetVector<Value *>> LiveOut;
250 // The type of the internal cache used inside the findBasePointers family
251 // of functions. From the callers perspective, this is an opaque type and
252 // should not be inspected.
254 // In the actual implementation this caches two relations:
255 // - The base relation itself (i.e. this pointer is based on that one)
256 // - The base defining value relation (i.e. before base_phi insertion)
257 // Generally, after the execution of a full findBasePointer call, only the
258 // base relation will remain. Internally, we add a mixture of the two
259 // types, then update all the second type to the first type
260 using DefiningValueMapTy = MapVector<Value *, Value *>;
261 using StatepointLiveSetTy = SetVector<Value *>;
262 using RematerializedValueMapTy =
263 MapVector<AssertingVH<Instruction>, AssertingVH<Value>>;
265 struct PartiallyConstructedSafepointRecord {
266 /// The set of values known to be live across this safepoint
267 StatepointLiveSetTy LiveSet;
269 /// Mapping from live pointers to a base-defining-value
270 MapVector<Value *, Value *> PointerToBase;
272 /// The *new* gc.statepoint instruction itself. This produces the token
273 /// that normal path gc.relocates and the gc.result are tied to.
274 Instruction *StatepointToken;
276 /// Instruction to which exceptional gc relocates are attached
277 /// Makes it easier to iterate through them during relocationViaAlloca.
278 Instruction *UnwindToken;
280 /// Record live values we are rematerialized instead of relocating.
281 /// They are not included into 'LiveSet' field.
282 /// Maps rematerialized copy to it's original value.
283 RematerializedValueMapTy RematerializedValues;
286 } // end anonymous namespace
288 static ArrayRef<Use> GetDeoptBundleOperands(ImmutableCallSite CS) {
289 Optional<OperandBundleUse> DeoptBundle =
290 CS.getOperandBundle(LLVMContext::OB_deopt);
292 if (!DeoptBundle.hasValue()) {
293 assert(AllowStatepointWithNoDeoptInfo &&
294 "Found non-leaf call without deopt info!");
298 return DeoptBundle.getValue().Inputs;
301 /// Compute the live-in set for every basic block in the function
302 static void computeLiveInValues(DominatorTree &DT, Function &F,
303 GCPtrLivenessData &Data);
305 /// Given results from the dataflow liveness computation, find the set of live
306 /// Values at a particular instruction.
307 static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data,
308 StatepointLiveSetTy &out);
310 // TODO: Once we can get to the GCStrategy, this becomes
311 // Optional<bool> isGCManagedPointer(const Type *Ty) const override {
313 static bool isGCPointerType(Type *T) {
314 if (auto *PT = dyn_cast<PointerType>(T))
315 // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
316 // GC managed heap. We know that a pointer into this heap needs to be
317 // updated and that no other pointer does.
318 return PT->getAddressSpace() == 1;
322 // Return true if this type is one which a) is a gc pointer or contains a GC
323 // pointer and b) is of a type this code expects to encounter as a live value.
324 // (The insertion code will assert that a type which matches (a) and not (b)
325 // is not encountered.)
326 static bool isHandledGCPointerType(Type *T) {
327 // We fully support gc pointers
328 if (isGCPointerType(T))
330 // We partially support vectors of gc pointers. The code will assert if it
331 // can't handle something.
332 if (auto VT = dyn_cast<VectorType>(T))
333 if (isGCPointerType(VT->getElementType()))
339 /// Returns true if this type contains a gc pointer whether we know how to
340 /// handle that type or not.
341 static bool containsGCPtrType(Type *Ty) {
342 if (isGCPointerType(Ty))
344 if (VectorType *VT = dyn_cast<VectorType>(Ty))
345 return isGCPointerType(VT->getScalarType());
346 if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
347 return containsGCPtrType(AT->getElementType());
348 if (StructType *ST = dyn_cast<StructType>(Ty))
349 return llvm::any_of(ST->subtypes(), containsGCPtrType);
353 // Returns true if this is a type which a) is a gc pointer or contains a GC
354 // pointer and b) is of a type which the code doesn't expect (i.e. first class
355 // aggregates). Used to trip assertions.
356 static bool isUnhandledGCPointerType(Type *Ty) {
357 return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty);
361 // Return the name of the value suffixed with the provided value, or if the
362 // value didn't have a name, the default value specified.
363 static std::string suffixed_name_or(Value *V, StringRef Suffix,
364 StringRef DefaultName) {
365 return V->hasName() ? (V->getName() + Suffix).str() : DefaultName.str();
368 // Conservatively identifies any definitions which might be live at the
369 // given instruction. The analysis is performed immediately before the
370 // given instruction. Values defined by that instruction are not considered
371 // live. Values used by that instruction are considered live.
373 analyzeParsePointLiveness(DominatorTree &DT,
374 GCPtrLivenessData &OriginalLivenessData, CallSite CS,
375 PartiallyConstructedSafepointRecord &Result) {
376 Instruction *Inst = CS.getInstruction();
378 StatepointLiveSetTy LiveSet;
379 findLiveSetAtInst(Inst, OriginalLivenessData, LiveSet);
382 dbgs() << "Live Variables:\n";
383 for (Value *V : LiveSet)
384 dbgs() << " " << V->getName() << " " << *V << "\n";
386 if (PrintLiveSetSize) {
387 dbgs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n";
388 dbgs() << "Number live values: " << LiveSet.size() << "\n";
390 Result.LiveSet = LiveSet;
393 static bool isKnownBaseResult(Value *V);
397 /// A single base defining value - An immediate base defining value for an
398 /// instruction 'Def' is an input to 'Def' whose base is also a base of 'Def'.
399 /// For instructions which have multiple pointer [vector] inputs or that
400 /// transition between vector and scalar types, there is no immediate base
401 /// defining value. The 'base defining value' for 'Def' is the transitive
402 /// closure of this relation stopping at the first instruction which has no
403 /// immediate base defining value. The b.d.v. might itself be a base pointer,
404 /// but it can also be an arbitrary derived pointer.
405 struct BaseDefiningValueResult {
406 /// Contains the value which is the base defining value.
409 /// True if the base defining value is also known to be an actual base
411 const bool IsKnownBase;
413 BaseDefiningValueResult(Value *BDV, bool IsKnownBase)
414 : BDV(BDV), IsKnownBase(IsKnownBase) {
416 // Check consistency between new and old means of checking whether a BDV is
418 bool MustBeBase = isKnownBaseResult(BDV);
419 assert(!MustBeBase || MustBeBase == IsKnownBase);
424 } // end anonymous namespace
426 static BaseDefiningValueResult findBaseDefiningValue(Value *I);
428 /// Return a base defining value for the 'Index' element of the given vector
429 /// instruction 'I'. If Index is null, returns a BDV for the entire vector
430 /// 'I'. As an optimization, this method will try to determine when the
431 /// element is known to already be a base pointer. If this can be established,
432 /// the second value in the returned pair will be true. Note that either a
433 /// vector or a pointer typed value can be returned. For the former, the
434 /// vector returned is a BDV (and possibly a base) of the entire vector 'I'.
435 /// If the later, the return pointer is a BDV (or possibly a base) for the
436 /// particular element in 'I'.
437 static BaseDefiningValueResult
438 findBaseDefiningValueOfVector(Value *I) {
439 // Each case parallels findBaseDefiningValue below, see that code for
440 // detailed motivation.
442 if (isa<Argument>(I))
443 // An incoming argument to the function is a base pointer
444 return BaseDefiningValueResult(I, true);
446 if (isa<Constant>(I))
447 // Base of constant vector consists only of constant null pointers.
448 // For reasoning see similar case inside 'findBaseDefiningValue' function.
449 return BaseDefiningValueResult(ConstantAggregateZero::get(I->getType()),
452 if (isa<LoadInst>(I))
453 return BaseDefiningValueResult(I, true);
455 if (isa<InsertElementInst>(I))
456 // We don't know whether this vector contains entirely base pointers or
457 // not. To be conservatively correct, we treat it as a BDV and will
458 // duplicate code as needed to construct a parallel vector of bases.
459 return BaseDefiningValueResult(I, false);
461 if (isa<ShuffleVectorInst>(I))
462 // We don't know whether this vector contains entirely base pointers or
463 // not. To be conservatively correct, we treat it as a BDV and will
464 // duplicate code as needed to construct a parallel vector of bases.
465 // TODO: There a number of local optimizations which could be applied here
466 // for particular sufflevector patterns.
467 return BaseDefiningValueResult(I, false);
469 // The behavior of getelementptr instructions is the same for vector and
470 // non-vector data types.
471 if (auto *GEP = dyn_cast<GetElementPtrInst>(I))
472 return findBaseDefiningValue(GEP->getPointerOperand());
474 // If the pointer comes through a bitcast of a vector of pointers to
475 // a vector of another type of pointer, then look through the bitcast
476 if (auto *BC = dyn_cast<BitCastInst>(I))
477 return findBaseDefiningValue(BC->getOperand(0));
479 // We assume that functions in the source language only return base
480 // pointers. This should probably be generalized via attributes to support
481 // both source language and internal functions.
482 if (isa<CallInst>(I) || isa<InvokeInst>(I))
483 return BaseDefiningValueResult(I, true);
485 // A PHI or Select is a base defining value. The outer findBasePointer
486 // algorithm is responsible for constructing a base value for this BDV.
487 assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
488 "unknown vector instruction - no base found for vector element");
489 return BaseDefiningValueResult(I, false);
492 /// Helper function for findBasePointer - Will return a value which either a)
493 /// defines the base pointer for the input, b) blocks the simple search
494 /// (i.e. a PHI or Select of two derived pointers), or c) involves a change
495 /// from pointer to vector type or back.
496 static BaseDefiningValueResult findBaseDefiningValue(Value *I) {
497 assert(I->getType()->isPtrOrPtrVectorTy() &&
498 "Illegal to ask for the base pointer of a non-pointer type");
500 if (I->getType()->isVectorTy())
501 return findBaseDefiningValueOfVector(I);
503 if (isa<Argument>(I))
504 // An incoming argument to the function is a base pointer
505 // We should have never reached here if this argument isn't an gc value
506 return BaseDefiningValueResult(I, true);
508 if (isa<Constant>(I)) {
509 // We assume that objects with a constant base (e.g. a global) can't move
510 // and don't need to be reported to the collector because they are always
511 // live. Besides global references, all kinds of constants (e.g. undef,
512 // constant expressions, null pointers) can be introduced by the inliner or
513 // the optimizer, especially on dynamically dead paths.
514 // Here we treat all of them as having single null base. By doing this we
515 // trying to avoid problems reporting various conflicts in a form of
516 // "phi (const1, const2)" or "phi (const, regular gc ptr)".
517 // See constant.ll file for relevant test cases.
519 return BaseDefiningValueResult(
520 ConstantPointerNull::get(cast<PointerType>(I->getType())), true);
523 if (CastInst *CI = dyn_cast<CastInst>(I)) {
524 Value *Def = CI->stripPointerCasts();
525 // If stripping pointer casts changes the address space there is an
526 // addrspacecast in between.
527 assert(cast<PointerType>(Def->getType())->getAddressSpace() ==
528 cast<PointerType>(CI->getType())->getAddressSpace() &&
529 "unsupported addrspacecast");
530 // If we find a cast instruction here, it means we've found a cast which is
531 // not simply a pointer cast (i.e. an inttoptr). We don't know how to
532 // handle int->ptr conversion.
533 assert(!isa<CastInst>(Def) && "shouldn't find another cast here");
534 return findBaseDefiningValue(Def);
537 if (isa<LoadInst>(I))
538 // The value loaded is an gc base itself
539 return BaseDefiningValueResult(I, true);
541 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
542 // The base of this GEP is the base
543 return findBaseDefiningValue(GEP->getPointerOperand());
545 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
546 switch (II->getIntrinsicID()) {
548 // fall through to general call handling
550 case Intrinsic::experimental_gc_statepoint:
551 llvm_unreachable("statepoints don't produce pointers");
552 case Intrinsic::experimental_gc_relocate:
553 // Rerunning safepoint insertion after safepoints are already
554 // inserted is not supported. It could probably be made to work,
555 // but why are you doing this? There's no good reason.
556 llvm_unreachable("repeat safepoint insertion is not supported");
557 case Intrinsic::gcroot:
558 // Currently, this mechanism hasn't been extended to work with gcroot.
559 // There's no reason it couldn't be, but I haven't thought about the
560 // implications much.
562 "interaction with the gcroot mechanism is not supported");
565 // We assume that functions in the source language only return base
566 // pointers. This should probably be generalized via attributes to support
567 // both source language and internal functions.
568 if (isa<CallInst>(I) || isa<InvokeInst>(I))
569 return BaseDefiningValueResult(I, true);
571 // TODO: I have absolutely no idea how to implement this part yet. It's not
572 // necessarily hard, I just haven't really looked at it yet.
573 assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented");
575 if (isa<AtomicCmpXchgInst>(I))
576 // A CAS is effectively a atomic store and load combined under a
577 // predicate. From the perspective of base pointers, we just treat it
579 return BaseDefiningValueResult(I, true);
581 assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are "
582 "binary ops which don't apply to pointers");
584 // The aggregate ops. Aggregates can either be in the heap or on the
585 // stack, but in either case, this is simply a field load. As a result,
586 // this is a defining definition of the base just like a load is.
587 if (isa<ExtractValueInst>(I))
588 return BaseDefiningValueResult(I, true);
590 // We should never see an insert vector since that would require we be
591 // tracing back a struct value not a pointer value.
592 assert(!isa<InsertValueInst>(I) &&
593 "Base pointer for a struct is meaningless");
595 // An extractelement produces a base result exactly when it's input does.
596 // We may need to insert a parallel instruction to extract the appropriate
597 // element out of the base vector corresponding to the input. Given this,
598 // it's analogous to the phi and select case even though it's not a merge.
599 if (isa<ExtractElementInst>(I))
600 // Note: There a lot of obvious peephole cases here. This are deliberately
601 // handled after the main base pointer inference algorithm to make writing
602 // test cases to exercise that code easier.
603 return BaseDefiningValueResult(I, false);
605 // The last two cases here don't return a base pointer. Instead, they
606 // return a value which dynamically selects from among several base
607 // derived pointers (each with it's own base potentially). It's the job of
608 // the caller to resolve these.
609 assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
610 "missing instruction case in findBaseDefiningValing");
611 return BaseDefiningValueResult(I, false);
614 /// Returns the base defining value for this value.
615 static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) {
616 Value *&Cached = Cache[I];
618 Cached = findBaseDefiningValue(I).BDV;
619 LLVM_DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> "
620 << Cached->getName() << "\n");
622 assert(Cache[I] != nullptr);
626 /// Return a base pointer for this value if known. Otherwise, return it's
627 /// base defining value.
628 static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) {
629 Value *Def = findBaseDefiningValueCached(I, Cache);
630 auto Found = Cache.find(Def);
631 if (Found != Cache.end()) {
632 // Either a base-of relation, or a self reference. Caller must check.
633 return Found->second;
635 // Only a BDV available
639 /// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV,
640 /// is it known to be a base pointer? Or do we need to continue searching.
641 static bool isKnownBaseResult(Value *V) {
642 if (!isa<PHINode>(V) && !isa<SelectInst>(V) &&
643 !isa<ExtractElementInst>(V) && !isa<InsertElementInst>(V) &&
644 !isa<ShuffleVectorInst>(V)) {
645 // no recursion possible
648 if (isa<Instruction>(V) &&
649 cast<Instruction>(V)->getMetadata("is_base_value")) {
650 // This is a previously inserted base phi or select. We know
651 // that this is a base value.
655 // We need to keep searching
661 /// Models the state of a single base defining value in the findBasePointer
662 /// algorithm for determining where a new instruction is needed to propagate
663 /// the base of this BDV.
666 enum Status { Unknown, Base, Conflict };
668 BDVState() : BaseValue(nullptr) {}
670 explicit BDVState(Status Status, Value *BaseValue = nullptr)
671 : Status(Status), BaseValue(BaseValue) {
672 assert(Status != Base || BaseValue);
675 explicit BDVState(Value *BaseValue) : Status(Base), BaseValue(BaseValue) {}
677 Status getStatus() const { return Status; }
678 Value *getBaseValue() const { return BaseValue; }
680 bool isBase() const { return getStatus() == Base; }
681 bool isUnknown() const { return getStatus() == Unknown; }
682 bool isConflict() const { return getStatus() == Conflict; }
684 bool operator==(const BDVState &Other) const {
685 return BaseValue == Other.BaseValue && Status == Other.Status;
688 bool operator!=(const BDVState &other) const { return !(*this == other); }
696 void print(raw_ostream &OS) const {
697 switch (getStatus()) {
708 OS << " (" << getBaseValue() << " - "
709 << (getBaseValue() ? getBaseValue()->getName() : "nullptr") << "): ";
713 Status Status = Unknown;
714 AssertingVH<Value> BaseValue; // Non-null only if Status == Base.
717 } // end anonymous namespace
720 static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) {
726 static BDVState meetBDVStateImpl(const BDVState &LHS, const BDVState &RHS) {
727 switch (LHS.getStatus()) {
728 case BDVState::Unknown:
732 assert(LHS.getBaseValue() && "can't be null");
737 if (LHS.getBaseValue() == RHS.getBaseValue()) {
738 assert(LHS == RHS && "equality broken!");
741 return BDVState(BDVState::Conflict);
743 assert(RHS.isConflict() && "only three states!");
744 return BDVState(BDVState::Conflict);
746 case BDVState::Conflict:
749 llvm_unreachable("only three states!");
752 // Values of type BDVState form a lattice, and this function implements the meet
754 static BDVState meetBDVState(const BDVState &LHS, const BDVState &RHS) {
755 BDVState Result = meetBDVStateImpl(LHS, RHS);
756 assert(Result == meetBDVStateImpl(RHS, LHS) &&
757 "Math is wrong: meet does not commute!");
761 /// For a given value or instruction, figure out what base ptr its derived from.
762 /// For gc objects, this is simply itself. On success, returns a value which is
763 /// the base pointer. (This is reliable and can be used for relocation.) On
764 /// failure, returns nullptr.
765 static Value *findBasePointer(Value *I, DefiningValueMapTy &Cache) {
766 Value *Def = findBaseOrBDV(I, Cache);
768 if (isKnownBaseResult(Def))
771 // Here's the rough algorithm:
772 // - For every SSA value, construct a mapping to either an actual base
773 // pointer or a PHI which obscures the base pointer.
774 // - Construct a mapping from PHI to unknown TOP state. Use an
775 // optimistic algorithm to propagate base pointer information. Lattice
780 // When algorithm terminates, all PHIs will either have a single concrete
781 // base or be in a conflict state.
782 // - For every conflict, insert a dummy PHI node without arguments. Add
783 // these to the base[Instruction] = BasePtr mapping. For every
784 // non-conflict, add the actual base.
785 // - For every conflict, add arguments for the base[a] of each input
788 // Note: A simpler form of this would be to add the conflict form of all
789 // PHIs without running the optimistic algorithm. This would be
790 // analogous to pessimistic data flow and would likely lead to an
791 // overall worse solution.
794 auto isExpectedBDVType = [](Value *BDV) {
795 return isa<PHINode>(BDV) || isa<SelectInst>(BDV) ||
796 isa<ExtractElementInst>(BDV) || isa<InsertElementInst>(BDV) ||
797 isa<ShuffleVectorInst>(BDV);
801 // Once populated, will contain a mapping from each potentially non-base BDV
802 // to a lattice value (described above) which corresponds to that BDV.
803 // We use the order of insertion (DFS over the def/use graph) to provide a
804 // stable deterministic ordering for visiting DenseMaps (which are unordered)
805 // below. This is important for deterministic compilation.
806 MapVector<Value *, BDVState> States;
808 // Recursively fill in all base defining values reachable from the initial
809 // one for which we don't already know a definite base value for
811 SmallVector<Value*, 16> Worklist;
812 Worklist.push_back(Def);
813 States.insert({Def, BDVState()});
814 while (!Worklist.empty()) {
815 Value *Current = Worklist.pop_back_val();
816 assert(!isKnownBaseResult(Current) && "why did it get added?");
818 auto visitIncomingValue = [&](Value *InVal) {
819 Value *Base = findBaseOrBDV(InVal, Cache);
820 if (isKnownBaseResult(Base))
821 // Known bases won't need new instructions introduced and can be
824 assert(isExpectedBDVType(Base) && "the only non-base values "
825 "we see should be base defining values");
826 if (States.insert(std::make_pair(Base, BDVState())).second)
827 Worklist.push_back(Base);
829 if (PHINode *PN = dyn_cast<PHINode>(Current)) {
830 for (Value *InVal : PN->incoming_values())
831 visitIncomingValue(InVal);
832 } else if (SelectInst *SI = dyn_cast<SelectInst>(Current)) {
833 visitIncomingValue(SI->getTrueValue());
834 visitIncomingValue(SI->getFalseValue());
835 } else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) {
836 visitIncomingValue(EE->getVectorOperand());
837 } else if (auto *IE = dyn_cast<InsertElementInst>(Current)) {
838 visitIncomingValue(IE->getOperand(0)); // vector operand
839 visitIncomingValue(IE->getOperand(1)); // scalar operand
840 } else if (auto *SV = dyn_cast<ShuffleVectorInst>(Current)) {
841 visitIncomingValue(SV->getOperand(0));
842 visitIncomingValue(SV->getOperand(1));
845 llvm_unreachable("Unimplemented instruction case");
851 LLVM_DEBUG(dbgs() << "States after initialization:\n");
852 for (auto Pair : States) {
853 LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
857 // Return a phi state for a base defining value. We'll generate a new
858 // base state for known bases and expect to find a cached state otherwise.
859 auto getStateForBDV = [&](Value *baseValue) {
860 if (isKnownBaseResult(baseValue))
861 return BDVState(baseValue);
862 auto I = States.find(baseValue);
863 assert(I != States.end() && "lookup failed!");
867 bool Progress = true;
870 const size_t OldSize = States.size();
873 // We're only changing values in this loop, thus safe to keep iterators.
874 // Since this is computing a fixed point, the order of visit does not
875 // effect the result. TODO: We could use a worklist here and make this run
877 for (auto Pair : States) {
878 Value *BDV = Pair.first;
879 assert(!isKnownBaseResult(BDV) && "why did it get added?");
881 // Given an input value for the current instruction, return a BDVState
882 // instance which represents the BDV of that value.
883 auto getStateForInput = [&](Value *V) mutable {
884 Value *BDV = findBaseOrBDV(V, Cache);
885 return getStateForBDV(BDV);
889 if (SelectInst *SI = dyn_cast<SelectInst>(BDV)) {
890 NewState = meetBDVState(NewState, getStateForInput(SI->getTrueValue()));
892 meetBDVState(NewState, getStateForInput(SI->getFalseValue()));
893 } else if (PHINode *PN = dyn_cast<PHINode>(BDV)) {
894 for (Value *Val : PN->incoming_values())
895 NewState = meetBDVState(NewState, getStateForInput(Val));
896 } else if (auto *EE = dyn_cast<ExtractElementInst>(BDV)) {
897 // The 'meet' for an extractelement is slightly trivial, but it's still
898 // useful in that it drives us to conflict if our input is.
900 meetBDVState(NewState, getStateForInput(EE->getVectorOperand()));
901 } else if (auto *IE = dyn_cast<InsertElementInst>(BDV)){
902 // Given there's a inherent type mismatch between the operands, will
903 // *always* produce Conflict.
904 NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(0)));
905 NewState = meetBDVState(NewState, getStateForInput(IE->getOperand(1)));
907 // The only instance this does not return a Conflict is when both the
908 // vector operands are the same vector.
909 auto *SV = cast<ShuffleVectorInst>(BDV);
910 NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(0)));
911 NewState = meetBDVState(NewState, getStateForInput(SV->getOperand(1)));
914 BDVState OldState = States[BDV];
915 if (OldState != NewState) {
917 States[BDV] = NewState;
921 assert(OldSize == States.size() &&
922 "fixed point shouldn't be adding any new nodes to state");
926 LLVM_DEBUG(dbgs() << "States after meet iteration:\n");
927 for (auto Pair : States) {
928 LLVM_DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
932 // Insert Phis for all conflicts
933 // TODO: adjust naming patterns to avoid this order of iteration dependency
934 for (auto Pair : States) {
935 Instruction *I = cast<Instruction>(Pair.first);
936 BDVState State = Pair.second;
937 assert(!isKnownBaseResult(I) && "why did it get added?");
938 assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
940 // extractelement instructions are a bit special in that we may need to
941 // insert an extract even when we know an exact base for the instruction.
942 // The problem is that we need to convert from a vector base to a scalar
943 // base for the particular indice we're interested in.
944 if (State.isBase() && isa<ExtractElementInst>(I) &&
945 isa<VectorType>(State.getBaseValue()->getType())) {
946 auto *EE = cast<ExtractElementInst>(I);
947 // TODO: In many cases, the new instruction is just EE itself. We should
948 // exploit this, but can't do it here since it would break the invariant
949 // about the BDV not being known to be a base.
950 auto *BaseInst = ExtractElementInst::Create(
951 State.getBaseValue(), EE->getIndexOperand(), "base_ee", EE);
952 BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
953 States[I] = BDVState(BDVState::Base, BaseInst);
956 // Since we're joining a vector and scalar base, they can never be the
957 // same. As a result, we should always see insert element having reached
958 // the conflict state.
959 assert(!isa<InsertElementInst>(I) || State.isConflict());
961 if (!State.isConflict())
964 /// Create and insert a new instruction which will represent the base of
965 /// the given instruction 'I'.
966 auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* {
967 if (isa<PHINode>(I)) {
968 BasicBlock *BB = I->getParent();
969 int NumPreds = pred_size(BB);
970 assert(NumPreds > 0 && "how did we reach here");
971 std::string Name = suffixed_name_or(I, ".base", "base_phi");
972 return PHINode::Create(I->getType(), NumPreds, Name, I);
973 } else if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
974 // The undef will be replaced later
975 UndefValue *Undef = UndefValue::get(SI->getType());
976 std::string Name = suffixed_name_or(I, ".base", "base_select");
977 return SelectInst::Create(SI->getCondition(), Undef, Undef, Name, SI);
978 } else if (auto *EE = dyn_cast<ExtractElementInst>(I)) {
979 UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType());
980 std::string Name = suffixed_name_or(I, ".base", "base_ee");
981 return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name,
983 } else if (auto *IE = dyn_cast<InsertElementInst>(I)) {
984 UndefValue *VecUndef = UndefValue::get(IE->getOperand(0)->getType());
985 UndefValue *ScalarUndef = UndefValue::get(IE->getOperand(1)->getType());
986 std::string Name = suffixed_name_or(I, ".base", "base_ie");
987 return InsertElementInst::Create(VecUndef, ScalarUndef,
988 IE->getOperand(2), Name, IE);
990 auto *SV = cast<ShuffleVectorInst>(I);
991 UndefValue *VecUndef = UndefValue::get(SV->getOperand(0)->getType());
992 std::string Name = suffixed_name_or(I, ".base", "base_sv");
993 return new ShuffleVectorInst(VecUndef, VecUndef, SV->getOperand(2),
997 Instruction *BaseInst = MakeBaseInstPlaceholder(I);
998 // Add metadata marking this as a base value
999 BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
1000 States[I] = BDVState(BDVState::Conflict, BaseInst);
1003 // Returns a instruction which produces the base pointer for a given
1004 // instruction. The instruction is assumed to be an input to one of the BDVs
1005 // seen in the inference algorithm above. As such, we must either already
1006 // know it's base defining value is a base, or have inserted a new
1007 // instruction to propagate the base of it's BDV and have entered that newly
1008 // introduced instruction into the state table. In either case, we are
1009 // assured to be able to determine an instruction which produces it's base
1011 auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) {
1012 Value *BDV = findBaseOrBDV(Input, Cache);
1013 Value *Base = nullptr;
1014 if (isKnownBaseResult(BDV)) {
1017 // Either conflict or base.
1018 assert(States.count(BDV));
1019 Base = States[BDV].getBaseValue();
1021 assert(Base && "Can't be null");
1022 // The cast is needed since base traversal may strip away bitcasts
1023 if (Base->getType() != Input->getType() && InsertPt)
1024 Base = new BitCastInst(Base, Input->getType(), "cast", InsertPt);
1028 // Fixup all the inputs of the new PHIs. Visit order needs to be
1029 // deterministic and predictable because we're naming newly created
1031 for (auto Pair : States) {
1032 Instruction *BDV = cast<Instruction>(Pair.first);
1033 BDVState State = Pair.second;
1035 assert(!isKnownBaseResult(BDV) && "why did it get added?");
1036 assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
1037 if (!State.isConflict())
1040 if (PHINode *BasePHI = dyn_cast<PHINode>(State.getBaseValue())) {
1041 PHINode *PN = cast<PHINode>(BDV);
1042 unsigned NumPHIValues = PN->getNumIncomingValues();
1043 for (unsigned i = 0; i < NumPHIValues; i++) {
1044 Value *InVal = PN->getIncomingValue(i);
1045 BasicBlock *InBB = PN->getIncomingBlock(i);
1047 // If we've already seen InBB, add the same incoming value
1048 // we added for it earlier. The IR verifier requires phi
1049 // nodes with multiple entries from the same basic block
1050 // to have the same incoming value for each of those
1051 // entries. If we don't do this check here and basephi
1052 // has a different type than base, we'll end up adding two
1053 // bitcasts (and hence two distinct values) as incoming
1054 // values for the same basic block.
1056 int BlockIndex = BasePHI->getBasicBlockIndex(InBB);
1057 if (BlockIndex != -1) {
1058 Value *OldBase = BasePHI->getIncomingValue(BlockIndex);
1059 BasePHI->addIncoming(OldBase, InBB);
1062 Value *Base = getBaseForInput(InVal, nullptr);
1063 // In essence this assert states: the only way two values
1064 // incoming from the same basic block may be different is by
1065 // being different bitcasts of the same value. A cleanup
1066 // that remains TODO is changing findBaseOrBDV to return an
1067 // llvm::Value of the correct type (and still remain pure).
1068 // This will remove the need to add bitcasts.
1069 assert(Base->stripPointerCasts() == OldBase->stripPointerCasts() &&
1070 "Sanity -- findBaseOrBDV should be pure!");
1075 // Find the instruction which produces the base for each input. We may
1076 // need to insert a bitcast in the incoming block.
1077 // TODO: Need to split critical edges if insertion is needed
1078 Value *Base = getBaseForInput(InVal, InBB->getTerminator());
1079 BasePHI->addIncoming(Base, InBB);
1081 assert(BasePHI->getNumIncomingValues() == NumPHIValues);
1082 } else if (SelectInst *BaseSI =
1083 dyn_cast<SelectInst>(State.getBaseValue())) {
1084 SelectInst *SI = cast<SelectInst>(BDV);
1086 // Find the instruction which produces the base for each input.
1087 // We may need to insert a bitcast.
1088 BaseSI->setTrueValue(getBaseForInput(SI->getTrueValue(), BaseSI));
1089 BaseSI->setFalseValue(getBaseForInput(SI->getFalseValue(), BaseSI));
1090 } else if (auto *BaseEE =
1091 dyn_cast<ExtractElementInst>(State.getBaseValue())) {
1092 Value *InVal = cast<ExtractElementInst>(BDV)->getVectorOperand();
1093 // Find the instruction which produces the base for each input. We may
1094 // need to insert a bitcast.
1095 BaseEE->setOperand(0, getBaseForInput(InVal, BaseEE));
1096 } else if (auto *BaseIE = dyn_cast<InsertElementInst>(State.getBaseValue())){
1097 auto *BdvIE = cast<InsertElementInst>(BDV);
1098 auto UpdateOperand = [&](int OperandIdx) {
1099 Value *InVal = BdvIE->getOperand(OperandIdx);
1100 Value *Base = getBaseForInput(InVal, BaseIE);
1101 BaseIE->setOperand(OperandIdx, Base);
1103 UpdateOperand(0); // vector operand
1104 UpdateOperand(1); // scalar operand
1106 auto *BaseSV = cast<ShuffleVectorInst>(State.getBaseValue());
1107 auto *BdvSV = cast<ShuffleVectorInst>(BDV);
1108 auto UpdateOperand = [&](int OperandIdx) {
1109 Value *InVal = BdvSV->getOperand(OperandIdx);
1110 Value *Base = getBaseForInput(InVal, BaseSV);
1111 BaseSV->setOperand(OperandIdx, Base);
1113 UpdateOperand(0); // vector operand
1114 UpdateOperand(1); // vector operand
1118 // Cache all of our results so we can cheaply reuse them
1119 // NOTE: This is actually two caches: one of the base defining value
1120 // relation and one of the base pointer relation! FIXME
1121 for (auto Pair : States) {
1122 auto *BDV = Pair.first;
1123 Value *Base = Pair.second.getBaseValue();
1124 assert(BDV && Base);
1125 assert(!isKnownBaseResult(BDV) && "why did it get added?");
1128 dbgs() << "Updating base value cache"
1129 << " for: " << BDV->getName() << " from: "
1130 << (Cache.count(BDV) ? Cache[BDV]->getName().str() : "none")
1131 << " to: " << Base->getName() << "\n");
1133 if (Cache.count(BDV)) {
1134 assert(isKnownBaseResult(Base) &&
1135 "must be something we 'know' is a base pointer");
1136 // Once we transition from the BDV relation being store in the Cache to
1137 // the base relation being stored, it must be stable
1138 assert((!isKnownBaseResult(Cache[BDV]) || Cache[BDV] == Base) &&
1139 "base relation should be stable");
1143 assert(Cache.count(Def));
1147 // For a set of live pointers (base and/or derived), identify the base
1148 // pointer of the object which they are derived from. This routine will
1149 // mutate the IR graph as needed to make the 'base' pointer live at the
1150 // definition site of 'derived'. This ensures that any use of 'derived' can
1151 // also use 'base'. This may involve the insertion of a number of
1152 // additional PHI nodes.
1154 // preconditions: live is a set of pointer type Values
1156 // side effects: may insert PHI nodes into the existing CFG, will preserve
1157 // CFG, will not remove or mutate any existing nodes
1159 // post condition: PointerToBase contains one (derived, base) pair for every
1160 // pointer in live. Note that derived can be equal to base if the original
1161 // pointer was a base pointer.
1163 findBasePointers(const StatepointLiveSetTy &live,
1164 MapVector<Value *, Value *> &PointerToBase,
1165 DominatorTree *DT, DefiningValueMapTy &DVCache) {
1166 for (Value *ptr : live) {
1167 Value *base = findBasePointer(ptr, DVCache);
1168 assert(base && "failed to find base pointer");
1169 PointerToBase[ptr] = base;
1170 assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) ||
1171 DT->dominates(cast<Instruction>(base)->getParent(),
1172 cast<Instruction>(ptr)->getParent())) &&
1173 "The base we found better dominate the derived pointer");
1177 /// Find the required based pointers (and adjust the live set) for the given
1179 static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache,
1181 PartiallyConstructedSafepointRecord &result) {
1182 MapVector<Value *, Value *> PointerToBase;
1183 findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache);
1185 if (PrintBasePointers) {
1186 errs() << "Base Pairs (w/o Relocation):\n";
1187 for (auto &Pair : PointerToBase) {
1188 errs() << " derived ";
1189 Pair.first->printAsOperand(errs(), false);
1191 Pair.second->printAsOperand(errs(), false);
1196 result.PointerToBase = PointerToBase;
1199 /// Given an updated version of the dataflow liveness results, update the
1200 /// liveset and base pointer maps for the call site CS.
1201 static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
1203 PartiallyConstructedSafepointRecord &result);
1205 static void recomputeLiveInValues(
1206 Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
1207 MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
1208 // TODO-PERF: reuse the original liveness, then simply run the dataflow
1209 // again. The old values are still live and will help it stabilize quickly.
1210 GCPtrLivenessData RevisedLivenessData;
1211 computeLiveInValues(DT, F, RevisedLivenessData);
1212 for (size_t i = 0; i < records.size(); i++) {
1213 struct PartiallyConstructedSafepointRecord &info = records[i];
1214 recomputeLiveInValues(RevisedLivenessData, toUpdate[i], info);
1218 // When inserting gc.relocate and gc.result calls, we need to ensure there are
1219 // no uses of the original value / return value between the gc.statepoint and
1220 // the gc.relocate / gc.result call. One case which can arise is a phi node
1221 // starting one of the successor blocks. We also need to be able to insert the
1222 // gc.relocates only on the path which goes through the statepoint. We might
1223 // need to split an edge to make this possible.
1225 normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent,
1226 DominatorTree &DT) {
1227 BasicBlock *Ret = BB;
1228 if (!BB->getUniquePredecessor())
1229 Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT);
1231 // Now that 'Ret' has unique predecessor we can safely remove all phi nodes
1233 FoldSingleEntryPHINodes(Ret);
1234 assert(!isa<PHINode>(Ret->begin()) &&
1235 "All PHI nodes should have been removed!");
1237 // At this point, we can safely insert a gc.relocate or gc.result as the first
1238 // instruction in Ret if needed.
1242 // Create new attribute set containing only attributes which can be transferred
1243 // from original call to the safepoint.
1244 static AttributeList legalizeCallAttributes(AttributeList AL) {
1248 // Remove the readonly, readnone, and statepoint function attributes.
1249 AttrBuilder FnAttrs = AL.getFnAttributes();
1250 FnAttrs.removeAttribute(Attribute::ReadNone);
1251 FnAttrs.removeAttribute(Attribute::ReadOnly);
1252 for (Attribute A : AL.getFnAttributes()) {
1253 if (isStatepointDirectiveAttr(A))
1257 // Just skip parameter and return attributes for now
1258 LLVMContext &Ctx = AL.getContext();
1259 return AttributeList::get(Ctx, AttributeList::FunctionIndex,
1260 AttributeSet::get(Ctx, FnAttrs));
1263 /// Helper function to place all gc relocates necessary for the given
1266 /// liveVariables - list of variables to be relocated.
1267 /// liveStart - index of the first live variable.
1268 /// basePtrs - base pointers.
1269 /// statepointToken - statepoint instruction to which relocates should be
1271 /// Builder - Llvm IR builder to be used to construct new calls.
1272 static void CreateGCRelocates(ArrayRef<Value *> LiveVariables,
1273 const int LiveStart,
1274 ArrayRef<Value *> BasePtrs,
1275 Instruction *StatepointToken,
1276 IRBuilder<> Builder) {
1277 if (LiveVariables.empty())
1280 auto FindIndex = [](ArrayRef<Value *> LiveVec, Value *Val) {
1281 auto ValIt = llvm::find(LiveVec, Val);
1282 assert(ValIt != LiveVec.end() && "Val not found in LiveVec!");
1283 size_t Index = std::distance(LiveVec.begin(), ValIt);
1284 assert(Index < LiveVec.size() && "Bug in std::find?");
1287 Module *M = StatepointToken->getModule();
1289 // All gc_relocate are generated as i8 addrspace(1)* (or a vector type whose
1290 // element type is i8 addrspace(1)*). We originally generated unique
1291 // declarations for each pointer type, but this proved problematic because
1292 // the intrinsic mangling code is incomplete and fragile. Since we're moving
1293 // towards a single unified pointer type anyways, we can just cast everything
1294 // to an i8* of the right address space. A bitcast is added later to convert
1295 // gc_relocate to the actual value's type.
1296 auto getGCRelocateDecl = [&] (Type *Ty) {
1297 assert(isHandledGCPointerType(Ty));
1298 auto AS = Ty->getScalarType()->getPointerAddressSpace();
1299 Type *NewTy = Type::getInt8PtrTy(M->getContext(), AS);
1300 if (auto *VT = dyn_cast<VectorType>(Ty))
1301 NewTy = VectorType::get(NewTy, VT->getNumElements());
1302 return Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate,
1306 // Lazily populated map from input types to the canonicalized form mentioned
1307 // in the comment above. This should probably be cached somewhere more
1309 DenseMap<Type*, Value*> TypeToDeclMap;
1311 for (unsigned i = 0; i < LiveVariables.size(); i++) {
1312 // Generate the gc.relocate call and save the result
1314 Builder.getInt32(LiveStart + FindIndex(LiveVariables, BasePtrs[i]));
1315 Value *LiveIdx = Builder.getInt32(LiveStart + i);
1317 Type *Ty = LiveVariables[i]->getType();
1318 if (!TypeToDeclMap.count(Ty))
1319 TypeToDeclMap[Ty] = getGCRelocateDecl(Ty);
1320 Value *GCRelocateDecl = TypeToDeclMap[Ty];
1322 // only specify a debug name if we can give a useful one
1323 CallInst *Reloc = Builder.CreateCall(
1324 GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx},
1325 suffixed_name_or(LiveVariables[i], ".relocated", ""));
1326 // Trick CodeGen into thinking there are lots of free registers at this
1328 Reloc->setCallingConv(CallingConv::Cold);
1334 /// This struct is used to defer RAUWs and `eraseFromParent` s. Using this
1335 /// avoids having to worry about keeping around dangling pointers to Values.
1336 class DeferredReplacement {
1337 AssertingVH<Instruction> Old;
1338 AssertingVH<Instruction> New;
1339 bool IsDeoptimize = false;
1341 DeferredReplacement() = default;
1344 static DeferredReplacement createRAUW(Instruction *Old, Instruction *New) {
1345 assert(Old != New && Old && New &&
1346 "Cannot RAUW equal values or to / from null!");
1348 DeferredReplacement D;
1354 static DeferredReplacement createDelete(Instruction *ToErase) {
1355 DeferredReplacement D;
1360 static DeferredReplacement createDeoptimizeReplacement(Instruction *Old) {
1362 auto *F = cast<CallInst>(Old)->getCalledFunction();
1363 assert(F && F->getIntrinsicID() == Intrinsic::experimental_deoptimize &&
1364 "Only way to construct a deoptimize deferred replacement");
1366 DeferredReplacement D;
1368 D.IsDeoptimize = true;
1372 /// Does the task represented by this instance.
1373 void doReplacement() {
1374 Instruction *OldI = Old;
1375 Instruction *NewI = New;
1377 assert(OldI != NewI && "Disallowed at construction?!");
1378 assert((!IsDeoptimize || !New) &&
1379 "Deoptimize intrinsics are not replaced!");
1385 OldI->replaceAllUsesWith(NewI);
1388 // Note: we've inserted instructions, so the call to llvm.deoptimize may
1389 // not necessarily be followed by the matching return.
1390 auto *RI = cast<ReturnInst>(OldI->getParent()->getTerminator());
1391 new UnreachableInst(RI->getContext(), RI);
1392 RI->eraseFromParent();
1395 OldI->eraseFromParent();
1399 } // end anonymous namespace
1401 static StringRef getDeoptLowering(CallSite CS) {
1402 const char *DeoptLowering = "deopt-lowering";
1403 if (CS.hasFnAttr(DeoptLowering)) {
1404 // FIXME: CallSite has a *really* confusing interface around attributes
1406 const AttributeList &CSAS = CS.getAttributes();
1407 if (CSAS.hasAttribute(AttributeList::FunctionIndex, DeoptLowering))
1408 return CSAS.getAttribute(AttributeList::FunctionIndex, DeoptLowering)
1409 .getValueAsString();
1410 Function *F = CS.getCalledFunction();
1411 assert(F && F->hasFnAttribute(DeoptLowering));
1412 return F->getFnAttribute(DeoptLowering).getValueAsString();
1414 return "live-through";
1418 makeStatepointExplicitImpl(const CallSite CS, /* to replace */
1419 const SmallVectorImpl<Value *> &BasePtrs,
1420 const SmallVectorImpl<Value *> &LiveVariables,
1421 PartiallyConstructedSafepointRecord &Result,
1422 std::vector<DeferredReplacement> &Replacements) {
1423 assert(BasePtrs.size() == LiveVariables.size());
1425 // Then go ahead and use the builder do actually do the inserts. We insert
1426 // immediately before the previous instruction under the assumption that all
1427 // arguments will be available here. We can't insert afterwards since we may
1428 // be replacing a terminator.
1429 Instruction *InsertBefore = CS.getInstruction();
1430 IRBuilder<> Builder(InsertBefore);
1432 ArrayRef<Value *> GCArgs(LiveVariables);
1433 uint64_t StatepointID = StatepointDirectives::DefaultStatepointID;
1434 uint32_t NumPatchBytes = 0;
1435 uint32_t Flags = uint32_t(StatepointFlags::None);
1437 ArrayRef<Use> CallArgs(CS.arg_begin(), CS.arg_end());
1438 ArrayRef<Use> DeoptArgs = GetDeoptBundleOperands(CS);
1439 ArrayRef<Use> TransitionArgs;
1440 if (auto TransitionBundle =
1441 CS.getOperandBundle(LLVMContext::OB_gc_transition)) {
1442 Flags |= uint32_t(StatepointFlags::GCTransition);
1443 TransitionArgs = TransitionBundle->Inputs;
1446 // Instead of lowering calls to @llvm.experimental.deoptimize as normal calls
1447 // with a return value, we lower then as never returning calls to
1448 // __llvm_deoptimize that are followed by unreachable to get better codegen.
1449 bool IsDeoptimize = false;
1451 StatepointDirectives SD =
1452 parseStatepointDirectivesFromAttrs(CS.getAttributes());
1453 if (SD.NumPatchBytes)
1454 NumPatchBytes = *SD.NumPatchBytes;
1455 if (SD.StatepointID)
1456 StatepointID = *SD.StatepointID;
1458 // Pass through the requested lowering if any. The default is live-through.
1459 StringRef DeoptLowering = getDeoptLowering(CS);
1460 if (DeoptLowering.equals("live-in"))
1461 Flags |= uint32_t(StatepointFlags::DeoptLiveIn);
1463 assert(DeoptLowering.equals("live-through") && "Unsupported value!");
1466 Value *CallTarget = CS.getCalledValue();
1467 if (Function *F = dyn_cast<Function>(CallTarget)) {
1468 if (F->getIntrinsicID() == Intrinsic::experimental_deoptimize) {
1469 // Calls to llvm.experimental.deoptimize are lowered to calls to the
1470 // __llvm_deoptimize symbol. We want to resolve this now, since the
1471 // verifier does not allow taking the address of an intrinsic function.
1473 SmallVector<Type *, 8> DomainTy;
1474 for (Value *Arg : CallArgs)
1475 DomainTy.push_back(Arg->getType());
1476 auto *FTy = FunctionType::get(Type::getVoidTy(F->getContext()), DomainTy,
1477 /* isVarArg = */ false);
1479 // Note: CallTarget can be a bitcast instruction of a symbol if there are
1480 // calls to @llvm.experimental.deoptimize with different argument types in
1481 // the same module. This is fine -- we assume the frontend knew what it
1482 // was doing when generating this kind of IR.
1484 F->getParent()->getOrInsertFunction("__llvm_deoptimize", FTy);
1486 IsDeoptimize = true;
1490 // Create the statepoint given all the arguments
1491 Instruction *Token = nullptr;
1493 CallInst *ToReplace = cast<CallInst>(CS.getInstruction());
1494 CallInst *Call = Builder.CreateGCStatepointCall(
1495 StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs,
1496 TransitionArgs, DeoptArgs, GCArgs, "safepoint_token");
1498 Call->setTailCallKind(ToReplace->getTailCallKind());
1499 Call->setCallingConv(ToReplace->getCallingConv());
1501 // Currently we will fail on parameter attributes and on certain
1502 // function attributes. In case if we can handle this set of attributes -
1503 // set up function attrs directly on statepoint and return attrs later for
1504 // gc_result intrinsic.
1505 Call->setAttributes(legalizeCallAttributes(ToReplace->getAttributes()));
1509 // Put the following gc_result and gc_relocate calls immediately after the
1510 // the old call (which we're about to delete)
1511 assert(ToReplace->getNextNode() && "Not a terminator, must have next!");
1512 Builder.SetInsertPoint(ToReplace->getNextNode());
1513 Builder.SetCurrentDebugLocation(ToReplace->getNextNode()->getDebugLoc());
1515 InvokeInst *ToReplace = cast<InvokeInst>(CS.getInstruction());
1517 // Insert the new invoke into the old block. We'll remove the old one in a
1518 // moment at which point this will become the new terminator for the
1520 InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
1521 StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(),
1522 ToReplace->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs,
1523 GCArgs, "statepoint_token");
1525 Invoke->setCallingConv(ToReplace->getCallingConv());
1527 // Currently we will fail on parameter attributes and on certain
1528 // function attributes. In case if we can handle this set of attributes -
1529 // set up function attrs directly on statepoint and return attrs later for
1530 // gc_result intrinsic.
1531 Invoke->setAttributes(legalizeCallAttributes(ToReplace->getAttributes()));
1535 // Generate gc relocates in exceptional path
1536 BasicBlock *UnwindBlock = ToReplace->getUnwindDest();
1537 assert(!isa<PHINode>(UnwindBlock->begin()) &&
1538 UnwindBlock->getUniquePredecessor() &&
1539 "can't safely insert in this block!");
1541 Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt());
1542 Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc());
1544 // Attach exceptional gc relocates to the landingpad.
1545 Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst();
1546 Result.UnwindToken = ExceptionalToken;
1548 const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
1549 CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, ExceptionalToken,
1552 // Generate gc relocates and returns for normal block
1553 BasicBlock *NormalDest = ToReplace->getNormalDest();
1554 assert(!isa<PHINode>(NormalDest->begin()) &&
1555 NormalDest->getUniquePredecessor() &&
1556 "can't safely insert in this block!");
1558 Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt());
1560 // gc relocates will be generated later as if it were regular call
1563 assert(Token && "Should be set in one of the above branches!");
1566 // If we're wrapping an @llvm.experimental.deoptimize in a statepoint, we
1567 // transform the tail-call like structure to a call to a void function
1568 // followed by unreachable to get better codegen.
1569 Replacements.push_back(
1570 DeferredReplacement::createDeoptimizeReplacement(CS.getInstruction()));
1572 Token->setName("statepoint_token");
1573 if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) {
1575 CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : "";
1576 CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name);
1577 GCResult->setAttributes(
1578 AttributeList::get(GCResult->getContext(), AttributeList::ReturnIndex,
1579 CS.getAttributes().getRetAttributes()));
1581 // We cannot RAUW or delete CS.getInstruction() because it could be in the
1582 // live set of some other safepoint, in which case that safepoint's
1583 // PartiallyConstructedSafepointRecord will hold a raw pointer to this
1584 // llvm::Instruction. Instead, we defer the replacement and deletion to
1585 // after the live sets have been made explicit in the IR, and we no longer
1586 // have raw pointers to worry about.
1587 Replacements.emplace_back(
1588 DeferredReplacement::createRAUW(CS.getInstruction(), GCResult));
1590 Replacements.emplace_back(
1591 DeferredReplacement::createDelete(CS.getInstruction()));
1595 Result.StatepointToken = Token;
1597 // Second, create a gc.relocate for every live variable
1598 const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
1599 CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, Token, Builder);
1602 // Replace an existing gc.statepoint with a new one and a set of gc.relocates
1603 // which make the relocations happening at this safepoint explicit.
1605 // WARNING: Does not do any fixup to adjust users of the original live
1606 // values. That's the callers responsibility.
1608 makeStatepointExplicit(DominatorTree &DT, CallSite CS,
1609 PartiallyConstructedSafepointRecord &Result,
1610 std::vector<DeferredReplacement> &Replacements) {
1611 const auto &LiveSet = Result.LiveSet;
1612 const auto &PointerToBase = Result.PointerToBase;
1614 // Convert to vector for efficient cross referencing.
1615 SmallVector<Value *, 64> BaseVec, LiveVec;
1616 LiveVec.reserve(LiveSet.size());
1617 BaseVec.reserve(LiveSet.size());
1618 for (Value *L : LiveSet) {
1619 LiveVec.push_back(L);
1620 assert(PointerToBase.count(L));
1621 Value *Base = PointerToBase.find(L)->second;
1622 BaseVec.push_back(Base);
1624 assert(LiveVec.size() == BaseVec.size());
1626 // Do the actual rewriting and delete the old statepoint
1627 makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements);
1630 // Helper function for the relocationViaAlloca.
1632 // It receives iterator to the statepoint gc relocates and emits a store to the
1633 // assigned location (via allocaMap) for the each one of them. It adds the
1634 // visited values into the visitedLiveValues set, which we will later use them
1635 // for sanity checking.
1637 insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs,
1638 DenseMap<Value *, Value *> &AllocaMap,
1639 DenseSet<Value *> &VisitedLiveValues) {
1640 for (User *U : GCRelocs) {
1641 GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U);
1645 Value *OriginalValue = Relocate->getDerivedPtr();
1646 assert(AllocaMap.count(OriginalValue));
1647 Value *Alloca = AllocaMap[OriginalValue];
1649 // Emit store into the related alloca
1650 // All gc_relocates are i8 addrspace(1)* typed, and it must be bitcasted to
1651 // the correct type according to alloca.
1652 assert(Relocate->getNextNode() &&
1653 "Should always have one since it's not a terminator");
1654 IRBuilder<> Builder(Relocate->getNextNode());
1655 Value *CastedRelocatedValue =
1656 Builder.CreateBitCast(Relocate,
1657 cast<AllocaInst>(Alloca)->getAllocatedType(),
1658 suffixed_name_or(Relocate, ".casted", ""));
1660 StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca);
1661 Store->insertAfter(cast<Instruction>(CastedRelocatedValue));
1664 VisitedLiveValues.insert(OriginalValue);
1669 // Helper function for the "relocationViaAlloca". Similar to the
1670 // "insertRelocationStores" but works for rematerialized values.
1671 static void insertRematerializationStores(
1672 const RematerializedValueMapTy &RematerializedValues,
1673 DenseMap<Value *, Value *> &AllocaMap,
1674 DenseSet<Value *> &VisitedLiveValues) {
1675 for (auto RematerializedValuePair: RematerializedValues) {
1676 Instruction *RematerializedValue = RematerializedValuePair.first;
1677 Value *OriginalValue = RematerializedValuePair.second;
1679 assert(AllocaMap.count(OriginalValue) &&
1680 "Can not find alloca for rematerialized value");
1681 Value *Alloca = AllocaMap[OriginalValue];
1683 StoreInst *Store = new StoreInst(RematerializedValue, Alloca);
1684 Store->insertAfter(RematerializedValue);
1687 VisitedLiveValues.insert(OriginalValue);
1692 /// Do all the relocation update via allocas and mem2reg
1693 static void relocationViaAlloca(
1694 Function &F, DominatorTree &DT, ArrayRef<Value *> Live,
1695 ArrayRef<PartiallyConstructedSafepointRecord> Records) {
1697 // record initial number of (static) allocas; we'll check we have the same
1698 // number when we get done.
1699 int InitialAllocaNum = 0;
1700 for (Instruction &I : F.getEntryBlock())
1701 if (isa<AllocaInst>(I))
1705 // TODO-PERF: change data structures, reserve
1706 DenseMap<Value *, Value *> AllocaMap;
1707 SmallVector<AllocaInst *, 200> PromotableAllocas;
1708 // Used later to chack that we have enough allocas to store all values
1709 std::size_t NumRematerializedValues = 0;
1710 PromotableAllocas.reserve(Live.size());
1712 // Emit alloca for "LiveValue" and record it in "allocaMap" and
1713 // "PromotableAllocas"
1714 const DataLayout &DL = F.getParent()->getDataLayout();
1715 auto emitAllocaFor = [&](Value *LiveValue) {
1716 AllocaInst *Alloca = new AllocaInst(LiveValue->getType(),
1717 DL.getAllocaAddrSpace(), "",
1718 F.getEntryBlock().getFirstNonPHI());
1719 AllocaMap[LiveValue] = Alloca;
1720 PromotableAllocas.push_back(Alloca);
1723 // Emit alloca for each live gc pointer
1724 for (Value *V : Live)
1727 // Emit allocas for rematerialized values
1728 for (const auto &Info : Records)
1729 for (auto RematerializedValuePair : Info.RematerializedValues) {
1730 Value *OriginalValue = RematerializedValuePair.second;
1731 if (AllocaMap.count(OriginalValue) != 0)
1734 emitAllocaFor(OriginalValue);
1735 ++NumRematerializedValues;
1738 // The next two loops are part of the same conceptual operation. We need to
1739 // insert a store to the alloca after the original def and at each
1740 // redefinition. We need to insert a load before each use. These are split
1741 // into distinct loops for performance reasons.
1743 // Update gc pointer after each statepoint: either store a relocated value or
1744 // null (if no relocated value was found for this gc pointer and it is not a
1745 // gc_result). This must happen before we update the statepoint with load of
1746 // alloca otherwise we lose the link between statepoint and old def.
1747 for (const auto &Info : Records) {
1748 Value *Statepoint = Info.StatepointToken;
1750 // This will be used for consistency check
1751 DenseSet<Value *> VisitedLiveValues;
1753 // Insert stores for normal statepoint gc relocates
1754 insertRelocationStores(Statepoint->users(), AllocaMap, VisitedLiveValues);
1756 // In case if it was invoke statepoint
1757 // we will insert stores for exceptional path gc relocates.
1758 if (isa<InvokeInst>(Statepoint)) {
1759 insertRelocationStores(Info.UnwindToken->users(), AllocaMap,
1763 // Do similar thing with rematerialized values
1764 insertRematerializationStores(Info.RematerializedValues, AllocaMap,
1767 if (ClobberNonLive) {
1768 // As a debugging aid, pretend that an unrelocated pointer becomes null at
1769 // the gc.statepoint. This will turn some subtle GC problems into
1770 // slightly easier to debug SEGVs. Note that on large IR files with
1771 // lots of gc.statepoints this is extremely costly both memory and time
1773 SmallVector<AllocaInst *, 64> ToClobber;
1774 for (auto Pair : AllocaMap) {
1775 Value *Def = Pair.first;
1776 AllocaInst *Alloca = cast<AllocaInst>(Pair.second);
1778 // This value was relocated
1779 if (VisitedLiveValues.count(Def)) {
1782 ToClobber.push_back(Alloca);
1785 auto InsertClobbersAt = [&](Instruction *IP) {
1786 for (auto *AI : ToClobber) {
1787 auto PT = cast<PointerType>(AI->getAllocatedType());
1788 Constant *CPN = ConstantPointerNull::get(PT);
1789 StoreInst *Store = new StoreInst(CPN, AI);
1790 Store->insertBefore(IP);
1794 // Insert the clobbering stores. These may get intermixed with the
1795 // gc.results and gc.relocates, but that's fine.
1796 if (auto II = dyn_cast<InvokeInst>(Statepoint)) {
1797 InsertClobbersAt(&*II->getNormalDest()->getFirstInsertionPt());
1798 InsertClobbersAt(&*II->getUnwindDest()->getFirstInsertionPt());
1800 InsertClobbersAt(cast<Instruction>(Statepoint)->getNextNode());
1805 // Update use with load allocas and add store for gc_relocated.
1806 for (auto Pair : AllocaMap) {
1807 Value *Def = Pair.first;
1808 Value *Alloca = Pair.second;
1810 // We pre-record the uses of allocas so that we dont have to worry about
1811 // later update that changes the user information..
1813 SmallVector<Instruction *, 20> Uses;
1814 // PERF: trade a linear scan for repeated reallocation
1815 Uses.reserve(Def->getNumUses());
1816 for (User *U : Def->users()) {
1817 if (!isa<ConstantExpr>(U)) {
1818 // If the def has a ConstantExpr use, then the def is either a
1819 // ConstantExpr use itself or null. In either case
1820 // (recursively in the first, directly in the second), the oop
1821 // it is ultimately dependent on is null and this particular
1822 // use does not need to be fixed up.
1823 Uses.push_back(cast<Instruction>(U));
1827 llvm::sort(Uses.begin(), Uses.end());
1828 auto Last = std::unique(Uses.begin(), Uses.end());
1829 Uses.erase(Last, Uses.end());
1831 for (Instruction *Use : Uses) {
1832 if (isa<PHINode>(Use)) {
1833 PHINode *Phi = cast<PHINode>(Use);
1834 for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) {
1835 if (Def == Phi->getIncomingValue(i)) {
1836 LoadInst *Load = new LoadInst(
1837 Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
1838 Phi->setIncomingValue(i, Load);
1842 LoadInst *Load = new LoadInst(Alloca, "", Use);
1843 Use->replaceUsesOfWith(Def, Load);
1847 // Emit store for the initial gc value. Store must be inserted after load,
1848 // otherwise store will be in alloca's use list and an extra load will be
1849 // inserted before it.
1850 StoreInst *Store = new StoreInst(Def, Alloca);
1851 if (Instruction *Inst = dyn_cast<Instruction>(Def)) {
1852 if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) {
1853 // InvokeInst is a TerminatorInst so the store need to be inserted
1854 // into its normal destination block.
1855 BasicBlock *NormalDest = Invoke->getNormalDest();
1856 Store->insertBefore(NormalDest->getFirstNonPHI());
1858 assert(!Inst->isTerminator() &&
1859 "The only TerminatorInst that can produce a value is "
1860 "InvokeInst which is handled above.");
1861 Store->insertAfter(Inst);
1864 assert(isa<Argument>(Def));
1865 Store->insertAfter(cast<Instruction>(Alloca));
1869 assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues &&
1870 "we must have the same allocas with lives");
1871 if (!PromotableAllocas.empty()) {
1872 // Apply mem2reg to promote alloca to SSA
1873 PromoteMemToReg(PromotableAllocas, DT);
1877 for (auto &I : F.getEntryBlock())
1878 if (isa<AllocaInst>(I))
1880 assert(InitialAllocaNum == 0 && "We must not introduce any extra allocas");
1884 /// Implement a unique function which doesn't require we sort the input
1885 /// vector. Doing so has the effect of changing the output of a couple of
1886 /// tests in ways which make them less useful in testing fused safepoints.
1887 template <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) {
1888 SmallSet<T, 8> Seen;
1889 Vec.erase(remove_if(Vec, [&](const T &V) { return !Seen.insert(V).second; }),
1893 /// Insert holders so that each Value is obviously live through the entire
1894 /// lifetime of the call.
1895 static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values,
1896 SmallVectorImpl<CallInst *> &Holders) {
1898 // No values to hold live, might as well not insert the empty holder
1901 Module *M = CS.getInstruction()->getModule();
1902 // Use a dummy vararg function to actually hold the values live
1903 Function *Func = cast<Function>(M->getOrInsertFunction(
1904 "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true)));
1906 // For call safepoints insert dummy calls right after safepoint
1907 Holders.push_back(CallInst::Create(Func, Values, "",
1908 &*++CS.getInstruction()->getIterator()));
1911 // For invoke safepooints insert dummy calls both in normal and
1912 // exceptional destination blocks
1913 auto *II = cast<InvokeInst>(CS.getInstruction());
1914 Holders.push_back(CallInst::Create(
1915 Func, Values, "", &*II->getNormalDest()->getFirstInsertionPt()));
1916 Holders.push_back(CallInst::Create(
1917 Func, Values, "", &*II->getUnwindDest()->getFirstInsertionPt()));
1920 static void findLiveReferences(
1921 Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
1922 MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
1923 GCPtrLivenessData OriginalLivenessData;
1924 computeLiveInValues(DT, F, OriginalLivenessData);
1925 for (size_t i = 0; i < records.size(); i++) {
1926 struct PartiallyConstructedSafepointRecord &info = records[i];
1927 analyzeParsePointLiveness(DT, OriginalLivenessData, toUpdate[i], info);
1931 // Helper function for the "rematerializeLiveValues". It walks use chain
1932 // starting from the "CurrentValue" until it reaches the root of the chain, i.e.
1933 // the base or a value it cannot process. Only "simple" values are processed
1934 // (currently it is GEP's and casts). The returned root is examined by the
1935 // callers of findRematerializableChainToBasePointer. Fills "ChainToBase" array
1936 // with all visited values.
1937 static Value* findRematerializableChainToBasePointer(
1938 SmallVectorImpl<Instruction*> &ChainToBase,
1939 Value *CurrentValue) {
1940 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) {
1941 ChainToBase.push_back(GEP);
1942 return findRematerializableChainToBasePointer(ChainToBase,
1943 GEP->getPointerOperand());
1946 if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) {
1947 if (!CI->isNoopCast(CI->getModule()->getDataLayout()))
1950 ChainToBase.push_back(CI);
1951 return findRematerializableChainToBasePointer(ChainToBase,
1955 // We have reached the root of the chain, which is either equal to the base or
1956 // is the first unsupported value along the use chain.
1957 return CurrentValue;
1960 // Helper function for the "rematerializeLiveValues". Compute cost of the use
1961 // chain we are going to rematerialize.
1963 chainToBasePointerCost(SmallVectorImpl<Instruction*> &Chain,
1964 TargetTransformInfo &TTI) {
1967 for (Instruction *Instr : Chain) {
1968 if (CastInst *CI = dyn_cast<CastInst>(Instr)) {
1969 assert(CI->isNoopCast(CI->getModule()->getDataLayout()) &&
1970 "non noop cast is found during rematerialization");
1972 Type *SrcTy = CI->getOperand(0)->getType();
1973 Cost += TTI.getCastInstrCost(CI->getOpcode(), CI->getType(), SrcTy, CI);
1975 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Instr)) {
1976 // Cost of the address calculation
1977 Type *ValTy = GEP->getSourceElementType();
1978 Cost += TTI.getAddressComputationCost(ValTy);
1980 // And cost of the GEP itself
1981 // TODO: Use TTI->getGEPCost here (it exists, but appears to be not
1982 // allowed for the external usage)
1983 if (!GEP->hasAllConstantIndices())
1987 llvm_unreachable("unsupported instruction type during rematerialization");
1994 static bool AreEquivalentPhiNodes(PHINode &OrigRootPhi, PHINode &AlternateRootPhi) {
1995 unsigned PhiNum = OrigRootPhi.getNumIncomingValues();
1996 if (PhiNum != AlternateRootPhi.getNumIncomingValues() ||
1997 OrigRootPhi.getParent() != AlternateRootPhi.getParent())
1999 // Map of incoming values and their corresponding basic blocks of
2001 SmallDenseMap<Value *, BasicBlock *, 8> CurrentIncomingValues;
2002 for (unsigned i = 0; i < PhiNum; i++)
2003 CurrentIncomingValues[OrigRootPhi.getIncomingValue(i)] =
2004 OrigRootPhi.getIncomingBlock(i);
2006 // Both current and base PHIs should have same incoming values and
2007 // the same basic blocks corresponding to the incoming values.
2008 for (unsigned i = 0; i < PhiNum; i++) {
2010 CurrentIncomingValues.find(AlternateRootPhi.getIncomingValue(i));
2011 if (CIVI == CurrentIncomingValues.end())
2013 BasicBlock *CurrentIncomingBB = CIVI->second;
2014 if (CurrentIncomingBB != AlternateRootPhi.getIncomingBlock(i))
2020 // From the statepoint live set pick values that are cheaper to recompute then
2021 // to relocate. Remove this values from the live set, rematerialize them after
2022 // statepoint and record them in "Info" structure. Note that similar to
2023 // relocated values we don't do any user adjustments here.
2024 static void rematerializeLiveValues(CallSite CS,
2025 PartiallyConstructedSafepointRecord &Info,
2026 TargetTransformInfo &TTI) {
2027 const unsigned int ChainLengthThreshold = 10;
2029 // Record values we are going to delete from this statepoint live set.
2030 // We can not di this in following loop due to iterator invalidation.
2031 SmallVector<Value *, 32> LiveValuesToBeDeleted;
2033 for (Value *LiveValue: Info.LiveSet) {
2034 // For each live pointer find its defining chain
2035 SmallVector<Instruction *, 3> ChainToBase;
2036 assert(Info.PointerToBase.count(LiveValue));
2037 Value *RootOfChain =
2038 findRematerializableChainToBasePointer(ChainToBase,
2041 // Nothing to do, or chain is too long
2042 if ( ChainToBase.size() == 0 ||
2043 ChainToBase.size() > ChainLengthThreshold)
2046 // Handle the scenario where the RootOfChain is not equal to the
2047 // Base Value, but they are essentially the same phi values.
2048 if (RootOfChain != Info.PointerToBase[LiveValue]) {
2049 PHINode *OrigRootPhi = dyn_cast<PHINode>(RootOfChain);
2050 PHINode *AlternateRootPhi = dyn_cast<PHINode>(Info.PointerToBase[LiveValue]);
2051 if (!OrigRootPhi || !AlternateRootPhi)
2053 // PHI nodes that have the same incoming values, and belonging to the same
2054 // basic blocks are essentially the same SSA value. When the original phi
2055 // has incoming values with different base pointers, the original phi is
2056 // marked as conflict, and an additional `AlternateRootPhi` with the same
2057 // incoming values get generated by the findBasePointer function. We need
2058 // to identify the newly generated AlternateRootPhi (.base version of phi)
2059 // and RootOfChain (the original phi node itself) are the same, so that we
2060 // can rematerialize the gep and casts. This is a workaround for the
2061 // deficiency in the findBasePointer algorithm.
2062 if (!AreEquivalentPhiNodes(*OrigRootPhi, *AlternateRootPhi))
2064 // Now that the phi nodes are proved to be the same, assert that
2065 // findBasePointer's newly generated AlternateRootPhi is present in the
2066 // liveset of the call.
2067 assert(Info.LiveSet.count(AlternateRootPhi));
2069 // Compute cost of this chain
2070 unsigned Cost = chainToBasePointerCost(ChainToBase, TTI);
2071 // TODO: We can also account for cases when we will be able to remove some
2072 // of the rematerialized values by later optimization passes. I.e if
2073 // we rematerialized several intersecting chains. Or if original values
2074 // don't have any uses besides this statepoint.
2076 // For invokes we need to rematerialize each chain twice - for normal and
2077 // for unwind basic blocks. Model this by multiplying cost by two.
2078 if (CS.isInvoke()) {
2081 // If it's too expensive - skip it
2082 if (Cost >= RematerializationThreshold)
2085 // Remove value from the live set
2086 LiveValuesToBeDeleted.push_back(LiveValue);
2088 // Clone instructions and record them inside "Info" structure
2090 // Walk backwards to visit top-most instructions first
2091 std::reverse(ChainToBase.begin(), ChainToBase.end());
2093 // Utility function which clones all instructions from "ChainToBase"
2094 // and inserts them before "InsertBefore". Returns rematerialized value
2095 // which should be used after statepoint.
2096 auto rematerializeChain = [&ChainToBase](
2097 Instruction *InsertBefore, Value *RootOfChain, Value *AlternateLiveBase) {
2098 Instruction *LastClonedValue = nullptr;
2099 Instruction *LastValue = nullptr;
2100 for (Instruction *Instr: ChainToBase) {
2101 // Only GEP's and casts are supported as we need to be careful to not
2102 // introduce any new uses of pointers not in the liveset.
2103 // Note that it's fine to introduce new uses of pointers which were
2104 // otherwise not used after this statepoint.
2105 assert(isa<GetElementPtrInst>(Instr) || isa<CastInst>(Instr));
2107 Instruction *ClonedValue = Instr->clone();
2108 ClonedValue->insertBefore(InsertBefore);
2109 ClonedValue->setName(Instr->getName() + ".remat");
2111 // If it is not first instruction in the chain then it uses previously
2112 // cloned value. We should update it to use cloned value.
2113 if (LastClonedValue) {
2115 ClonedValue->replaceUsesOfWith(LastValue, LastClonedValue);
2117 for (auto OpValue : ClonedValue->operand_values()) {
2118 // Assert that cloned instruction does not use any instructions from
2119 // this chain other than LastClonedValue
2120 assert(!is_contained(ChainToBase, OpValue) &&
2121 "incorrect use in rematerialization chain");
2122 // Assert that the cloned instruction does not use the RootOfChain
2123 // or the AlternateLiveBase.
2124 assert(OpValue != RootOfChain && OpValue != AlternateLiveBase);
2128 // For the first instruction, replace the use of unrelocated base i.e.
2129 // RootOfChain/OrigRootPhi, with the corresponding PHI present in the
2130 // live set. They have been proved to be the same PHI nodes. Note
2131 // that the *only* use of the RootOfChain in the ChainToBase list is
2132 // the first Value in the list.
2133 if (RootOfChain != AlternateLiveBase)
2134 ClonedValue->replaceUsesOfWith(RootOfChain, AlternateLiveBase);
2137 LastClonedValue = ClonedValue;
2140 assert(LastClonedValue);
2141 return LastClonedValue;
2144 // Different cases for calls and invokes. For invokes we need to clone
2145 // instructions both on normal and unwind path.
2147 Instruction *InsertBefore = CS.getInstruction()->getNextNode();
2148 assert(InsertBefore);
2149 Instruction *RematerializedValue = rematerializeChain(
2150 InsertBefore, RootOfChain, Info.PointerToBase[LiveValue]);
2151 Info.RematerializedValues[RematerializedValue] = LiveValue;
2153 InvokeInst *Invoke = cast<InvokeInst>(CS.getInstruction());
2155 Instruction *NormalInsertBefore =
2156 &*Invoke->getNormalDest()->getFirstInsertionPt();
2157 Instruction *UnwindInsertBefore =
2158 &*Invoke->getUnwindDest()->getFirstInsertionPt();
2160 Instruction *NormalRematerializedValue = rematerializeChain(
2161 NormalInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]);
2162 Instruction *UnwindRematerializedValue = rematerializeChain(
2163 UnwindInsertBefore, RootOfChain, Info.PointerToBase[LiveValue]);
2165 Info.RematerializedValues[NormalRematerializedValue] = LiveValue;
2166 Info.RematerializedValues[UnwindRematerializedValue] = LiveValue;
2170 // Remove rematerializaed values from the live set
2171 for (auto LiveValue: LiveValuesToBeDeleted) {
2172 Info.LiveSet.remove(LiveValue);
2176 static bool insertParsePoints(Function &F, DominatorTree &DT,
2177 TargetTransformInfo &TTI,
2178 SmallVectorImpl<CallSite> &ToUpdate) {
2180 // sanity check the input
2181 std::set<CallSite> Uniqued;
2182 Uniqued.insert(ToUpdate.begin(), ToUpdate.end());
2183 assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!");
2185 for (CallSite CS : ToUpdate)
2186 assert(CS.getInstruction()->getFunction() == &F);
2189 // When inserting gc.relocates for invokes, we need to be able to insert at
2190 // the top of the successor blocks. See the comment on
2191 // normalForInvokeSafepoint on exactly what is needed. Note that this step
2192 // may restructure the CFG.
2193 for (CallSite CS : ToUpdate) {
2196 auto *II = cast<InvokeInst>(CS.getInstruction());
2197 normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT);
2198 normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT);
2201 // A list of dummy calls added to the IR to keep various values obviously
2202 // live in the IR. We'll remove all of these when done.
2203 SmallVector<CallInst *, 64> Holders;
2205 // Insert a dummy call with all of the deopt operands we'll need for the
2206 // actual safepoint insertion as arguments. This ensures reference operands
2207 // in the deopt argument list are considered live through the safepoint (and
2208 // thus makes sure they get relocated.)
2209 for (CallSite CS : ToUpdate) {
2210 SmallVector<Value *, 64> DeoptValues;
2212 for (Value *Arg : GetDeoptBundleOperands(CS)) {
2213 assert(!isUnhandledGCPointerType(Arg->getType()) &&
2214 "support for FCA unimplemented");
2215 if (isHandledGCPointerType(Arg->getType()))
2216 DeoptValues.push_back(Arg);
2219 insertUseHolderAfter(CS, DeoptValues, Holders);
2222 SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size());
2224 // A) Identify all gc pointers which are statically live at the given call
2226 findLiveReferences(F, DT, ToUpdate, Records);
2228 // B) Find the base pointers for each live pointer
2229 /* scope for caching */ {
2230 // Cache the 'defining value' relation used in the computation and
2231 // insertion of base phis and selects. This ensures that we don't insert
2232 // large numbers of duplicate base_phis.
2233 DefiningValueMapTy DVCache;
2235 for (size_t i = 0; i < Records.size(); i++) {
2236 PartiallyConstructedSafepointRecord &info = Records[i];
2237 findBasePointers(DT, DVCache, ToUpdate[i], info);
2239 } // end of cache scope
2241 // The base phi insertion logic (for any safepoint) may have inserted new
2242 // instructions which are now live at some safepoint. The simplest such
2245 // phi a <-- will be a new base_phi here
2246 // safepoint 1 <-- that needs to be live here
2250 // We insert some dummy calls after each safepoint to definitely hold live
2251 // the base pointers which were identified for that safepoint. We'll then
2252 // ask liveness for _every_ base inserted to see what is now live. Then we
2253 // remove the dummy calls.
2254 Holders.reserve(Holders.size() + Records.size());
2255 for (size_t i = 0; i < Records.size(); i++) {
2256 PartiallyConstructedSafepointRecord &Info = Records[i];
2258 SmallVector<Value *, 128> Bases;
2259 for (auto Pair : Info.PointerToBase)
2260 Bases.push_back(Pair.second);
2262 insertUseHolderAfter(ToUpdate[i], Bases, Holders);
2265 // By selecting base pointers, we've effectively inserted new uses. Thus, we
2266 // need to rerun liveness. We may *also* have inserted new defs, but that's
2267 // not the key issue.
2268 recomputeLiveInValues(F, DT, ToUpdate, Records);
2270 if (PrintBasePointers) {
2271 for (auto &Info : Records) {
2272 errs() << "Base Pairs: (w/Relocation)\n";
2273 for (auto Pair : Info.PointerToBase) {
2274 errs() << " derived ";
2275 Pair.first->printAsOperand(errs(), false);
2277 Pair.second->printAsOperand(errs(), false);
2283 // It is possible that non-constant live variables have a constant base. For
2284 // example, a GEP with a variable offset from a global. In this case we can
2285 // remove it from the liveset. We already don't add constants to the liveset
2286 // because we assume they won't move at runtime and the GC doesn't need to be
2287 // informed about them. The same reasoning applies if the base is constant.
2288 // Note that the relocation placement code relies on this filtering for
2289 // correctness as it expects the base to be in the liveset, which isn't true
2290 // if the base is constant.
2291 for (auto &Info : Records)
2292 for (auto &BasePair : Info.PointerToBase)
2293 if (isa<Constant>(BasePair.second))
2294 Info.LiveSet.remove(BasePair.first);
2296 for (CallInst *CI : Holders)
2297 CI->eraseFromParent();
2301 // In order to reduce live set of statepoint we might choose to rematerialize
2302 // some values instead of relocating them. This is purely an optimization and
2303 // does not influence correctness.
2304 for (size_t i = 0; i < Records.size(); i++)
2305 rematerializeLiveValues(ToUpdate[i], Records[i], TTI);
2307 // We need this to safely RAUW and delete call or invoke return values that
2308 // may themselves be live over a statepoint. For details, please see usage in
2309 // makeStatepointExplicitImpl.
2310 std::vector<DeferredReplacement> Replacements;
2312 // Now run through and replace the existing statepoints with new ones with
2313 // the live variables listed. We do not yet update uses of the values being
2314 // relocated. We have references to live variables that need to
2315 // survive to the last iteration of this loop. (By construction, the
2316 // previous statepoint can not be a live variable, thus we can and remove
2317 // the old statepoint calls as we go.)
2318 for (size_t i = 0; i < Records.size(); i++)
2319 makeStatepointExplicit(DT, ToUpdate[i], Records[i], Replacements);
2321 ToUpdate.clear(); // prevent accident use of invalid CallSites
2323 for (auto &PR : Replacements)
2326 Replacements.clear();
2328 for (auto &Info : Records) {
2329 // These live sets may contain state Value pointers, since we replaced calls
2330 // with operand bundles with calls wrapped in gc.statepoint, and some of
2331 // those calls may have been def'ing live gc pointers. Clear these out to
2332 // avoid accidentally using them.
2334 // TODO: We should create a separate data structure that does not contain
2335 // these live sets, and migrate to using that data structure from this point
2337 Info.LiveSet.clear();
2338 Info.PointerToBase.clear();
2341 // Do all the fixups of the original live variables to their relocated selves
2342 SmallVector<Value *, 128> Live;
2343 for (size_t i = 0; i < Records.size(); i++) {
2344 PartiallyConstructedSafepointRecord &Info = Records[i];
2346 // We can't simply save the live set from the original insertion. One of
2347 // the live values might be the result of a call which needs a safepoint.
2348 // That Value* no longer exists and we need to use the new gc_result.
2349 // Thankfully, the live set is embedded in the statepoint (and updated), so
2350 // we just grab that.
2351 Statepoint Statepoint(Info.StatepointToken);
2352 Live.insert(Live.end(), Statepoint.gc_args_begin(),
2353 Statepoint.gc_args_end());
2355 // Do some basic sanity checks on our liveness results before performing
2356 // relocation. Relocation can and will turn mistakes in liveness results
2357 // into non-sensical code which is must harder to debug.
2358 // TODO: It would be nice to test consistency as well
2359 assert(DT.isReachableFromEntry(Info.StatepointToken->getParent()) &&
2360 "statepoint must be reachable or liveness is meaningless");
2361 for (Value *V : Statepoint.gc_args()) {
2362 if (!isa<Instruction>(V))
2363 // Non-instruction values trivial dominate all possible uses
2365 auto *LiveInst = cast<Instruction>(V);
2366 assert(DT.isReachableFromEntry(LiveInst->getParent()) &&
2367 "unreachable values should never be live");
2368 assert(DT.dominates(LiveInst, Info.StatepointToken) &&
2369 "basic SSA liveness expectation violated by liveness analysis");
2373 unique_unsorted(Live);
2377 for (auto *Ptr : Live)
2378 assert(isHandledGCPointerType(Ptr->getType()) &&
2379 "must be a gc pointer type");
2382 relocationViaAlloca(F, DT, Live, Records);
2383 return !Records.empty();
2386 // Handles both return values and arguments for Functions and CallSites.
2387 template <typename AttrHolder>
2388 static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH,
2391 if (AH.getDereferenceableBytes(Index))
2392 R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable,
2393 AH.getDereferenceableBytes(Index)));
2394 if (AH.getDereferenceableOrNullBytes(Index))
2395 R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull,
2396 AH.getDereferenceableOrNullBytes(Index)));
2397 if (AH.getAttributes().hasAttribute(Index, Attribute::NoAlias))
2398 R.addAttribute(Attribute::NoAlias);
2401 AH.setAttributes(AH.getAttributes().removeAttributes(Ctx, Index, R));
2404 static void stripNonValidAttributesFromPrototype(Function &F) {
2405 LLVMContext &Ctx = F.getContext();
2407 for (Argument &A : F.args())
2408 if (isa<PointerType>(A.getType()))
2409 RemoveNonValidAttrAtIndex(Ctx, F,
2410 A.getArgNo() + AttributeList::FirstArgIndex);
2412 if (isa<PointerType>(F.getReturnType()))
2413 RemoveNonValidAttrAtIndex(Ctx, F, AttributeList::ReturnIndex);
2416 /// Certain metadata on instructions are invalid after running RS4GC.
2417 /// Optimizations that run after RS4GC can incorrectly use this metadata to
2418 /// optimize functions. We drop such metadata on the instruction.
2419 static void stripInvalidMetadataFromInstruction(Instruction &I) {
2420 if (!isa<LoadInst>(I) && !isa<StoreInst>(I))
2422 // These are the attributes that are still valid on loads and stores after
2424 // The metadata implying dereferenceability and noalias are (conservatively)
2425 // dropped. This is because semantically, after RewriteStatepointsForGC runs,
2426 // all calls to gc.statepoint "free" the entire heap. Also, gc.statepoint can
2427 // touch the entire heap including noalias objects. Note: The reasoning is
2428 // same as stripping the dereferenceability and noalias attributes that are
2429 // analogous to the metadata counterparts.
2430 // We also drop the invariant.load metadata on the load because that metadata
2431 // implies the address operand to the load points to memory that is never
2432 // changed once it became dereferenceable. This is no longer true after RS4GC.
2433 // Similar reasoning applies to invariant.group metadata, which applies to
2434 // loads within a group.
2435 unsigned ValidMetadataAfterRS4GC[] = {LLVMContext::MD_tbaa,
2436 LLVMContext::MD_range,
2437 LLVMContext::MD_alias_scope,
2438 LLVMContext::MD_nontemporal,
2439 LLVMContext::MD_nonnull,
2440 LLVMContext::MD_align,
2441 LLVMContext::MD_type};
2443 // Drops all metadata on the instruction other than ValidMetadataAfterRS4GC.
2444 I.dropUnknownNonDebugMetadata(ValidMetadataAfterRS4GC);
2447 static void stripNonValidDataFromBody(Function &F) {
2451 LLVMContext &Ctx = F.getContext();
2452 MDBuilder Builder(Ctx);
2454 // Set of invariantstart instructions that we need to remove.
2455 // Use this to avoid invalidating the instruction iterator.
2456 SmallVector<IntrinsicInst*, 12> InvariantStartInstructions;
2458 for (Instruction &I : instructions(F)) {
2459 // invariant.start on memory location implies that the referenced memory
2460 // location is constant and unchanging. This is no longer true after
2461 // RewriteStatepointsForGC runs because there can be calls to gc.statepoint
2462 // which frees the entire heap and the presence of invariant.start allows
2463 // the optimizer to sink the load of a memory location past a statepoint,
2464 // which is incorrect.
2465 if (auto *II = dyn_cast<IntrinsicInst>(&I))
2466 if (II->getIntrinsicID() == Intrinsic::invariant_start) {
2467 InvariantStartInstructions.push_back(II);
2471 if (MDNode *Tag = I.getMetadata(LLVMContext::MD_tbaa)) {
2472 MDNode *MutableTBAA = Builder.createMutableTBAAAccessTag(Tag);
2473 I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA);
2476 stripInvalidMetadataFromInstruction(I);
2478 if (CallSite CS = CallSite(&I)) {
2479 for (int i = 0, e = CS.arg_size(); i != e; i++)
2480 if (isa<PointerType>(CS.getArgument(i)->getType()))
2481 RemoveNonValidAttrAtIndex(Ctx, CS, i + AttributeList::FirstArgIndex);
2482 if (isa<PointerType>(CS.getType()))
2483 RemoveNonValidAttrAtIndex(Ctx, CS, AttributeList::ReturnIndex);
2487 // Delete the invariant.start instructions and RAUW undef.
2488 for (auto *II : InvariantStartInstructions) {
2489 II->replaceAllUsesWith(UndefValue::get(II->getType()));
2490 II->eraseFromParent();
2494 /// Returns true if this function should be rewritten by this pass. The main
2495 /// point of this function is as an extension point for custom logic.
2496 static bool shouldRewriteStatepointsIn(Function &F) {
2497 // TODO: This should check the GCStrategy
2499 const auto &FunctionGCName = F.getGC();
2500 const StringRef StatepointExampleName("statepoint-example");
2501 const StringRef CoreCLRName("coreclr");
2502 return (StatepointExampleName == FunctionGCName) ||
2503 (CoreCLRName == FunctionGCName);
2508 static void stripNonValidData(Module &M) {
2510 assert(llvm::any_of(M, shouldRewriteStatepointsIn) && "precondition!");
2513 for (Function &F : M)
2514 stripNonValidAttributesFromPrototype(F);
2516 for (Function &F : M)
2517 stripNonValidDataFromBody(F);
2520 bool RewriteStatepointsForGC::runOnFunction(Function &F, DominatorTree &DT,
2521 TargetTransformInfo &TTI,
2522 const TargetLibraryInfo &TLI) {
2523 assert(!F.isDeclaration() && !F.empty() &&
2524 "need function body to rewrite statepoints in");
2525 assert(shouldRewriteStatepointsIn(F) && "mismatch in rewrite decision");
2527 auto NeedsRewrite = [&TLI](Instruction &I) {
2528 if (ImmutableCallSite CS = ImmutableCallSite(&I))
2529 return !callsGCLeafFunction(CS, TLI) && !isStatepoint(CS);
2534 // Delete any unreachable statepoints so that we don't have unrewritten
2535 // statepoints surviving this pass. This makes testing easier and the
2536 // resulting IR less confusing to human readers.
2537 DeferredDominance DD(DT);
2538 bool MadeChange = removeUnreachableBlocks(F, nullptr, &DD);
2541 // Gather all the statepoints which need rewritten. Be careful to only
2542 // consider those in reachable code since we need to ask dominance queries
2543 // when rewriting. We'll delete the unreachable ones in a moment.
2544 SmallVector<CallSite, 64> ParsePointNeeded;
2545 for (Instruction &I : instructions(F)) {
2546 // TODO: only the ones with the flag set!
2547 if (NeedsRewrite(I)) {
2548 // NOTE removeUnreachableBlocks() is stronger than
2549 // DominatorTree::isReachableFromEntry(). In other words
2550 // removeUnreachableBlocks can remove some blocks for which
2551 // isReachableFromEntry() returns true.
2552 assert(DT.isReachableFromEntry(I.getParent()) &&
2553 "no unreachable blocks expected");
2554 ParsePointNeeded.push_back(CallSite(&I));
2558 // Return early if no work to do.
2559 if (ParsePointNeeded.empty())
2562 // As a prepass, go ahead and aggressively destroy single entry phi nodes.
2563 // These are created by LCSSA. They have the effect of increasing the size
2564 // of liveness sets for no good reason. It may be harder to do this post
2565 // insertion since relocations and base phis can confuse things.
2566 for (BasicBlock &BB : F)
2567 if (BB.getUniquePredecessor()) {
2569 FoldSingleEntryPHINodes(&BB);
2572 // Before we start introducing relocations, we want to tweak the IR a bit to
2573 // avoid unfortunate code generation effects. The main example is that we
2574 // want to try to make sure the comparison feeding a branch is after any
2575 // safepoints. Otherwise, we end up with a comparison of pre-relocation
2576 // values feeding a branch after relocation. This is semantically correct,
2577 // but results in extra register pressure since both the pre-relocation and
2578 // post-relocation copies must be available in registers. For code without
2579 // relocations this is handled elsewhere, but teaching the scheduler to
2580 // reverse the transform we're about to do would be slightly complex.
2581 // Note: This may extend the live range of the inputs to the icmp and thus
2582 // increase the liveset of any statepoint we move over. This is profitable
2583 // as long as all statepoints are in rare blocks. If we had in-register
2584 // lowering for live values this would be a much safer transform.
2585 auto getConditionInst = [](TerminatorInst *TI) -> Instruction* {
2586 if (auto *BI = dyn_cast<BranchInst>(TI))
2587 if (BI->isConditional())
2588 return dyn_cast<Instruction>(BI->getCondition());
2589 // TODO: Extend this to handle switches
2592 for (BasicBlock &BB : F) {
2593 TerminatorInst *TI = BB.getTerminator();
2594 if (auto *Cond = getConditionInst(TI))
2595 // TODO: Handle more than just ICmps here. We should be able to move
2596 // most instructions without side effects or memory access.
2597 if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) {
2599 Cond->moveBefore(TI);
2603 MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded);
2607 // liveness computation via standard dataflow
2608 // -------------------------------------------------------------------
2610 // TODO: Consider using bitvectors for liveness, the set of potentially
2611 // interesting values should be small and easy to pre-compute.
2613 /// Compute the live-in set for the location rbegin starting from
2614 /// the live-out set of the basic block
2615 static void computeLiveInValues(BasicBlock::reverse_iterator Begin,
2616 BasicBlock::reverse_iterator End,
2617 SetVector<Value *> &LiveTmp) {
2618 for (auto &I : make_range(Begin, End)) {
2619 // KILL/Def - Remove this definition from LiveIn
2622 // Don't consider *uses* in PHI nodes, we handle their contribution to
2623 // predecessor blocks when we seed the LiveOut sets
2624 if (isa<PHINode>(I))
2627 // USE - Add to the LiveIn set for this instruction
2628 for (Value *V : I.operands()) {
2629 assert(!isUnhandledGCPointerType(V->getType()) &&
2630 "support for FCA unimplemented");
2631 if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
2632 // The choice to exclude all things constant here is slightly subtle.
2633 // There are two independent reasons:
2634 // - We assume that things which are constant (from LLVM's definition)
2635 // do not move at runtime. For example, the address of a global
2636 // variable is fixed, even though it's contents may not be.
2637 // - Second, we can't disallow arbitrary inttoptr constants even
2638 // if the language frontend does. Optimization passes are free to
2639 // locally exploit facts without respect to global reachability. This
2640 // can create sections of code which are dynamically unreachable and
2641 // contain just about anything. (see constants.ll in tests)
2648 static void computeLiveOutSeed(BasicBlock *BB, SetVector<Value *> &LiveTmp) {
2649 for (BasicBlock *Succ : successors(BB)) {
2650 for (auto &I : *Succ) {
2651 PHINode *PN = dyn_cast<PHINode>(&I);
2655 Value *V = PN->getIncomingValueForBlock(BB);
2656 assert(!isUnhandledGCPointerType(V->getType()) &&
2657 "support for FCA unimplemented");
2658 if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V))
2664 static SetVector<Value *> computeKillSet(BasicBlock *BB) {
2665 SetVector<Value *> KillSet;
2666 for (Instruction &I : *BB)
2667 if (isHandledGCPointerType(I.getType()))
2673 /// Check that the items in 'Live' dominate 'TI'. This is used as a basic
2674 /// sanity check for the liveness computation.
2675 static void checkBasicSSA(DominatorTree &DT, SetVector<Value *> &Live,
2676 TerminatorInst *TI, bool TermOkay = false) {
2677 for (Value *V : Live) {
2678 if (auto *I = dyn_cast<Instruction>(V)) {
2679 // The terminator can be a member of the LiveOut set. LLVM's definition
2680 // of instruction dominance states that V does not dominate itself. As
2681 // such, we need to special case this to allow it.
2682 if (TermOkay && TI == I)
2684 assert(DT.dominates(I, TI) &&
2685 "basic SSA liveness expectation violated by liveness analysis");
2690 /// Check that all the liveness sets used during the computation of liveness
2691 /// obey basic SSA properties. This is useful for finding cases where we miss
2693 static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data,
2695 checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator());
2696 checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true);
2697 checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator());
2701 static void computeLiveInValues(DominatorTree &DT, Function &F,
2702 GCPtrLivenessData &Data) {
2703 SmallSetVector<BasicBlock *, 32> Worklist;
2705 // Seed the liveness for each individual block
2706 for (BasicBlock &BB : F) {
2707 Data.KillSet[&BB] = computeKillSet(&BB);
2708 Data.LiveSet[&BB].clear();
2709 computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB]);
2712 for (Value *Kill : Data.KillSet[&BB])
2713 assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill");
2716 Data.LiveOut[&BB] = SetVector<Value *>();
2717 computeLiveOutSeed(&BB, Data.LiveOut[&BB]);
2718 Data.LiveIn[&BB] = Data.LiveSet[&BB];
2719 Data.LiveIn[&BB].set_union(Data.LiveOut[&BB]);
2720 Data.LiveIn[&BB].set_subtract(Data.KillSet[&BB]);
2721 if (!Data.LiveIn[&BB].empty())
2722 Worklist.insert(pred_begin(&BB), pred_end(&BB));
2725 // Propagate that liveness until stable
2726 while (!Worklist.empty()) {
2727 BasicBlock *BB = Worklist.pop_back_val();
2729 // Compute our new liveout set, then exit early if it hasn't changed despite
2730 // the contribution of our successor.
2731 SetVector<Value *> LiveOut = Data.LiveOut[BB];
2732 const auto OldLiveOutSize = LiveOut.size();
2733 for (BasicBlock *Succ : successors(BB)) {
2734 assert(Data.LiveIn.count(Succ));
2735 LiveOut.set_union(Data.LiveIn[Succ]);
2737 // assert OutLiveOut is a subset of LiveOut
2738 if (OldLiveOutSize == LiveOut.size()) {
2739 // If the sets are the same size, then we didn't actually add anything
2740 // when unioning our successors LiveIn. Thus, the LiveIn of this block
2744 Data.LiveOut[BB] = LiveOut;
2746 // Apply the effects of this basic block
2747 SetVector<Value *> LiveTmp = LiveOut;
2748 LiveTmp.set_union(Data.LiveSet[BB]);
2749 LiveTmp.set_subtract(Data.KillSet[BB]);
2751 assert(Data.LiveIn.count(BB));
2752 const SetVector<Value *> &OldLiveIn = Data.LiveIn[BB];
2753 // assert: OldLiveIn is a subset of LiveTmp
2754 if (OldLiveIn.size() != LiveTmp.size()) {
2755 Data.LiveIn[BB] = LiveTmp;
2756 Worklist.insert(pred_begin(BB), pred_end(BB));
2758 } // while (!Worklist.empty())
2761 // Sanity check our output against SSA properties. This helps catch any
2762 // missing kills during the above iteration.
2763 for (BasicBlock &BB : F)
2764 checkBasicSSA(DT, Data, BB);
2768 static void findLiveSetAtInst(Instruction *Inst, GCPtrLivenessData &Data,
2769 StatepointLiveSetTy &Out) {
2770 BasicBlock *BB = Inst->getParent();
2772 // Note: The copy is intentional and required
2773 assert(Data.LiveOut.count(BB));
2774 SetVector<Value *> LiveOut = Data.LiveOut[BB];
2776 // We want to handle the statepoint itself oddly. It's
2777 // call result is not live (normal), nor are it's arguments
2778 // (unless they're used again later). This adjustment is
2779 // specifically what we need to relocate
2780 computeLiveInValues(BB->rbegin(), ++Inst->getIterator().getReverse(),
2782 LiveOut.remove(Inst);
2783 Out.insert(LiveOut.begin(), LiveOut.end());
2786 static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
2788 PartiallyConstructedSafepointRecord &Info) {
2789 Instruction *Inst = CS.getInstruction();
2790 StatepointLiveSetTy Updated;
2791 findLiveSetAtInst(Inst, RevisedLivenessData, Updated);
2793 // We may have base pointers which are now live that weren't before. We need
2794 // to update the PointerToBase structure to reflect this.
2795 for (auto V : Updated)
2796 if (Info.PointerToBase.insert({V, V}).second) {
2797 assert(isKnownBaseResult(V) &&
2798 "Can't find base for unexpected live value!");
2803 for (auto V : Updated)
2804 assert(Info.PointerToBase.count(V) &&
2805 "Must be able to find base for live value!");
2808 // Remove any stale base mappings - this can happen since our liveness is
2809 // more precise then the one inherent in the base pointer analysis.
2810 DenseSet<Value *> ToErase;
2811 for (auto KVPair : Info.PointerToBase)
2812 if (!Updated.count(KVPair.first))
2813 ToErase.insert(KVPair.first);
2815 for (auto *V : ToErase)
2816 Info.PointerToBase.erase(V);
2819 for (auto KVPair : Info.PointerToBase)
2820 assert(Updated.count(KVPair.first) && "record for non-live value");
2823 Info.LiveSet = Updated;