1 //===-- StatepointLowering.cpp - SDAGBuilder's statepoint code -----------===//
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 // This file includes support code use by SelectionDAGBuilder when lowering a
11 // statepoint sequence in SelectionDAG IR.
13 //===----------------------------------------------------------------------===//
15 #include "StatepointLowering.h"
16 #include "SelectionDAGBuilder.h"
17 #include "llvm/ADT/SmallSet.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/CodeGen/FunctionLoweringInfo.h"
20 #include "llvm/CodeGen/GCMetadata.h"
21 #include "llvm/CodeGen/GCStrategy.h"
22 #include "llvm/CodeGen/SelectionDAG.h"
23 #include "llvm/CodeGen/StackMaps.h"
24 #include "llvm/IR/CallingConv.h"
25 #include "llvm/IR/Instructions.h"
26 #include "llvm/IR/IntrinsicInst.h"
27 #include "llvm/IR/Intrinsics.h"
28 #include "llvm/IR/Statepoint.h"
29 #include "llvm/Target/TargetLowering.h"
33 #define DEBUG_TYPE "statepoint-lowering"
35 STATISTIC(NumSlotsAllocatedForStatepoints,
36 "Number of stack slots allocated for statepoints");
37 STATISTIC(NumOfStatepoints, "Number of statepoint nodes encountered");
38 STATISTIC(StatepointMaxSlotsRequired,
39 "Maximum number of stack slots required for a singe statepoint");
41 static void pushStackMapConstant(SmallVectorImpl<SDValue>& Ops,
42 SelectionDAGBuilder &Builder, uint64_t Value) {
43 SDLoc L = Builder.getCurSDLoc();
44 Ops.push_back(Builder.DAG.getTargetConstant(StackMaps::ConstantOp, L,
46 Ops.push_back(Builder.DAG.getTargetConstant(Value, L, MVT::i64));
49 void StatepointLoweringState::startNewStatepoint(SelectionDAGBuilder &Builder) {
51 assert(PendingGCRelocateCalls.empty() &&
52 "Trying to visit statepoint before finished processing previous one");
54 NextSlotToAllocate = 0;
55 // Need to resize this on each safepoint - we need the two to stay in
56 // sync and the clear patterns of a SelectionDAGBuilder have no relation
57 // to FunctionLoweringInfo.
58 AllocatedStackSlots.resize(Builder.FuncInfo.StatepointStackSlots.size());
59 for (size_t i = 0; i < AllocatedStackSlots.size(); i++) {
60 AllocatedStackSlots[i] = false;
64 void StatepointLoweringState::clear() {
66 AllocatedStackSlots.clear();
67 assert(PendingGCRelocateCalls.empty() &&
68 "cleared before statepoint sequence completed");
72 StatepointLoweringState::allocateStackSlot(EVT ValueType,
73 SelectionDAGBuilder &Builder) {
75 NumSlotsAllocatedForStatepoints++;
77 // The basic scheme here is to first look for a previously created stack slot
78 // which is not in use (accounting for the fact arbitrary slots may already
79 // be reserved), or to create a new stack slot and use it.
81 // If this doesn't succeed in 40000 iterations, something is seriously wrong
82 for (int i = 0; i < 40000; i++) {
83 assert(Builder.FuncInfo.StatepointStackSlots.size() ==
84 AllocatedStackSlots.size() &&
86 const size_t NumSlots = AllocatedStackSlots.size();
87 assert(NextSlotToAllocate <= NumSlots && "broken invariant");
89 if (NextSlotToAllocate >= NumSlots) {
90 assert(NextSlotToAllocate == NumSlots);
92 if (NumSlots + 1 > StatepointMaxSlotsRequired) {
93 StatepointMaxSlotsRequired = NumSlots + 1;
96 SDValue SpillSlot = Builder.DAG.CreateStackTemporary(ValueType);
97 const unsigned FI = cast<FrameIndexSDNode>(SpillSlot)->getIndex();
98 Builder.FuncInfo.StatepointStackSlots.push_back(FI);
99 AllocatedStackSlots.push_back(true);
102 if (!AllocatedStackSlots[NextSlotToAllocate]) {
103 const int FI = Builder.FuncInfo.StatepointStackSlots[NextSlotToAllocate];
104 AllocatedStackSlots[NextSlotToAllocate] = true;
105 return Builder.DAG.getFrameIndex(FI, ValueType);
107 // Note: We deliberately choose to advance this only on the failing path.
108 // Doing so on the suceeding path involes a bit of complexity that caused a
109 // minor bug previously. Unless performance shows this matters, please
110 // keep this code as simple as possible.
111 NextSlotToAllocate++;
113 llvm_unreachable("infinite loop?");
116 /// Utility function for reservePreviousStackSlotForValue. Tries to find
117 /// stack slot index to which we have spilled value for previous statepoints.
118 /// LookUpDepth specifies maximum DFS depth this function is allowed to look.
119 static Optional<int> findPreviousSpillSlot(const Value *Val,
120 SelectionDAGBuilder &Builder,
122 // Can not look any futher - give up now
123 if (LookUpDepth <= 0)
124 return Optional<int>();
126 // Spill location is known for gc relocates
127 if (isGCRelocate(Val)) {
128 GCRelocateOperands RelocOps(cast<Instruction>(Val));
130 FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap =
131 Builder.FuncInfo.StatepointRelocatedValues[RelocOps.getStatepoint()];
133 auto It = SpillMap.find(RelocOps.getDerivedPtr());
134 if (It == SpillMap.end())
135 return Optional<int>();
140 // Look through bitcast instructions.
141 if (const BitCastInst *Cast = dyn_cast<BitCastInst>(Val)) {
142 return findPreviousSpillSlot(Cast->getOperand(0), Builder, LookUpDepth - 1);
145 // Look through phi nodes
146 // All incoming values should have same known stack slot, otherwise result
148 if (const PHINode *Phi = dyn_cast<PHINode>(Val)) {
149 Optional<int> MergedResult = None;
151 for (auto &IncomingValue : Phi->incoming_values()) {
152 Optional<int> SpillSlot =
153 findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth - 1);
154 if (!SpillSlot.hasValue())
155 return Optional<int>();
157 if (MergedResult.hasValue() && *MergedResult != *SpillSlot)
158 return Optional<int>();
160 MergedResult = SpillSlot;
165 // TODO: We can do better for PHI nodes. In cases like this:
166 // ptr = phi(relocated_pointer, not_relocated_pointer)
168 // We will return that stack slot for ptr is unknown. And later we might
169 // assign different stack slots for ptr and relocated_pointer. This limits
170 // llvm's ability to remove redundant stores.
171 // Unfortunately it's hard to accomplish in current infrastructure.
172 // We use this function to eliminate spill store completely, while
173 // in example we still need to emit store, but instead of any location
174 // we need to use special "preferred" location.
176 // TODO: handle simple updates. If a value is modified and the original
177 // value is no longer live, it would be nice to put the modified value in the
178 // same slot. This allows folding of the memory accesses for some
179 // instructions types (like an increment).
183 // However we need to be careful for cases like this:
187 // Here we want to reserve spill slot for 'i', but not for 'i+1'. If we just
188 // put handling of simple modifications in this function like it's done
189 // for bitcasts we might end up reserving i's slot for 'i+1' because order in
190 // which we visit values is unspecified.
192 // Don't know any information about this instruction
193 return Optional<int>();
196 /// Try to find existing copies of the incoming values in stack slots used for
197 /// statepoint spilling. If we can find a spill slot for the incoming value,
198 /// mark that slot as allocated, and reuse the same slot for this safepoint.
199 /// This helps to avoid series of loads and stores that only serve to resuffle
200 /// values on the stack between calls.
201 static void reservePreviousStackSlotForValue(const Value *IncomingValue,
202 SelectionDAGBuilder &Builder) {
204 SDValue Incoming = Builder.getValue(IncomingValue);
206 if (isa<ConstantSDNode>(Incoming) || isa<FrameIndexSDNode>(Incoming)) {
207 // We won't need to spill this, so no need to check for previously
208 // allocated stack slots
212 SDValue OldLocation = Builder.StatepointLowering.getLocation(Incoming);
213 if (OldLocation.getNode())
214 // duplicates in input
217 const int LookUpDepth = 6;
218 Optional<int> Index =
219 findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth);
220 if (!Index.hasValue())
223 auto Itr = std::find(Builder.FuncInfo.StatepointStackSlots.begin(),
224 Builder.FuncInfo.StatepointStackSlots.end(), *Index);
225 assert(Itr != Builder.FuncInfo.StatepointStackSlots.end() &&
226 "value spilled to the unknown stack slot");
228 // This is one of our dedicated lowering slots
230 std::distance(Builder.FuncInfo.StatepointStackSlots.begin(), Itr);
231 if (Builder.StatepointLowering.isStackSlotAllocated(Offset)) {
232 // stack slot already assigned to someone else, can't use it!
233 // TODO: currently we reserve space for gc arguments after doing
234 // normal allocation for deopt arguments. We should reserve for
235 // _all_ deopt and gc arguments, then start allocating. This
236 // will prevent some moves being inserted when vm state changes,
237 // but gc state doesn't between two calls.
240 // Reserve this stack slot
241 Builder.StatepointLowering.reserveStackSlot(Offset);
243 // Cache this slot so we find it when going through the normal
245 SDValue Loc = Builder.DAG.getTargetFrameIndex(*Index, Incoming.getValueType());
246 Builder.StatepointLowering.setLocation(Incoming, Loc);
249 /// Remove any duplicate (as SDValues) from the derived pointer pairs. This
250 /// is not required for correctness. It's purpose is to reduce the size of
251 /// StackMap section. It has no effect on the number of spill slots required
252 /// or the actual lowering.
253 static void removeDuplicatesGCPtrs(SmallVectorImpl<const Value *> &Bases,
254 SmallVectorImpl<const Value *> &Ptrs,
255 SmallVectorImpl<const Value *> &Relocs,
256 SelectionDAGBuilder &Builder) {
258 // This is horribly ineffecient, but I don't care right now
259 SmallSet<SDValue, 64> Seen;
261 SmallVector<const Value *, 64> NewBases, NewPtrs, NewRelocs;
262 for (size_t i = 0; i < Ptrs.size(); i++) {
263 SDValue SD = Builder.getValue(Ptrs[i]);
264 // Only add non-duplicates
265 if (Seen.count(SD) == 0) {
266 NewBases.push_back(Bases[i]);
267 NewPtrs.push_back(Ptrs[i]);
268 NewRelocs.push_back(Relocs[i]);
272 assert(Bases.size() >= NewBases.size());
273 assert(Ptrs.size() >= NewPtrs.size());
274 assert(Relocs.size() >= NewRelocs.size());
278 assert(Ptrs.size() == Bases.size());
279 assert(Ptrs.size() == Relocs.size());
282 /// Extract call from statepoint, lower it and return pointer to the
283 /// call node. Also update NodeMap so that getValue(statepoint) will
284 /// reference lowered call result
286 lowerCallFromStatepoint(ImmutableStatepoint ISP, MachineBasicBlock *LandingPad,
287 SelectionDAGBuilder &Builder,
288 SmallVectorImpl<SDValue> &PendingExports) {
290 ImmutableCallSite CS(ISP.getCallSite());
292 SDValue ActualCallee = Builder.getValue(ISP.getCalledValue());
294 assert(CS.getCallingConv() != CallingConv::AnyReg &&
295 "anyregcc is not supported on statepoints!");
297 Type *DefTy = ISP.getActualReturnType();
298 bool HasDef = !DefTy->isVoidTy();
300 SDValue ReturnValue, CallEndVal;
301 std::tie(ReturnValue, CallEndVal) = Builder.lowerCallOperands(
302 ISP.getCallSite(), ImmutableStatepoint::CallArgsBeginPos,
303 ISP.getNumCallArgs(), ActualCallee, DefTy, LandingPad,
304 false /* IsPatchPoint */);
306 SDNode *CallEnd = CallEndVal.getNode();
308 // Get a call instruction from the call sequence chain. Tail calls are not
309 // allowed. The following code is essentially reverse engineering X86's
312 // We are expecting DAG to have the following form:
314 // ch = eh_label (only in case of invoke statepoint)
315 // ch, glue = callseq_start ch
316 // ch, glue = X86::Call ch, glue
317 // ch, glue = callseq_end ch, glue
318 // get_return_value ch, glue
320 // get_return_value can either be a CopyFromReg to grab the return value from
321 // %RAX, or it can be a LOAD to load a value returned by reference via a stack
324 if (HasDef && (CallEnd->getOpcode() == ISD::CopyFromReg ||
325 CallEnd->getOpcode() == ISD::LOAD))
326 CallEnd = CallEnd->getOperand(0).getNode();
328 assert(CallEnd->getOpcode() == ISD::CALLSEQ_END && "expected!");
332 // Result value will be used in different basic block for invokes
333 // so we need to export it now. But statepoint call has a different type
334 // than the actuall call. It means that standart exporting mechanism will
335 // create register of the wrong type. So instead we need to create
336 // register with correct type and save value into it manually.
337 // TODO: To eliminate this problem we can remove gc.result intrinsics
338 // completelly and make statepoint call to return a tuple.
339 unsigned Reg = Builder.FuncInfo.CreateRegs(ISP.getActualReturnType());
341 *Builder.DAG.getContext(), Builder.DAG.getTargetLoweringInfo(),
342 Builder.DAG.getDataLayout(), Reg, ISP.getActualReturnType());
343 SDValue Chain = Builder.DAG.getEntryNode();
345 RFV.getCopyToRegs(ReturnValue, Builder.DAG, Builder.getCurSDLoc(), Chain,
347 PendingExports.push_back(Chain);
348 Builder.FuncInfo.ValueMap[CS.getInstruction()] = Reg;
350 // The value of the statepoint itself will be the value of call itself.
351 // We'll replace the actually call node shortly. gc_result will grab
353 Builder.setValue(CS.getInstruction(), ReturnValue);
356 // The token value is never used from here on, just generate a poison value
357 Builder.setValue(CS.getInstruction(),
358 Builder.DAG.getIntPtrConstant(-1, Builder.getCurSDLoc()));
361 return CallEnd->getOperand(0).getNode();
364 /// Callect all gc pointers coming into statepoint intrinsic, clean them up,
365 /// and return two arrays:
366 /// Bases - base pointers incoming to this statepoint
367 /// Ptrs - derived pointers incoming to this statepoint
368 /// Relocs - the gc_relocate corresponding to each base/ptr pair
369 /// Elements of this arrays should be in one-to-one correspondence with each
370 /// other i.e Bases[i], Ptrs[i] are from the same gcrelocate call
371 static void getIncomingStatepointGCValues(
372 SmallVectorImpl<const Value *> &Bases, SmallVectorImpl<const Value *> &Ptrs,
373 SmallVectorImpl<const Value *> &Relocs, ImmutableStatepoint StatepointSite,
374 SelectionDAGBuilder &Builder) {
375 for (GCRelocateOperands relocateOpers : StatepointSite.getRelocates()) {
376 Relocs.push_back(relocateOpers.getUnderlyingCallSite().getInstruction());
377 Bases.push_back(relocateOpers.getBasePtr());
378 Ptrs.push_back(relocateOpers.getDerivedPtr());
381 // Remove any redundant llvm::Values which map to the same SDValue as another
382 // input. Also has the effect of removing duplicates in the original
383 // llvm::Value input list as well. This is a useful optimization for
384 // reducing the size of the StackMap section. It has no other impact.
385 removeDuplicatesGCPtrs(Bases, Ptrs, Relocs, Builder);
387 assert(Bases.size() == Ptrs.size() && Ptrs.size() == Relocs.size());
390 /// Spill a value incoming to the statepoint. It might be either part of
392 /// or gcstate. In both cases unconditionally spill it on the stack unless it
393 /// is a null constant. Return pair with first element being frame index
394 /// containing saved value and second element with outgoing chain from the
396 static std::pair<SDValue, SDValue>
397 spillIncomingStatepointValue(SDValue Incoming, SDValue Chain,
398 SelectionDAGBuilder &Builder) {
399 SDValue Loc = Builder.StatepointLowering.getLocation(Incoming);
401 // Emit new store if we didn't do it for this ptr before
402 if (!Loc.getNode()) {
403 Loc = Builder.StatepointLowering.allocateStackSlot(Incoming.getValueType(),
405 assert(isa<FrameIndexSDNode>(Loc));
406 int Index = cast<FrameIndexSDNode>(Loc)->getIndex();
407 // We use TargetFrameIndex so that isel will not select it into LEA
408 Loc = Builder.DAG.getTargetFrameIndex(Index, Incoming.getValueType());
410 // TODO: We can create TokenFactor node instead of
411 // chaining stores one after another, this may allow
412 // a bit more optimal scheduling for them
413 Chain = Builder.DAG.getStore(Chain, Builder.getCurSDLoc(), Incoming, Loc,
414 MachinePointerInfo::getFixedStack(Index),
417 Builder.StatepointLowering.setLocation(Incoming, Loc);
420 assert(Loc.getNode());
421 return std::make_pair(Loc, Chain);
424 /// Lower a single value incoming to a statepoint node. This value can be
425 /// either a deopt value or a gc value, the handling is the same. We special
426 /// case constants and allocas, then fall back to spilling if required.
427 static void lowerIncomingStatepointValue(SDValue Incoming,
428 SmallVectorImpl<SDValue> &Ops,
429 SelectionDAGBuilder &Builder) {
430 SDValue Chain = Builder.getRoot();
432 if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Incoming)) {
433 // If the original value was a constant, make sure it gets recorded as
434 // such in the stackmap. This is required so that the consumer can
435 // parse any internal format to the deopt state. It also handles null
436 // pointers and other constant pointers in GC states
437 pushStackMapConstant(Ops, Builder, C->getSExtValue());
438 } else if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) {
439 // This handles allocas as arguments to the statepoint (this is only
440 // really meaningful for a deopt value. For GC, we'd be trying to
441 // relocate the address of the alloca itself?)
442 Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
443 Incoming.getValueType()));
445 // Otherwise, locate a spill slot and explicitly spill it so it
446 // can be found by the runtime later. We currently do not support
447 // tracking values through callee saved registers to their eventual
448 // spill location. This would be a useful optimization, but would
449 // need to be optional since it requires a lot of complexity on the
450 // runtime side which not all would support.
451 std::pair<SDValue, SDValue> Res =
452 spillIncomingStatepointValue(Incoming, Chain, Builder);
453 Ops.push_back(Res.first);
457 Builder.DAG.setRoot(Chain);
460 /// Lower deopt state and gc pointer arguments of the statepoint. The actual
461 /// lowering is described in lowerIncomingStatepointValue. This function is
462 /// responsible for lowering everything in the right position and playing some
463 /// tricks to avoid redundant stack manipulation where possible. On
464 /// completion, 'Ops' will contain ready to use operands for machine code
465 /// statepoint. The chain nodes will have already been created and the DAG root
466 /// will be set to the last value spilled (if any were).
467 static void lowerStatepointMetaArgs(SmallVectorImpl<SDValue> &Ops,
468 ImmutableStatepoint StatepointSite,
469 SelectionDAGBuilder &Builder) {
471 // Lower the deopt and gc arguments for this statepoint. Layout will
472 // be: deopt argument length, deopt arguments.., gc arguments...
474 SmallVector<const Value *, 64> Bases, Ptrs, Relocations;
475 getIncomingStatepointGCValues(Bases, Ptrs, Relocations, StatepointSite,
479 // Check that each of the gc pointer and bases we've gotten out of the
480 // safepoint is something the strategy thinks might be a pointer into the GC
481 // heap. This is basically just here to help catch errors during statepoint
482 // insertion. TODO: This should actually be in the Verifier, but we can't get
483 // to the GCStrategy from there (yet).
484 GCStrategy &S = Builder.GFI->getStrategy();
485 for (const Value *V : Bases) {
486 auto Opt = S.isGCManagedPointer(V);
487 if (Opt.hasValue()) {
488 assert(Opt.getValue() &&
489 "non gc managed base pointer found in statepoint");
492 for (const Value *V : Ptrs) {
493 auto Opt = S.isGCManagedPointer(V);
494 if (Opt.hasValue()) {
495 assert(Opt.getValue() &&
496 "non gc managed derived pointer found in statepoint");
499 for (const Value *V : Relocations) {
500 auto Opt = S.isGCManagedPointer(V);
501 if (Opt.hasValue()) {
502 assert(Opt.getValue() && "non gc managed pointer relocated");
507 // Before we actually start lowering (and allocating spill slots for values),
508 // reserve any stack slots which we judge to be profitable to reuse for a
509 // particular value. This is purely an optimization over the code below and
510 // doesn't change semantics at all. It is important for performance that we
511 // reserve slots for both deopt and gc values before lowering either.
512 for (const Value *V : StatepointSite.vm_state_args()) {
513 reservePreviousStackSlotForValue(V, Builder);
515 for (unsigned i = 0; i < Bases.size(); ++i) {
516 reservePreviousStackSlotForValue(Bases[i], Builder);
517 reservePreviousStackSlotForValue(Ptrs[i], Builder);
520 // First, prefix the list with the number of unique values to be
521 // lowered. Note that this is the number of *Values* not the
522 // number of SDValues required to lower them.
523 const int NumVMSArgs = StatepointSite.getNumTotalVMSArgs();
524 pushStackMapConstant(Ops, Builder, NumVMSArgs);
526 assert(NumVMSArgs == std::distance(StatepointSite.vm_state_begin(),
527 StatepointSite.vm_state_end()));
529 // The vm state arguments are lowered in an opaque manner. We do
530 // not know what type of values are contained within. We skip the
531 // first one since that happens to be the total number we lowered
532 // explicitly just above. We could have left it in the loop and
533 // not done it explicitly, but it's far easier to understand this
535 for (const Value *V : StatepointSite.vm_state_args()) {
536 SDValue Incoming = Builder.getValue(V);
537 lowerIncomingStatepointValue(Incoming, Ops, Builder);
540 // Finally, go ahead and lower all the gc arguments. There's no prefixed
541 // length for this one. After lowering, we'll have the base and pointer
542 // arrays interwoven with each (lowered) base pointer immediately followed by
543 // it's (lowered) derived pointer. i.e
544 // (base[0], ptr[0], base[1], ptr[1], ...)
545 for (unsigned i = 0; i < Bases.size(); ++i) {
546 const Value *Base = Bases[i];
547 lowerIncomingStatepointValue(Builder.getValue(Base), Ops, Builder);
549 const Value *Ptr = Ptrs[i];
550 lowerIncomingStatepointValue(Builder.getValue(Ptr), Ops, Builder);
553 // If there are any explicit spill slots passed to the statepoint, record
554 // them, but otherwise do not do anything special. These are user provided
555 // allocas and give control over placement to the consumer. In this case,
556 // it is the contents of the slot which may get updated, not the pointer to
558 for (Value *V : StatepointSite.gc_args()) {
559 SDValue Incoming = Builder.getValue(V);
560 if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) {
561 // This handles allocas as arguments to the statepoint
562 Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
563 Incoming.getValueType()));
567 // Record computed locations for all lowered values.
568 // This can not be embedded in lowering loops as we need to record *all*
569 // values, while previous loops account only values with unique SDValues.
570 const Instruction *StatepointInstr =
571 StatepointSite.getCallSite().getInstruction();
572 FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap =
573 Builder.FuncInfo.StatepointRelocatedValues[StatepointInstr];
575 for (GCRelocateOperands RelocateOpers : StatepointSite.getRelocates()) {
576 const Value *V = RelocateOpers.getDerivedPtr();
577 SDValue SDV = Builder.getValue(V);
578 SDValue Loc = Builder.StatepointLowering.getLocation(SDV);
581 SpillMap[V] = cast<FrameIndexSDNode>(Loc)->getIndex();
583 // Record value as visited, but not spilled. This is case for allocas
584 // and constants. For this values we can avoid emiting spill load while
585 // visiting corresponding gc_relocate.
586 // Actually we do not need to record them in this map at all.
587 // We do this only to check that we are not relocating any unvisited value.
590 // Default llvm mechanisms for exporting values which are used in
591 // different basic blocks does not work for gc relocates.
592 // Note that it would be incorrect to teach llvm that all relocates are
593 // uses of the corresponging values so that it would automatically
594 // export them. Relocates of the spilled values does not use original
596 if (StatepointSite.getCallSite().isInvoke())
597 Builder.ExportFromCurrentBlock(V);
602 void SelectionDAGBuilder::visitStatepoint(const CallInst &CI) {
603 // Check some preconditions for sanity
604 assert(isStatepoint(&CI) &&
605 "function called must be the statepoint function");
607 LowerStatepoint(ImmutableStatepoint(&CI));
610 void SelectionDAGBuilder::LowerStatepoint(
611 ImmutableStatepoint ISP, MachineBasicBlock *LandingPad /*=nullptr*/) {
612 // The basic scheme here is that information about both the original call and
613 // the safepoint is encoded in the CallInst. We create a temporary call and
614 // lower it, then reverse engineer the calling sequence.
618 StatepointLowering.startNewStatepoint(*this);
620 ImmutableCallSite CS(ISP.getCallSite());
623 // Consistency check. Don't do this for invokes. It would be too
624 // expensive to preserve this information across different basic blocks
625 if (!CS.isInvoke()) {
626 for (const User *U : CS->users()) {
627 const CallInst *Call = cast<CallInst>(U);
628 if (isGCRelocate(Call))
629 StatepointLowering.scheduleRelocCall(*Call);
635 // If this is a malformed statepoint, report it early to simplify debugging.
636 // This should catch any IR level mistake that's made when constructing or
637 // transforming statepoints.
640 // Check that the associated GCStrategy expects to encounter statepoints.
641 assert(GFI->getStrategy().useStatepoints() &&
642 "GCStrategy does not expect to encounter statepoints");
645 // Lower statepoint vmstate and gcstate arguments
646 SmallVector<SDValue, 10> LoweredMetaArgs;
647 lowerStatepointMetaArgs(LoweredMetaArgs, ISP, *this);
649 // Get call node, we will replace it later with statepoint
651 lowerCallFromStatepoint(ISP, LandingPad, *this, PendingExports);
653 // Construct the actual GC_TRANSITION_START, STATEPOINT, and GC_TRANSITION_END
654 // nodes with all the appropriate arguments and return values.
656 // Call Node: Chain, Target, {Args}, RegMask, [Glue]
657 SDValue Chain = CallNode->getOperand(0);
660 bool CallHasIncomingGlue = CallNode->getGluedNode();
661 if (CallHasIncomingGlue) {
662 // Glue is always last operand
663 Glue = CallNode->getOperand(CallNode->getNumOperands() - 1);
666 // Build the GC_TRANSITION_START node if necessary.
668 // The operands to the GC_TRANSITION_{START,END} nodes are laid out in the
669 // order in which they appear in the call to the statepoint intrinsic. If
670 // any of the operands is a pointer-typed, that operand is immediately
671 // followed by a SRCVALUE for the pointer that may be used during lowering
672 // (e.g. to form MachinePointerInfo values for loads/stores).
673 const bool IsGCTransition =
674 (ISP.getFlags() & (uint64_t)StatepointFlags::GCTransition) ==
675 (uint64_t)StatepointFlags::GCTransition;
676 if (IsGCTransition) {
677 SmallVector<SDValue, 8> TSOps;
680 TSOps.push_back(Chain);
682 // Add GC transition arguments
683 for (const Value *V : ISP.gc_transition_args()) {
684 TSOps.push_back(getValue(V));
685 if (V->getType()->isPointerTy())
686 TSOps.push_back(DAG.getSrcValue(V));
689 // Add glue if necessary
690 if (CallHasIncomingGlue)
691 TSOps.push_back(Glue);
693 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
695 SDValue GCTransitionStart =
696 DAG.getNode(ISD::GC_TRANSITION_START, getCurSDLoc(), NodeTys, TSOps);
698 Chain = GCTransitionStart.getValue(0);
699 Glue = GCTransitionStart.getValue(1);
702 // TODO: Currently, all of these operands are being marked as read/write in
703 // PrologEpilougeInserter.cpp, we should special case the VMState arguments
704 // and flags to be read-only.
705 SmallVector<SDValue, 40> Ops;
707 // Add the <id> and <numBytes> constants.
708 Ops.push_back(DAG.getTargetConstant(ISP.getID(), getCurSDLoc(), MVT::i64));
710 DAG.getTargetConstant(ISP.getNumPatchBytes(), getCurSDLoc(), MVT::i32));
712 // Calculate and push starting position of vmstate arguments
713 // Get number of arguments incoming directly into call node
714 unsigned NumCallRegArgs =
715 CallNode->getNumOperands() - (CallHasIncomingGlue ? 4 : 3);
716 Ops.push_back(DAG.getTargetConstant(NumCallRegArgs, getCurSDLoc(), MVT::i32));
719 SDValue CallTarget = SDValue(CallNode->getOperand(1).getNode(), 0);
720 Ops.push_back(CallTarget);
722 // Add call arguments
723 // Get position of register mask in the call
724 SDNode::op_iterator RegMaskIt;
725 if (CallHasIncomingGlue)
726 RegMaskIt = CallNode->op_end() - 2;
728 RegMaskIt = CallNode->op_end() - 1;
729 Ops.insert(Ops.end(), CallNode->op_begin() + 2, RegMaskIt);
731 // Add a constant argument for the calling convention
732 pushStackMapConstant(Ops, *this, CS.getCallingConv());
734 // Add a constant argument for the flags
735 uint64_t Flags = ISP.getFlags();
737 ((Flags & ~(uint64_t)StatepointFlags::MaskAll) == 0)
738 && "unknown flag used");
739 pushStackMapConstant(Ops, *this, Flags);
741 // Insert all vmstate and gcstate arguments
742 Ops.insert(Ops.end(), LoweredMetaArgs.begin(), LoweredMetaArgs.end());
744 // Add register mask from call node
745 Ops.push_back(*RegMaskIt);
748 Ops.push_back(Chain);
750 // Same for the glue, but we add it only if original call had it
754 // Compute return values. Provide a glue output since we consume one as
755 // input. This allows someone else to chain off us as needed.
756 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
758 SDNode *StatepointMCNode =
759 DAG.getMachineNode(TargetOpcode::STATEPOINT, getCurSDLoc(), NodeTys, Ops);
761 SDNode *SinkNode = StatepointMCNode;
763 // Build the GC_TRANSITION_END node if necessary.
765 // See the comment above regarding GC_TRANSITION_START for the layout of
766 // the operands to the GC_TRANSITION_END node.
767 if (IsGCTransition) {
768 SmallVector<SDValue, 8> TEOps;
771 TEOps.push_back(SDValue(StatepointMCNode, 0));
773 // Add GC transition arguments
774 for (const Value *V : ISP.gc_transition_args()) {
775 TEOps.push_back(getValue(V));
776 if (V->getType()->isPointerTy())
777 TEOps.push_back(DAG.getSrcValue(V));
781 TEOps.push_back(SDValue(StatepointMCNode, 1));
783 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
785 SDValue GCTransitionStart =
786 DAG.getNode(ISD::GC_TRANSITION_END, getCurSDLoc(), NodeTys, TEOps);
788 SinkNode = GCTransitionStart.getNode();
791 // Replace original call
792 DAG.ReplaceAllUsesWith(CallNode, SinkNode); // This may update Root
793 // Remove originall call node
794 DAG.DeleteNode(CallNode);
796 // DON'T set the root - under the assumption that it's already set past the
797 // inserted node we created.
799 // TODO: A better future implementation would be to emit a single variable
800 // argument, variable return value STATEPOINT node here and then hookup the
801 // return value of each gc.relocate to the respective output of the
802 // previously emitted STATEPOINT value. Unfortunately, this doesn't appear
803 // to actually be possible today.
806 void SelectionDAGBuilder::visitGCResult(const CallInst &CI) {
807 // The result value of the gc_result is simply the result of the actual
808 // call. We've already emitted this, so just grab the value.
809 Instruction *I = cast<Instruction>(CI.getArgOperand(0));
810 assert(isStatepoint(I) && "first argument must be a statepoint token");
812 if (isa<InvokeInst>(I)) {
813 // For invokes we should have stored call result in a virtual register.
814 // We can not use default getValue() functionality to copy value from this
815 // register because statepoint and actuall call return types can be
816 // different, and getValue() will use CopyFromReg of the wrong type,
817 // which is always i32 in our case.
818 PointerType *CalleeType = cast<PointerType>(
819 ImmutableStatepoint(I).getCalledValue()->getType());
821 cast<FunctionType>(CalleeType->getElementType())->getReturnType();
822 SDValue CopyFromReg = getCopyFromRegs(I, RetTy);
824 assert(CopyFromReg.getNode());
825 setValue(&CI, CopyFromReg);
827 setValue(&CI, getValue(I));
831 void SelectionDAGBuilder::visitGCRelocate(const CallInst &CI) {
832 GCRelocateOperands RelocateOpers(&CI);
836 // We skip this check for invoke statepoints. It would be too expensive to
837 // preserve validation info through different basic blocks.
838 if (!RelocateOpers.isTiedToInvoke()) {
839 StatepointLowering.relocCallVisited(CI);
843 const Value *DerivedPtr = RelocateOpers.getDerivedPtr();
844 SDValue SD = getValue(DerivedPtr);
846 FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap =
847 FuncInfo.StatepointRelocatedValues[RelocateOpers.getStatepoint()];
849 // We should have recorded location for this pointer
850 assert(SpillMap.count(DerivedPtr) && "Relocating not lowered gc value");
851 Optional<int> DerivedPtrLocation = SpillMap[DerivedPtr];
853 // We didn't need to spill these special cases (constants and allocas).
854 // See the handling in spillIncomingValueForStatepoint for detail.
855 if (!DerivedPtrLocation) {
860 SDValue SpillSlot = DAG.getTargetFrameIndex(*DerivedPtrLocation,
863 // Be conservative: flush all pending loads
864 // TODO: Probably we can be less restrictive on this,
865 // it may allow more scheduling opprtunities
866 SDValue Chain = getRoot();
869 DAG.getLoad(SpillSlot.getValueType(), getCurSDLoc(), Chain, SpillSlot,
870 MachinePointerInfo::getFixedStack(*DerivedPtrLocation),
871 false, false, false, 0);
873 // Again, be conservative, don't emit pending loads
874 DAG.setRoot(SpillLoad.getValue(1));
876 assert(SpillLoad.getNode());
877 setValue(&CI, SpillLoad);