1 //===- StatepointLowering.cpp - SDAGBuilder's statepoint code -------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file includes support code use by SelectionDAGBuilder when lowering a
11 // statepoint sequence in SelectionDAG IR.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "StatepointLowering.h"
16 #include "SelectionDAGBuilder.h"
17 #include "llvm/ADT/ArrayRef.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/None.h"
20 #include "llvm/ADT/Optional.h"
21 #include "llvm/ADT/STLExtras.h"
22 #include "llvm/ADT/SmallVector.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/CodeGen/FunctionLoweringInfo.h"
25 #include "llvm/CodeGen/GCMetadata.h"
26 #include "llvm/CodeGen/GCStrategy.h"
27 #include "llvm/CodeGen/ISDOpcodes.h"
28 #include "llvm/CodeGen/MachineFrameInfo.h"
29 #include "llvm/CodeGen/MachineFunction.h"
30 #include "llvm/CodeGen/MachineMemOperand.h"
31 #include "llvm/CodeGen/RuntimeLibcalls.h"
32 #include "llvm/CodeGen/SelectionDAG.h"
33 #include "llvm/CodeGen/SelectionDAGNodes.h"
34 #include "llvm/CodeGen/StackMaps.h"
35 #include "llvm/CodeGen/TargetLowering.h"
36 #include "llvm/CodeGen/TargetOpcodes.h"
37 #include "llvm/IR/CallingConv.h"
38 #include "llvm/IR/DerivedTypes.h"
39 #include "llvm/IR/Instruction.h"
40 #include "llvm/IR/Instructions.h"
41 #include "llvm/IR/LLVMContext.h"
42 #include "llvm/IR/Statepoint.h"
43 #include "llvm/IR/Type.h"
44 #include "llvm/Support/Casting.h"
45 #include "llvm/Support/MachineValueType.h"
46 #include "llvm/Target/TargetMachine.h"
47 #include "llvm/Target/TargetOptions.h"
48 #include <cassert>
49 #include <cstddef>
50 #include <cstdint>
51 #include <iterator>
52 #include <tuple>
53 #include <utility>
54
55 using namespace llvm;
56
57 #define DEBUG_TYPE "statepoint-lowering"
58
59 STATISTIC(NumSlotsAllocatedForStatepoints,
60 "Number of stack slots allocated for statepoints");
61 STATISTIC(NumOfStatepoints, "Number of statepoint nodes encountered");
62 STATISTIC(StatepointMaxSlotsRequired,
63 "Maximum number of stack slots required for a singe statepoint");
64
pushStackMapConstant(SmallVectorImpl<SDValue> & Ops,SelectionDAGBuilder & Builder,uint64_t Value)65 static void pushStackMapConstant(SmallVectorImpl<SDValue>& Ops,
66 SelectionDAGBuilder &Builder, uint64_t Value) {
67 SDLoc L = Builder.getCurSDLoc();
68 Ops.push_back(Builder.DAG.getTargetConstant(StackMaps::ConstantOp, L,
69 MVT::i64));
70 Ops.push_back(Builder.DAG.getTargetConstant(Value, L, MVT::i64));
71 }
72
startNewStatepoint(SelectionDAGBuilder & Builder)73 void StatepointLoweringState::startNewStatepoint(SelectionDAGBuilder &Builder) {
74 // Consistency check
75 assert(PendingGCRelocateCalls.empty() &&
76 "Trying to visit statepoint before finished processing previous one");
77 Locations.clear();
78 NextSlotToAllocate = 0;
79 // Need to resize this on each safepoint - we need the two to stay in sync and
80 // the clear patterns of a SelectionDAGBuilder have no relation to
81 // FunctionLoweringInfo. Also need to ensure used bits get cleared.
82 AllocatedStackSlots.clear();
83 AllocatedStackSlots.resize(Builder.FuncInfo.StatepointStackSlots.size());
84 }
85
clear()86 void StatepointLoweringState::clear() {
87 Locations.clear();
88 AllocatedStackSlots.clear();
89 assert(PendingGCRelocateCalls.empty() &&
90 "cleared before statepoint sequence completed");
91 }
92
93 SDValue
allocateStackSlot(EVT ValueType,SelectionDAGBuilder & Builder)94 StatepointLoweringState::allocateStackSlot(EVT ValueType,
95 SelectionDAGBuilder &Builder) {
96 NumSlotsAllocatedForStatepoints++;
97 MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo();
98
99 unsigned SpillSize = ValueType.getStoreSize();
100 assert((SpillSize * 8) == ValueType.getSizeInBits() && "Size not in bytes?");
101
102 // First look for a previously created stack slot which is not in
103 // use (accounting for the fact arbitrary slots may already be
104 // reserved), or to create a new stack slot and use it.
105
106 const size_t NumSlots = AllocatedStackSlots.size();
107 assert(NextSlotToAllocate <= NumSlots && "Broken invariant");
108
109 assert(AllocatedStackSlots.size() ==
110 Builder.FuncInfo.StatepointStackSlots.size() &&
111 "Broken invariant");
112
113 for (; NextSlotToAllocate < NumSlots; NextSlotToAllocate++) {
114 if (!AllocatedStackSlots.test(NextSlotToAllocate)) {
115 const int FI = Builder.FuncInfo.StatepointStackSlots[NextSlotToAllocate];
116 if (MFI.getObjectSize(FI) == SpillSize) {
117 AllocatedStackSlots.set(NextSlotToAllocate);
118 // TODO: Is ValueType the right thing to use here?
119 return Builder.DAG.getFrameIndex(FI, ValueType);
120 }
121 }
122 }
123
124 // Couldn't find a free slot, so create a new one:
125
126 SDValue SpillSlot = Builder.DAG.CreateStackTemporary(ValueType);
127 const unsigned FI = cast<FrameIndexSDNode>(SpillSlot)->getIndex();
128 MFI.markAsStatepointSpillSlotObjectIndex(FI);
129
130 Builder.FuncInfo.StatepointStackSlots.push_back(FI);
131 AllocatedStackSlots.resize(AllocatedStackSlots.size()+1, true);
132 assert(AllocatedStackSlots.size() ==
133 Builder.FuncInfo.StatepointStackSlots.size() &&
134 "Broken invariant");
135
136 StatepointMaxSlotsRequired.updateMax(
137 Builder.FuncInfo.StatepointStackSlots.size());
138
139 return SpillSlot;
140 }
141
142 /// Utility function for reservePreviousStackSlotForValue. Tries to find
143 /// stack slot index to which we have spilled value for previous statepoints.
144 /// LookUpDepth specifies maximum DFS depth this function is allowed to look.
findPreviousSpillSlot(const Value * Val,SelectionDAGBuilder & Builder,int LookUpDepth)145 static Optional<int> findPreviousSpillSlot(const Value *Val,
146 SelectionDAGBuilder &Builder,
147 int LookUpDepth) {
148 // Can not look any further - give up now
149 if (LookUpDepth <= 0)
150 return None;
151
152 // Spill location is known for gc relocates
153 if (const auto *Relocate = dyn_cast<GCRelocateInst>(Val)) {
154 const auto &SpillMap =
155 Builder.FuncInfo.StatepointSpillMaps[Relocate->getStatepoint()];
156
157 auto It = SpillMap.find(Relocate->getDerivedPtr());
158 if (It == SpillMap.end())
159 return None;
160
161 return It->second;
162 }
163
164 // Look through bitcast instructions.
165 if (const BitCastInst *Cast = dyn_cast<BitCastInst>(Val))
166 return findPreviousSpillSlot(Cast->getOperand(0), Builder, LookUpDepth - 1);
167
168 // Look through phi nodes
169 // All incoming values should have same known stack slot, otherwise result
170 // is unknown.
171 if (const PHINode *Phi = dyn_cast<PHINode>(Val)) {
172 Optional<int> MergedResult = None;
173
174 for (auto &IncomingValue : Phi->incoming_values()) {
175 Optional<int> SpillSlot =
176 findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth - 1);
177 if (!SpillSlot.hasValue())
178 return None;
179
180 if (MergedResult.hasValue() && *MergedResult != *SpillSlot)
181 return None;
182
183 MergedResult = SpillSlot;
184 }
185 return MergedResult;
186 }
187
188 // TODO: We can do better for PHI nodes. In cases like this:
189 // ptr = phi(relocated_pointer, not_relocated_pointer)
190 // statepoint(ptr)
191 // We will return that stack slot for ptr is unknown. And later we might
192 // assign different stack slots for ptr and relocated_pointer. This limits
193 // llvm's ability to remove redundant stores.
194 // Unfortunately it's hard to accomplish in current infrastructure.
195 // We use this function to eliminate spill store completely, while
196 // in example we still need to emit store, but instead of any location
197 // we need to use special "preferred" location.
198
199 // TODO: handle simple updates. If a value is modified and the original
200 // value is no longer live, it would be nice to put the modified value in the
201 // same slot. This allows folding of the memory accesses for some
202 // instructions types (like an increment).
203 // statepoint (i)
204 // i1 = i+1
205 // statepoint (i1)
206 // However we need to be careful for cases like this:
207 // statepoint(i)
208 // i1 = i+1
209 // statepoint(i, i1)
210 // Here we want to reserve spill slot for 'i', but not for 'i+1'. If we just
211 // put handling of simple modifications in this function like it's done
212 // for bitcasts we might end up reserving i's slot for 'i+1' because order in
213 // which we visit values is unspecified.
214
215 // Don't know any information about this instruction
216 return None;
217 }
218
219 /// Try to find existing copies of the incoming values in stack slots used for
220 /// statepoint spilling. If we can find a spill slot for the incoming value,
221 /// mark that slot as allocated, and reuse the same slot for this safepoint.
222 /// This helps to avoid series of loads and stores that only serve to reshuffle
223 /// values on the stack between calls.
reservePreviousStackSlotForValue(const Value * IncomingValue,SelectionDAGBuilder & Builder)224 static void reservePreviousStackSlotForValue(const Value *IncomingValue,
225 SelectionDAGBuilder &Builder) {
226 SDValue Incoming = Builder.getValue(IncomingValue);
227
228 if (isa<ConstantSDNode>(Incoming) || isa<FrameIndexSDNode>(Incoming)) {
229 // We won't need to spill this, so no need to check for previously
230 // allocated stack slots
231 return;
232 }
233
234 SDValue OldLocation = Builder.StatepointLowering.getLocation(Incoming);
235 if (OldLocation.getNode())
236 // Duplicates in input
237 return;
238
239 const int LookUpDepth = 6;
240 Optional<int> Index =
241 findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth);
242 if (!Index.hasValue())
243 return;
244
245 const auto &StatepointSlots = Builder.FuncInfo.StatepointStackSlots;
246
247 auto SlotIt = find(StatepointSlots, *Index);
248 assert(SlotIt != StatepointSlots.end() &&
249 "Value spilled to the unknown stack slot");
250
251 // This is one of our dedicated lowering slots
252 const int Offset = std::distance(StatepointSlots.begin(), SlotIt);
253 if (Builder.StatepointLowering.isStackSlotAllocated(Offset)) {
254 // stack slot already assigned to someone else, can't use it!
255 // TODO: currently we reserve space for gc arguments after doing
256 // normal allocation for deopt arguments. We should reserve for
257 // _all_ deopt and gc arguments, then start allocating. This
258 // will prevent some moves being inserted when vm state changes,
259 // but gc state doesn't between two calls.
260 return;
261 }
262 // Reserve this stack slot
263 Builder.StatepointLowering.reserveStackSlot(Offset);
264
265 // Cache this slot so we find it when going through the normal
266 // assignment loop.
267 SDValue Loc =
268 Builder.DAG.getTargetFrameIndex(*Index, Builder.getFrameIndexTy());
269 Builder.StatepointLowering.setLocation(Incoming, Loc);
270 }
271
272 /// Remove any duplicate (as SDValues) from the derived pointer pairs. This
273 /// is not required for correctness. It's purpose is to reduce the size of
274 /// StackMap section. It has no effect on the number of spill slots required
275 /// or the actual lowering.
276 static void
removeDuplicateGCPtrs(SmallVectorImpl<const Value * > & Bases,SmallVectorImpl<const Value * > & Ptrs,SmallVectorImpl<const GCRelocateInst * > & Relocs,SelectionDAGBuilder & Builder,FunctionLoweringInfo::StatepointSpillMap & SSM)277 removeDuplicateGCPtrs(SmallVectorImpl<const Value *> &Bases,
278 SmallVectorImpl<const Value *> &Ptrs,
279 SmallVectorImpl<const GCRelocateInst *> &Relocs,
280 SelectionDAGBuilder &Builder,
281 FunctionLoweringInfo::StatepointSpillMap &SSM) {
282 DenseMap<SDValue, const Value *> Seen;
283
284 SmallVector<const Value *, 64> NewBases, NewPtrs;
285 SmallVector<const GCRelocateInst *, 64> NewRelocs;
286 for (size_t i = 0, e = Ptrs.size(); i < e; i++) {
287 SDValue SD = Builder.getValue(Ptrs[i]);
288 auto SeenIt = Seen.find(SD);
289
290 if (SeenIt == Seen.end()) {
291 // Only add non-duplicates
292 NewBases.push_back(Bases[i]);
293 NewPtrs.push_back(Ptrs[i]);
294 NewRelocs.push_back(Relocs[i]);
295 Seen[SD] = Ptrs[i];
296 } else {
297 // Duplicate pointer found, note in SSM and move on:
298 SSM.DuplicateMap[Ptrs[i]] = SeenIt->second;
299 }
300 }
301 assert(Bases.size() >= NewBases.size());
302 assert(Ptrs.size() >= NewPtrs.size());
303 assert(Relocs.size() >= NewRelocs.size());
304 Bases = NewBases;
305 Ptrs = NewPtrs;
306 Relocs = NewRelocs;
307 assert(Ptrs.size() == Bases.size());
308 assert(Ptrs.size() == Relocs.size());
309 }
310
311 /// Extract call from statepoint, lower it and return pointer to the
312 /// call node. Also update NodeMap so that getValue(statepoint) will
313 /// reference lowered call result
lowerCallFromStatepointLoweringInfo(SelectionDAGBuilder::StatepointLoweringInfo & SI,SelectionDAGBuilder & Builder,SmallVectorImpl<SDValue> & PendingExports)314 static std::pair<SDValue, SDNode *> lowerCallFromStatepointLoweringInfo(
315 SelectionDAGBuilder::StatepointLoweringInfo &SI,
316 SelectionDAGBuilder &Builder, SmallVectorImpl<SDValue> &PendingExports) {
317 SDValue ReturnValue, CallEndVal;
318 std::tie(ReturnValue, CallEndVal) =
319 Builder.lowerInvokable(SI.CLI, SI.EHPadBB);
320 SDNode *CallEnd = CallEndVal.getNode();
321
322 // Get a call instruction from the call sequence chain. Tail calls are not
323 // allowed. The following code is essentially reverse engineering X86's
324 // LowerCallTo.
325 //
326 // We are expecting DAG to have the following form:
327 //
328 // ch = eh_label (only in case of invoke statepoint)
329 // ch, glue = callseq_start ch
330 // ch, glue = X86::Call ch, glue
331 // ch, glue = callseq_end ch, glue
332 // get_return_value ch, glue
333 //
334 // get_return_value can either be a sequence of CopyFromReg instructions
335 // to grab the return value from the return register(s), or it can be a LOAD
336 // to load a value returned by reference via a stack slot.
337
338 bool HasDef = !SI.CLI.RetTy->isVoidTy();
339 if (HasDef) {
340 if (CallEnd->getOpcode() == ISD::LOAD)
341 CallEnd = CallEnd->getOperand(0).getNode();
342 else
343 while (CallEnd->getOpcode() == ISD::CopyFromReg)
344 CallEnd = CallEnd->getOperand(0).getNode();
345 }
346
347 assert(CallEnd->getOpcode() == ISD::CALLSEQ_END && "expected!");
348 return std::make_pair(ReturnValue, CallEnd->getOperand(0).getNode());
349 }
350
351 /// Spill a value incoming to the statepoint. It might be either part of
352 /// vmstate
353 /// or gcstate. In both cases unconditionally spill it on the stack unless it
354 /// is a null constant. Return pair with first element being frame index
355 /// containing saved value and second element with outgoing chain from the
356 /// emitted store
357 static std::pair<SDValue, SDValue>
spillIncomingStatepointValue(SDValue Incoming,SDValue Chain,SelectionDAGBuilder & Builder)358 spillIncomingStatepointValue(SDValue Incoming, SDValue Chain,
359 SelectionDAGBuilder &Builder) {
360 SDValue Loc = Builder.StatepointLowering.getLocation(Incoming);
361
362 // Emit new store if we didn't do it for this ptr before
363 if (!Loc.getNode()) {
364 Loc = Builder.StatepointLowering.allocateStackSlot(Incoming.getValueType(),
365 Builder);
366 int Index = cast<FrameIndexSDNode>(Loc)->getIndex();
367 // We use TargetFrameIndex so that isel will not select it into LEA
368 Loc = Builder.DAG.getTargetFrameIndex(Index, Builder.getFrameIndexTy());
369
370 // TODO: We can create TokenFactor node instead of
371 // chaining stores one after another, this may allow
372 // a bit more optimal scheduling for them
373
374 #ifndef NDEBUG
375 // Right now we always allocate spill slots that are of the same
376 // size as the value we're about to spill (the size of spillee can
377 // vary since we spill vectors of pointers too). At some point we
378 // can consider allowing spills of smaller values to larger slots
379 // (i.e. change the '==' in the assert below to a '>=').
380 MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo();
381 assert((MFI.getObjectSize(Index) * 8) == Incoming.getValueSizeInBits() &&
382 "Bad spill: stack slot does not match!");
383 #endif
384
385 Chain = Builder.DAG.getStore(Chain, Builder.getCurSDLoc(), Incoming, Loc,
386 MachinePointerInfo::getFixedStack(
387 Builder.DAG.getMachineFunction(), Index));
388
389 Builder.StatepointLowering.setLocation(Incoming, Loc);
390 }
391
392 assert(Loc.getNode());
393 return std::make_pair(Loc, Chain);
394 }
395
396 /// Lower a single value incoming to a statepoint node. This value can be
397 /// either a deopt value or a gc value, the handling is the same. We special
398 /// case constants and allocas, then fall back to spilling if required.
lowerIncomingStatepointValue(SDValue Incoming,bool LiveInOnly,SmallVectorImpl<SDValue> & Ops,SelectionDAGBuilder & Builder)399 static void lowerIncomingStatepointValue(SDValue Incoming, bool LiveInOnly,
400 SmallVectorImpl<SDValue> &Ops,
401 SelectionDAGBuilder &Builder) {
402 SDValue Chain = Builder.getRoot();
403
404 if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Incoming)) {
405 // If the original value was a constant, make sure it gets recorded as
406 // such in the stackmap. This is required so that the consumer can
407 // parse any internal format to the deopt state. It also handles null
408 // pointers and other constant pointers in GC states. Note the constant
409 // vectors do not appear to actually hit this path and that anything larger
410 // than an i64 value (not type!) will fail asserts here.
411 pushStackMapConstant(Ops, Builder, C->getSExtValue());
412 } else if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) {
413 // This handles allocas as arguments to the statepoint (this is only
414 // really meaningful for a deopt value. For GC, we'd be trying to
415 // relocate the address of the alloca itself?)
416 assert(Incoming.getValueType() == Builder.getFrameIndexTy() &&
417 "Incoming value is a frame index!");
418 Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
419 Builder.getFrameIndexTy()));
420 } else if (LiveInOnly) {
421 // If this value is live in (not live-on-return, or live-through), we can
422 // treat it the same way patchpoint treats it's "live in" values. We'll
423 // end up folding some of these into stack references, but they'll be
424 // handled by the register allocator. Note that we do not have the notion
425 // of a late use so these values might be placed in registers which are
426 // clobbered by the call. This is fine for live-in.
427 Ops.push_back(Incoming);
428 } else {
429 // Otherwise, locate a spill slot and explicitly spill it so it
430 // can be found by the runtime later. We currently do not support
431 // tracking values through callee saved registers to their eventual
432 // spill location. This would be a useful optimization, but would
433 // need to be optional since it requires a lot of complexity on the
434 // runtime side which not all would support.
435 auto Res = spillIncomingStatepointValue(Incoming, Chain, Builder);
436 Ops.push_back(Res.first);
437 Chain = Res.second;
438 }
439
440 Builder.DAG.setRoot(Chain);
441 }
442
443 /// Lower deopt state and gc pointer arguments of the statepoint. The actual
444 /// lowering is described in lowerIncomingStatepointValue. This function is
445 /// responsible for lowering everything in the right position and playing some
446 /// tricks to avoid redundant stack manipulation where possible. On
447 /// completion, 'Ops' will contain ready to use operands for machine code
448 /// statepoint. The chain nodes will have already been created and the DAG root
449 /// will be set to the last value spilled (if any were).
450 static void
lowerStatepointMetaArgs(SmallVectorImpl<SDValue> & Ops,SelectionDAGBuilder::StatepointLoweringInfo & SI,SelectionDAGBuilder & Builder)451 lowerStatepointMetaArgs(SmallVectorImpl<SDValue> &Ops,
452 SelectionDAGBuilder::StatepointLoweringInfo &SI,
453 SelectionDAGBuilder &Builder) {
454 // Lower the deopt and gc arguments for this statepoint. Layout will be:
455 // deopt argument length, deopt arguments.., gc arguments...
456 #ifndef NDEBUG
457 if (auto *GFI = Builder.GFI) {
458 // Check that each of the gc pointer and bases we've gotten out of the
459 // safepoint is something the strategy thinks might be a pointer (or vector
460 // of pointers) into the GC heap. This is basically just here to help catch
461 // errors during statepoint insertion. TODO: This should actually be in the
462 // Verifier, but we can't get to the GCStrategy from there (yet).
463 GCStrategy &S = GFI->getStrategy();
464 for (const Value *V : SI.Bases) {
465 auto Opt = S.isGCManagedPointer(V->getType()->getScalarType());
466 if (Opt.hasValue()) {
467 assert(Opt.getValue() &&
468 "non gc managed base pointer found in statepoint");
469 }
470 }
471 for (const Value *V : SI.Ptrs) {
472 auto Opt = S.isGCManagedPointer(V->getType()->getScalarType());
473 if (Opt.hasValue()) {
474 assert(Opt.getValue() &&
475 "non gc managed derived pointer found in statepoint");
476 }
477 }
478 assert(SI.Bases.size() == SI.Ptrs.size() && "Pointer without base!");
479 } else {
480 assert(SI.Bases.empty() && "No gc specified, so cannot relocate pointers!");
481 assert(SI.Ptrs.empty() && "No gc specified, so cannot relocate pointers!");
482 }
483 #endif
484
485 // Figure out what lowering strategy we're going to use for each part
486 // Note: Is is conservatively correct to lower both "live-in" and "live-out"
487 // as "live-through". A "live-through" variable is one which is "live-in",
488 // "live-out", and live throughout the lifetime of the call (i.e. we can find
489 // it from any PC within the transitive callee of the statepoint). In
490 // particular, if the callee spills callee preserved registers we may not
491 // be able to find a value placed in that register during the call. This is
492 // fine for live-out, but not for live-through. If we were willing to make
493 // assumptions about the code generator producing the callee, we could
494 // potentially allow live-through values in callee saved registers.
495 const bool LiveInDeopt =
496 SI.StatepointFlags & (uint64_t)StatepointFlags::DeoptLiveIn;
497
498 auto isGCValue =[&](const Value *V) {
499 return is_contained(SI.Ptrs, V) || is_contained(SI.Bases, V);
500 };
501
502 // Before we actually start lowering (and allocating spill slots for values),
503 // reserve any stack slots which we judge to be profitable to reuse for a
504 // particular value. This is purely an optimization over the code below and
505 // doesn't change semantics at all. It is important for performance that we
506 // reserve slots for both deopt and gc values before lowering either.
507 for (const Value *V : SI.DeoptState) {
508 if (!LiveInDeopt || isGCValue(V))
509 reservePreviousStackSlotForValue(V, Builder);
510 }
511 for (unsigned i = 0; i < SI.Bases.size(); ++i) {
512 reservePreviousStackSlotForValue(SI.Bases[i], Builder);
513 reservePreviousStackSlotForValue(SI.Ptrs[i], Builder);
514 }
515
516 // First, prefix the list with the number of unique values to be
517 // lowered. Note that this is the number of *Values* not the
518 // number of SDValues required to lower them.
519 const int NumVMSArgs = SI.DeoptState.size();
520 pushStackMapConstant(Ops, Builder, NumVMSArgs);
521
522 // The vm state arguments are lowered in an opaque manner. We do not know
523 // what type of values are contained within.
524 for (const Value *V : SI.DeoptState) {
525 SDValue Incoming;
526 // If this is a function argument at a static frame index, generate it as
527 // the frame index.
528 if (const Argument *Arg = dyn_cast<Argument>(V)) {
529 int FI = Builder.FuncInfo.getArgumentFrameIndex(Arg);
530 if (FI != INT_MAX)
531 Incoming = Builder.DAG.getFrameIndex(FI, Builder.getFrameIndexTy());
532 }
533 if (!Incoming.getNode())
534 Incoming = Builder.getValue(V);
535 const bool LiveInValue = LiveInDeopt && !isGCValue(V);
536 lowerIncomingStatepointValue(Incoming, LiveInValue, Ops, Builder);
537 }
538
539 // Finally, go ahead and lower all the gc arguments. There's no prefixed
540 // length for this one. After lowering, we'll have the base and pointer
541 // arrays interwoven with each (lowered) base pointer immediately followed by
542 // it's (lowered) derived pointer. i.e
543 // (base[0], ptr[0], base[1], ptr[1], ...)
544 for (unsigned i = 0; i < SI.Bases.size(); ++i) {
545 const Value *Base = SI.Bases[i];
546 lowerIncomingStatepointValue(Builder.getValue(Base), /*LiveInOnly*/ false,
547 Ops, Builder);
548
549 const Value *Ptr = SI.Ptrs[i];
550 lowerIncomingStatepointValue(Builder.getValue(Ptr), /*LiveInOnly*/ false,
551 Ops, Builder);
552 }
553
554 // If there are any explicit spill slots passed to the statepoint, record
555 // them, but otherwise do not do anything special. These are user provided
556 // allocas and give control over placement to the consumer. In this case,
557 // it is the contents of the slot which may get updated, not the pointer to
558 // the alloca
559 for (Value *V : SI.GCArgs) {
560 SDValue Incoming = Builder.getValue(V);
561 if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) {
562 // This handles allocas as arguments to the statepoint
563 assert(Incoming.getValueType() == Builder.getFrameIndexTy() &&
564 "Incoming value is a frame index!");
565 Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
566 Builder.getFrameIndexTy()));
567 }
568 }
569
570 // Record computed locations for all lowered values.
571 // This can not be embedded in lowering loops as we need to record *all*
572 // values, while previous loops account only values with unique SDValues.
573 const Instruction *StatepointInstr = SI.StatepointInstr;
574 auto &SpillMap = Builder.FuncInfo.StatepointSpillMaps[StatepointInstr];
575
576 for (const GCRelocateInst *Relocate : SI.GCRelocates) {
577 const Value *V = Relocate->getDerivedPtr();
578 SDValue SDV = Builder.getValue(V);
579 SDValue Loc = Builder.StatepointLowering.getLocation(SDV);
580
581 if (Loc.getNode()) {
582 SpillMap.SlotMap[V] = cast<FrameIndexSDNode>(Loc)->getIndex();
583 } else {
584 // Record value as visited, but not spilled. This is case for allocas
585 // and constants. For this values we can avoid emitting spill load while
586 // visiting corresponding gc_relocate.
587 // Actually we do not need to record them in this map at all.
588 // We do this only to check that we are not relocating any unvisited
589 // value.
590 SpillMap.SlotMap[V] = None;
591
592 // Default llvm mechanisms for exporting values which are used in
593 // different basic blocks does not work for gc relocates.
594 // Note that it would be incorrect to teach llvm that all relocates are
595 // uses of the corresponding values so that it would automatically
596 // export them. Relocates of the spilled values does not use original
597 // value.
598 if (Relocate->getParent() != StatepointInstr->getParent())
599 Builder.ExportFromCurrentBlock(V);
600 }
601 }
602 }
603
LowerAsSTATEPOINT(SelectionDAGBuilder::StatepointLoweringInfo & SI)604 SDValue SelectionDAGBuilder::LowerAsSTATEPOINT(
605 SelectionDAGBuilder::StatepointLoweringInfo &SI) {
606 // The basic scheme here is that information about both the original call and
607 // the safepoint is encoded in the CallInst. We create a temporary call and
608 // lower it, then reverse engineer the calling sequence.
609
610 NumOfStatepoints++;
611 // Clear state
612 StatepointLowering.startNewStatepoint(*this);
613
614 #ifndef NDEBUG
615 // We schedule gc relocates before removeDuplicateGCPtrs since we _will_
616 // encounter the duplicate gc relocates we elide in removeDuplicateGCPtrs.
617 for (auto *Reloc : SI.GCRelocates)
618 if (Reloc->getParent() == SI.StatepointInstr->getParent())
619 StatepointLowering.scheduleRelocCall(*Reloc);
620 #endif
621
622 // Remove any redundant llvm::Values which map to the same SDValue as another
623 // input. Also has the effect of removing duplicates in the original
624 // llvm::Value input list as well. This is a useful optimization for
625 // reducing the size of the StackMap section. It has no other impact.
626 removeDuplicateGCPtrs(SI.Bases, SI.Ptrs, SI.GCRelocates, *this,
627 FuncInfo.StatepointSpillMaps[SI.StatepointInstr]);
628 assert(SI.Bases.size() == SI.Ptrs.size() &&
629 SI.Ptrs.size() == SI.GCRelocates.size());
630
631 // Lower statepoint vmstate and gcstate arguments
632 SmallVector<SDValue, 10> LoweredMetaArgs;
633 lowerStatepointMetaArgs(LoweredMetaArgs, SI, *this);
634
635 // Now that we've emitted the spills, we need to update the root so that the
636 // call sequence is ordered correctly.
637 SI.CLI.setChain(getRoot());
638
639 // Get call node, we will replace it later with statepoint
640 SDValue ReturnVal;
641 SDNode *CallNode;
642 std::tie(ReturnVal, CallNode) =
643 lowerCallFromStatepointLoweringInfo(SI, *this, PendingExports);
644
645 // Construct the actual GC_TRANSITION_START, STATEPOINT, and GC_TRANSITION_END
646 // nodes with all the appropriate arguments and return values.
647
648 // Call Node: Chain, Target, {Args}, RegMask, [Glue]
649 SDValue Chain = CallNode->getOperand(0);
650
651 SDValue Glue;
652 bool CallHasIncomingGlue = CallNode->getGluedNode();
653 if (CallHasIncomingGlue) {
654 // Glue is always last operand
655 Glue = CallNode->getOperand(CallNode->getNumOperands() - 1);
656 }
657
658 // Build the GC_TRANSITION_START node if necessary.
659 //
660 // The operands to the GC_TRANSITION_{START,END} nodes are laid out in the
661 // order in which they appear in the call to the statepoint intrinsic. If
662 // any of the operands is a pointer-typed, that operand is immediately
663 // followed by a SRCVALUE for the pointer that may be used during lowering
664 // (e.g. to form MachinePointerInfo values for loads/stores).
665 const bool IsGCTransition =
666 (SI.StatepointFlags & (uint64_t)StatepointFlags::GCTransition) ==
667 (uint64_t)StatepointFlags::GCTransition;
668 if (IsGCTransition) {
669 SmallVector<SDValue, 8> TSOps;
670
671 // Add chain
672 TSOps.push_back(Chain);
673
674 // Add GC transition arguments
675 for (const Value *V : SI.GCTransitionArgs) {
676 TSOps.push_back(getValue(V));
677 if (V->getType()->isPointerTy())
678 TSOps.push_back(DAG.getSrcValue(V));
679 }
680
681 // Add glue if necessary
682 if (CallHasIncomingGlue)
683 TSOps.push_back(Glue);
684
685 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
686
687 SDValue GCTransitionStart =
688 DAG.getNode(ISD::GC_TRANSITION_START, getCurSDLoc(), NodeTys, TSOps);
689
690 Chain = GCTransitionStart.getValue(0);
691 Glue = GCTransitionStart.getValue(1);
692 }
693
694 // TODO: Currently, all of these operands are being marked as read/write in
695 // PrologEpilougeInserter.cpp, we should special case the VMState arguments
696 // and flags to be read-only.
697 SmallVector<SDValue, 40> Ops;
698
699 // Add the <id> and <numBytes> constants.
700 Ops.push_back(DAG.getTargetConstant(SI.ID, getCurSDLoc(), MVT::i64));
701 Ops.push_back(
702 DAG.getTargetConstant(SI.NumPatchBytes, getCurSDLoc(), MVT::i32));
703
704 // Calculate and push starting position of vmstate arguments
705 // Get number of arguments incoming directly into call node
706 unsigned NumCallRegArgs =
707 CallNode->getNumOperands() - (CallHasIncomingGlue ? 4 : 3);
708 Ops.push_back(DAG.getTargetConstant(NumCallRegArgs, getCurSDLoc(), MVT::i32));
709
710 // Add call target
711 SDValue CallTarget = SDValue(CallNode->getOperand(1).getNode(), 0);
712 Ops.push_back(CallTarget);
713
714 // Add call arguments
715 // Get position of register mask in the call
716 SDNode::op_iterator RegMaskIt;
717 if (CallHasIncomingGlue)
718 RegMaskIt = CallNode->op_end() - 2;
719 else
720 RegMaskIt = CallNode->op_end() - 1;
721 Ops.insert(Ops.end(), CallNode->op_begin() + 2, RegMaskIt);
722
723 // Add a constant argument for the calling convention
724 pushStackMapConstant(Ops, *this, SI.CLI.CallConv);
725
726 // Add a constant argument for the flags
727 uint64_t Flags = SI.StatepointFlags;
728 assert(((Flags & ~(uint64_t)StatepointFlags::MaskAll) == 0) &&
729 "Unknown flag used");
730 pushStackMapConstant(Ops, *this, Flags);
731
732 // Insert all vmstate and gcstate arguments
733 Ops.insert(Ops.end(), LoweredMetaArgs.begin(), LoweredMetaArgs.end());
734
735 // Add register mask from call node
736 Ops.push_back(*RegMaskIt);
737
738 // Add chain
739 Ops.push_back(Chain);
740
741 // Same for the glue, but we add it only if original call had it
742 if (Glue.getNode())
743 Ops.push_back(Glue);
744
745 // Compute return values. Provide a glue output since we consume one as
746 // input. This allows someone else to chain off us as needed.
747 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
748
749 SDNode *StatepointMCNode =
750 DAG.getMachineNode(TargetOpcode::STATEPOINT, getCurSDLoc(), NodeTys, Ops);
751
752 SDNode *SinkNode = StatepointMCNode;
753
754 // Build the GC_TRANSITION_END node if necessary.
755 //
756 // See the comment above regarding GC_TRANSITION_START for the layout of
757 // the operands to the GC_TRANSITION_END node.
758 if (IsGCTransition) {
759 SmallVector<SDValue, 8> TEOps;
760
761 // Add chain
762 TEOps.push_back(SDValue(StatepointMCNode, 0));
763
764 // Add GC transition arguments
765 for (const Value *V : SI.GCTransitionArgs) {
766 TEOps.push_back(getValue(V));
767 if (V->getType()->isPointerTy())
768 TEOps.push_back(DAG.getSrcValue(V));
769 }
770
771 // Add glue
772 TEOps.push_back(SDValue(StatepointMCNode, 1));
773
774 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
775
776 SDValue GCTransitionStart =
777 DAG.getNode(ISD::GC_TRANSITION_END, getCurSDLoc(), NodeTys, TEOps);
778
779 SinkNode = GCTransitionStart.getNode();
780 }
781
782 // Replace original call
783 DAG.ReplaceAllUsesWith(CallNode, SinkNode); // This may update Root
784 // Remove original call node
785 DAG.DeleteNode(CallNode);
786
787 // DON'T set the root - under the assumption that it's already set past the
788 // inserted node we created.
789
790 // TODO: A better future implementation would be to emit a single variable
791 // argument, variable return value STATEPOINT node here and then hookup the
792 // return value of each gc.relocate to the respective output of the
793 // previously emitted STATEPOINT value. Unfortunately, this doesn't appear
794 // to actually be possible today.
795
796 return ReturnVal;
797 }
798
799 void
LowerStatepoint(ImmutableStatepoint ISP,const BasicBlock * EHPadBB)800 SelectionDAGBuilder::LowerStatepoint(ImmutableStatepoint ISP,
801 const BasicBlock *EHPadBB /*= nullptr*/) {
802 assert(ISP.getCallSite().getCallingConv() != CallingConv::AnyReg &&
803 "anyregcc is not supported on statepoints!");
804
805 #ifndef NDEBUG
806 // If this is a malformed statepoint, report it early to simplify debugging.
807 // This should catch any IR level mistake that's made when constructing or
808 // transforming statepoints.
809 ISP.verify();
810
811 // Check that the associated GCStrategy expects to encounter statepoints.
812 assert(GFI->getStrategy().useStatepoints() &&
813 "GCStrategy does not expect to encounter statepoints");
814 #endif
815
816 SDValue ActualCallee;
817
818 if (ISP.getNumPatchBytes() > 0) {
819 // If we've been asked to emit a nop sequence instead of a call instruction
820 // for this statepoint then don't lower the call target, but use a constant
821 // `null` instead. Not lowering the call target lets statepoint clients get
822 // away without providing a physical address for the symbolic call target at
823 // link time.
824
825 const auto &TLI = DAG.getTargetLoweringInfo();
826 const auto &DL = DAG.getDataLayout();
827
828 unsigned AS = ISP.getCalledValue()->getType()->getPointerAddressSpace();
829 ActualCallee = DAG.getConstant(0, getCurSDLoc(), TLI.getPointerTy(DL, AS));
830 } else {
831 ActualCallee = getValue(ISP.getCalledValue());
832 }
833
834 StatepointLoweringInfo SI(DAG);
835 populateCallLoweringInfo(SI.CLI, ISP.getCallSite(),
836 ImmutableStatepoint::CallArgsBeginPos,
837 ISP.getNumCallArgs(), ActualCallee,
838 ISP.getActualReturnType(), false /* IsPatchPoint */);
839
840 for (const GCRelocateInst *Relocate : ISP.getRelocates()) {
841 SI.GCRelocates.push_back(Relocate);
842 SI.Bases.push_back(Relocate->getBasePtr());
843 SI.Ptrs.push_back(Relocate->getDerivedPtr());
844 }
845
846 SI.GCArgs = ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end());
847 SI.StatepointInstr = ISP.getInstruction();
848 SI.GCTransitionArgs =
849 ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end());
850 SI.ID = ISP.getID();
851 SI.DeoptState = ArrayRef<const Use>(ISP.deopt_begin(), ISP.deopt_end());
852 SI.StatepointFlags = ISP.getFlags();
853 SI.NumPatchBytes = ISP.getNumPatchBytes();
854 SI.EHPadBB = EHPadBB;
855
856 SDValue ReturnValue = LowerAsSTATEPOINT(SI);
857
858 // Export the result value if needed
859 const GCResultInst *GCResult = ISP.getGCResult();
860 Type *RetTy = ISP.getActualReturnType();
861 if (!RetTy->isVoidTy() && GCResult) {
862 if (GCResult->getParent() != ISP.getCallSite().getParent()) {
863 // Result value will be used in a different basic block so we need to
864 // export it now. Default exporting mechanism will not work here because
865 // statepoint call has a different type than the actual call. It means
866 // that by default llvm will create export register of the wrong type
867 // (always i32 in our case). So instead we need to create export register
868 // with correct type manually.
869 // TODO: To eliminate this problem we can remove gc.result intrinsics
870 // completely and make statepoint call to return a tuple.
871 unsigned Reg = FuncInfo.CreateRegs(RetTy);
872 RegsForValue RFV(*DAG.getContext(), DAG.getTargetLoweringInfo(),
873 DAG.getDataLayout(), Reg, RetTy,
874 ISP.getCallSite().getCallingConv());
875 SDValue Chain = DAG.getEntryNode();
876
877 RFV.getCopyToRegs(ReturnValue, DAG, getCurSDLoc(), Chain, nullptr);
878 PendingExports.push_back(Chain);
879 FuncInfo.ValueMap[ISP.getInstruction()] = Reg;
880 } else {
881 // Result value will be used in a same basic block. Don't export it or
882 // perform any explicit register copies.
883 // We'll replace the actuall call node shortly. gc_result will grab
884 // this value.
885 setValue(ISP.getInstruction(), ReturnValue);
886 }
887 } else {
888 // The token value is never used from here on, just generate a poison value
889 setValue(ISP.getInstruction(), DAG.getIntPtrConstant(-1, getCurSDLoc()));
890 }
891 }
892
LowerCallSiteWithDeoptBundleImpl(ImmutableCallSite CS,SDValue Callee,const BasicBlock * EHPadBB,bool VarArgDisallowed,bool ForceVoidReturnTy)893 void SelectionDAGBuilder::LowerCallSiteWithDeoptBundleImpl(
894 ImmutableCallSite CS, SDValue Callee, const BasicBlock *EHPadBB,
895 bool VarArgDisallowed, bool ForceVoidReturnTy) {
896 StatepointLoweringInfo SI(DAG);
897 unsigned ArgBeginIndex = CS.arg_begin() - CS.getInstruction()->op_begin();
898 populateCallLoweringInfo(
899 SI.CLI, CS, ArgBeginIndex, CS.getNumArgOperands(), Callee,
900 ForceVoidReturnTy ? Type::getVoidTy(*DAG.getContext()) : CS.getType(),
901 false);
902 if (!VarArgDisallowed)
903 SI.CLI.IsVarArg = CS.getFunctionType()->isVarArg();
904
905 auto DeoptBundle = *CS.getOperandBundle(LLVMContext::OB_deopt);
906
907 unsigned DefaultID = StatepointDirectives::DeoptBundleStatepointID;
908
909 auto SD = parseStatepointDirectivesFromAttrs(CS.getAttributes());
910 SI.ID = SD.StatepointID.getValueOr(DefaultID);
911 SI.NumPatchBytes = SD.NumPatchBytes.getValueOr(0);
912
913 SI.DeoptState =
914 ArrayRef<const Use>(DeoptBundle.Inputs.begin(), DeoptBundle.Inputs.end());
915 SI.StatepointFlags = static_cast<uint64_t>(StatepointFlags::None);
916 SI.EHPadBB = EHPadBB;
917
918 // NB! The GC arguments are deliberately left empty.
919
920 if (SDValue ReturnVal = LowerAsSTATEPOINT(SI)) {
921 const Instruction *Inst = CS.getInstruction();
922 ReturnVal = lowerRangeToAssertZExt(DAG, *Inst, ReturnVal);
923 setValue(Inst, ReturnVal);
924 }
925 }
926
LowerCallSiteWithDeoptBundle(ImmutableCallSite CS,SDValue Callee,const BasicBlock * EHPadBB)927 void SelectionDAGBuilder::LowerCallSiteWithDeoptBundle(
928 ImmutableCallSite CS, SDValue Callee, const BasicBlock *EHPadBB) {
929 LowerCallSiteWithDeoptBundleImpl(CS, Callee, EHPadBB,
930 /* VarArgDisallowed = */ false,
931 /* ForceVoidReturnTy = */ false);
932 }
933
visitGCResult(const GCResultInst & CI)934 void SelectionDAGBuilder::visitGCResult(const GCResultInst &CI) {
935 // The result value of the gc_result is simply the result of the actual
936 // call. We've already emitted this, so just grab the value.
937 const Instruction *I = CI.getStatepoint();
938
939 if (I->getParent() != CI.getParent()) {
940 // Statepoint is in different basic block so we should have stored call
941 // result in a virtual register.
942 // We can not use default getValue() functionality to copy value from this
943 // register because statepoint and actual call return types can be
944 // different, and getValue() will use CopyFromReg of the wrong type,
945 // which is always i32 in our case.
946 PointerType *CalleeType = cast<PointerType>(
947 ImmutableStatepoint(I).getCalledValue()->getType());
948 Type *RetTy =
949 cast<FunctionType>(CalleeType->getElementType())->getReturnType();
950 SDValue CopyFromReg = getCopyFromRegs(I, RetTy);
951
952 assert(CopyFromReg.getNode());
953 setValue(&CI, CopyFromReg);
954 } else {
955 setValue(&CI, getValue(I));
956 }
957 }
958
visitGCRelocate(const GCRelocateInst & Relocate)959 void SelectionDAGBuilder::visitGCRelocate(const GCRelocateInst &Relocate) {
960 #ifndef NDEBUG
961 // Consistency check
962 // We skip this check for relocates not in the same basic block as their
963 // statepoint. It would be too expensive to preserve validation info through
964 // different basic blocks.
965 if (Relocate.getStatepoint()->getParent() == Relocate.getParent())
966 StatepointLowering.relocCallVisited(Relocate);
967
968 auto *Ty = Relocate.getType()->getScalarType();
969 if (auto IsManaged = GFI->getStrategy().isGCManagedPointer(Ty))
970 assert(*IsManaged && "Non gc managed pointer relocated!");
971 #endif
972
973 const Value *DerivedPtr = Relocate.getDerivedPtr();
974 SDValue SD = getValue(DerivedPtr);
975
976 auto &SpillMap = FuncInfo.StatepointSpillMaps[Relocate.getStatepoint()];
977 auto SlotIt = SpillMap.find(DerivedPtr);
978 assert(SlotIt != SpillMap.end() && "Relocating not lowered gc value");
979 Optional<int> DerivedPtrLocation = SlotIt->second;
980
981 // We didn't need to spill these special cases (constants and allocas).
982 // See the handling in spillIncomingValueForStatepoint for detail.
983 if (!DerivedPtrLocation) {
984 setValue(&Relocate, SD);
985 return;
986 }
987
988 SDValue SpillSlot =
989 DAG.getTargetFrameIndex(*DerivedPtrLocation, getFrameIndexTy());
990
991 // Be conservative: flush all pending loads
992 // TODO: Probably we can be less restrictive on this,
993 // it may allow more scheduling opportunities.
994 SDValue Chain = getRoot();
995
996 SDValue SpillLoad =
997 DAG.getLoad(DAG.getTargetLoweringInfo().getValueType(DAG.getDataLayout(),
998 Relocate.getType()),
999 getCurSDLoc(), Chain, SpillSlot,
1000 MachinePointerInfo::getFixedStack(DAG.getMachineFunction(),
1001 *DerivedPtrLocation));
1002
1003 // Again, be conservative, don't emit pending loads
1004 DAG.setRoot(SpillLoad.getValue(1));
1005
1006 assert(SpillLoad.getNode());
1007 setValue(&Relocate, SpillLoad);
1008 }
1009
LowerDeoptimizeCall(const CallInst * CI)1010 void SelectionDAGBuilder::LowerDeoptimizeCall(const CallInst *CI) {
1011 const auto &TLI = DAG.getTargetLoweringInfo();
1012 SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(RTLIB::DEOPTIMIZE),
1013 TLI.getPointerTy(DAG.getDataLayout()));
1014
1015 // We don't lower calls to __llvm_deoptimize as varargs, but as a regular
1016 // call. We also do not lower the return value to any virtual register, and
1017 // change the immediately following return to a trap instruction.
1018 LowerCallSiteWithDeoptBundleImpl(CI, Callee, /* EHPadBB = */ nullptr,
1019 /* VarArgDisallowed = */ true,
1020 /* ForceVoidReturnTy = */ true);
1021 }
1022
LowerDeoptimizingReturn()1023 void SelectionDAGBuilder::LowerDeoptimizingReturn() {
1024 // We do not lower the return value from llvm.deoptimize to any virtual
1025 // register, and change the immediately following return to a trap
1026 // instruction.
1027 if (DAG.getTarget().Options.TrapUnreachable)
1028 DAG.setRoot(
1029 DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, DAG.getRoot()));
1030 }
1031