1//===- StatepointLowering.cpp - SDAGBuilder's statepoint code -------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file includes support code use by SelectionDAGBuilder when lowering a
10// statepoint sequence in SelectionDAG IR.
11//
12//===----------------------------------------------------------------------===//
13
14#include "StatepointLowering.h"
15#include "SelectionDAGBuilder.h"
16#include "llvm/ADT/ArrayRef.h"
17#include "llvm/ADT/STLExtras.h"
18#include "llvm/ADT/SetVector.h"
19#include "llvm/ADT/SmallBitVector.h"
20#include "llvm/ADT/SmallSet.h"
21#include "llvm/ADT/SmallVector.h"
22#include "llvm/ADT/Statistic.h"
23#include "llvm/CodeGen/FunctionLoweringInfo.h"
24#include "llvm/CodeGen/GCMetadata.h"
25#include "llvm/CodeGen/ISDOpcodes.h"
26#include "llvm/CodeGen/MachineFrameInfo.h"
27#include "llvm/CodeGen/MachineFunction.h"
28#include "llvm/CodeGen/MachineMemOperand.h"
29#include "llvm/CodeGen/RuntimeLibcalls.h"
30#include "llvm/CodeGen/SelectionDAG.h"
31#include "llvm/CodeGen/SelectionDAGNodes.h"
32#include "llvm/CodeGen/StackMaps.h"
33#include "llvm/CodeGen/TargetLowering.h"
34#include "llvm/CodeGen/TargetOpcodes.h"
35#include "llvm/CodeGenTypes/MachineValueType.h"
36#include "llvm/IR/CallingConv.h"
37#include "llvm/IR/DerivedTypes.h"
38#include "llvm/IR/GCStrategy.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/CommandLine.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
55using namespace llvm;
56
57#define DEBUG_TYPE "statepoint-lowering"
58
59STATISTIC(NumSlotsAllocatedForStatepoints,
60 "Number of stack slots allocated for statepoints");
61STATISTIC(NumOfStatepoints, "Number of statepoint nodes encountered");
62STATISTIC(StatepointMaxSlotsRequired,
63 "Maximum number of stack slots required for a singe statepoint");
64
65static cl::opt<bool> UseRegistersForDeoptValues(
66 "use-registers-for-deopt-values", cl::Hidden, cl::init(Val: false),
67 cl::desc("Allow using registers for non pointer deopt args"));
68
69static cl::opt<bool> UseRegistersForGCPointersInLandingPad(
70 "use-registers-for-gc-values-in-landing-pad", cl::Hidden, cl::init(Val: false),
71 cl::desc("Allow using registers for gc pointer in landing pad"));
72
73static cl::opt<unsigned> MaxRegistersForGCPointers(
74 "max-registers-for-gc-values", cl::Hidden, cl::init(Val: 0),
75 cl::desc("Max number of VRegs allowed to pass GC pointer meta args in"));
76
77typedef FunctionLoweringInfo::StatepointRelocationRecord RecordType;
78
79static void pushStackMapConstant(SmallVectorImpl<SDValue>& Ops,
80 SelectionDAGBuilder &Builder, uint64_t Value) {
81 SDLoc L = Builder.getCurSDLoc();
82 Ops.push_back(Elt: Builder.DAG.getTargetConstant(StackMaps::ConstantOp, L,
83 MVT::i64));
84 Ops.push_back(Elt: Builder.DAG.getTargetConstant(Value, L, MVT::i64));
85}
86
87void StatepointLoweringState::startNewStatepoint(SelectionDAGBuilder &Builder) {
88 // Consistency check
89 assert(PendingGCRelocateCalls.empty() &&
90 "Trying to visit statepoint before finished processing previous one");
91 Locations.clear();
92 NextSlotToAllocate = 0;
93 // Need to resize this on each safepoint - we need the two to stay in sync and
94 // the clear patterns of a SelectionDAGBuilder have no relation to
95 // FunctionLoweringInfo. Also need to ensure used bits get cleared.
96 AllocatedStackSlots.clear();
97 AllocatedStackSlots.resize(N: Builder.FuncInfo.StatepointStackSlots.size());
98}
99
100void StatepointLoweringState::clear() {
101 Locations.clear();
102 AllocatedStackSlots.clear();
103 assert(PendingGCRelocateCalls.empty() &&
104 "cleared before statepoint sequence completed");
105}
106
107SDValue
108StatepointLoweringState::allocateStackSlot(EVT ValueType,
109 SelectionDAGBuilder &Builder) {
110 NumSlotsAllocatedForStatepoints++;
111 MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo();
112
113 unsigned SpillSize = ValueType.getStoreSize();
114 assert((SpillSize * 8) ==
115 (-8u & (7 + ValueType.getSizeInBits())) && // Round up modulo 8.
116 "Size not in bytes?");
117
118 // First look for a previously created stack slot which is not in
119 // use (accounting for the fact arbitrary slots may already be
120 // reserved), or to create a new stack slot and use it.
121
122 const size_t NumSlots = AllocatedStackSlots.size();
123 assert(NextSlotToAllocate <= NumSlots && "Broken invariant");
124
125 assert(AllocatedStackSlots.size() ==
126 Builder.FuncInfo.StatepointStackSlots.size() &&
127 "Broken invariant");
128
129 for (; NextSlotToAllocate < NumSlots; NextSlotToAllocate++) {
130 if (!AllocatedStackSlots.test(Idx: NextSlotToAllocate)) {
131 const int FI = Builder.FuncInfo.StatepointStackSlots[NextSlotToAllocate];
132 if (MFI.getObjectSize(ObjectIdx: FI) == SpillSize) {
133 AllocatedStackSlots.set(NextSlotToAllocate);
134 // TODO: Is ValueType the right thing to use here?
135 return Builder.DAG.getFrameIndex(FI, VT: ValueType);
136 }
137 }
138 }
139
140 // Couldn't find a free slot, so create a new one:
141
142 SDValue SpillSlot = Builder.DAG.CreateStackTemporary(VT: ValueType);
143 const unsigned FI = cast<FrameIndexSDNode>(Val&: SpillSlot)->getIndex();
144 MFI.markAsStatepointSpillSlotObjectIndex(ObjectIdx: FI);
145
146 Builder.FuncInfo.StatepointStackSlots.push_back(Elt: FI);
147 AllocatedStackSlots.resize(N: AllocatedStackSlots.size()+1, t: true);
148 assert(AllocatedStackSlots.size() ==
149 Builder.FuncInfo.StatepointStackSlots.size() &&
150 "Broken invariant");
151
152 StatepointMaxSlotsRequired.updateMax(
153 V: Builder.FuncInfo.StatepointStackSlots.size());
154
155 return SpillSlot;
156}
157
158/// Utility function for reservePreviousStackSlotForValue. Tries to find
159/// stack slot index to which we have spilled value for previous statepoints.
160/// LookUpDepth specifies maximum DFS depth this function is allowed to look.
161static std::optional<int> findPreviousSpillSlot(const Value *Val,
162 SelectionDAGBuilder &Builder,
163 int LookUpDepth) {
164 // Can not look any further - give up now
165 if (LookUpDepth <= 0)
166 return std::nullopt;
167
168 // Spill location is known for gc relocates
169 if (const auto *Relocate = dyn_cast<GCRelocateInst>(Val)) {
170 const Value *Statepoint = Relocate->getStatepoint();
171 assert((isa<GCStatepointInst>(Statepoint) || isa<UndefValue>(Statepoint)) &&
172 "GetStatepoint must return one of two types");
173 if (isa<UndefValue>(Val: Statepoint))
174 return std::nullopt;
175
176 const auto &RelocationMap = Builder.FuncInfo.StatepointRelocationMaps
177 [cast<GCStatepointInst>(Val: Statepoint)];
178
179 auto It = RelocationMap.find(Val: Relocate);
180 if (It == RelocationMap.end())
181 return std::nullopt;
182
183 auto &Record = It->second;
184 if (Record.type != RecordType::Spill)
185 return std::nullopt;
186
187 return Record.payload.FI;
188 }
189
190 // Look through bitcast instructions.
191 if (const BitCastInst *Cast = dyn_cast<BitCastInst>(Val))
192 return findPreviousSpillSlot(Val: Cast->getOperand(i_nocapture: 0), Builder, LookUpDepth: LookUpDepth - 1);
193
194 // Look through phi nodes
195 // All incoming values should have same known stack slot, otherwise result
196 // is unknown.
197 if (const PHINode *Phi = dyn_cast<PHINode>(Val)) {
198 std::optional<int> MergedResult;
199
200 for (const auto &IncomingValue : Phi->incoming_values()) {
201 std::optional<int> SpillSlot =
202 findPreviousSpillSlot(Val: IncomingValue, Builder, LookUpDepth: LookUpDepth - 1);
203 if (!SpillSlot)
204 return std::nullopt;
205
206 if (MergedResult && *MergedResult != *SpillSlot)
207 return std::nullopt;
208
209 MergedResult = SpillSlot;
210 }
211 return MergedResult;
212 }
213
214 // TODO: We can do better for PHI nodes. In cases like this:
215 // ptr = phi(relocated_pointer, not_relocated_pointer)
216 // statepoint(ptr)
217 // We will return that stack slot for ptr is unknown. And later we might
218 // assign different stack slots for ptr and relocated_pointer. This limits
219 // llvm's ability to remove redundant stores.
220 // Unfortunately it's hard to accomplish in current infrastructure.
221 // We use this function to eliminate spill store completely, while
222 // in example we still need to emit store, but instead of any location
223 // we need to use special "preferred" location.
224
225 // TODO: handle simple updates. If a value is modified and the original
226 // value is no longer live, it would be nice to put the modified value in the
227 // same slot. This allows folding of the memory accesses for some
228 // instructions types (like an increment).
229 // statepoint (i)
230 // i1 = i+1
231 // statepoint (i1)
232 // However we need to be careful for cases like this:
233 // statepoint(i)
234 // i1 = i+1
235 // statepoint(i, i1)
236 // Here we want to reserve spill slot for 'i', but not for 'i+1'. If we just
237 // put handling of simple modifications in this function like it's done
238 // for bitcasts we might end up reserving i's slot for 'i+1' because order in
239 // which we visit values is unspecified.
240
241 // Don't know any information about this instruction
242 return std::nullopt;
243}
244
245/// Return true if-and-only-if the given SDValue can be lowered as either a
246/// constant argument or a stack reference. The key point is that the value
247/// doesn't need to be spilled or tracked as a vreg use.
248static bool willLowerDirectly(SDValue Incoming) {
249 // We are making an unchecked assumption that the frame size <= 2^16 as that
250 // is the largest offset which can be encoded in the stackmap format.
251 if (isa<FrameIndexSDNode>(Val: Incoming))
252 return true;
253
254 // The largest constant describeable in the StackMap format is 64 bits.
255 // Potential Optimization: Constants values are sign extended by consumer,
256 // and thus there are many constants of static type > 64 bits whose value
257 // happens to be sext(Con64) and could thus be lowered directly.
258 if (Incoming.getValueType().getSizeInBits() > 64)
259 return false;
260
261 return isIntOrFPConstant(V: Incoming) || Incoming.isUndef();
262}
263
264/// Try to find existing copies of the incoming values in stack slots used for
265/// statepoint spilling. If we can find a spill slot for the incoming value,
266/// mark that slot as allocated, and reuse the same slot for this safepoint.
267/// This helps to avoid series of loads and stores that only serve to reshuffle
268/// values on the stack between calls.
269static void reservePreviousStackSlotForValue(const Value *IncomingValue,
270 SelectionDAGBuilder &Builder) {
271 SDValue Incoming = Builder.getValue(V: IncomingValue);
272
273 // If we won't spill this, we don't need to check for previously allocated
274 // stack slots.
275 if (willLowerDirectly(Incoming))
276 return;
277
278 SDValue OldLocation = Builder.StatepointLowering.getLocation(Val: Incoming);
279 if (OldLocation.getNode())
280 // Duplicates in input
281 return;
282
283 const int LookUpDepth = 6;
284 std::optional<int> Index =
285 findPreviousSpillSlot(Val: IncomingValue, Builder, LookUpDepth);
286 if (!Index)
287 return;
288
289 const auto &StatepointSlots = Builder.FuncInfo.StatepointStackSlots;
290
291 auto SlotIt = find(Range: StatepointSlots, Val: *Index);
292 assert(SlotIt != StatepointSlots.end() &&
293 "Value spilled to the unknown stack slot");
294
295 // This is one of our dedicated lowering slots
296 const int Offset = std::distance(first: StatepointSlots.begin(), last: SlotIt);
297 if (Builder.StatepointLowering.isStackSlotAllocated(Offset)) {
298 // stack slot already assigned to someone else, can't use it!
299 // TODO: currently we reserve space for gc arguments after doing
300 // normal allocation for deopt arguments. We should reserve for
301 // _all_ deopt and gc arguments, then start allocating. This
302 // will prevent some moves being inserted when vm state changes,
303 // but gc state doesn't between two calls.
304 return;
305 }
306 // Reserve this stack slot
307 Builder.StatepointLowering.reserveStackSlot(Offset);
308
309 // Cache this slot so we find it when going through the normal
310 // assignment loop.
311 SDValue Loc =
312 Builder.DAG.getTargetFrameIndex(FI: *Index, VT: Builder.getFrameIndexTy());
313 Builder.StatepointLowering.setLocation(Val: Incoming, Location: Loc);
314}
315
316/// Extract call from statepoint, lower it and return pointer to the
317/// call node. Also update NodeMap so that getValue(statepoint) will
318/// reference lowered call result
319static std::pair<SDValue, SDNode *> lowerCallFromStatepointLoweringInfo(
320 SelectionDAGBuilder::StatepointLoweringInfo &SI,
321 SelectionDAGBuilder &Builder) {
322 SDValue ReturnValue, CallEndVal;
323 std::tie(args&: ReturnValue, args&: CallEndVal) =
324 Builder.lowerInvokable(CLI&: SI.CLI, EHPadBB: SI.EHPadBB);
325 SDNode *CallEnd = CallEndVal.getNode();
326
327 // Get a call instruction from the call sequence chain. Tail calls are not
328 // allowed. The following code is essentially reverse engineering X86's
329 // LowerCallTo.
330 //
331 // We are expecting DAG to have the following form:
332 //
333 // ch = eh_label (only in case of invoke statepoint)
334 // ch, glue = callseq_start ch
335 // ch, glue = X86::Call ch, glue
336 // ch, glue = callseq_end ch, glue
337 // get_return_value ch, glue
338 //
339 // get_return_value can either be a sequence of CopyFromReg instructions
340 // to grab the return value from the return register(s), or it can be a LOAD
341 // to load a value returned by reference via a stack slot.
342
343 bool HasDef = !SI.CLI.RetTy->isVoidTy();
344 if (HasDef) {
345 if (CallEnd->getOpcode() == ISD::LOAD)
346 CallEnd = CallEnd->getOperand(Num: 0).getNode();
347 else
348 while (CallEnd->getOpcode() == ISD::CopyFromReg)
349 CallEnd = CallEnd->getOperand(Num: 0).getNode();
350 }
351
352 assert(CallEnd->getOpcode() == ISD::CALLSEQ_END && "expected!");
353 return std::make_pair(x&: ReturnValue, y: CallEnd->getOperand(Num: 0).getNode());
354}
355
356static MachineMemOperand* getMachineMemOperand(MachineFunction &MF,
357 FrameIndexSDNode &FI) {
358 auto PtrInfo = MachinePointerInfo::getFixedStack(MF, FI: FI.getIndex());
359 auto MMOFlags = MachineMemOperand::MOStore |
360 MachineMemOperand::MOLoad | MachineMemOperand::MOVolatile;
361 auto &MFI = MF.getFrameInfo();
362 return MF.getMachineMemOperand(PtrInfo, f: MMOFlags,
363 s: MFI.getObjectSize(ObjectIdx: FI.getIndex()),
364 base_alignment: MFI.getObjectAlign(ObjectIdx: FI.getIndex()));
365}
366
367/// Spill a value incoming to the statepoint. It might be either part of
368/// vmstate
369/// or gcstate. In both cases unconditionally spill it on the stack unless it
370/// is a null constant. Return pair with first element being frame index
371/// containing saved value and second element with outgoing chain from the
372/// emitted store
373static std::tuple<SDValue, SDValue, MachineMemOperand*>
374spillIncomingStatepointValue(SDValue Incoming, SDValue Chain,
375 SelectionDAGBuilder &Builder) {
376 SDValue Loc = Builder.StatepointLowering.getLocation(Val: Incoming);
377 MachineMemOperand* MMO = nullptr;
378
379 // Emit new store if we didn't do it for this ptr before
380 if (!Loc.getNode()) {
381 Loc = Builder.StatepointLowering.allocateStackSlot(ValueType: Incoming.getValueType(),
382 Builder);
383 int Index = cast<FrameIndexSDNode>(Val&: Loc)->getIndex();
384 // We use TargetFrameIndex so that isel will not select it into LEA
385 Loc = Builder.DAG.getTargetFrameIndex(FI: Index, VT: Builder.getFrameIndexTy());
386
387 // Right now we always allocate spill slots that are of the same
388 // size as the value we're about to spill (the size of spillee can
389 // vary since we spill vectors of pointers too). At some point we
390 // can consider allowing spills of smaller values to larger slots
391 // (i.e. change the '==' in the assert below to a '>=').
392 MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo();
393 assert((MFI.getObjectSize(Index) * 8) ==
394 (-8 & (7 + // Round up modulo 8.
395 (int64_t)Incoming.getValueSizeInBits())) &&
396 "Bad spill: stack slot does not match!");
397
398 // Note: Using the alignment of the spill slot (rather than the abi or
399 // preferred alignment) is required for correctness when dealing with spill
400 // slots with preferred alignments larger than frame alignment..
401 auto &MF = Builder.DAG.getMachineFunction();
402 auto PtrInfo = MachinePointerInfo::getFixedStack(MF, FI: Index);
403 auto *StoreMMO = MF.getMachineMemOperand(
404 PtrInfo, f: MachineMemOperand::MOStore, s: MFI.getObjectSize(ObjectIdx: Index),
405 base_alignment: MFI.getObjectAlign(ObjectIdx: Index));
406 Chain = Builder.DAG.getStore(Chain, dl: Builder.getCurSDLoc(), Val: Incoming, Ptr: Loc,
407 MMO: StoreMMO);
408
409 MMO = getMachineMemOperand(MF, FI&: *cast<FrameIndexSDNode>(Val&: Loc));
410
411 Builder.StatepointLowering.setLocation(Val: Incoming, Location: Loc);
412 }
413
414 assert(Loc.getNode());
415 return std::make_tuple(args&: Loc, args&: Chain, args&: MMO);
416}
417
418/// Lower a single value incoming to a statepoint node. This value can be
419/// either a deopt value or a gc value, the handling is the same. We special
420/// case constants and allocas, then fall back to spilling if required.
421static void
422lowerIncomingStatepointValue(SDValue Incoming, bool RequireSpillSlot,
423 SmallVectorImpl<SDValue> &Ops,
424 SmallVectorImpl<MachineMemOperand *> &MemRefs,
425 SelectionDAGBuilder &Builder) {
426
427 if (willLowerDirectly(Incoming)) {
428 if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Val&: Incoming)) {
429 // This handles allocas as arguments to the statepoint (this is only
430 // really meaningful for a deopt value. For GC, we'd be trying to
431 // relocate the address of the alloca itself?)
432 assert(Incoming.getValueType() == Builder.getFrameIndexTy() &&
433 "Incoming value is a frame index!");
434 Ops.push_back(Elt: Builder.DAG.getTargetFrameIndex(FI: FI->getIndex(),
435 VT: Builder.getFrameIndexTy()));
436
437 auto &MF = Builder.DAG.getMachineFunction();
438 auto *MMO = getMachineMemOperand(MF, FI&: *FI);
439 MemRefs.push_back(Elt: MMO);
440 return;
441 }
442
443 assert(Incoming.getValueType().getSizeInBits() <= 64);
444
445 if (Incoming.isUndef()) {
446 // Put an easily recognized constant that's unlikely to be a valid
447 // value so that uses of undef by the consumer of the stackmap is
448 // easily recognized. This is legal since the compiler is always
449 // allowed to chose an arbitrary value for undef.
450 pushStackMapConstant(Ops, Builder, Value: 0xFEFEFEFE);
451 return;
452 }
453
454 // If the original value was a constant, make sure it gets recorded as
455 // such in the stackmap. This is required so that the consumer can
456 // parse any internal format to the deopt state. It also handles null
457 // pointers and other constant pointers in GC states.
458 if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Val&: Incoming)) {
459 pushStackMapConstant(Ops, Builder, Value: C->getSExtValue());
460 return;
461 } else if (ConstantFPSDNode *C = dyn_cast<ConstantFPSDNode>(Val&: Incoming)) {
462 pushStackMapConstant(Ops, Builder,
463 Value: C->getValueAPF().bitcastToAPInt().getZExtValue());
464 return;
465 }
466
467 llvm_unreachable("unhandled direct lowering case");
468 }
469
470
471
472 if (!RequireSpillSlot) {
473 // If this value is live in (not live-on-return, or live-through), we can
474 // treat it the same way patchpoint treats it's "live in" values. We'll
475 // end up folding some of these into stack references, but they'll be
476 // handled by the register allocator. Note that we do not have the notion
477 // of a late use so these values might be placed in registers which are
478 // clobbered by the call. This is fine for live-in. For live-through
479 // fix-up pass should be executed to force spilling of such registers.
480 Ops.push_back(Elt: Incoming);
481 } else {
482 // Otherwise, locate a spill slot and explicitly spill it so it can be
483 // found by the runtime later. Note: We know all of these spills are
484 // independent, but don't bother to exploit that chain wise. DAGCombine
485 // will happily do so as needed, so doing it here would be a small compile
486 // time win at most.
487 SDValue Chain = Builder.getRoot();
488 auto Res = spillIncomingStatepointValue(Incoming, Chain, Builder);
489 Ops.push_back(Elt: std::get<0>(t&: Res));
490 if (auto *MMO = std::get<2>(t&: Res))
491 MemRefs.push_back(Elt: MMO);
492 Chain = std::get<1>(t&: Res);
493 Builder.DAG.setRoot(Chain);
494 }
495
496}
497
498/// Return true if value V represents the GC value. The behavior is conservative
499/// in case it is not sure that value is not GC the function returns true.
500static bool isGCValue(const Value *V, SelectionDAGBuilder &Builder) {
501 auto *Ty = V->getType();
502 if (!Ty->isPtrOrPtrVectorTy())
503 return false;
504 if (auto *GFI = Builder.GFI)
505 if (auto IsManaged = GFI->getStrategy().isGCManagedPointer(Ty))
506 return *IsManaged;
507 return true; // conservative
508}
509
510/// Lower deopt state and gc pointer arguments of the statepoint. The actual
511/// lowering is described in lowerIncomingStatepointValue. This function is
512/// responsible for lowering everything in the right position and playing some
513/// tricks to avoid redundant stack manipulation where possible. On
514/// completion, 'Ops' will contain ready to use operands for machine code
515/// statepoint. The chain nodes will have already been created and the DAG root
516/// will be set to the last value spilled (if any were).
517static void
518lowerStatepointMetaArgs(SmallVectorImpl<SDValue> &Ops,
519 SmallVectorImpl<MachineMemOperand *> &MemRefs,
520 SmallVectorImpl<SDValue> &GCPtrs,
521 DenseMap<SDValue, int> &LowerAsVReg,
522 SelectionDAGBuilder::StatepointLoweringInfo &SI,
523 SelectionDAGBuilder &Builder) {
524 // Lower the deopt and gc arguments for this statepoint. Layout will be:
525 // deopt argument length, deopt arguments.., gc arguments...
526
527 // Figure out what lowering strategy we're going to use for each part
528 // Note: It is conservatively correct to lower both "live-in" and "live-out"
529 // as "live-through". A "live-through" variable is one which is "live-in",
530 // "live-out", and live throughout the lifetime of the call (i.e. we can find
531 // it from any PC within the transitive callee of the statepoint). In
532 // particular, if the callee spills callee preserved registers we may not
533 // be able to find a value placed in that register during the call. This is
534 // fine for live-out, but not for live-through. If we were willing to make
535 // assumptions about the code generator producing the callee, we could
536 // potentially allow live-through values in callee saved registers.
537 const bool LiveInDeopt =
538 SI.StatepointFlags & (uint64_t)StatepointFlags::DeoptLiveIn;
539
540 // Decide which deriver pointers will go on VRegs
541 unsigned MaxVRegPtrs = MaxRegistersForGCPointers.getValue();
542
543 // Pointers used on exceptional path of invoke statepoint.
544 // We cannot assing them to VRegs.
545 SmallSet<SDValue, 8> LPadPointers;
546 if (!UseRegistersForGCPointersInLandingPad)
547 if (const auto *StInvoke =
548 dyn_cast_or_null<InvokeInst>(Val: SI.StatepointInstr)) {
549 LandingPadInst *LPI = StInvoke->getLandingPadInst();
550 for (const auto *Relocate : SI.GCRelocates)
551 if (Relocate->getOperand(i_nocapture: 0) == LPI) {
552 LPadPointers.insert(V: Builder.getValue(V: Relocate->getBasePtr()));
553 LPadPointers.insert(V: Builder.getValue(V: Relocate->getDerivedPtr()));
554 }
555 }
556
557 LLVM_DEBUG(dbgs() << "Deciding how to lower GC Pointers:\n");
558
559 // List of unique lowered GC Pointer values.
560 SmallSetVector<SDValue, 16> LoweredGCPtrs;
561 // Map lowered GC Pointer value to the index in above vector
562 DenseMap<SDValue, unsigned> GCPtrIndexMap;
563
564 unsigned CurNumVRegs = 0;
565
566 auto canPassGCPtrOnVReg = [&](SDValue SD) {
567 if (SD.getValueType().isVector())
568 return false;
569 if (LPadPointers.count(V: SD))
570 return false;
571 return !willLowerDirectly(Incoming: SD);
572 };
573
574 auto processGCPtr = [&](const Value *V) {
575 SDValue PtrSD = Builder.getValue(V);
576 if (!LoweredGCPtrs.insert(X: PtrSD))
577 return; // skip duplicates
578 GCPtrIndexMap[PtrSD] = LoweredGCPtrs.size() - 1;
579
580 assert(!LowerAsVReg.count(PtrSD) && "must not have been seen");
581 if (LowerAsVReg.size() == MaxVRegPtrs)
582 return;
583 assert(V->getType()->isVectorTy() == PtrSD.getValueType().isVector() &&
584 "IR and SD types disagree");
585 if (!canPassGCPtrOnVReg(PtrSD)) {
586 LLVM_DEBUG(dbgs() << "direct/spill "; PtrSD.dump(&Builder.DAG));
587 return;
588 }
589 LLVM_DEBUG(dbgs() << "vreg "; PtrSD.dump(&Builder.DAG));
590 LowerAsVReg[PtrSD] = CurNumVRegs++;
591 };
592
593 // Process derived pointers first to give them more chance to go on VReg.
594 for (const Value *V : SI.Ptrs)
595 processGCPtr(V);
596 for (const Value *V : SI.Bases)
597 processGCPtr(V);
598
599 LLVM_DEBUG(dbgs() << LowerAsVReg.size() << " pointers will go in vregs\n");
600
601 auto requireSpillSlot = [&](const Value *V) {
602 if (!Builder.DAG.getTargetLoweringInfo().isTypeLegal(
603 VT: Builder.getValue(V).getValueType()))
604 return true;
605 if (isGCValue(V, Builder))
606 return !LowerAsVReg.count(Val: Builder.getValue(V));
607 return !(LiveInDeopt || UseRegistersForDeoptValues);
608 };
609
610 // Before we actually start lowering (and allocating spill slots for values),
611 // reserve any stack slots which we judge to be profitable to reuse for a
612 // particular value. This is purely an optimization over the code below and
613 // doesn't change semantics at all. It is important for performance that we
614 // reserve slots for both deopt and gc values before lowering either.
615 for (const Value *V : SI.DeoptState) {
616 if (requireSpillSlot(V))
617 reservePreviousStackSlotForValue(IncomingValue: V, Builder);
618 }
619
620 for (const Value *V : SI.Ptrs) {
621 SDValue SDV = Builder.getValue(V);
622 if (!LowerAsVReg.count(Val: SDV))
623 reservePreviousStackSlotForValue(IncomingValue: V, Builder);
624 }
625
626 for (const Value *V : SI.Bases) {
627 SDValue SDV = Builder.getValue(V);
628 if (!LowerAsVReg.count(Val: SDV))
629 reservePreviousStackSlotForValue(IncomingValue: V, Builder);
630 }
631
632 // First, prefix the list with the number of unique values to be
633 // lowered. Note that this is the number of *Values* not the
634 // number of SDValues required to lower them.
635 const int NumVMSArgs = SI.DeoptState.size();
636 pushStackMapConstant(Ops, Builder, Value: NumVMSArgs);
637
638 // The vm state arguments are lowered in an opaque manner. We do not know
639 // what type of values are contained within.
640 LLVM_DEBUG(dbgs() << "Lowering deopt state\n");
641 for (const Value *V : SI.DeoptState) {
642 SDValue Incoming;
643 // If this is a function argument at a static frame index, generate it as
644 // the frame index.
645 if (const Argument *Arg = dyn_cast<Argument>(Val: V)) {
646 int FI = Builder.FuncInfo.getArgumentFrameIndex(A: Arg);
647 if (FI != INT_MAX)
648 Incoming = Builder.DAG.getFrameIndex(FI, VT: Builder.getFrameIndexTy());
649 }
650 if (!Incoming.getNode())
651 Incoming = Builder.getValue(V);
652 LLVM_DEBUG(dbgs() << "Value " << *V
653 << " requireSpillSlot = " << requireSpillSlot(V) << "\n");
654 lowerIncomingStatepointValue(Incoming, RequireSpillSlot: requireSpillSlot(V), Ops, MemRefs,
655 Builder);
656 }
657
658 // Finally, go ahead and lower all the gc arguments.
659 pushStackMapConstant(Ops, Builder, Value: LoweredGCPtrs.size());
660 for (SDValue SDV : LoweredGCPtrs)
661 lowerIncomingStatepointValue(Incoming: SDV, RequireSpillSlot: !LowerAsVReg.count(Val: SDV), Ops, MemRefs,
662 Builder);
663
664 // Copy to out vector. LoweredGCPtrs will be empty after this point.
665 GCPtrs = LoweredGCPtrs.takeVector();
666
667 // If there are any explicit spill slots passed to the statepoint, record
668 // them, but otherwise do not do anything special. These are user provided
669 // allocas and give control over placement to the consumer. In this case,
670 // it is the contents of the slot which may get updated, not the pointer to
671 // the alloca
672 SmallVector<SDValue, 4> Allocas;
673 for (Value *V : SI.GCArgs) {
674 SDValue Incoming = Builder.getValue(V);
675 if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Val&: Incoming)) {
676 // This handles allocas as arguments to the statepoint
677 assert(Incoming.getValueType() == Builder.getFrameIndexTy() &&
678 "Incoming value is a frame index!");
679 Allocas.push_back(Elt: Builder.DAG.getTargetFrameIndex(
680 FI: FI->getIndex(), VT: Builder.getFrameIndexTy()));
681
682 auto &MF = Builder.DAG.getMachineFunction();
683 auto *MMO = getMachineMemOperand(MF, FI&: *FI);
684 MemRefs.push_back(Elt: MMO);
685 }
686 }
687 pushStackMapConstant(Ops, Builder, Value: Allocas.size());
688 Ops.append(in_start: Allocas.begin(), in_end: Allocas.end());
689
690 // Now construct GC base/derived map;
691 pushStackMapConstant(Ops, Builder, Value: SI.Ptrs.size());
692 SDLoc L = Builder.getCurSDLoc();
693 for (unsigned i = 0; i < SI.Ptrs.size(); ++i) {
694 SDValue Base = Builder.getValue(V: SI.Bases[i]);
695 assert(GCPtrIndexMap.count(Base) && "base not found in index map");
696 Ops.push_back(
697 Elt: Builder.DAG.getTargetConstant(GCPtrIndexMap[Base], L, MVT::i64));
698 SDValue Derived = Builder.getValue(V: SI.Ptrs[i]);
699 assert(GCPtrIndexMap.count(Derived) && "derived not found in index map");
700 Ops.push_back(
701 Elt: Builder.DAG.getTargetConstant(GCPtrIndexMap[Derived], L, MVT::i64));
702 }
703}
704
705SDValue SelectionDAGBuilder::LowerAsSTATEPOINT(
706 SelectionDAGBuilder::StatepointLoweringInfo &SI) {
707 // The basic scheme here is that information about both the original call and
708 // the safepoint is encoded in the CallInst. We create a temporary call and
709 // lower it, then reverse engineer the calling sequence.
710
711 NumOfStatepoints++;
712 // Clear state
713 StatepointLowering.startNewStatepoint(Builder&: *this);
714 assert(SI.Bases.size() == SI.Ptrs.size() && "Pointer without base!");
715 assert((GFI || SI.Bases.empty()) &&
716 "No gc specified, so cannot relocate pointers!");
717
718 LLVM_DEBUG(if (SI.StatepointInstr) dbgs()
719 << "Lowering statepoint " << *SI.StatepointInstr << "\n");
720#ifndef NDEBUG
721 for (const auto *Reloc : SI.GCRelocates)
722 if (Reloc->getParent() == SI.StatepointInstr->getParent())
723 StatepointLowering.scheduleRelocCall(RelocCall: *Reloc);
724#endif
725
726 // Lower statepoint vmstate and gcstate arguments
727
728 // All lowered meta args.
729 SmallVector<SDValue, 10> LoweredMetaArgs;
730 // Lowered GC pointers (subset of above).
731 SmallVector<SDValue, 16> LoweredGCArgs;
732 SmallVector<MachineMemOperand*, 16> MemRefs;
733 // Maps derived pointer SDValue to statepoint result of relocated pointer.
734 DenseMap<SDValue, int> LowerAsVReg;
735 lowerStatepointMetaArgs(Ops&: LoweredMetaArgs, MemRefs, GCPtrs&: LoweredGCArgs, LowerAsVReg,
736 SI, Builder&: *this);
737
738 // Now that we've emitted the spills, we need to update the root so that the
739 // call sequence is ordered correctly.
740 SI.CLI.setChain(getRoot());
741
742 // Get call node, we will replace it later with statepoint
743 SDValue ReturnVal;
744 SDNode *CallNode;
745 std::tie(args&: ReturnVal, args&: CallNode) = lowerCallFromStatepointLoweringInfo(SI, Builder&: *this);
746
747 // Construct the actual GC_TRANSITION_START, STATEPOINT, and GC_TRANSITION_END
748 // nodes with all the appropriate arguments and return values.
749
750 // Call Node: Chain, Target, {Args}, RegMask, [Glue]
751 SDValue Chain = CallNode->getOperand(Num: 0);
752
753 SDValue Glue;
754 bool CallHasIncomingGlue = CallNode->getGluedNode();
755 if (CallHasIncomingGlue) {
756 // Glue is always last operand
757 Glue = CallNode->getOperand(Num: CallNode->getNumOperands() - 1);
758 }
759
760 // Build the GC_TRANSITION_START node if necessary.
761 //
762 // The operands to the GC_TRANSITION_{START,END} nodes are laid out in the
763 // order in which they appear in the call to the statepoint intrinsic. If
764 // any of the operands is a pointer-typed, that operand is immediately
765 // followed by a SRCVALUE for the pointer that may be used during lowering
766 // (e.g. to form MachinePointerInfo values for loads/stores).
767 const bool IsGCTransition =
768 (SI.StatepointFlags & (uint64_t)StatepointFlags::GCTransition) ==
769 (uint64_t)StatepointFlags::GCTransition;
770 if (IsGCTransition) {
771 SmallVector<SDValue, 8> TSOps;
772
773 // Add chain
774 TSOps.push_back(Elt: Chain);
775
776 // Add GC transition arguments
777 for (const Value *V : SI.GCTransitionArgs) {
778 TSOps.push_back(Elt: getValue(V));
779 if (V->getType()->isPointerTy())
780 TSOps.push_back(Elt: DAG.getSrcValue(v: V));
781 }
782
783 // Add glue if necessary
784 if (CallHasIncomingGlue)
785 TSOps.push_back(Elt: Glue);
786
787 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
788
789 SDValue GCTransitionStart =
790 DAG.getNode(Opcode: ISD::GC_TRANSITION_START, DL: getCurSDLoc(), VTList: NodeTys, Ops: TSOps);
791
792 Chain = GCTransitionStart.getValue(R: 0);
793 Glue = GCTransitionStart.getValue(R: 1);
794 }
795
796 // TODO: Currently, all of these operands are being marked as read/write in
797 // PrologEpilougeInserter.cpp, we should special case the VMState arguments
798 // and flags to be read-only.
799 SmallVector<SDValue, 40> Ops;
800
801 // Add the <id> and <numBytes> constants.
802 Ops.push_back(Elt: DAG.getTargetConstant(SI.ID, getCurSDLoc(), MVT::i64));
803 Ops.push_back(
804 Elt: DAG.getTargetConstant(SI.NumPatchBytes, getCurSDLoc(), MVT::i32));
805
806 // Calculate and push starting position of vmstate arguments
807 // Get number of arguments incoming directly into call node
808 unsigned NumCallRegArgs =
809 CallNode->getNumOperands() - (CallHasIncomingGlue ? 4 : 3);
810 Ops.push_back(Elt: DAG.getTargetConstant(NumCallRegArgs, getCurSDLoc(), MVT::i32));
811
812 // Add call target
813 SDValue CallTarget = SDValue(CallNode->getOperand(Num: 1).getNode(), 0);
814 Ops.push_back(Elt: CallTarget);
815
816 // Add call arguments
817 // Get position of register mask in the call
818 SDNode::op_iterator RegMaskIt;
819 if (CallHasIncomingGlue)
820 RegMaskIt = CallNode->op_end() - 2;
821 else
822 RegMaskIt = CallNode->op_end() - 1;
823 Ops.insert(I: Ops.end(), From: CallNode->op_begin() + 2, To: RegMaskIt);
824
825 // Add a constant argument for the calling convention
826 pushStackMapConstant(Ops, Builder&: *this, Value: SI.CLI.CallConv);
827
828 // Add a constant argument for the flags
829 uint64_t Flags = SI.StatepointFlags;
830 assert(((Flags & ~(uint64_t)StatepointFlags::MaskAll) == 0) &&
831 "Unknown flag used");
832 pushStackMapConstant(Ops, Builder&: *this, Value: Flags);
833
834 // Insert all vmstate and gcstate arguments
835 llvm::append_range(C&: Ops, R&: LoweredMetaArgs);
836
837 // Add register mask from call node
838 Ops.push_back(Elt: *RegMaskIt);
839
840 // Add chain
841 Ops.push_back(Elt: Chain);
842
843 // Same for the glue, but we add it only if original call had it
844 if (Glue.getNode())
845 Ops.push_back(Elt: Glue);
846
847 // Compute return values. Provide a glue output since we consume one as
848 // input. This allows someone else to chain off us as needed.
849 SmallVector<EVT, 8> NodeTys;
850 for (auto SD : LoweredGCArgs) {
851 if (!LowerAsVReg.count(Val: SD))
852 continue;
853 NodeTys.push_back(Elt: SD.getValueType());
854 }
855 LLVM_DEBUG(dbgs() << "Statepoint has " << NodeTys.size() << " results\n");
856 assert(NodeTys.size() == LowerAsVReg.size() && "Inconsistent GC Ptr lowering");
857 NodeTys.push_back(MVT::Elt: Other);
858 NodeTys.push_back(MVT::Elt: Glue);
859
860 unsigned NumResults = NodeTys.size();
861 MachineSDNode *StatepointMCNode =
862 DAG.getMachineNode(Opcode: TargetOpcode::STATEPOINT, dl: getCurSDLoc(), ResultTys: NodeTys, Ops);
863 DAG.setNodeMemRefs(N: StatepointMCNode, NewMemRefs: MemRefs);
864
865 // For values lowered to tied-defs, create the virtual registers if used
866 // in other blocks. For local gc.relocate record appropriate statepoint
867 // result in StatepointLoweringState.
868 DenseMap<SDValue, Register> VirtRegs;
869 for (const auto *Relocate : SI.GCRelocates) {
870 Value *Derived = Relocate->getDerivedPtr();
871 SDValue SD = getValue(V: Derived);
872 if (!LowerAsVReg.count(Val: SD))
873 continue;
874
875 SDValue Relocated = SDValue(StatepointMCNode, LowerAsVReg[SD]);
876
877 // Handle local relocate. Note that different relocates might
878 // map to the same SDValue.
879 if (SI.StatepointInstr->getParent() == Relocate->getParent()) {
880 SDValue Res = StatepointLowering.getLocation(Val: SD);
881 if (Res)
882 assert(Res == Relocated);
883 else
884 StatepointLowering.setLocation(Val: SD, Location: Relocated);
885 continue;
886 }
887
888 // Handle multiple gc.relocates of the same input efficiently.
889 if (VirtRegs.count(Val: SD))
890 continue;
891
892 auto *RetTy = Relocate->getType();
893 Register Reg = FuncInfo.CreateRegs(Ty: RetTy);
894 RegsForValue RFV(*DAG.getContext(), DAG.getTargetLoweringInfo(),
895 DAG.getDataLayout(), Reg, RetTy, std::nullopt);
896 SDValue Chain = DAG.getRoot();
897 RFV.getCopyToRegs(Val: Relocated, DAG, dl: getCurSDLoc(), Chain, Glue: nullptr);
898 PendingExports.push_back(Elt: Chain);
899
900 VirtRegs[SD] = Reg;
901 }
902
903 // Record for later use how each relocation was lowered. This is needed to
904 // allow later gc.relocates to mirror the lowering chosen.
905 const Instruction *StatepointInstr = SI.StatepointInstr;
906 auto &RelocationMap = FuncInfo.StatepointRelocationMaps[StatepointInstr];
907 for (const GCRelocateInst *Relocate : SI.GCRelocates) {
908 const Value *V = Relocate->getDerivedPtr();
909 SDValue SDV = getValue(V);
910 SDValue Loc = StatepointLowering.getLocation(Val: SDV);
911
912 bool IsLocal = (Relocate->getParent() == StatepointInstr->getParent());
913
914 RecordType Record;
915 if (IsLocal && LowerAsVReg.count(Val: SDV)) {
916 // Result is already stored in StatepointLowering
917 Record.type = RecordType::SDValueNode;
918 } else if (LowerAsVReg.count(Val: SDV)) {
919 Record.type = RecordType::VReg;
920 assert(VirtRegs.count(SDV));
921 Record.payload.Reg = VirtRegs[SDV];
922 } else if (Loc.getNode()) {
923 Record.type = RecordType::Spill;
924 Record.payload.FI = cast<FrameIndexSDNode>(Val&: Loc)->getIndex();
925 } else {
926 Record.type = RecordType::NoRelocate;
927 // If we didn't relocate a value, we'll essentialy end up inserting an
928 // additional use of the original value when lowering the gc.relocate.
929 // We need to make sure the value is available at the new use, which
930 // might be in another block.
931 if (Relocate->getParent() != StatepointInstr->getParent())
932 ExportFromCurrentBlock(V);
933 }
934 RelocationMap[Relocate] = Record;
935 }
936
937
938
939 SDNode *SinkNode = StatepointMCNode;
940
941 // Build the GC_TRANSITION_END node if necessary.
942 //
943 // See the comment above regarding GC_TRANSITION_START for the layout of
944 // the operands to the GC_TRANSITION_END node.
945 if (IsGCTransition) {
946 SmallVector<SDValue, 8> TEOps;
947
948 // Add chain
949 TEOps.push_back(Elt: SDValue(StatepointMCNode, NumResults - 2));
950
951 // Add GC transition arguments
952 for (const Value *V : SI.GCTransitionArgs) {
953 TEOps.push_back(Elt: getValue(V));
954 if (V->getType()->isPointerTy())
955 TEOps.push_back(Elt: DAG.getSrcValue(v: V));
956 }
957
958 // Add glue
959 TEOps.push_back(Elt: SDValue(StatepointMCNode, NumResults - 1));
960
961 SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
962
963 SDValue GCTransitionStart =
964 DAG.getNode(Opcode: ISD::GC_TRANSITION_END, DL: getCurSDLoc(), VTList: NodeTys, Ops: TEOps);
965
966 SinkNode = GCTransitionStart.getNode();
967 }
968
969 // Replace original call
970 // Call: ch,glue = CALL ...
971 // Statepoint: [gc relocates],ch,glue = STATEPOINT ...
972 unsigned NumSinkValues = SinkNode->getNumValues();
973 SDValue StatepointValues[2] = {SDValue(SinkNode, NumSinkValues - 2),
974 SDValue(SinkNode, NumSinkValues - 1)};
975 DAG.ReplaceAllUsesWith(From: CallNode, To: StatepointValues);
976 // Remove original call node
977 DAG.DeleteNode(N: CallNode);
978
979 // Since we always emit CopyToRegs (even for local relocates), we must
980 // update root, so that they are emitted before any local uses.
981 (void)getControlRoot();
982
983 // TODO: A better future implementation would be to emit a single variable
984 // argument, variable return value STATEPOINT node here and then hookup the
985 // return value of each gc.relocate to the respective output of the
986 // previously emitted STATEPOINT value. Unfortunately, this doesn't appear
987 // to actually be possible today.
988
989 return ReturnVal;
990}
991
992/// Return two gc.results if present. First result is a block local
993/// gc.result, second result is a non-block local gc.result. Corresponding
994/// entry will be nullptr if not present.
995static std::pair<const GCResultInst*, const GCResultInst*>
996getGCResultLocality(const GCStatepointInst &S) {
997 std::pair<const GCResultInst *, const GCResultInst*> Res(nullptr, nullptr);
998 for (const auto *U : S.users()) {
999 auto *GRI = dyn_cast<GCResultInst>(Val: U);
1000 if (!GRI)
1001 continue;
1002 if (GRI->getParent() == S.getParent())
1003 Res.first = GRI;
1004 else
1005 Res.second = GRI;
1006 }
1007 return Res;
1008}
1009
1010void
1011SelectionDAGBuilder::LowerStatepoint(const GCStatepointInst &I,
1012 const BasicBlock *EHPadBB /*= nullptr*/) {
1013 assert(I.getCallingConv() != CallingConv::AnyReg &&
1014 "anyregcc is not supported on statepoints!");
1015
1016#ifndef NDEBUG
1017 // Check that the associated GCStrategy expects to encounter statepoints.
1018 assert(GFI->getStrategy().useStatepoints() &&
1019 "GCStrategy does not expect to encounter statepoints");
1020#endif
1021
1022 SDValue ActualCallee;
1023 SDValue Callee = getValue(V: I.getActualCalledOperand());
1024
1025 if (I.getNumPatchBytes() > 0) {
1026 // If we've been asked to emit a nop sequence instead of a call instruction
1027 // for this statepoint then don't lower the call target, but use a constant
1028 // `undef` instead. Not lowering the call target lets statepoint clients
1029 // get away without providing a physical address for the symbolic call
1030 // target at link time.
1031 ActualCallee = DAG.getUNDEF(VT: Callee.getValueType());
1032 } else {
1033 ActualCallee = Callee;
1034 }
1035
1036 const auto GCResultLocality = getGCResultLocality(S: I);
1037 AttributeSet retAttrs;
1038 if (GCResultLocality.first)
1039 retAttrs = GCResultLocality.first->getAttributes().getRetAttrs();
1040
1041 StatepointLoweringInfo SI(DAG);
1042 populateCallLoweringInfo(CLI&: SI.CLI, Call: &I, ArgIdx: GCStatepointInst::CallArgsBeginPos,
1043 NumArgs: I.getNumCallArgs(), Callee: ActualCallee,
1044 ReturnTy: I.getActualReturnType(), RetAttrs: retAttrs,
1045 /*IsPatchPoint=*/false);
1046
1047 // There may be duplication in the gc.relocate list; such as two copies of
1048 // each relocation on normal and exceptional path for an invoke. We only
1049 // need to spill once and record one copy in the stackmap, but we need to
1050 // reload once per gc.relocate. (Dedupping gc.relocates is trickier and best
1051 // handled as a CSE problem elsewhere.)
1052 // TODO: There a couple of major stackmap size optimizations we could do
1053 // here if we wished.
1054 // 1) If we've encountered a derived pair {B, D}, we don't need to actually
1055 // record {B,B} if it's seen later.
1056 // 2) Due to rematerialization, actual derived pointers are somewhat rare;
1057 // given that, we could change the format to record base pointer relocations
1058 // separately with half the space. This would require a format rev and a
1059 // fairly major rework of the STATEPOINT node though.
1060 SmallSet<SDValue, 8> Seen;
1061 for (const GCRelocateInst *Relocate : I.getGCRelocates()) {
1062 SI.GCRelocates.push_back(Elt: Relocate);
1063
1064 SDValue DerivedSD = getValue(V: Relocate->getDerivedPtr());
1065 if (Seen.insert(V: DerivedSD).second) {
1066 SI.Bases.push_back(Elt: Relocate->getBasePtr());
1067 SI.Ptrs.push_back(Elt: Relocate->getDerivedPtr());
1068 }
1069 }
1070
1071 // If we find a deopt value which isn't explicitly added, we need to
1072 // ensure it gets lowered such that gc cycles occurring before the
1073 // deoptimization event during the lifetime of the call don't invalidate
1074 // the pointer we're deopting with. Note that we assume that all
1075 // pointers passed to deopt are base pointers; relaxing that assumption
1076 // would require relatively large changes to how we represent relocations.
1077 for (Value *V : I.deopt_operands()) {
1078 if (!isGCValue(V, Builder&: *this))
1079 continue;
1080 if (Seen.insert(V: getValue(V)).second) {
1081 SI.Bases.push_back(Elt: V);
1082 SI.Ptrs.push_back(Elt: V);
1083 }
1084 }
1085
1086 SI.GCArgs = ArrayRef<const Use>(I.gc_args_begin(), I.gc_args_end());
1087 SI.StatepointInstr = &I;
1088 SI.ID = I.getID();
1089
1090 SI.DeoptState = ArrayRef<const Use>(I.deopt_begin(), I.deopt_end());
1091 SI.GCTransitionArgs = ArrayRef<const Use>(I.gc_transition_args_begin(),
1092 I.gc_transition_args_end());
1093
1094 SI.StatepointFlags = I.getFlags();
1095 SI.NumPatchBytes = I.getNumPatchBytes();
1096 SI.EHPadBB = EHPadBB;
1097
1098 SDValue ReturnValue = LowerAsSTATEPOINT(SI);
1099
1100 // Export the result value if needed
1101 if (!GCResultLocality.first && !GCResultLocality.second) {
1102 // The return value is not needed, just generate a poison value.
1103 // Note: This covers the void return case.
1104 setValue(V: &I, NewN: DAG.getIntPtrConstant(Val: -1, DL: getCurSDLoc()));
1105 return;
1106 }
1107
1108 if (GCResultLocality.first) {
1109 // Result value will be used in a same basic block. Don't export it or
1110 // perform any explicit register copies. The gc_result will simply grab
1111 // this value.
1112 setValue(V: &I, NewN: ReturnValue);
1113 }
1114
1115 if (!GCResultLocality.second)
1116 return;
1117 // Result value will be used in a different basic block so we need to export
1118 // it now. Default exporting mechanism will not work here because statepoint
1119 // call has a different type than the actual call. It means that by default
1120 // llvm will create export register of the wrong type (always i32 in our
1121 // case). So instead we need to create export register with correct type
1122 // manually.
1123 // TODO: To eliminate this problem we can remove gc.result intrinsics
1124 // completely and make statepoint call to return a tuple.
1125 Type *RetTy = GCResultLocality.second->getType();
1126 Register Reg = FuncInfo.CreateRegs(Ty: RetTy);
1127 RegsForValue RFV(*DAG.getContext(), DAG.getTargetLoweringInfo(),
1128 DAG.getDataLayout(), Reg, RetTy,
1129 I.getCallingConv());
1130 SDValue Chain = DAG.getEntryNode();
1131
1132 RFV.getCopyToRegs(Val: ReturnValue, DAG, dl: getCurSDLoc(), Chain, Glue: nullptr);
1133 PendingExports.push_back(Elt: Chain);
1134 FuncInfo.ValueMap[&I] = Reg;
1135}
1136
1137void SelectionDAGBuilder::LowerCallSiteWithDeoptBundleImpl(
1138 const CallBase *Call, SDValue Callee, const BasicBlock *EHPadBB,
1139 bool VarArgDisallowed, bool ForceVoidReturnTy) {
1140 StatepointLoweringInfo SI(DAG);
1141 unsigned ArgBeginIndex = Call->arg_begin() - Call->op_begin();
1142 populateCallLoweringInfo(
1143 CLI&: SI.CLI, Call, ArgIdx: ArgBeginIndex, NumArgs: Call->arg_size(), Callee,
1144 ReturnTy: ForceVoidReturnTy ? Type::getVoidTy(C&: *DAG.getContext()) : Call->getType(),
1145 RetAttrs: Call->getAttributes().getRetAttrs(), /*IsPatchPoint=*/false);
1146 if (!VarArgDisallowed)
1147 SI.CLI.IsVarArg = Call->getFunctionType()->isVarArg();
1148
1149 auto DeoptBundle = *Call->getOperandBundle(ID: LLVMContext::OB_deopt);
1150
1151 unsigned DefaultID = StatepointDirectives::DeoptBundleStatepointID;
1152
1153 auto SD = parseStatepointDirectivesFromAttrs(AS: Call->getAttributes());
1154 SI.ID = SD.StatepointID.value_or(u&: DefaultID);
1155 SI.NumPatchBytes = SD.NumPatchBytes.value_or(u: 0);
1156
1157 SI.DeoptState =
1158 ArrayRef<const Use>(DeoptBundle.Inputs.begin(), DeoptBundle.Inputs.end());
1159 SI.StatepointFlags = static_cast<uint64_t>(StatepointFlags::None);
1160 SI.EHPadBB = EHPadBB;
1161
1162 // NB! The GC arguments are deliberately left empty.
1163
1164 LLVM_DEBUG(dbgs() << "Lowering call with deopt bundle " << *Call << "\n");
1165 if (SDValue ReturnVal = LowerAsSTATEPOINT(SI)) {
1166 ReturnVal = lowerRangeToAssertZExt(DAG, I: *Call, Op: ReturnVal);
1167 setValue(V: Call, NewN: ReturnVal);
1168 }
1169}
1170
1171void SelectionDAGBuilder::LowerCallSiteWithDeoptBundle(
1172 const CallBase *Call, SDValue Callee, const BasicBlock *EHPadBB) {
1173 LowerCallSiteWithDeoptBundleImpl(Call, Callee, EHPadBB,
1174 /* VarArgDisallowed = */ false,
1175 /* ForceVoidReturnTy = */ false);
1176}
1177
1178void SelectionDAGBuilder::visitGCResult(const GCResultInst &CI) {
1179 // The result value of the gc_result is simply the result of the actual
1180 // call. We've already emitted this, so just grab the value.
1181 const Value *SI = CI.getStatepoint();
1182 assert((isa<GCStatepointInst>(SI) || isa<UndefValue>(SI)) &&
1183 "GetStatepoint must return one of two types");
1184 if (isa<UndefValue>(Val: SI))
1185 return;
1186
1187 if (cast<GCStatepointInst>(Val: SI)->getParent() == CI.getParent()) {
1188 setValue(V: &CI, NewN: getValue(V: SI));
1189 return;
1190 }
1191 // Statepoint is in different basic block so we should have stored call
1192 // result in a virtual register.
1193 // We can not use default getValue() functionality to copy value from this
1194 // register because statepoint and actual call return types can be
1195 // different, and getValue() will use CopyFromReg of the wrong type,
1196 // which is always i32 in our case.
1197 Type *RetTy = CI.getType();
1198 SDValue CopyFromReg = getCopyFromRegs(V: SI, Ty: RetTy);
1199
1200 assert(CopyFromReg.getNode());
1201 setValue(V: &CI, NewN: CopyFromReg);
1202}
1203
1204void SelectionDAGBuilder::visitGCRelocate(const GCRelocateInst &Relocate) {
1205 const Value *Statepoint = Relocate.getStatepoint();
1206#ifndef NDEBUG
1207 // Consistency check
1208 // We skip this check for relocates not in the same basic block as their
1209 // statepoint. It would be too expensive to preserve validation info through
1210 // different basic blocks.
1211 assert((isa<GCStatepointInst>(Statepoint) || isa<UndefValue>(Statepoint)) &&
1212 "GetStatepoint must return one of two types");
1213 if (isa<UndefValue>(Val: Statepoint))
1214 return;
1215
1216 if (cast<GCStatepointInst>(Val: Statepoint)->getParent() == Relocate.getParent())
1217 StatepointLowering.relocCallVisited(RelocCall: Relocate);
1218#endif
1219
1220 const Value *DerivedPtr = Relocate.getDerivedPtr();
1221 auto &RelocationMap =
1222 FuncInfo.StatepointRelocationMaps[cast<GCStatepointInst>(Val: Statepoint)];
1223 auto SlotIt = RelocationMap.find(Val: &Relocate);
1224 assert(SlotIt != RelocationMap.end() && "Relocating not lowered gc value");
1225 const RecordType &Record = SlotIt->second;
1226
1227 // If relocation was done via virtual register..
1228 if (Record.type == RecordType::SDValueNode) {
1229 assert(cast<GCStatepointInst>(Statepoint)->getParent() ==
1230 Relocate.getParent() &&
1231 "Nonlocal gc.relocate mapped via SDValue");
1232 SDValue SDV = StatepointLowering.getLocation(Val: getValue(V: DerivedPtr));
1233 assert(SDV.getNode() && "empty SDValue");
1234 setValue(V: &Relocate, NewN: SDV);
1235 return;
1236 }
1237 if (Record.type == RecordType::VReg) {
1238 Register InReg = Record.payload.Reg;
1239 RegsForValue RFV(*DAG.getContext(), DAG.getTargetLoweringInfo(),
1240 DAG.getDataLayout(), InReg, Relocate.getType(),
1241 std::nullopt); // This is not an ABI copy.
1242 // We generate copy to/from regs even for local uses, hence we must
1243 // chain with current root to ensure proper ordering of copies w.r.t.
1244 // statepoint.
1245 SDValue Chain = DAG.getRoot();
1246 SDValue Relocation = RFV.getCopyFromRegs(DAG, FuncInfo, dl: getCurSDLoc(),
1247 Chain, Glue: nullptr, V: nullptr);
1248 setValue(V: &Relocate, NewN: Relocation);
1249 return;
1250 }
1251
1252 if (Record.type == RecordType::Spill) {
1253 unsigned Index = Record.payload.FI;
1254 SDValue SpillSlot = DAG.getTargetFrameIndex(FI: Index, VT: getFrameIndexTy());
1255
1256 // All the reloads are independent and are reading memory only modified by
1257 // statepoints (i.e. no other aliasing stores); informing SelectionDAG of
1258 // this lets CSE kick in for free and allows reordering of
1259 // instructions if possible. The lowering for statepoint sets the root,
1260 // so this is ordering all reloads with the either
1261 // a) the statepoint node itself, or
1262 // b) the entry of the current block for an invoke statepoint.
1263 const SDValue Chain = DAG.getRoot(); // != Builder.getRoot()
1264
1265 auto &MF = DAG.getMachineFunction();
1266 auto &MFI = MF.getFrameInfo();
1267 auto PtrInfo = MachinePointerInfo::getFixedStack(MF, FI: Index);
1268 auto *LoadMMO = MF.getMachineMemOperand(PtrInfo, f: MachineMemOperand::MOLoad,
1269 s: MFI.getObjectSize(ObjectIdx: Index),
1270 base_alignment: MFI.getObjectAlign(ObjectIdx: Index));
1271
1272 auto LoadVT = DAG.getTargetLoweringInfo().getValueType(DL: DAG.getDataLayout(),
1273 Ty: Relocate.getType());
1274
1275 SDValue SpillLoad =
1276 DAG.getLoad(VT: LoadVT, dl: getCurSDLoc(), Chain, Ptr: SpillSlot, MMO: LoadMMO);
1277 PendingLoads.push_back(Elt: SpillLoad.getValue(R: 1));
1278
1279 assert(SpillLoad.getNode());
1280 setValue(V: &Relocate, NewN: SpillLoad);
1281 return;
1282 }
1283
1284 assert(Record.type == RecordType::NoRelocate);
1285 SDValue SD = getValue(V: DerivedPtr);
1286
1287 if (SD.isUndef() && SD.getValueType().getSizeInBits() <= 64) {
1288 // Lowering relocate(undef) as arbitrary constant. Current constant value
1289 // is chosen such that it's unlikely to be a valid pointer.
1290 setValue(V: &Relocate, NewN: DAG.getConstant(0xFEFEFEFE, SDLoc(SD), MVT::i64));
1291 return;
1292 }
1293
1294 // We didn't need to spill these special cases (constants and allocas).
1295 // See the handling in spillIncomingValueForStatepoint for detail.
1296 setValue(V: &Relocate, NewN: SD);
1297}
1298
1299void SelectionDAGBuilder::LowerDeoptimizeCall(const CallInst *CI) {
1300 const auto &TLI = DAG.getTargetLoweringInfo();
1301 SDValue Callee = DAG.getExternalSymbol(Sym: TLI.getLibcallName(Call: RTLIB::DEOPTIMIZE),
1302 VT: TLI.getPointerTy(DL: DAG.getDataLayout()));
1303
1304 // We don't lower calls to __llvm_deoptimize as varargs, but as a regular
1305 // call. We also do not lower the return value to any virtual register, and
1306 // change the immediately following return to a trap instruction.
1307 LowerCallSiteWithDeoptBundleImpl(Call: CI, Callee, /* EHPadBB = */ nullptr,
1308 /* VarArgDisallowed = */ true,
1309 /* ForceVoidReturnTy = */ true);
1310}
1311
1312void SelectionDAGBuilder::LowerDeoptimizingReturn() {
1313 // We do not lower the return value from llvm.deoptimize to any virtual
1314 // register, and change the immediately following return to a trap
1315 // instruction.
1316 if (DAG.getTarget().Options.TrapUnreachable)
1317 DAG.setRoot(
1318 DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, DAG.getRoot()));
1319}
1320

source code of llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp