| //===-- StatepointLowering.cpp - SDAGBuilder's statepoint code -----------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file includes support code use by SelectionDAGBuilder when lowering a |
| // statepoint sequence in SelectionDAG IR. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "StatepointLowering.h" |
| #include "SelectionDAGBuilder.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/CodeGen/FunctionLoweringInfo.h" |
| #include "llvm/CodeGen/MachineFrameInfo.h" |
| #include "llvm/CodeGen/GCMetadata.h" |
| #include "llvm/CodeGen/GCStrategy.h" |
| #include "llvm/CodeGen/SelectionDAG.h" |
| #include "llvm/CodeGen/StackMaps.h" |
| #include "llvm/IR/CallingConv.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/Statepoint.h" |
| #include "llvm/Target/TargetLowering.h" |
| #include <algorithm> |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "statepoint-lowering" |
| |
| STATISTIC(NumSlotsAllocatedForStatepoints, |
| "Number of stack slots allocated for statepoints"); |
| STATISTIC(NumOfStatepoints, "Number of statepoint nodes encountered"); |
| STATISTIC(StatepointMaxSlotsRequired, |
| "Maximum number of stack slots required for a singe statepoint"); |
| |
| static void pushStackMapConstant(SmallVectorImpl<SDValue>& Ops, |
| SelectionDAGBuilder &Builder, uint64_t Value) { |
| SDLoc L = Builder.getCurSDLoc(); |
| Ops.push_back(Builder.DAG.getTargetConstant(StackMaps::ConstantOp, L, |
| MVT::i64)); |
| Ops.push_back(Builder.DAG.getTargetConstant(Value, L, MVT::i64)); |
| } |
| |
| void StatepointLoweringState::startNewStatepoint(SelectionDAGBuilder &Builder) { |
| // Consistency check |
| assert(PendingGCRelocateCalls.empty() && |
| "Trying to visit statepoint before finished processing previous one"); |
| Locations.clear(); |
| NextSlotToAllocate = 0; |
| // Need to resize this on each safepoint - we need the two to stay in |
| // sync and the clear patterns of a SelectionDAGBuilder have no relation |
| // to FunctionLoweringInfo. |
| AllocatedStackSlots.resize(Builder.FuncInfo.StatepointStackSlots.size()); |
| for (size_t i = 0; i < AllocatedStackSlots.size(); i++) { |
| AllocatedStackSlots[i] = false; |
| } |
| } |
| |
| void StatepointLoweringState::clear() { |
| Locations.clear(); |
| AllocatedStackSlots.clear(); |
| assert(PendingGCRelocateCalls.empty() && |
| "cleared before statepoint sequence completed"); |
| } |
| |
| SDValue |
| StatepointLoweringState::allocateStackSlot(EVT ValueType, |
| SelectionDAGBuilder &Builder) { |
| |
| NumSlotsAllocatedForStatepoints++; |
| |
| // The basic scheme here is to first look for a previously created stack slot |
| // which is not in use (accounting for the fact arbitrary slots may already |
| // be reserved), or to create a new stack slot and use it. |
| |
| // If this doesn't succeed in 40000 iterations, something is seriously wrong |
| for (int i = 0; i < 40000; i++) { |
| assert(Builder.FuncInfo.StatepointStackSlots.size() == |
| AllocatedStackSlots.size() && |
| "broken invariant"); |
| const size_t NumSlots = AllocatedStackSlots.size(); |
| assert(NextSlotToAllocate <= NumSlots && "broken invariant"); |
| |
| if (NextSlotToAllocate >= NumSlots) { |
| assert(NextSlotToAllocate == NumSlots); |
| // record stats |
| if (NumSlots + 1 > StatepointMaxSlotsRequired) { |
| StatepointMaxSlotsRequired = NumSlots + 1; |
| } |
| |
| SDValue SpillSlot = Builder.DAG.CreateStackTemporary(ValueType); |
| const unsigned FI = cast<FrameIndexSDNode>(SpillSlot)->getIndex(); |
| auto *MFI = Builder.DAG.getMachineFunction().getFrameInfo(); |
| MFI->markAsStatepointSpillSlotObjectIndex(FI); |
| |
| Builder.FuncInfo.StatepointStackSlots.push_back(FI); |
| AllocatedStackSlots.push_back(true); |
| return SpillSlot; |
| } |
| if (!AllocatedStackSlots[NextSlotToAllocate]) { |
| const int FI = Builder.FuncInfo.StatepointStackSlots[NextSlotToAllocate]; |
| AllocatedStackSlots[NextSlotToAllocate] = true; |
| return Builder.DAG.getFrameIndex(FI, ValueType); |
| } |
| // Note: We deliberately choose to advance this only on the failing path. |
| // Doing so on the succeeding path involves a bit of complexity that caused |
| // a minor bug previously. Unless performance shows this matters, please |
| // keep this code as simple as possible. |
| NextSlotToAllocate++; |
| } |
| llvm_unreachable("infinite loop?"); |
| } |
| |
| /// Utility function for reservePreviousStackSlotForValue. Tries to find |
| /// stack slot index to which we have spilled value for previous statepoints. |
| /// LookUpDepth specifies maximum DFS depth this function is allowed to look. |
| static Optional<int> findPreviousSpillSlot(const Value *Val, |
| SelectionDAGBuilder &Builder, |
| int LookUpDepth) { |
| // Can not look any further - give up now |
| if (LookUpDepth <= 0) |
| return Optional<int>(); |
| |
| // Spill location is known for gc relocates |
| if (const auto *Relocate = dyn_cast<GCRelocateInst>(Val)) { |
| FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap = |
| Builder.FuncInfo.StatepointRelocatedValues[Relocate->getStatepoint()]; |
| |
| auto It = SpillMap.find(Relocate->getDerivedPtr()); |
| if (It == SpillMap.end()) |
| return Optional<int>(); |
| |
| return It->second; |
| } |
| |
| // Look through bitcast instructions. |
| if (const BitCastInst *Cast = dyn_cast<BitCastInst>(Val)) { |
| return findPreviousSpillSlot(Cast->getOperand(0), Builder, LookUpDepth - 1); |
| } |
| |
| // Look through phi nodes |
| // All incoming values should have same known stack slot, otherwise result |
| // is unknown. |
| if (const PHINode *Phi = dyn_cast<PHINode>(Val)) { |
| Optional<int> MergedResult = None; |
| |
| for (auto &IncomingValue : Phi->incoming_values()) { |
| Optional<int> SpillSlot = |
| findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth - 1); |
| if (!SpillSlot.hasValue()) |
| return Optional<int>(); |
| |
| if (MergedResult.hasValue() && *MergedResult != *SpillSlot) |
| return Optional<int>(); |
| |
| MergedResult = SpillSlot; |
| } |
| return MergedResult; |
| } |
| |
| // TODO: We can do better for PHI nodes. In cases like this: |
| // ptr = phi(relocated_pointer, not_relocated_pointer) |
| // statepoint(ptr) |
| // We will return that stack slot for ptr is unknown. And later we might |
| // assign different stack slots for ptr and relocated_pointer. This limits |
| // llvm's ability to remove redundant stores. |
| // Unfortunately it's hard to accomplish in current infrastructure. |
| // We use this function to eliminate spill store completely, while |
| // in example we still need to emit store, but instead of any location |
| // we need to use special "preferred" location. |
| |
| // TODO: handle simple updates. If a value is modified and the original |
| // value is no longer live, it would be nice to put the modified value in the |
| // same slot. This allows folding of the memory accesses for some |
| // instructions types (like an increment). |
| // statepoint (i) |
| // i1 = i+1 |
| // statepoint (i1) |
| // However we need to be careful for cases like this: |
| // statepoint(i) |
| // i1 = i+1 |
| // statepoint(i, i1) |
| // Here we want to reserve spill slot for 'i', but not for 'i+1'. If we just |
| // put handling of simple modifications in this function like it's done |
| // for bitcasts we might end up reserving i's slot for 'i+1' because order in |
| // which we visit values is unspecified. |
| |
| // Don't know any information about this instruction |
| return Optional<int>(); |
| } |
| |
| /// Try to find existing copies of the incoming values in stack slots used for |
| /// statepoint spilling. If we can find a spill slot for the incoming value, |
| /// mark that slot as allocated, and reuse the same slot for this safepoint. |
| /// This helps to avoid series of loads and stores that only serve to reshuffle |
| /// values on the stack between calls. |
| static void reservePreviousStackSlotForValue(const Value *IncomingValue, |
| SelectionDAGBuilder &Builder) { |
| |
| SDValue Incoming = Builder.getValue(IncomingValue); |
| |
| if (isa<ConstantSDNode>(Incoming) || isa<FrameIndexSDNode>(Incoming)) { |
| // We won't need to spill this, so no need to check for previously |
| // allocated stack slots |
| return; |
| } |
| |
| SDValue OldLocation = Builder.StatepointLowering.getLocation(Incoming); |
| if (OldLocation.getNode()) |
| // duplicates in input |
| return; |
| |
| const int LookUpDepth = 6; |
| Optional<int> Index = |
| findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth); |
| if (!Index.hasValue()) |
| return; |
| |
| auto Itr = std::find(Builder.FuncInfo.StatepointStackSlots.begin(), |
| Builder.FuncInfo.StatepointStackSlots.end(), *Index); |
| assert(Itr != Builder.FuncInfo.StatepointStackSlots.end() && |
| "value spilled to the unknown stack slot"); |
| |
| // This is one of our dedicated lowering slots |
| const int Offset = |
| std::distance(Builder.FuncInfo.StatepointStackSlots.begin(), Itr); |
| if (Builder.StatepointLowering.isStackSlotAllocated(Offset)) { |
| // stack slot already assigned to someone else, can't use it! |
| // TODO: currently we reserve space for gc arguments after doing |
| // normal allocation for deopt arguments. We should reserve for |
| // _all_ deopt and gc arguments, then start allocating. This |
| // will prevent some moves being inserted when vm state changes, |
| // but gc state doesn't between two calls. |
| return; |
| } |
| // Reserve this stack slot |
| Builder.StatepointLowering.reserveStackSlot(Offset); |
| |
| // Cache this slot so we find it when going through the normal |
| // assignment loop. |
| SDValue Loc = Builder.DAG.getTargetFrameIndex(*Index, Incoming.getValueType()); |
| Builder.StatepointLowering.setLocation(Incoming, Loc); |
| } |
| |
| /// Remove any duplicate (as SDValues) from the derived pointer pairs. This |
| /// is not required for correctness. It's purpose is to reduce the size of |
| /// StackMap section. It has no effect on the number of spill slots required |
| /// or the actual lowering. |
| static void removeDuplicatesGCPtrs(SmallVectorImpl<const Value *> &Bases, |
| SmallVectorImpl<const Value *> &Ptrs, |
| SmallVectorImpl<const Value *> &Relocs, |
| SelectionDAGBuilder &Builder) { |
| |
| // This is horribly inefficient, but I don't care right now |
| SmallSet<SDValue, 64> Seen; |
| |
| SmallVector<const Value *, 64> NewBases, NewPtrs, NewRelocs; |
| for (size_t i = 0; i < Ptrs.size(); i++) { |
| SDValue SD = Builder.getValue(Ptrs[i]); |
| // Only add non-duplicates |
| if (Seen.count(SD) == 0) { |
| NewBases.push_back(Bases[i]); |
| NewPtrs.push_back(Ptrs[i]); |
| NewRelocs.push_back(Relocs[i]); |
| } |
| Seen.insert(SD); |
| } |
| assert(Bases.size() >= NewBases.size()); |
| assert(Ptrs.size() >= NewPtrs.size()); |
| assert(Relocs.size() >= NewRelocs.size()); |
| Bases = NewBases; |
| Ptrs = NewPtrs; |
| Relocs = NewRelocs; |
| assert(Ptrs.size() == Bases.size()); |
| assert(Ptrs.size() == Relocs.size()); |
| } |
| |
| /// Extract call from statepoint, lower it and return pointer to the |
| /// call node. Also update NodeMap so that getValue(statepoint) will |
| /// reference lowered call result |
| static SDNode * |
| lowerCallFromStatepoint(ImmutableStatepoint ISP, const BasicBlock *EHPadBB, |
| SelectionDAGBuilder &Builder, |
| SmallVectorImpl<SDValue> &PendingExports) { |
| |
| ImmutableCallSite CS(ISP.getCallSite()); |
| |
| SDValue ActualCallee; |
| |
| if (ISP.getNumPatchBytes() > 0) { |
| // If we've been asked to emit a nop sequence instead of a call instruction |
| // for this statepoint then don't lower the call target, but use a constant |
| // `null` instead. Not lowering the call target lets statepoint clients get |
| // away without providing a physical address for the symbolic call target at |
| // link time. |
| |
| const auto &TLI = Builder.DAG.getTargetLoweringInfo(); |
| const auto &DL = Builder.DAG.getDataLayout(); |
| |
| unsigned AS = ISP.getCalledValue()->getType()->getPointerAddressSpace(); |
| ActualCallee = Builder.DAG.getConstant(0, Builder.getCurSDLoc(), |
| TLI.getPointerTy(DL, AS)); |
| } else |
| ActualCallee = Builder.getValue(ISP.getCalledValue()); |
| |
| assert(CS.getCallingConv() != CallingConv::AnyReg && |
| "anyregcc is not supported on statepoints!"); |
| |
| Type *DefTy = ISP.getActualReturnType(); |
| bool HasDef = !DefTy->isVoidTy(); |
| |
| SDValue ReturnValue, CallEndVal; |
| std::tie(ReturnValue, CallEndVal) = Builder.lowerCallOperands( |
| ISP.getCallSite(), ImmutableStatepoint::CallArgsBeginPos, |
| ISP.getNumCallArgs(), ActualCallee, DefTy, EHPadBB, |
| false /* IsPatchPoint */); |
| |
| SDNode *CallEnd = CallEndVal.getNode(); |
| |
| // Get a call instruction from the call sequence chain. Tail calls are not |
| // allowed. The following code is essentially reverse engineering X86's |
| // LowerCallTo. |
| // |
| // We are expecting DAG to have the following form: |
| // |
| // ch = eh_label (only in case of invoke statepoint) |
| // ch, glue = callseq_start ch |
| // ch, glue = X86::Call ch, glue |
| // ch, glue = callseq_end ch, glue |
| // get_return_value ch, glue |
| // |
| // get_return_value can either be a sequence of CopyFromReg instructions |
| // to grab the return value from the return register(s), or it can be a LOAD |
| // to load a value returned by reference via a stack slot. |
| |
| if (HasDef) { |
| if (CallEnd->getOpcode() == ISD::LOAD) |
| CallEnd = CallEnd->getOperand(0).getNode(); |
| else |
| while (CallEnd->getOpcode() == ISD::CopyFromReg) |
| CallEnd = CallEnd->getOperand(0).getNode(); |
| } |
| |
| assert(CallEnd->getOpcode() == ISD::CALLSEQ_END && "expected!"); |
| |
| // Export the result value if needed |
| const Instruction *GCResult = ISP.getGCResult(); |
| if (HasDef && GCResult) { |
| if (GCResult->getParent() != CS.getParent()) { |
| // Result value will be used in a different basic block so we need to |
| // export it now. |
| // Default exporting mechanism will not work here because statepoint call |
| // has a different type than the actual call. It means that by default |
| // llvm will create export register of the wrong type (always i32 in our |
| // case). So instead we need to create export register with correct type |
| // manually. |
| // TODO: To eliminate this problem we can remove gc.result intrinsics |
| // completely and make statepoint call to return a tuple. |
| unsigned Reg = Builder.FuncInfo.CreateRegs(ISP.getActualReturnType()); |
| RegsForValue RFV( |
| *Builder.DAG.getContext(), Builder.DAG.getTargetLoweringInfo(), |
| Builder.DAG.getDataLayout(), Reg, ISP.getActualReturnType()); |
| SDValue Chain = Builder.DAG.getEntryNode(); |
| |
| RFV.getCopyToRegs(ReturnValue, Builder.DAG, Builder.getCurSDLoc(), Chain, |
| nullptr); |
| PendingExports.push_back(Chain); |
| Builder.FuncInfo.ValueMap[CS.getInstruction()] = Reg; |
| } else { |
| // Result value will be used in a same basic block. Don't export it or |
| // perform any explicit register copies. |
| // We'll replace the actuall call node shortly. gc_result will grab |
| // this value. |
| Builder.setValue(CS.getInstruction(), ReturnValue); |
| } |
| } else { |
| // The token value is never used from here on, just generate a poison value |
| Builder.setValue(CS.getInstruction(), |
| Builder.DAG.getIntPtrConstant(-1, Builder.getCurSDLoc())); |
| } |
| |
| return CallEnd->getOperand(0).getNode(); |
| } |
| |
| /// Callect all gc pointers coming into statepoint intrinsic, clean them up, |
| /// and return two arrays: |
| /// Bases - base pointers incoming to this statepoint |
| /// Ptrs - derived pointers incoming to this statepoint |
| /// Relocs - the gc_relocate corresponding to each base/ptr pair |
| /// Elements of this arrays should be in one-to-one correspondence with each |
| /// other i.e Bases[i], Ptrs[i] are from the same gcrelocate call |
| static void getIncomingStatepointGCValues( |
| SmallVectorImpl<const Value *> &Bases, SmallVectorImpl<const Value *> &Ptrs, |
| SmallVectorImpl<const Value *> &Relocs, ImmutableStatepoint StatepointSite, |
| SelectionDAGBuilder &Builder) { |
| for (const GCRelocateInst *Relocate : StatepointSite.getRelocates()) { |
| Relocs.push_back(Relocate); |
| Bases.push_back(Relocate->getBasePtr()); |
| Ptrs.push_back(Relocate->getDerivedPtr()); |
| } |
| |
| // Remove any redundant llvm::Values which map to the same SDValue as another |
| // input. Also has the effect of removing duplicates in the original |
| // llvm::Value input list as well. This is a useful optimization for |
| // reducing the size of the StackMap section. It has no other impact. |
| removeDuplicatesGCPtrs(Bases, Ptrs, Relocs, Builder); |
| |
| assert(Bases.size() == Ptrs.size() && Ptrs.size() == Relocs.size()); |
| } |
| |
| /// Spill a value incoming to the statepoint. It might be either part of |
| /// vmstate |
| /// or gcstate. In both cases unconditionally spill it on the stack unless it |
| /// is a null constant. Return pair with first element being frame index |
| /// containing saved value and second element with outgoing chain from the |
| /// emitted store |
| static std::pair<SDValue, SDValue> |
| spillIncomingStatepointValue(SDValue Incoming, SDValue Chain, |
| SelectionDAGBuilder &Builder) { |
| SDValue Loc = Builder.StatepointLowering.getLocation(Incoming); |
| |
| // Emit new store if we didn't do it for this ptr before |
| if (!Loc.getNode()) { |
| Loc = Builder.StatepointLowering.allocateStackSlot(Incoming.getValueType(), |
| Builder); |
| assert(isa<FrameIndexSDNode>(Loc)); |
| int Index = cast<FrameIndexSDNode>(Loc)->getIndex(); |
| // We use TargetFrameIndex so that isel will not select it into LEA |
| Loc = Builder.DAG.getTargetFrameIndex(Index, Incoming.getValueType()); |
| |
| // TODO: We can create TokenFactor node instead of |
| // chaining stores one after another, this may allow |
| // a bit more optimal scheduling for them |
| Chain = Builder.DAG.getStore(Chain, Builder.getCurSDLoc(), Incoming, Loc, |
| MachinePointerInfo::getFixedStack( |
| Builder.DAG.getMachineFunction(), Index), |
| false, false, 0); |
| |
| Builder.StatepointLowering.setLocation(Incoming, Loc); |
| } |
| |
| assert(Loc.getNode()); |
| return std::make_pair(Loc, Chain); |
| } |
| |
| /// Lower a single value incoming to a statepoint node. This value can be |
| /// either a deopt value or a gc value, the handling is the same. We special |
| /// case constants and allocas, then fall back to spilling if required. |
| static void lowerIncomingStatepointValue(SDValue Incoming, |
| SmallVectorImpl<SDValue> &Ops, |
| SelectionDAGBuilder &Builder) { |
| SDValue Chain = Builder.getRoot(); |
| |
| if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Incoming)) { |
| // If the original value was a constant, make sure it gets recorded as |
| // such in the stackmap. This is required so that the consumer can |
| // parse any internal format to the deopt state. It also handles null |
| // pointers and other constant pointers in GC states. Note the constant |
| // vectors do not appear to actually hit this path and that anything larger |
| // than an i64 value (not type!) will fail asserts here. |
| pushStackMapConstant(Ops, Builder, C->getSExtValue()); |
| } else if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) { |
| // This handles allocas as arguments to the statepoint (this is only |
| // really meaningful for a deopt value. For GC, we'd be trying to |
| // relocate the address of the alloca itself?) |
| Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(), |
| Incoming.getValueType())); |
| } else { |
| // Otherwise, locate a spill slot and explicitly spill it so it |
| // can be found by the runtime later. We currently do not support |
| // tracking values through callee saved registers to their eventual |
| // spill location. This would be a useful optimization, but would |
| // need to be optional since it requires a lot of complexity on the |
| // runtime side which not all would support. |
| std::pair<SDValue, SDValue> Res = |
| spillIncomingStatepointValue(Incoming, Chain, Builder); |
| Ops.push_back(Res.first); |
| Chain = Res.second; |
| } |
| |
| Builder.DAG.setRoot(Chain); |
| } |
| |
| /// Lower deopt state and gc pointer arguments of the statepoint. The actual |
| /// lowering is described in lowerIncomingStatepointValue. This function is |
| /// responsible for lowering everything in the right position and playing some |
| /// tricks to avoid redundant stack manipulation where possible. On |
| /// completion, 'Ops' will contain ready to use operands for machine code |
| /// statepoint. The chain nodes will have already been created and the DAG root |
| /// will be set to the last value spilled (if any were). |
| static void lowerStatepointMetaArgs(SmallVectorImpl<SDValue> &Ops, |
| ImmutableStatepoint StatepointSite, |
| SelectionDAGBuilder &Builder) { |
| |
| // Lower the deopt and gc arguments for this statepoint. Layout will |
| // be: deopt argument length, deopt arguments.., gc arguments... |
| |
| SmallVector<const Value *, 64> Bases, Ptrs, Relocations; |
| getIncomingStatepointGCValues(Bases, Ptrs, Relocations, StatepointSite, |
| Builder); |
| |
| #ifndef NDEBUG |
| // Check that each of the gc pointer and bases we've gotten out of the |
| // safepoint is something the strategy thinks might be a pointer (or vector |
| // of pointers) into the GC heap. This is basically just here to help catch |
| // errors during statepoint insertion. TODO: This should actually be in the |
| // Verifier, but we can't get to the GCStrategy from there (yet). |
| GCStrategy &S = Builder.GFI->getStrategy(); |
| for (const Value *V : Bases) { |
| auto Opt = S.isGCManagedPointer(V->getType()->getScalarType()); |
| if (Opt.hasValue()) { |
| assert(Opt.getValue() && |
| "non gc managed base pointer found in statepoint"); |
| } |
| } |
| for (const Value *V : Ptrs) { |
| auto Opt = S.isGCManagedPointer(V->getType()->getScalarType()); |
| if (Opt.hasValue()) { |
| assert(Opt.getValue() && |
| "non gc managed derived pointer found in statepoint"); |
| } |
| } |
| for (const Value *V : Relocations) { |
| auto Opt = S.isGCManagedPointer(V->getType()->getScalarType()); |
| if (Opt.hasValue()) { |
| assert(Opt.getValue() && "non gc managed pointer relocated"); |
| } |
| } |
| #endif |
| |
| // Before we actually start lowering (and allocating spill slots for values), |
| // reserve any stack slots which we judge to be profitable to reuse for a |
| // particular value. This is purely an optimization over the code below and |
| // doesn't change semantics at all. It is important for performance that we |
| // reserve slots for both deopt and gc values before lowering either. |
| for (const Value *V : StatepointSite.vm_state_args()) { |
| reservePreviousStackSlotForValue(V, Builder); |
| } |
| for (unsigned i = 0; i < Bases.size(); ++i) { |
| reservePreviousStackSlotForValue(Bases[i], Builder); |
| reservePreviousStackSlotForValue(Ptrs[i], Builder); |
| } |
| |
| // First, prefix the list with the number of unique values to be |
| // lowered. Note that this is the number of *Values* not the |
| // number of SDValues required to lower them. |
| const int NumVMSArgs = StatepointSite.getNumTotalVMSArgs(); |
| pushStackMapConstant(Ops, Builder, NumVMSArgs); |
| |
| assert(NumVMSArgs == std::distance(StatepointSite.vm_state_begin(), |
| StatepointSite.vm_state_end())); |
| |
| // The vm state arguments are lowered in an opaque manner. We do |
| // not know what type of values are contained within. We skip the |
| // first one since that happens to be the total number we lowered |
| // explicitly just above. We could have left it in the loop and |
| // not done it explicitly, but it's far easier to understand this |
| // way. |
| for (const Value *V : StatepointSite.vm_state_args()) { |
| SDValue Incoming = Builder.getValue(V); |
| lowerIncomingStatepointValue(Incoming, Ops, Builder); |
| } |
| |
| // Finally, go ahead and lower all the gc arguments. There's no prefixed |
| // length for this one. After lowering, we'll have the base and pointer |
| // arrays interwoven with each (lowered) base pointer immediately followed by |
| // it's (lowered) derived pointer. i.e |
| // (base[0], ptr[0], base[1], ptr[1], ...) |
| for (unsigned i = 0; i < Bases.size(); ++i) { |
| const Value *Base = Bases[i]; |
| lowerIncomingStatepointValue(Builder.getValue(Base), Ops, Builder); |
| |
| const Value *Ptr = Ptrs[i]; |
| lowerIncomingStatepointValue(Builder.getValue(Ptr), Ops, Builder); |
| } |
| |
| // If there are any explicit spill slots passed to the statepoint, record |
| // them, but otherwise do not do anything special. These are user provided |
| // allocas and give control over placement to the consumer. In this case, |
| // it is the contents of the slot which may get updated, not the pointer to |
| // the alloca |
| for (Value *V : StatepointSite.gc_args()) { |
| SDValue Incoming = Builder.getValue(V); |
| if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) { |
| // This handles allocas as arguments to the statepoint |
| Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(), |
| Incoming.getValueType())); |
| } |
| } |
| |
| // Record computed locations for all lowered values. |
| // This can not be embedded in lowering loops as we need to record *all* |
| // values, while previous loops account only values with unique SDValues. |
| const Instruction *StatepointInstr = |
| StatepointSite.getCallSite().getInstruction(); |
| FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap = |
| Builder.FuncInfo.StatepointRelocatedValues[StatepointInstr]; |
| |
| for (const GCRelocateInst *Relocate : StatepointSite.getRelocates()) { |
| const Value *V = Relocate->getDerivedPtr(); |
| SDValue SDV = Builder.getValue(V); |
| SDValue Loc = Builder.StatepointLowering.getLocation(SDV); |
| |
| if (Loc.getNode()) { |
| SpillMap[V] = cast<FrameIndexSDNode>(Loc)->getIndex(); |
| } else { |
| // Record value as visited, but not spilled. This is case for allocas |
| // and constants. For this values we can avoid emitting spill load while |
| // visiting corresponding gc_relocate. |
| // Actually we do not need to record them in this map at all. |
| // We do this only to check that we are not relocating any unvisited |
| // value. |
| SpillMap[V] = None; |
| |
| // Default llvm mechanisms for exporting values which are used in |
| // different basic blocks does not work for gc relocates. |
| // Note that it would be incorrect to teach llvm that all relocates are |
| // uses of the corresponding values so that it would automatically |
| // export them. Relocates of the spilled values does not use original |
| // value. |
| if (Relocate->getParent() != StatepointInstr->getParent()) |
| Builder.ExportFromCurrentBlock(V); |
| } |
| } |
| } |
| |
| void SelectionDAGBuilder::visitStatepoint(const CallInst &CI) { |
| // Check some preconditions for sanity |
| assert(isStatepoint(&CI) && |
| "function called must be the statepoint function"); |
| |
| LowerStatepoint(ImmutableStatepoint(&CI)); |
| } |
| |
| void SelectionDAGBuilder::LowerStatepoint( |
| ImmutableStatepoint ISP, const BasicBlock *EHPadBB /*= nullptr*/) { |
| // The basic scheme here is that information about both the original call and |
| // the safepoint is encoded in the CallInst. We create a temporary call and |
| // lower it, then reverse engineer the calling sequence. |
| |
| NumOfStatepoints++; |
| // Clear state |
| StatepointLowering.startNewStatepoint(*this); |
| |
| ImmutableCallSite CS(ISP.getCallSite()); |
| |
| #ifndef NDEBUG |
| // Consistency check. Check only relocates in the same basic block as thier |
| // statepoint. |
| for (const User *U : CS->users()) { |
| const CallInst *Call = cast<CallInst>(U); |
| if (isa<GCRelocateInst>(Call) && Call->getParent() == CS.getParent()) |
| StatepointLowering.scheduleRelocCall(*Call); |
| } |
| #endif |
| |
| #ifndef NDEBUG |
| // If this is a malformed statepoint, report it early to simplify debugging. |
| // This should catch any IR level mistake that's made when constructing or |
| // transforming statepoints. |
| ISP.verify(); |
| |
| // Check that the associated GCStrategy expects to encounter statepoints. |
| assert(GFI->getStrategy().useStatepoints() && |
| "GCStrategy does not expect to encounter statepoints"); |
| #endif |
| |
| // Lower statepoint vmstate and gcstate arguments |
| SmallVector<SDValue, 10> LoweredMetaArgs; |
| lowerStatepointMetaArgs(LoweredMetaArgs, ISP, *this); |
| |
| // Get call node, we will replace it later with statepoint |
| SDNode *CallNode = |
| lowerCallFromStatepoint(ISP, EHPadBB, *this, PendingExports); |
| |
| // Construct the actual GC_TRANSITION_START, STATEPOINT, and GC_TRANSITION_END |
| // nodes with all the appropriate arguments and return values. |
| |
| // Call Node: Chain, Target, {Args}, RegMask, [Glue] |
| SDValue Chain = CallNode->getOperand(0); |
| |
| SDValue Glue; |
| bool CallHasIncomingGlue = CallNode->getGluedNode(); |
| if (CallHasIncomingGlue) { |
| // Glue is always last operand |
| Glue = CallNode->getOperand(CallNode->getNumOperands() - 1); |
| } |
| |
| // Build the GC_TRANSITION_START node if necessary. |
| // |
| // The operands to the GC_TRANSITION_{START,END} nodes are laid out in the |
| // order in which they appear in the call to the statepoint intrinsic. If |
| // any of the operands is a pointer-typed, that operand is immediately |
| // followed by a SRCVALUE for the pointer that may be used during lowering |
| // (e.g. to form MachinePointerInfo values for loads/stores). |
| const bool IsGCTransition = |
| (ISP.getFlags() & (uint64_t)StatepointFlags::GCTransition) == |
| (uint64_t)StatepointFlags::GCTransition; |
| if (IsGCTransition) { |
| SmallVector<SDValue, 8> TSOps; |
| |
| // Add chain |
| TSOps.push_back(Chain); |
| |
| // Add GC transition arguments |
| for (const Value *V : ISP.gc_transition_args()) { |
| TSOps.push_back(getValue(V)); |
| if (V->getType()->isPointerTy()) |
| TSOps.push_back(DAG.getSrcValue(V)); |
| } |
| |
| // Add glue if necessary |
| if (CallHasIncomingGlue) |
| TSOps.push_back(Glue); |
| |
| SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue); |
| |
| SDValue GCTransitionStart = |
| DAG.getNode(ISD::GC_TRANSITION_START, getCurSDLoc(), NodeTys, TSOps); |
| |
| Chain = GCTransitionStart.getValue(0); |
| Glue = GCTransitionStart.getValue(1); |
| } |
| |
| // TODO: Currently, all of these operands are being marked as read/write in |
| // PrologEpilougeInserter.cpp, we should special case the VMState arguments |
| // and flags to be read-only. |
| SmallVector<SDValue, 40> Ops; |
| |
| // Add the <id> and <numBytes> constants. |
| Ops.push_back(DAG.getTargetConstant(ISP.getID(), getCurSDLoc(), MVT::i64)); |
| Ops.push_back( |
| DAG.getTargetConstant(ISP.getNumPatchBytes(), getCurSDLoc(), MVT::i32)); |
| |
| // Calculate and push starting position of vmstate arguments |
| // Get number of arguments incoming directly into call node |
| unsigned NumCallRegArgs = |
| CallNode->getNumOperands() - (CallHasIncomingGlue ? 4 : 3); |
| Ops.push_back(DAG.getTargetConstant(NumCallRegArgs, getCurSDLoc(), MVT::i32)); |
| |
| // Add call target |
| SDValue CallTarget = SDValue(CallNode->getOperand(1).getNode(), 0); |
| Ops.push_back(CallTarget); |
| |
| // Add call arguments |
| // Get position of register mask in the call |
| SDNode::op_iterator RegMaskIt; |
| if (CallHasIncomingGlue) |
| RegMaskIt = CallNode->op_end() - 2; |
| else |
| RegMaskIt = CallNode->op_end() - 1; |
| Ops.insert(Ops.end(), CallNode->op_begin() + 2, RegMaskIt); |
| |
| // Add a constant argument for the calling convention |
| pushStackMapConstant(Ops, *this, CS.getCallingConv()); |
| |
| // Add a constant argument for the flags |
| uint64_t Flags = ISP.getFlags(); |
| assert( |
| ((Flags & ~(uint64_t)StatepointFlags::MaskAll) == 0) |
| && "unknown flag used"); |
| pushStackMapConstant(Ops, *this, Flags); |
| |
| // Insert all vmstate and gcstate arguments |
| Ops.insert(Ops.end(), LoweredMetaArgs.begin(), LoweredMetaArgs.end()); |
| |
| // Add register mask from call node |
| Ops.push_back(*RegMaskIt); |
| |
| // Add chain |
| Ops.push_back(Chain); |
| |
| // Same for the glue, but we add it only if original call had it |
| if (Glue.getNode()) |
| Ops.push_back(Glue); |
| |
| // Compute return values. Provide a glue output since we consume one as |
| // input. This allows someone else to chain off us as needed. |
| SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue); |
| |
| SDNode *StatepointMCNode = |
| DAG.getMachineNode(TargetOpcode::STATEPOINT, getCurSDLoc(), NodeTys, Ops); |
| |
| SDNode *SinkNode = StatepointMCNode; |
| |
| // Build the GC_TRANSITION_END node if necessary. |
| // |
| // See the comment above regarding GC_TRANSITION_START for the layout of |
| // the operands to the GC_TRANSITION_END node. |
| if (IsGCTransition) { |
| SmallVector<SDValue, 8> TEOps; |
| |
| // Add chain |
| TEOps.push_back(SDValue(StatepointMCNode, 0)); |
| |
| // Add GC transition arguments |
| for (const Value *V : ISP.gc_transition_args()) { |
| TEOps.push_back(getValue(V)); |
| if (V->getType()->isPointerTy()) |
| TEOps.push_back(DAG.getSrcValue(V)); |
| } |
| |
| // Add glue |
| TEOps.push_back(SDValue(StatepointMCNode, 1)); |
| |
| SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue); |
| |
| SDValue GCTransitionStart = |
| DAG.getNode(ISD::GC_TRANSITION_END, getCurSDLoc(), NodeTys, TEOps); |
| |
| SinkNode = GCTransitionStart.getNode(); |
| } |
| |
| // Replace original call |
| DAG.ReplaceAllUsesWith(CallNode, SinkNode); // This may update Root |
| // Remove original call node |
| DAG.DeleteNode(CallNode); |
| |
| // DON'T set the root - under the assumption that it's already set past the |
| // inserted node we created. |
| |
| // TODO: A better future implementation would be to emit a single variable |
| // argument, variable return value STATEPOINT node here and then hookup the |
| // return value of each gc.relocate to the respective output of the |
| // previously emitted STATEPOINT value. Unfortunately, this doesn't appear |
| // to actually be possible today. |
| } |
| |
| void SelectionDAGBuilder::visitGCResult(const CallInst &CI) { |
| // The result value of the gc_result is simply the result of the actual |
| // call. We've already emitted this, so just grab the value. |
| Instruction *I = cast<Instruction>(CI.getArgOperand(0)); |
| assert(isStatepoint(I) && "first argument must be a statepoint token"); |
| |
| if (I->getParent() != CI.getParent()) { |
| // Statepoint is in different basic block so we should have stored call |
| // result in a virtual register. |
| // We can not use default getValue() functionality to copy value from this |
| // register because statepoint and actuall call return types can be |
| // different, and getValue() will use CopyFromReg of the wrong type, |
| // which is always i32 in our case. |
| PointerType *CalleeType = cast<PointerType>( |
| ImmutableStatepoint(I).getCalledValue()->getType()); |
| Type *RetTy = |
| cast<FunctionType>(CalleeType->getElementType())->getReturnType(); |
| SDValue CopyFromReg = getCopyFromRegs(I, RetTy); |
| |
| assert(CopyFromReg.getNode()); |
| setValue(&CI, CopyFromReg); |
| } else { |
| setValue(&CI, getValue(I)); |
| } |
| } |
| |
| void SelectionDAGBuilder::visitGCRelocate(const GCRelocateInst &Relocate) { |
| #ifndef NDEBUG |
| // Consistency check |
| // We skip this check for relocates not in the same basic block as thier |
| // statepoint. It would be too expensive to preserve validation info through |
| // different basic blocks. |
| if (Relocate.getStatepoint()->getParent() == Relocate.getParent()) { |
| StatepointLowering.relocCallVisited(Relocate); |
| } |
| #endif |
| |
| const Value *DerivedPtr = Relocate.getDerivedPtr(); |
| SDValue SD = getValue(DerivedPtr); |
| |
| FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap = |
| FuncInfo.StatepointRelocatedValues[Relocate.getStatepoint()]; |
| |
| // We should have recorded location for this pointer |
| assert(SpillMap.count(DerivedPtr) && "Relocating not lowered gc value"); |
| Optional<int> DerivedPtrLocation = SpillMap[DerivedPtr]; |
| |
| // We didn't need to spill these special cases (constants and allocas). |
| // See the handling in spillIncomingValueForStatepoint for detail. |
| if (!DerivedPtrLocation) { |
| setValue(&Relocate, SD); |
| return; |
| } |
| |
| SDValue SpillSlot = DAG.getTargetFrameIndex(*DerivedPtrLocation, |
| SD.getValueType()); |
| |
| // Be conservative: flush all pending loads |
| // TODO: Probably we can be less restrictive on this, |
| // it may allow more scheduling opportunities. |
| SDValue Chain = getRoot(); |
| |
| SDValue SpillLoad = |
| DAG.getLoad(SpillSlot.getValueType(), getCurSDLoc(), Chain, SpillSlot, |
| MachinePointerInfo::getFixedStack(DAG.getMachineFunction(), |
| *DerivedPtrLocation), |
| false, false, false, 0); |
| |
| // Again, be conservative, don't emit pending loads |
| DAG.setRoot(SpillLoad.getValue(1)); |
| |
| assert(SpillLoad.getNode()); |
| setValue(&Relocate, SpillLoad); |
| } |