//===- StatepointLowering.cpp - SDAGBuilder's statepoint code -------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // 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/ArrayRef.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/None.h" #include "llvm/ADT/Optional.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallSet.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/CodeGen/FunctionLoweringInfo.h" #include "llvm/CodeGen/GCMetadata.h" #include "llvm/CodeGen/GCStrategy.h" #include "llvm/CodeGen/ISDOpcodes.h" #include "llvm/CodeGen/MachineFrameInfo.h" #include "llvm/CodeGen/MachineFunction.h" #include "llvm/CodeGen/MachineMemOperand.h" #include "llvm/CodeGen/RuntimeLibcalls.h" #include "llvm/CodeGen/SelectionDAG.h" #include "llvm/CodeGen/SelectionDAGNodes.h" #include "llvm/CodeGen/StackMaps.h" #include "llvm/CodeGen/TargetLowering.h" #include "llvm/CodeGen/TargetOpcodes.h" #include "llvm/IR/CallingConv.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Instruction.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Statepoint.h" #include "llvm/IR/Type.h" #include "llvm/Support/Casting.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/MachineValueType.h" #include "llvm/Target/TargetMachine.h" #include "llvm/Target/TargetOptions.h" #include #include #include #include #include #include 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"); cl::opt UseRegistersForDeoptValues( "use-registers-for-deopt-values", cl::Hidden, cl::init(false), cl::desc("Allow using registers for non pointer deopt args")); static void pushStackMapConstant(SmallVectorImpl& 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. Also need to ensure used bits get cleared. AllocatedStackSlots.clear(); AllocatedStackSlots.resize(Builder.FuncInfo.StatepointStackSlots.size()); } void StatepointLoweringState::clear() { Locations.clear(); AllocatedStackSlots.clear(); assert(PendingGCRelocateCalls.empty() && "cleared before statepoint sequence completed"); } SDValue StatepointLoweringState::allocateStackSlot(EVT ValueType, SelectionDAGBuilder &Builder) { NumSlotsAllocatedForStatepoints++; MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo(); unsigned SpillSize = ValueType.getStoreSize(); assert((SpillSize * 8) == ValueType.getSizeInBits() && "Size not in bytes?"); // 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. const size_t NumSlots = AllocatedStackSlots.size(); assert(NextSlotToAllocate <= NumSlots && "Broken invariant"); assert(AllocatedStackSlots.size() == Builder.FuncInfo.StatepointStackSlots.size() && "Broken invariant"); for (; NextSlotToAllocate < NumSlots; NextSlotToAllocate++) { if (!AllocatedStackSlots.test(NextSlotToAllocate)) { const int FI = Builder.FuncInfo.StatepointStackSlots[NextSlotToAllocate]; if (MFI.getObjectSize(FI) == SpillSize) { AllocatedStackSlots.set(NextSlotToAllocate); // TODO: Is ValueType the right thing to use here? return Builder.DAG.getFrameIndex(FI, ValueType); } } } // Couldn't find a free slot, so create a new one: SDValue SpillSlot = Builder.DAG.CreateStackTemporary(ValueType); const unsigned FI = cast(SpillSlot)->getIndex(); MFI.markAsStatepointSpillSlotObjectIndex(FI); Builder.FuncInfo.StatepointStackSlots.push_back(FI); AllocatedStackSlots.resize(AllocatedStackSlots.size()+1, true); assert(AllocatedStackSlots.size() == Builder.FuncInfo.StatepointStackSlots.size() && "Broken invariant"); StatepointMaxSlotsRequired.updateMax( Builder.FuncInfo.StatepointStackSlots.size()); return SpillSlot; } /// 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 findPreviousSpillSlot(const Value *Val, SelectionDAGBuilder &Builder, int LookUpDepth) { // Can not look any further - give up now if (LookUpDepth <= 0) return None; // Spill location is known for gc relocates if (const auto *Relocate = dyn_cast(Val)) { const auto &SpillMap = Builder.FuncInfo.StatepointSpillMaps[Relocate->getStatepoint()]; auto It = SpillMap.find(Relocate->getDerivedPtr()); if (It == SpillMap.end()) return None; return It->second; } // Look through bitcast instructions. if (const BitCastInst *Cast = dyn_cast(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(Val)) { Optional MergedResult = None; for (auto &IncomingValue : Phi->incoming_values()) { Optional SpillSlot = findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth - 1); if (!SpillSlot.hasValue()) return None; if (MergedResult.hasValue() && *MergedResult != *SpillSlot) return None; 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 None; } /// Return true if-and-only-if the given SDValue can be lowered as either a /// constant argument or a stack reference. The key point is that the value /// doesn't need to be spilled or tracked as a vreg use. static bool willLowerDirectly(SDValue Incoming) { // We are making an unchecked assumption that the frame size <= 2^16 as that // is the largest offset which can be encoded in the stackmap format. if (isa(Incoming)) return true; // The largest constant describeable in the StackMap format is 64 bits. // Potential Optimization: Constants values are sign extended by consumer, // and thus there are many constants of static type > 64 bits whose value // happens to be sext(Con64) and could thus be lowered directly. if (Incoming.getValueType().getSizeInBits() > 64) return false; return (isa(Incoming) || isa(Incoming) || Incoming.isUndef()); } /// 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 we won't spill this, we don't need to check for previously allocated // stack slots. if (willLowerDirectly(Incoming)) return; SDValue OldLocation = Builder.StatepointLowering.getLocation(Incoming); if (OldLocation.getNode()) // Duplicates in input return; const int LookUpDepth = 6; Optional Index = findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth); if (!Index.hasValue()) return; const auto &StatepointSlots = Builder.FuncInfo.StatepointStackSlots; auto SlotIt = find(StatepointSlots, *Index); assert(SlotIt != StatepointSlots.end() && "Value spilled to the unknown stack slot"); // This is one of our dedicated lowering slots const int Offset = std::distance(StatepointSlots.begin(), SlotIt); 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, Builder.getFrameIndexTy()); Builder.StatepointLowering.setLocation(Incoming, Loc); } /// 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 std::pair lowerCallFromStatepointLoweringInfo( SelectionDAGBuilder::StatepointLoweringInfo &SI, SelectionDAGBuilder &Builder, SmallVectorImpl &PendingExports) { SDValue ReturnValue, CallEndVal; std::tie(ReturnValue, CallEndVal) = Builder.lowerInvokable(SI.CLI, SI.EHPadBB); 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. bool HasDef = !SI.CLI.RetTy->isVoidTy(); 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!"); return std::make_pair(ReturnValue, CallEnd->getOperand(0).getNode()); } static MachineMemOperand* getMachineMemOperand(MachineFunction &MF, FrameIndexSDNode &FI) { auto PtrInfo = MachinePointerInfo::getFixedStack(MF, FI.getIndex()); auto MMOFlags = MachineMemOperand::MOStore | MachineMemOperand::MOLoad | MachineMemOperand::MOVolatile; auto &MFI = MF.getFrameInfo(); return MF.getMachineMemOperand(PtrInfo, MMOFlags, MFI.getObjectSize(FI.getIndex()), MFI.getObjectAlign(FI.getIndex())); } /// 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::tuple spillIncomingStatepointValue(SDValue Incoming, SDValue Chain, SelectionDAGBuilder &Builder) { SDValue Loc = Builder.StatepointLowering.getLocation(Incoming); MachineMemOperand* MMO = nullptr; // Emit new store if we didn't do it for this ptr before if (!Loc.getNode()) { Loc = Builder.StatepointLowering.allocateStackSlot(Incoming.getValueType(), Builder); int Index = cast(Loc)->getIndex(); // We use TargetFrameIndex so that isel will not select it into LEA Loc = Builder.DAG.getTargetFrameIndex(Index, Builder.getFrameIndexTy()); // Right now we always allocate spill slots that are of the same // size as the value we're about to spill (the size of spillee can // vary since we spill vectors of pointers too). At some point we // can consider allowing spills of smaller values to larger slots // (i.e. change the '==' in the assert below to a '>='). MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo(); assert((MFI.getObjectSize(Index) * 8) == (int64_t)Incoming.getValueSizeInBits() && "Bad spill: stack slot does not match!"); // Note: Using the alignment of the spill slot (rather than the abi or // preferred alignment) is required for correctness when dealing with spill // slots with preferred alignments larger than frame alignment.. auto &MF = Builder.DAG.getMachineFunction(); auto PtrInfo = MachinePointerInfo::getFixedStack(MF, Index); auto *StoreMMO = MF.getMachineMemOperand( PtrInfo, MachineMemOperand::MOStore, MFI.getObjectSize(Index), MFI.getObjectAlign(Index)); Chain = Builder.DAG.getStore(Chain, Builder.getCurSDLoc(), Incoming, Loc, StoreMMO); MMO = getMachineMemOperand(MF, *cast(Loc)); Builder.StatepointLowering.setLocation(Incoming, Loc); } assert(Loc.getNode()); return std::make_tuple(Loc, Chain, MMO); } /// 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, bool RequireSpillSlot, SmallVectorImpl &Ops, SmallVectorImpl &MemRefs, SelectionDAGBuilder &Builder) { if (willLowerDirectly(Incoming)) { if (FrameIndexSDNode *FI = dyn_cast(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?) assert(Incoming.getValueType() == Builder.getFrameIndexTy() && "Incoming value is a frame index!"); Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(), Builder.getFrameIndexTy())); auto &MF = Builder.DAG.getMachineFunction(); auto *MMO = getMachineMemOperand(MF, *FI); MemRefs.push_back(MMO); return; } assert(Incoming.getValueType().getSizeInBits() <= 64); if (Incoming.isUndef()) { // Put an easily recognized constant that's unlikely to be a valid // value so that uses of undef by the consumer of the stackmap is // easily recognized. This is legal since the compiler is always // allowed to chose an arbitrary value for undef. pushStackMapConstant(Ops, Builder, 0xFEFEFEFE); return; } // 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. if (ConstantSDNode *C = dyn_cast(Incoming)) { pushStackMapConstant(Ops, Builder, C->getSExtValue()); return; } else if (ConstantFPSDNode *C = dyn_cast(Incoming)) { pushStackMapConstant(Ops, Builder, C->getValueAPF().bitcastToAPInt().getZExtValue()); return; } llvm_unreachable("unhandled direct lowering case"); } if (!RequireSpillSlot) { // If this value is live in (not live-on-return, or live-through), we can // treat it the same way patchpoint treats it's "live in" values. We'll // end up folding some of these into stack references, but they'll be // handled by the register allocator. Note that we do not have the notion // of a late use so these values might be placed in registers which are // clobbered by the call. This is fine for live-in. For live-through // fix-up pass should be executed to force spilling of such registers. Ops.push_back(Incoming); } else { // Otherwise, locate a spill slot and explicitly spill it so it can be // found by the runtime later. Note: We know all of these spills are // independent, but don't bother to exploit that chain wise. DAGCombine // will happily do so as needed, so doing it here would be a small compile // time win at most. SDValue Chain = Builder.getRoot(); auto Res = spillIncomingStatepointValue(Incoming, Chain, Builder); Ops.push_back(std::get<0>(Res)); if (auto *MMO = std::get<2>(Res)) MemRefs.push_back(MMO); Chain = std::get<1>(Res);; 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 &Ops, SmallVectorImpl &MemRefs, SelectionDAGBuilder::StatepointLoweringInfo &SI, SelectionDAGBuilder &Builder) { // Lower the deopt and gc arguments for this statepoint. Layout will be: // deopt argument length, deopt arguments.., gc arguments... #ifndef NDEBUG if (auto *GFI = Builder.GFI) { // 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 = GFI->getStrategy(); for (const Value *V : SI.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 : SI.Ptrs) { auto Opt = S.isGCManagedPointer(V->getType()->getScalarType()); if (Opt.hasValue()) { assert(Opt.getValue() && "non gc managed derived pointer found in statepoint"); } } assert(SI.Bases.size() == SI.Ptrs.size() && "Pointer without base!"); } else { assert(SI.Bases.empty() && "No gc specified, so cannot relocate pointers!"); assert(SI.Ptrs.empty() && "No gc specified, so cannot relocate pointers!"); } #endif // Figure out what lowering strategy we're going to use for each part // Note: Is is conservatively correct to lower both "live-in" and "live-out" // as "live-through". A "live-through" variable is one which is "live-in", // "live-out", and live throughout the lifetime of the call (i.e. we can find // it from any PC within the transitive callee of the statepoint). In // particular, if the callee spills callee preserved registers we may not // be able to find a value placed in that register during the call. This is // fine for live-out, but not for live-through. If we were willing to make // assumptions about the code generator producing the callee, we could // potentially allow live-through values in callee saved registers. const bool LiveInDeopt = SI.StatepointFlags & (uint64_t)StatepointFlags::DeoptLiveIn; auto isGCValue = [&](const Value *V) { auto *Ty = V->getType(); if (!Ty->isPtrOrPtrVectorTy()) return false; if (auto *GFI = Builder.GFI) if (auto IsManaged = GFI->getStrategy().isGCManagedPointer(Ty)) return *IsManaged; return true; // conservative }; auto requireSpillSlot = [&](const Value *V) { return !(LiveInDeopt || UseRegistersForDeoptValues) || isGCValue(V); }; // 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 : SI.DeoptState) { if (requireSpillSlot(V)) reservePreviousStackSlotForValue(V, Builder); } for (unsigned i = 0; i < SI.Bases.size(); ++i) { reservePreviousStackSlotForValue(SI.Bases[i], Builder); reservePreviousStackSlotForValue(SI.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 = SI.DeoptState.size(); pushStackMapConstant(Ops, Builder, NumVMSArgs); // The vm state arguments are lowered in an opaque manner. We do not know // what type of values are contained within. for (const Value *V : SI.DeoptState) { SDValue Incoming; // If this is a function argument at a static frame index, generate it as // the frame index. if (const Argument *Arg = dyn_cast(V)) { int FI = Builder.FuncInfo.getArgumentFrameIndex(Arg); if (FI != INT_MAX) Incoming = Builder.DAG.getFrameIndex(FI, Builder.getFrameIndexTy()); } if (!Incoming.getNode()) Incoming = Builder.getValue(V); lowerIncomingStatepointValue(Incoming, requireSpillSlot(V), Ops, MemRefs, 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 < SI.Bases.size(); ++i) { const Value *Base = SI.Bases[i]; lowerIncomingStatepointValue(Builder.getValue(Base), /*RequireSpillSlot*/ true, Ops, MemRefs, Builder); const Value *Ptr = SI.Ptrs[i]; lowerIncomingStatepointValue(Builder.getValue(Ptr), /*RequireSpillSlot*/ true, Ops, MemRefs, 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 : SI.GCArgs) { SDValue Incoming = Builder.getValue(V); if (FrameIndexSDNode *FI = dyn_cast(Incoming)) { // This handles allocas as arguments to the statepoint assert(Incoming.getValueType() == Builder.getFrameIndexTy() && "Incoming value is a frame index!"); Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(), Builder.getFrameIndexTy())); auto &MF = Builder.DAG.getMachineFunction(); auto *MMO = getMachineMemOperand(MF, *FI); MemRefs.push_back(MMO); } } // 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 = SI.StatepointInstr; auto &SpillMap = Builder.FuncInfo.StatepointSpillMaps[StatepointInstr]; for (const GCRelocateInst *Relocate : SI.GCRelocates) { const Value *V = Relocate->getDerivedPtr(); SDValue SDV = Builder.getValue(V); SDValue Loc = Builder.StatepointLowering.getLocation(SDV); if (Loc.getNode()) { SpillMap[V] = cast(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); } } } SDValue SelectionDAGBuilder::LowerAsSTATEPOINT( SelectionDAGBuilder::StatepointLoweringInfo &SI) { // 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); assert(SI.Bases.size() == SI.Ptrs.size() && SI.Ptrs.size() <= SI.GCRelocates.size()); #ifndef NDEBUG for (auto *Reloc : SI.GCRelocates) if (Reloc->getParent() == SI.StatepointInstr->getParent()) StatepointLowering.scheduleRelocCall(*Reloc); #endif // Lower statepoint vmstate and gcstate arguments SmallVector LoweredMetaArgs; SmallVector MemRefs; lowerStatepointMetaArgs(LoweredMetaArgs, MemRefs, SI, *this); // Now that we've emitted the spills, we need to update the root so that the // call sequence is ordered correctly. SI.CLI.setChain(getRoot()); // Get call node, we will replace it later with statepoint SDValue ReturnVal; SDNode *CallNode; std::tie(ReturnVal, CallNode) = lowerCallFromStatepointLoweringInfo(SI, *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 = (SI.StatepointFlags & (uint64_t)StatepointFlags::GCTransition) == (uint64_t)StatepointFlags::GCTransition; if (IsGCTransition) { SmallVector TSOps; // Add chain TSOps.push_back(Chain); // Add GC transition arguments for (const Value *V : SI.GCTransitionArgs) { 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 Ops; // Add the and constants. Ops.push_back(DAG.getTargetConstant(SI.ID, getCurSDLoc(), MVT::i64)); Ops.push_back( DAG.getTargetConstant(SI.NumPatchBytes, 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, SI.CLI.CallConv); // Add a constant argument for the flags uint64_t Flags = SI.StatepointFlags; 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); MachineSDNode *StatepointMCNode = DAG.getMachineNode(TargetOpcode::STATEPOINT, getCurSDLoc(), NodeTys, Ops); DAG.setNodeMemRefs(StatepointMCNode, MemRefs); 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 TEOps; // Add chain TEOps.push_back(SDValue(StatepointMCNode, 0)); // Add GC transition arguments for (const Value *V : SI.GCTransitionArgs) { 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. return ReturnVal; } void SelectionDAGBuilder::LowerStatepoint(const GCStatepointInst &I, const BasicBlock *EHPadBB /*= nullptr*/) { assert(I.getCallingConv() != CallingConv::AnyReg && "anyregcc is not supported on statepoints!"); #ifndef NDEBUG // Check that the associated GCStrategy expects to encounter statepoints. assert(GFI->getStrategy().useStatepoints() && "GCStrategy does not expect to encounter statepoints"); #endif SDValue ActualCallee; SDValue Callee = getValue(I.getActualCalledOperand()); if (I.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 // `undef` instead. Not lowering the call target lets statepoint clients // get away without providing a physical address for the symbolic call // target at link time. ActualCallee = DAG.getUNDEF(Callee.getValueType()); } else { ActualCallee = Callee; } StatepointLoweringInfo SI(DAG); populateCallLoweringInfo(SI.CLI, &I, GCStatepointInst::CallArgsBeginPos, I.getNumCallArgs(), ActualCallee, I.getActualReturnType(), false /* IsPatchPoint */); // There may be duplication in the gc.relocate list; such as two copies of // each relocation on normal and exceptional path for an invoke. We only // need to spill once and record one copy in the stackmap, but we need to // reload once per gc.relocate. (Dedupping gc.relocates is trickier and best // handled as a CSE problem elsewhere.) // TODO: There a couple of major stackmap size optimizations we could do // here if we wished. // 1) If we've encountered a derived pair {B, D}, we don't need to actually // record {B,B} if it's seen later. // 2) Due to rematerialization, actual derived pointers are somewhat rare; // given that, we could change the format to record base pointer relocations // separately with half the space. This would require a format rev and a // fairly major rework of the STATEPOINT node though. SmallSet Seen; for (const GCRelocateInst *Relocate : I.getGCRelocates()) { SI.GCRelocates.push_back(Relocate); SDValue DerivedSD = getValue(Relocate->getDerivedPtr()); if (Seen.insert(DerivedSD).second) { SI.Bases.push_back(Relocate->getBasePtr()); SI.Ptrs.push_back(Relocate->getDerivedPtr()); } } SI.GCArgs = ArrayRef(I.gc_args_begin(), I.gc_args_end()); SI.StatepointInstr = &I; SI.ID = I.getID(); SI.DeoptState = ArrayRef(I.deopt_begin(), I.deopt_end()); SI.GCTransitionArgs = ArrayRef(I.gc_transition_args_begin(), I.gc_transition_args_end()); SI.StatepointFlags = I.getFlags(); SI.NumPatchBytes = I.getNumPatchBytes(); SI.EHPadBB = EHPadBB; SDValue ReturnValue = LowerAsSTATEPOINT(SI); // Export the result value if needed const GCResultInst *GCResult = I.getGCResult(); Type *RetTy = I.getActualReturnType(); if (RetTy->isVoidTy() || !GCResult) { // The return value is not needed, just generate a poison value. setValue(&I, DAG.getIntPtrConstant(-1, getCurSDLoc())); return; } if (GCResult->getParent() == I.getParent()) { // Result value will be used in a same basic block. Don't export it or // perform any explicit register copies. The gc_result will simply grab // this value. setValue(&I, ReturnValue); return; } // 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 = FuncInfo.CreateRegs(RetTy); RegsForValue RFV(*DAG.getContext(), DAG.getTargetLoweringInfo(), DAG.getDataLayout(), Reg, RetTy, I.getCallingConv()); SDValue Chain = DAG.getEntryNode(); RFV.getCopyToRegs(ReturnValue, DAG, getCurSDLoc(), Chain, nullptr); PendingExports.push_back(Chain); FuncInfo.ValueMap[&I] = Reg; } void SelectionDAGBuilder::LowerCallSiteWithDeoptBundleImpl( const CallBase *Call, SDValue Callee, const BasicBlock *EHPadBB, bool VarArgDisallowed, bool ForceVoidReturnTy) { StatepointLoweringInfo SI(DAG); unsigned ArgBeginIndex = Call->arg_begin() - Call->op_begin(); populateCallLoweringInfo( SI.CLI, Call, ArgBeginIndex, Call->getNumArgOperands(), Callee, ForceVoidReturnTy ? Type::getVoidTy(*DAG.getContext()) : Call->getType(), false); if (!VarArgDisallowed) SI.CLI.IsVarArg = Call->getFunctionType()->isVarArg(); auto DeoptBundle = *Call->getOperandBundle(LLVMContext::OB_deopt); unsigned DefaultID = StatepointDirectives::DeoptBundleStatepointID; auto SD = parseStatepointDirectivesFromAttrs(Call->getAttributes()); SI.ID = SD.StatepointID.getValueOr(DefaultID); SI.NumPatchBytes = SD.NumPatchBytes.getValueOr(0); SI.DeoptState = ArrayRef(DeoptBundle.Inputs.begin(), DeoptBundle.Inputs.end()); SI.StatepointFlags = static_cast(StatepointFlags::None); SI.EHPadBB = EHPadBB; // NB! The GC arguments are deliberately left empty. if (SDValue ReturnVal = LowerAsSTATEPOINT(SI)) { ReturnVal = lowerRangeToAssertZExt(DAG, *Call, ReturnVal); setValue(Call, ReturnVal); } } void SelectionDAGBuilder::LowerCallSiteWithDeoptBundle( const CallBase *Call, SDValue Callee, const BasicBlock *EHPadBB) { LowerCallSiteWithDeoptBundleImpl(Call, Callee, EHPadBB, /* VarArgDisallowed = */ false, /* ForceVoidReturnTy = */ false); } void SelectionDAGBuilder::visitGCResult(const GCResultInst &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. const GCStatepointInst *SI = CI.getStatepoint(); if (SI->getParent() == CI.getParent()) { setValue(&CI, getValue(SI)); return; } // 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 actual call return types can be // different, and getValue() will use CopyFromReg of the wrong type, // which is always i32 in our case. Type *RetTy = SI->getActualReturnType(); SDValue CopyFromReg = getCopyFromRegs(SI, RetTy); assert(CopyFromReg.getNode()); setValue(&CI, CopyFromReg); } void SelectionDAGBuilder::visitGCRelocate(const GCRelocateInst &Relocate) { #ifndef NDEBUG // Consistency check // We skip this check for relocates not in the same basic block as their // statepoint. It would be too expensive to preserve validation info through // different basic blocks. if (Relocate.getStatepoint()->getParent() == Relocate.getParent()) StatepointLowering.relocCallVisited(Relocate); auto *Ty = Relocate.getType()->getScalarType(); if (auto IsManaged = GFI->getStrategy().isGCManagedPointer(Ty)) assert(*IsManaged && "Non gc managed pointer relocated!"); #endif const Value *DerivedPtr = Relocate.getDerivedPtr(); SDValue SD = getValue(DerivedPtr); if (SD.isUndef() && SD.getValueType().getSizeInBits() <= 64) { // Lowering relocate(undef) as arbitrary constant. Current constant value // is chosen such that it's unlikely to be a valid pointer. setValue(&Relocate, DAG.getTargetConstant(0xFEFEFEFE, SDLoc(SD), MVT::i64)); return; } auto &SpillMap = FuncInfo.StatepointSpillMaps[Relocate.getStatepoint()]; auto SlotIt = SpillMap.find(DerivedPtr); assert(SlotIt != SpillMap.end() && "Relocating not lowered gc value"); Optional DerivedPtrLocation = SlotIt->second; // 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; } unsigned Index = *DerivedPtrLocation; SDValue SpillSlot = DAG.getTargetFrameIndex(Index, getFrameIndexTy()); // All the reloads are independent and are reading memory only modified by // statepoints (i.e. no other aliasing stores); informing SelectionDAG of // this this let's CSE kick in for free and allows reordering of instructions // if possible. The lowering for statepoint sets the root, so this is // ordering all reloads with the either a) the statepoint node itself, or b) // the entry of the current block for an invoke statepoint. const SDValue Chain = DAG.getRoot(); // != Builder.getRoot() auto &MF = DAG.getMachineFunction(); auto &MFI = MF.getFrameInfo(); auto PtrInfo = MachinePointerInfo::getFixedStack(MF, Index); auto *LoadMMO = MF.getMachineMemOperand(PtrInfo, MachineMemOperand::MOLoad, MFI.getObjectSize(Index), MFI.getObjectAlign(Index)); auto LoadVT = DAG.getTargetLoweringInfo().getValueType(DAG.getDataLayout(), Relocate.getType()); SDValue SpillLoad = DAG.getLoad(LoadVT, getCurSDLoc(), Chain, SpillSlot, LoadMMO); PendingLoads.push_back(SpillLoad.getValue(1)); assert(SpillLoad.getNode()); setValue(&Relocate, SpillLoad); } void SelectionDAGBuilder::LowerDeoptimizeCall(const CallInst *CI) { const auto &TLI = DAG.getTargetLoweringInfo(); SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(RTLIB::DEOPTIMIZE), TLI.getPointerTy(DAG.getDataLayout())); // We don't lower calls to __llvm_deoptimize as varargs, but as a regular // call. We also do not lower the return value to any virtual register, and // change the immediately following return to a trap instruction. LowerCallSiteWithDeoptBundleImpl(CI, Callee, /* EHPadBB = */ nullptr, /* VarArgDisallowed = */ true, /* ForceVoidReturnTy = */ true); } void SelectionDAGBuilder::LowerDeoptimizingReturn() { // We do not lower the return value from llvm.deoptimize to any virtual // register, and change the immediately following return to a trap // instruction. if (DAG.getTarget().Options.TrapUnreachable) DAG.setRoot( DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, DAG.getRoot())); }