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Diffstat (limited to 'contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp')
| -rw-r--r-- | contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp | 878 |
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diff --git a/contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp b/contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp new file mode 100644 index 0000000..a6b3fc6 --- /dev/null +++ b/contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp @@ -0,0 +1,878 @@ +//===-- 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/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(); + 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 suceeding path involes 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 futher - give up now + if (LookUpDepth <= 0) + return Optional<int>(); + + // Spill location is known for gc relocates + if (isGCRelocate(Val)) { + GCRelocateOperands RelocOps(cast<Instruction>(Val)); + + FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap = + Builder.FuncInfo.StatepointRelocatedValues[RelocOps.getStatepoint()]; + + auto It = SpillMap.find(RelocOps.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 resuffle +/// 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 ineffecient, 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, MachineBasicBlock *LandingPad, + SelectionDAGBuilder &Builder, + SmallVectorImpl<SDValue> &PendingExports) { + + ImmutableCallSite CS(ISP.getCallSite()); + + SDValue ActualCallee = Builder.getValue(ISP.getActualCallee()); + + 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, LandingPad, + 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 CopyFromReg to grab the return value from + // %RAX, or it can be a LOAD to load a value returned by reference via a stack + // slot. + + if (HasDef && (CallEnd->getOpcode() == ISD::CopyFromReg || + CallEnd->getOpcode() == ISD::LOAD)) + CallEnd = CallEnd->getOperand(0).getNode(); + + assert(CallEnd->getOpcode() == ISD::CALLSEQ_END && "expected!"); + + if (HasDef) { + if (CS.isInvoke()) { + // Result value will be used in different basic block for invokes + // so we need to export it now. But statepoint call has a different type + // than the actuall call. It means that standart exporting mechanism will + // create register of the wrong type. So instead we need to create + // register with correct type and save value into it manually. + // TODO: To eliminate this problem we can remove gc.result intrinsics + // completelly and make statepoint call to return a tuple. + unsigned Reg = Builder.FuncInfo.CreateRegs(ISP.getActualReturnType()); + RegsForValue RFV(*Builder.DAG.getContext(), + Builder.DAG.getTargetLoweringInfo(), 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 { + // The value of the statepoint itself will be the value of call itself. + // We'll replace the actually 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 (GCRelocateOperands relocateOpers : StatepointSite.getRelocates()) { + Relocs.push_back(relocateOpers.getUnderlyingCallSite().getInstruction()); + Bases.push_back(relocateOpers.getBasePtr()); + Ptrs.push_back(relocateOpers.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(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 + 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 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); + if (Opt.hasValue()) { + assert(Opt.getValue() && + "non gc managed base pointer found in statepoint"); + } + } + for (const Value *V : Ptrs) { + auto Opt = S.isGCManagedPointer(V); + if (Opt.hasValue()) { + assert(Opt.getValue() && + "non gc managed derived pointer found in statepoint"); + } + } + for (const Value *V : Relocations) { + auto Opt = S.isGCManagedPointer(V); + 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 (GCRelocateOperands RelocateOpers : StatepointSite.getRelocates()) { + const Value *V = RelocateOpers.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 emiting 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 corresponging values so that it would automatically + // export them. Relocates of the spilled values does not use original + // value. + if (StatepointSite.getCallSite().isInvoke()) + 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, MachineBasicBlock *LandingPad /*=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. Don't do this for invokes. It would be too + // expensive to preserve this information across different basic blocks + if (!CS.isInvoke()) { + for (const User *U : CS->users()) { + const CallInst *Call = cast<CallInst>(U); + if (isGCRelocate(Call)) + 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, LandingPad, *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 originall 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 (isa<InvokeInst>(I)) { + // For invokes 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).getActualCallee()->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 CallInst &CI) { + GCRelocateOperands RelocateOpers(&CI); + +#ifndef NDEBUG + // Consistency check + // We skip this check for invoke statepoints. It would be too expensive to + // preserve validation info through different basic blocks. + if (!RelocateOpers.isTiedToInvoke()) { + StatepointLowering.relocCallVisited(CI); + } +#endif + + const Value *DerivedPtr = RelocateOpers.getDerivedPtr(); + SDValue SD = getValue(DerivedPtr); + + FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap = + FuncInfo.StatepointRelocatedValues[RelocateOpers.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(&CI, 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 opprtunities + SDValue Chain = getRoot(); + + SDValue SpillLoad = + DAG.getLoad(SpillSlot.getValueType(), getCurSDLoc(), Chain, SpillSlot, + MachinePointerInfo::getFixedStack(*DerivedPtrLocation), + false, false, false, 0); + + // Again, be conservative, don't emit pending loads + DAG.setRoot(SpillLoad.getValue(1)); + + assert(SpillLoad.getNode()); + setValue(&CI, SpillLoad); +} |
