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Diffstat (limited to 'contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp')
| -rw-r--r-- | contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp | 999 |
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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 000000000000..5d78bba86d73 --- /dev/null +++ b/contrib/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp @@ -0,0 +1,999 @@ +//===-- 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/MachineFrameInfo.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. 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.getSizeInBits() / 8; + 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<FrameIndexSDNode>(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<int> 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<GCRelocateInst>(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<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 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; +} + +/// 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; + + 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); +} + +/// 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 +removeDuplicateGCPtrs(SmallVectorImpl<const Value *> &Bases, + SmallVectorImpl<const Value *> &Ptrs, + SmallVectorImpl<const GCRelocateInst *> &Relocs, + SelectionDAGBuilder &Builder, + FunctionLoweringInfo::StatepointSpillMap &SSM) { + DenseMap<SDValue, const Value *> Seen; + + SmallVector<const Value *, 64> NewBases, NewPtrs; + SmallVector<const GCRelocateInst *, 64> NewRelocs; + for (size_t i = 0, e = Ptrs.size(); i < e; i++) { + SDValue SD = Builder.getValue(Ptrs[i]); + auto SeenIt = Seen.find(SD); + + if (SeenIt == Seen.end()) { + // Only add non-duplicates + NewBases.push_back(Bases[i]); + NewPtrs.push_back(Ptrs[i]); + NewRelocs.push_back(Relocs[i]); + Seen[SD] = Ptrs[i]; + } else { + // Duplicate pointer found, note in SSM and move on: + SSM.DuplicateMap[Ptrs[i]] = SeenIt->second; + } + } + 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 std::pair<SDValue, SDNode *> lowerCallFromStatepointLoweringInfo( + SelectionDAGBuilder::StatepointLoweringInfo &SI, + SelectionDAGBuilder &Builder, SmallVectorImpl<SDValue> &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()); +} + +/// 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); + int Index = cast<FrameIndexSDNode>(Loc)->getIndex(); + // We use TargetFrameIndex so that isel will not select it into LEA + Loc = Builder.DAG.getTargetFrameIndex(Index, Builder.getFrameIndexTy()); + + // TODO: We can create TokenFactor node instead of + // chaining stores one after another, this may allow + // a bit more optimal scheduling for them + +#ifndef NDEBUG + // 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) == Incoming.getValueSizeInBits() && + "Bad spill: stack slot does not match!"); +#endif + + Chain = Builder.DAG.getStore(Chain, Builder.getCurSDLoc(), Incoming, Loc, + MachinePointerInfo::getFixedStack( + Builder.DAG.getMachineFunction(), Index)); + + 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, bool LiveInOnly, + 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?) + assert(Incoming.getValueType() == Builder.getFrameIndexTy() && + "Incoming value is a frame index!"); + Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(), + Builder.getFrameIndexTy())); + } else if (LiveInOnly) { + // 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. + Ops.push_back(Incoming); + } 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. + auto 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, + 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) { + return is_contained(SI.Ptrs, V) || is_contained(SI.Bases, 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 (!LiveInDeopt || isGCValue(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 = Builder.getValue(V); + const bool LiveInValue = LiveInDeopt && !isGCValue(V); + lowerIncomingStatepointValue(Incoming, LiveInValue, 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 < SI.Bases.size(); ++i) { + const Value *Base = SI.Bases[i]; + lowerIncomingStatepointValue(Builder.getValue(Base), /*LiveInOnly*/ false, + Ops, Builder); + + const Value *Ptr = SI.Ptrs[i]; + lowerIncomingStatepointValue(Builder.getValue(Ptr), /*LiveInOnly*/ false, + 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 : SI.GCArgs) { + SDValue Incoming = Builder.getValue(V); + if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(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())); + } + } + + // 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.SlotMap[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.SlotMap[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); + +#ifndef NDEBUG + // We schedule gc relocates before removeDuplicateGCPtrs since we _will_ + // encounter the duplicate gc relocates we elide in removeDuplicateGCPtrs. + for (auto *Reloc : SI.GCRelocates) + if (Reloc->getParent() == SI.StatepointInstr->getParent()) + StatepointLowering.scheduleRelocCall(*Reloc); +#endif + + // 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. + removeDuplicateGCPtrs(SI.Bases, SI.Ptrs, SI.GCRelocates, *this, + FuncInfo.StatepointSpillMaps[SI.StatepointInstr]); + assert(SI.Bases.size() == SI.Ptrs.size() && + SI.Ptrs.size() == SI.GCRelocates.size()); + + // Lower statepoint vmstate and gcstate arguments + SmallVector<SDValue, 10> LoweredMetaArgs; + lowerStatepointMetaArgs(LoweredMetaArgs, 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<SDValue, 8> 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<SDValue, 40> Ops; + + // Add the <id> and <numBytes> 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); + + 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 : 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(ImmutableStatepoint ISP, + const BasicBlock *EHPadBB /*= nullptr*/) { + assert(ISP.getCallSite().getCallingConv() != CallingConv::AnyReg && + "anyregcc is not supported on statepoints!"); + +#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 + + 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 = DAG.getTargetLoweringInfo(); + const auto &DL = DAG.getDataLayout(); + + unsigned AS = ISP.getCalledValue()->getType()->getPointerAddressSpace(); + ActualCallee = DAG.getConstant(0, getCurSDLoc(), TLI.getPointerTy(DL, AS)); + } else { + ActualCallee = getValue(ISP.getCalledValue()); + } + + StatepointLoweringInfo SI(DAG); + populateCallLoweringInfo(SI.CLI, ISP.getCallSite(), + ImmutableStatepoint::CallArgsBeginPos, + ISP.getNumCallArgs(), ActualCallee, + ISP.getActualReturnType(), false /* IsPatchPoint */); + + for (const GCRelocateInst *Relocate : ISP.getRelocates()) { + SI.GCRelocates.push_back(Relocate); + SI.Bases.push_back(Relocate->getBasePtr()); + SI.Ptrs.push_back(Relocate->getDerivedPtr()); + } + + SI.GCArgs = ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end()); + SI.StatepointInstr = ISP.getInstruction(); + SI.GCTransitionArgs = + ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end()); + SI.ID = ISP.getID(); + SI.DeoptState = ArrayRef<const Use>(ISP.deopt_begin(), ISP.deopt_end()); + SI.StatepointFlags = ISP.getFlags(); + SI.NumPatchBytes = ISP.getNumPatchBytes(); + SI.EHPadBB = EHPadBB; + + SDValue ReturnValue = LowerAsSTATEPOINT(SI); + + // Export the result value if needed + const GCResultInst *GCResult = ISP.getGCResult(); + Type *RetTy = ISP.getActualReturnType(); + if (!RetTy->isVoidTy() && GCResult) { + if (GCResult->getParent() != ISP.getCallSite().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 = FuncInfo.CreateRegs(RetTy); + RegsForValue RFV(*DAG.getContext(), DAG.getTargetLoweringInfo(), + DAG.getDataLayout(), Reg, RetTy, true); + SDValue Chain = DAG.getEntryNode(); + + RFV.getCopyToRegs(ReturnValue, DAG, getCurSDLoc(), Chain, nullptr); + PendingExports.push_back(Chain); + FuncInfo.ValueMap[ISP.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. + setValue(ISP.getInstruction(), ReturnValue); + } + } else { + // The token value is never used from here on, just generate a poison value + setValue(ISP.getInstruction(), DAG.getIntPtrConstant(-1, getCurSDLoc())); + } +} + +void SelectionDAGBuilder::LowerCallSiteWithDeoptBundleImpl( + ImmutableCallSite CS, SDValue Callee, const BasicBlock *EHPadBB, + bool VarArgDisallowed, bool ForceVoidReturnTy) { + StatepointLoweringInfo SI(DAG); + unsigned ArgBeginIndex = CS.arg_begin() - CS.getInstruction()->op_begin(); + populateCallLoweringInfo( + SI.CLI, CS, ArgBeginIndex, CS.getNumArgOperands(), Callee, + ForceVoidReturnTy ? Type::getVoidTy(*DAG.getContext()) : CS.getType(), + false); + if (!VarArgDisallowed) + SI.CLI.IsVarArg = CS.getFunctionType()->isVarArg(); + + auto DeoptBundle = *CS.getOperandBundle(LLVMContext::OB_deopt); + + unsigned DefaultID = StatepointDirectives::DeoptBundleStatepointID; + + auto SD = parseStatepointDirectivesFromAttrs(CS.getAttributes()); + SI.ID = SD.StatepointID.getValueOr(DefaultID); + SI.NumPatchBytes = SD.NumPatchBytes.getValueOr(0); + + SI.DeoptState = + ArrayRef<const Use>(DeoptBundle.Inputs.begin(), DeoptBundle.Inputs.end()); + SI.StatepointFlags = static_cast<uint64_t>(StatepointFlags::None); + SI.EHPadBB = EHPadBB; + + // NB! The GC arguments are deliberately left empty. + + if (SDValue ReturnVal = LowerAsSTATEPOINT(SI)) { + const Instruction *Inst = CS.getInstruction(); + ReturnVal = lowerRangeToAssertZExt(DAG, *Inst, ReturnVal); + setValue(Inst, ReturnVal); + } +} + +void SelectionDAGBuilder::LowerCallSiteWithDeoptBundle( + ImmutableCallSite CS, SDValue Callee, const BasicBlock *EHPadBB) { + LowerCallSiteWithDeoptBundleImpl(CS, 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 Instruction *I = CI.getStatepoint(); + + 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 actual 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 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); + + auto &SpillMap = FuncInfo.StatepointSpillMaps[Relocate.getStatepoint()]; + auto SlotIt = SpillMap.find(DerivedPtr); + assert(SlotIt != SpillMap.end() && "Relocating not lowered gc value"); + Optional<int> 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; + } + + SDValue SpillSlot = + DAG.getTargetFrameIndex(*DerivedPtrLocation, getFrameIndexTy()); + + // 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(DAG.getTargetLoweringInfo().getValueType(DAG.getDataLayout(), + Relocate.getType()), + getCurSDLoc(), Chain, SpillSlot, + MachinePointerInfo::getFixedStack(DAG.getMachineFunction(), + *DerivedPtrLocation)); + + // Again, be conservative, don't emit pending loads + DAG.setRoot(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())); +} |