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llvm-project/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp

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//===- 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/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/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/MachineValueType.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/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <tuple>
#include <utility>
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.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<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()));
}
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