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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/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.getCalledValue());
assert(CS.getCallingConv() != CallingConv::AnyReg &&
"anyregcc is not supported on statepoints!");
Type *DefTy = ISP.getActualReturnType();
bool HasDef = !DefTy->isVoidTy();
SDValue ReturnValue, CallEndVal;
std::tie(ReturnValue, CallEndVal) = Builder.lowerCallOperands(
ISP.getCallSite(), ImmutableStatepoint::CallArgsBeginPos,
ISP.getNumCallArgs(), ActualCallee, DefTy, 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).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 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);
}
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