void Lowering::TreeNodeInfoInitGCWriteBarrier(GenTree* tree)
{
GenTreePtr dst = tree;
GenTreePtr addr = tree->gtOp.gtOp1;
GenTreePtr src = tree->gtOp.gtOp2;
if (addr->OperGet() == GT_LEA)
{
// In the case where we are doing a helper assignment, if the dst
// is an indir through an lea, we need to actually instantiate the
// lea in a register
GenTreeAddrMode* lea = addr->AsAddrMode();
short leaSrcCount = 0;
if (lea->Base() != nullptr)
{
leaSrcCount++;
}
if (lea->Index() != nullptr)
{
leaSrcCount++;
}
lea->gtLsraInfo.srcCount = leaSrcCount;
lea->gtLsraInfo.dstCount = 1;
}
#if NOGC_WRITE_BARRIERS
NYI_ARM("NOGC_WRITE_BARRIERS");
// For the NOGC JIT Helper calls
//
// the 'addr' goes into x14 (REG_WRITE_BARRIER_DST_BYREF)
// the 'src' goes into x15 (REG_WRITE_BARRIER)
//
addr->gtLsraInfo.setSrcCandidates(m_lsra, RBM_WRITE_BARRIER_DST_BYREF);
src->gtLsraInfo.setSrcCandidates(m_lsra, RBM_WRITE_BARRIER);
#else
// For the standard JIT Helper calls
// op1 goes into REG_ARG_0 and
// op2 goes into REG_ARG_1
//
addr->gtLsraInfo.setSrcCandidates(m_lsra, RBM_ARG_0);
src->gtLsraInfo.setSrcCandidates(m_lsra, RBM_ARG_1);
#endif // NOGC_WRITE_BARRIERS
// Both src and dst must reside in a register, which they should since we haven't set
// either of them as contained.
assert(addr->gtLsraInfo.dstCount == 1);
assert(src->gtLsraInfo.dstCount == 1);
}
GCInfo::WriteBarrierForm GCInfo::gcWriteBarrierFormFromTargetAddress(GenTreePtr tgtAddr)
{
GCInfo::WriteBarrierForm result = GCInfo::WBF_BarrierUnknown; // Default case, we have no information.
// If we store through an int to a GC_REF field, we'll assume that needs to use a checked barriers.
if (tgtAddr->TypeGet() == TYP_I_IMPL)
{
return GCInfo::WBF_BarrierChecked; // Why isn't this GCInfo::WBF_BarrierUnknown?
}
// Otherwise...
assert(tgtAddr->TypeGet() == TYP_BYREF);
bool simplifiedExpr = true;
while (simplifiedExpr)
{
simplifiedExpr = false;
tgtAddr = tgtAddr->gtSkipReloadOrCopy();
while (tgtAddr->OperGet() == GT_ADDR && tgtAddr->gtOp.gtOp1->OperGet() == GT_IND)
{
tgtAddr = tgtAddr->gtOp.gtOp1->gtOp.gtOp1;
simplifiedExpr = true;
assert(tgtAddr->TypeGet() == TYP_BYREF);
}
// For additions, one of the operands is a byref or a ref (and the other is not). Follow this down to its
// source.
while (tgtAddr->OperGet() == GT_ADD || tgtAddr->OperGet() == GT_LEA)
{
if (tgtAddr->OperGet() == GT_ADD)
{
if (tgtAddr->gtOp.gtOp1->TypeGet() == TYP_BYREF || tgtAddr->gtOp.gtOp1->TypeGet() == TYP_REF)
{
assert(!(tgtAddr->gtOp.gtOp2->TypeGet() == TYP_BYREF || tgtAddr->gtOp.gtOp2->TypeGet() == TYP_REF));
tgtAddr = tgtAddr->gtOp.gtOp1;
simplifiedExpr = true;
}
else if (tgtAddr->gtOp.gtOp2->TypeGet() == TYP_BYREF || tgtAddr->gtOp.gtOp2->TypeGet() == TYP_REF)
{
tgtAddr = tgtAddr->gtOp.gtOp2;
simplifiedExpr = true;
}
else
{
// We might have a native int. For example:
// const int 0
// + byref
// lclVar int V06 loc5 // this is a local declared "valuetype VType*"
return GCInfo::WBF_BarrierUnknown;
}
}
else
{
// Must be an LEA (i.e., an AddrMode)
assert(tgtAddr->OperGet() == GT_LEA);
tgtAddr = tgtAddr->AsAddrMode()->Base();
if (tgtAddr->TypeGet() == TYP_BYREF || tgtAddr->TypeGet() == TYP_REF)
{
simplifiedExpr = true;
}
else
{
// We might have a native int.
return GCInfo::WBF_BarrierUnknown;
}
}
}
}
if (tgtAddr->IsLocalAddrExpr() != nullptr)
{
// No need for a GC barrier when writing to a local variable.
return GCInfo::WBF_NoBarrier;
}
if (tgtAddr->OperGet() == GT_LCL_VAR || tgtAddr->OperGet() == GT_REG_VAR)
{
unsigned lclNum = 0;
if (tgtAddr->gtOper == GT_LCL_VAR)
{
lclNum = tgtAddr->gtLclVar.gtLclNum;
}
else
{
assert(tgtAddr->gtOper == GT_REG_VAR);
lclNum = tgtAddr->gtRegVar.gtLclNum;
}
LclVarDsc* varDsc = &compiler->lvaTable[lclNum];
// Instead of marking LclVar with 'lvStackByref',
// Consider decomposing the Value Number given to this LclVar to see if it was
// created using a GT_ADDR(GT_LCLVAR) or a GT_ADD( GT_ADDR(GT_LCLVAR), Constant)
// We may have an internal compiler temp created in fgMorphCopyBlock() that we know
// points at one of our stack local variables, it will have lvStackByref set to true.
//
if (varDsc->lvStackByref)
{
assert(varDsc->TypeGet() == TYP_BYREF);
return GCInfo::WBF_NoBarrier;
}
// We don't eliminate for inlined methods, where we (can) know where the "retBuff" points.
if (!compiler->compIsForInlining() && lclNum == compiler->info.compRetBuffArg)
{
assert(compiler->info.compRetType == TYP_STRUCT); // Else shouldn't have a ret buff.
// Are we assured that the ret buff pointer points into the stack of a caller?
if (compiler->info.compRetBuffDefStack)
{
#if 0
// This is an optional debugging mode. If the #if 0 above is changed to #if 1,
// every barrier we remove for stores to GC ref fields of a retbuff use a special
// helper that asserts that the target is not in the heap.
#ifdef DEBUG
return WBF_NoBarrier_CheckNotHeapInDebug;
#else
return WBF_NoBarrier;
#endif
#else // 0
return GCInfo::WBF_NoBarrier;
#endif // 0
}
}
}
if (tgtAddr->TypeGet() == TYP_REF)
{
return GCInfo::WBF_BarrierUnchecked;
}
// Otherwise, we have no information.
return GCInfo::WBF_BarrierUnknown;
}
//------------------------------------------------------------------------
// TreeNodeInfoInitIndir: Specify register requirements for address expression
// of an indirection operation.
//
// Arguments:
// indirTree - GT_IND, GT_STOREIND, block node or GT_NULLCHECK gentree node
//
void Lowering::TreeNodeInfoInitIndir(GenTreePtr indirTree)
{
assert(indirTree->OperIsIndir());
// If this is the rhs of a block copy (i.e. non-enregisterable struct),
// it has no register requirements.
if (indirTree->TypeGet() == TYP_STRUCT)
{
return;
}
GenTreePtr addr = indirTree->gtGetOp1();
TreeNodeInfo* info = &(indirTree->gtLsraInfo);
GenTreePtr base = nullptr;
GenTreePtr index = nullptr;
unsigned cns = 0;
unsigned mul;
bool rev;
bool modifiedSources = false;
bool makeContained = true;
if ((addr->OperGet() == GT_LEA) && IsSafeToContainMem(indirTree, addr))
{
GenTreeAddrMode* lea = addr->AsAddrMode();
base = lea->Base();
index = lea->Index();
cns = lea->gtOffset;
#ifdef _TARGET_ARM_
// ARM floating-point load/store doesn't support a form similar to integer
// ldr Rdst, [Rbase + Roffset] with offset in a register. The only supported
// form is vldr Rdst, [Rbase + imm] with a more limited constraint on the imm.
if (lea->HasIndex() || !emitter::emitIns_valid_imm_for_vldst_offset(cns))
{
if (indirTree->OperGet() == GT_STOREIND)
{
if (varTypeIsFloating(indirTree->AsStoreInd()->Data()))
{
makeContained = false;
}
}
else if (indirTree->OperGet() == GT_IND)
{
if (varTypeIsFloating(indirTree))
{
makeContained = false;
}
}
}
#endif
if (makeContained)
{
m_lsra->clearOperandCounts(addr);
addr->SetContained();
// The srcCount is decremented because addr is now "contained",
// then we account for the base and index below, if they are non-null.
info->srcCount--;
}
}
else if (comp->codeGen->genCreateAddrMode(addr, -1, true, 0, &rev, &base, &index, &mul, &cns, true /*nogen*/) &&
!(modifiedSources = AreSourcesPossiblyModifiedLocals(indirTree, base, index)))
{
// An addressing mode will be constructed that may cause some
// nodes to not need a register, and cause others' lifetimes to be extended
// to the GT_IND or even its parent if it's an assignment
assert(base != addr);
m_lsra->clearOperandCounts(addr);
addr->SetContained();
// Traverse the computation below GT_IND to find the operands
// for the addressing mode, marking the various constants and
// intermediate results as not consuming/producing.
// If the traversal were more complex, we might consider using
// a traversal function, but the addressing mode is only made
// up of simple arithmetic operators, and the code generator
// only traverses one leg of each node.
bool foundBase = (base == nullptr);
bool foundIndex = (index == nullptr);
GenTreePtr nextChild = nullptr;
for (GenTreePtr child = addr; child != nullptr && !child->OperIsLeaf(); child = nextChild)
{
nextChild = nullptr;
GenTreePtr op1 = child->gtOp.gtOp1;
GenTreePtr op2 = (child->OperIsBinary()) ? child->gtOp.gtOp2 : nullptr;
if (op1 == base)
{
foundBase = true;
}
else if (op1 == index)
{
foundIndex = true;
}
else
{
m_lsra->clearOperandCounts(op1);
op1->SetContained();
if (!op1->OperIsLeaf())
{
nextChild = op1;
}
}
if (op2 != nullptr)
{
if (op2 == base)
{
foundBase = true;
}
else if (op2 == index)
{
foundIndex = true;
}
else
{
m_lsra->clearOperandCounts(op2);
op2->SetContained();
if (!op2->OperIsLeaf())
{
assert(nextChild == nullptr);
nextChild = op2;
}
}
}
}
assert(foundBase && foundIndex);
info->srcCount--; // it gets incremented below.
}
else if (addr->gtOper == GT_ARR_ELEM)
{
// The GT_ARR_ELEM consumes all the indices and produces the offset.
// The array object lives until the mem access.
// We also consume the target register to which the address is
// computed
info->srcCount++;
assert(addr->gtLsraInfo.srcCount >= 2);
addr->gtLsraInfo.srcCount -= 1;
}
else
{
// it is nothing but a plain indir
info->srcCount--; // base gets added in below
base = addr;
}
if (!makeContained)
{
return;
}
if (base != nullptr)
{
info->srcCount++;
}
if (index != nullptr && !modifiedSources)
{
info->srcCount++;
}
// On ARM we may need a single internal register
// (when both conditions are true then we still only need a single internal register)
if ((index != nullptr) && (cns != 0))
{
// ARM does not support both Index and offset so we need an internal register
info->internalIntCount = 1;
}
else if (!emitter::emitIns_valid_imm_for_ldst_offset(cns, emitTypeSize(indirTree)))
{
// This offset can't be contained in the ldr/str instruction, so we need an internal register
info->internalIntCount = 1;
}
}
GCInfo::WriteBarrierForm GCInfo::gcIsWriteBarrierCandidate(GenTreePtr tgt, GenTreePtr assignVal)
{
#if FEATURE_WRITE_BARRIER
/* Are we storing a GC ptr? */
if (!varTypeIsGC(tgt->TypeGet()))
{
return WBF_NoBarrier;
}
/* Ignore any assignments of NULL */
// 'assignVal' can be the constant Null or something else (LclVar, etc..)
// that is known to be null via Value Numbering.
if (assignVal->GetVN(VNK_Liberal) == ValueNumStore::VNForNull())
{
return WBF_NoBarrier;
}
if (assignVal->gtOper == GT_CNS_INT && assignVal->gtIntCon.gtIconVal == 0)
{
return WBF_NoBarrier;
}
/* Where are we storing into? */
tgt = tgt->gtEffectiveVal();
switch (tgt->gtOper)
{
#ifndef LEGACY_BACKEND
case GT_STOREIND:
#endif // !LEGACY_BACKEND
case GT_IND: /* Could be the managed heap */
if (tgt->TypeGet() == TYP_BYREF)
{
// Byref values cannot be in managed heap.
// This case occurs for Span<T>.
return WBF_NoBarrier;
}
return gcWriteBarrierFormFromTargetAddress(tgt->gtOp.gtOp1);
case GT_LEA:
return gcWriteBarrierFormFromTargetAddress(tgt->AsAddrMode()->Base());
case GT_ARR_ELEM: /* Definitely in the managed heap */
case GT_CLS_VAR:
return WBF_BarrierUnchecked;
case GT_REG_VAR: /* Definitely not in the managed heap */
case GT_LCL_VAR:
case GT_LCL_FLD:
case GT_STORE_LCL_VAR:
case GT_STORE_LCL_FLD:
return WBF_NoBarrier;
default:
break;
}
assert(!"Missing case in gcIsWriteBarrierCandidate");
#endif
return WBF_NoBarrier;
}
