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JIT: relax constraint in conditional escape analysis #117222

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Jul 2, 2025
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JIT: relax constraint in conditional escape analysis #117222

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141 changes: 64 additions & 77 deletions src/coreclr/jit/objectalloc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3317,102 +3317,89 @@ void ObjectAllocator::CheckForGuardedAllocationOrCopy(BasicBlock* block,
//
if (data->OperIs(GT_ALLOCOBJ))
{
// See if this store is made under a successful GDV test.
// This may be an allocation of a concrete class under GDV.
//
GuardInfo controllingGDV;
if (IsGuarded(block, tree, &controllingGDV, /* testOutcome */ true))
// Find the local that will ultimately represent its uses (we have kept track of
// this during importation and GDV expansion). Note it is usually *not* lclNum.
//
// We will keep special track of all accesses to this local.
//
Compiler::NodeToUnsignedMap* const map = comp->getImpEnumeratorGdvLocalMap();
unsigned enumeratorLocal = BAD_VAR_NUM;
if (map->Lookup(data, &enumeratorLocal))
{
// This is the allocation of concrete class under GDV.
//
// Find the local that will ultimately represent its uses (we have kept track of
// this during importation and GDV expansion). Note it is usually *not* lclNum.
//
// We will keep special track of all accesses to this local.
// If it turns out we can't stack allocate this new object even if it does not escape,
// then don't bother setting up tracking. Note length here is just set to a nominal
// value that won't cause failure. We will do the real length check later if we decide to allocate.
//
Compiler::NodeToUnsignedMap* const map = comp->getImpEnumeratorGdvLocalMap();
unsigned enumeratorLocal = BAD_VAR_NUM;
if (map->Lookup(data, &enumeratorLocal))
CORINFO_CLASS_HANDLE clsHnd = data->AsAllocObj()->gtAllocObjClsHnd;
const char* reason = nullptr;
unsigned size = 0;
unsigned length = TARGET_POINTER_SIZE;
ObjectAllocationType oat = AllocationKind(data);
if (CanAllocateLclVarOnStack(enumeratorLocal, clsHnd, oat, length, &size, &reason,
/* preliminaryCheck */ true))
{
// If it turns out we can't stack allocate this new object even if it does not escape,
// then don't bother setting up tracking. Note length here is just set to a nominal
// value that won't cause failure. We will do the real length check later if we decide to allocate.
// We are going to conditionally track accesses to the enumerator local via a pseudo.
//
CORINFO_CLASS_HANDLE clsHnd = data->AsAllocObj()->gtAllocObjClsHnd;
const char* reason = nullptr;
unsigned size = 0;
unsigned length = TARGET_POINTER_SIZE;
ObjectAllocationType oat = AllocationKind(data);
if (CanAllocateLclVarOnStack(enumeratorLocal, clsHnd, oat, length, &size, &reason,
/* preliminaryCheck */ true))
const unsigned pseudoIndex = NewPseudoIndex();
assert(pseudoIndex != BAD_VAR_NUM);
bool added = m_EnumeratorLocalToPseudoIndexMap.AddOrUpdate(enumeratorLocal, pseudoIndex);

if (!added)
{
// We are going to conditionally track accesses to the enumerator local via a pseudo.
// Seems like we have multiple GDVs that can define this local.
// Carry on for now, but later we may see these collide
// and end up not cloning any of them.
//
const unsigned pseudoIndex = NewPseudoIndex();
assert(pseudoIndex != BAD_VAR_NUM);
bool added = m_EnumeratorLocalToPseudoIndexMap.AddOrUpdate(enumeratorLocal, pseudoIndex);

if (!added)
{
// Seems like we have multiple GDVs that can define this local.
// Carry on for now, but later we may see these collide
// and end up not cloning any of them.
//
// Since we are walking in RPO we may also be able to see that
// they are properly disjoint and things will work out just fine.
//
JITDUMP("Looks like enumerator var re-use (multiple defining GDVs)\n");
}

// We will query this info if we see CALL(enumeratorLocal)
// during subsequent analysis, to verify that access is
// under the same guard conditions.
// Since we are walking in RPO we may also be able to see that
// they are properly disjoint and things will work out just fine.
//
CompAllocator alloc(comp->getAllocator(CMK_ObjectAllocator));
CloneInfo* info = new (alloc) CloneInfo();
info->m_local = enumeratorLocal;
info->m_type = clsHnd;
info->m_pseudoIndex = pseudoIndex;
info->m_appearanceMap = new (alloc) EnumeratorVarMap(alloc);
info->m_allocBlock = block;
info->m_allocStmt = stmt;
info->m_allocTree = data;
info->m_domBlock = controllingGDV.m_block;
m_CloneMap.Set(pseudoIndex, info);

JITDUMP("Enumerator allocation [%06u]: will track accesses to V%02u guarded by type %s via",
comp->dspTreeID(data), enumeratorLocal, comp->eeGetClassName(clsHnd));
JITDUMPEXEC(DumpIndex(pseudoIndex));
JITDUMP("\n");

// If this is not a direct assignment to the enumerator var we also need to
// track the temps that will appear in between. Later we will rewrite these
// to a fresh set of temps.
//
if (lclNum != enumeratorLocal)
{
CheckForEnumeratorUse(enumeratorLocal, lclNum);
RecordAppearance(lclNum, block, stmt, use);
}
JITDUMP("Looks like enumerator var re-use (multiple defining GDVs)\n");
}
else

// We will query this info if we see CALL(enumeratorLocal)
// during subsequent analysis, to verify that access is
// under the same guard conditions.
//
CompAllocator alloc(comp->getAllocator(CMK_ObjectAllocator));
CloneInfo* info = new (alloc) CloneInfo();
info->m_local = enumeratorLocal;
info->m_type = clsHnd;
info->m_pseudoIndex = pseudoIndex;
info->m_appearanceMap = new (alloc) EnumeratorVarMap(alloc);
info->m_allocBlock = block;
info->m_allocStmt = stmt;
info->m_allocTree = data;
m_CloneMap.Set(pseudoIndex, info);

JITDUMP("Enumerator allocation [%06u]: will track accesses to V%02u guarded by type %s via",
comp->dspTreeID(data), enumeratorLocal, comp->eeGetClassName(clsHnd));
JITDUMPEXEC(DumpIndex(pseudoIndex));
JITDUMP("\n");

// If this is not a direct assignment to the enumerator var we also need to
// track the temps that will appear in between. Later we will rewrite these
// to a fresh set of temps.
//
if (lclNum != enumeratorLocal)
{
JITDUMP(
"Enumerator allocation [%06u]: enumerator type %s cannot be stack allocated, so not tracking enumerator local V%02u\n",
comp->dspTreeID(data), comp->eeGetClassName(clsHnd), enumeratorLocal);
CheckForEnumeratorUse(enumeratorLocal, lclNum);
RecordAppearance(lclNum, block, stmt, use);
}
}
else
{
// This allocation is not currently of interest
//
JITDUMP("Allocation [%06u] was not flagged for conditional escape tracking\n", comp->dspTreeID(data));
JITDUMP(
"Enumerator allocation [%06u]: enumerator type %s cannot be stack allocated, so not tracking enumerator local V%02u\n",
comp->dspTreeID(data), comp->eeGetClassName(clsHnd), enumeratorLocal);
}
}
else
{
// This allocation was not done under a GDV guard
// This allocation is not currently of interest
//
JITDUMP("Allocation [%06u] is not under a GDV guard\n", comp->dspTreeID(data));
JITDUMP("Allocation [%06u] was not flagged for conditional escape tracking\n", comp->dspTreeID(data));
}
}
else if (data->OperIs(GT_LCL_VAR, GT_BOX))
Expand Down
3 changes: 0 additions & 3 deletions src/coreclr/jit/objectalloc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -94,9 +94,6 @@ struct CloneInfo : public GuardInfo
Statement* m_allocStmt = nullptr;
BasicBlock* m_allocBlock = nullptr;

// Block holding the GDV test that decides if the enumerator will be allocated
BasicBlock* m_domBlock = nullptr;

// Blocks to clone (in order), and a set representation
// of the same
jitstd::vector<BasicBlock*>* m_blocksToClone = nullptr;
Expand Down
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