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Don't assume objects don't escape in pure helpers. #21177

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Don't assume objects don't escape in pure helpers. #21177

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12 changes: 5 additions & 7 deletions src/jit/objectalloc.cpp
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Expand Up @@ -579,14 +579,12 @@ bool ObjectAllocator::CanLclVarEscapeViaParentStack(ArrayStack<GenTree*>* parent

if (asCall->gtCallType == CT_HELPER)
{
const CorInfoHelpFunc helperNum = comp->eeGetHelperNum(asCall->gtCallMethHnd);
// TODO-ObjectStackAllocation: Special-case helpers here that
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@erozenfeld - is there a tracking issue for this TODO?

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@CarolEidt It's one of the items in todo list in https://github.com/dotnet/coreclr/issues/20253#issue-366568135 :

  • special case calls to helpers where arguments don't escape (this will require ensuring that the helpers report gc arguments as interior to gc)

// 1. Don't make objects escape.
// 2. Protect objects as interior (GCPROTECT_BEGININTERIOR() instead of GCPROTECT_BEGIN()).
// 3. Don't check that the object is in the heap in ValidateInner.

if (Compiler::s_helperCallProperties.IsPure(helperNum))
{
// Pure helpers don't modify the heap.
// TODO-ObjectStackAllocation: We may be able to special-case more helpers here.
canLclVarEscapeViaParentStack = false;
}
canLclVarEscapeViaParentStack = true;
}
break;
}
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10 changes: 6 additions & 4 deletions tests/src/JIT/opt/ObjectStackAllocation/ObjectStackAllocationTests.cs
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Expand Up @@ -101,10 +101,6 @@ public static int Main()

CallTestAndVerifyAllocation(AllocateSimpleClassesAndNECompareThem, 1, expectedAllocationKind);

CallTestAndVerifyAllocation(AllocateSimpleClassAndCheckType, 1, expectedAllocationKind);

CallTestAndVerifyAllocation(AllocateSimpleClassAndCast, 7, expectedAllocationKind);

CallTestAndVerifyAllocation(AllocateSimpleClassAndGetField, 7, expectedAllocationKind);

CallTestAndVerifyAllocation(AllocateClassWithNestedStructAndGetField, 5, expectedAllocationKind);
Expand All @@ -116,6 +112,12 @@ public static int Main()
expectedAllocationKind = AllocationKind.Heap;
}

// This test calls CORINFO_HELP_ISINSTANCEOFCLASS
CallTestAndVerifyAllocation(AllocateSimpleClassAndCheckType, 1, expectedAllocationKind);

// This test calls CORINFO_HELP_CHKCASTCLASS_SPECIAL
CallTestAndVerifyAllocation(AllocateSimpleClassAndCast, 7, expectedAllocationKind);

// Stack allocation of classes with GC fields is currently disabled
CallTestAndVerifyAllocation(AllocateSimpleClassWithGCFieldAndAddFields, 12, expectedAllocationKind);

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