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JIT: Add ordering side effects in fgMorphExpandInstanceField #92998

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Oct 5, 2023
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JIT: Add ordering side effects in fgMorphExpandInstanceField #92998

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50d4d4b
JIT: Add ordering side effects in fgMorphExpandInstanceField
jakobbotsch Oct 4, 2023
2afee5b
Revert naming convention change, rename Consumer -> User terminology
jakobbotsch Oct 5, 2023
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4 changes: 2 additions & 2 deletions src/coreclr/jit/compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5917,8 +5917,8 @@ class Compiler
// small; hence the other fields of MorphAddrContext.
struct MorphAddrContext
{
size_t m_totalOffset = 0; // Sum of offsets between the top-level indirection and here (current context).
bool m_used = false; // Whether this context was used to elide a null check.
GenTreeIndir* Consumer = nullptr; // Indirection using this address.
size_t TotalOffset = 0; // Sum of offsets between the top-level indirection and here (current context).
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nit: why change the naming style? We aren't very consistent with https://github.com/dotnet/runtime/blob/main/docs/coding-guidelines/clr-jit-coding-conventions.md#8.7, but we are pretty consistent to not capitalize local/field names.

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I reverted this... mainly I think the m_ prefix on fields meant to be used publicly looks off (I like the convention, but only for private fields, and I thought that's only where it applied).

};

#ifdef FEATURE_SIMD
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49 changes: 36 additions & 13 deletions src/coreclr/jit/morph.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5086,11 +5086,26 @@ GenTree* Compiler::fgMorphExpandInstanceField(GenTree* tree, MorphAddrContext* m
{
// A non-null context here implies our [+ some offset] parent is an indirection, one that
// will implicitly null-check the produced address.
addExplicitNullCheck = (mac == nullptr) || fgIsBigOffset(mac->m_totalOffset + fieldOffset);
addExplicitNullCheck = (mac == nullptr) || fgIsBigOffset(mac->TotalOffset + fieldOffset);

if (!addExplicitNullCheck)
// The transformation here turns a value dependency (FIELD_ADDR being a
// known non-null operand) into a control-flow dependency (introducing
// explicit COMMA(NULLCHECK, ...)). This effectively "disconnects" the
// null check from the parent of the FIELD_ADDR node. For the cases
// where we made use of non-nullness we need to make the dependency
// explicit now.
if (addExplicitNullCheck)
{
mac->m_used = true;
if (mac != nullptr)
{
mac->Consumer->SetHasOrderingSideEffect();
}
}
else
{
// We can elide the null check only by letting it happen as part of
// the consuming indirection, so it is no longer non-faulting.
mac->Consumer->gtFlags &= ~GTF_IND_NONFAULTING;
}
}

Expand Down Expand Up @@ -5153,6 +5168,13 @@ GenTree* Compiler::fgMorphExpandInstanceField(GenTree* tree, MorphAddrContext* m
}

addr = gtNewOperNode(GT_ADD, (objRefType == TYP_I_IMPL) ? TYP_I_IMPL : TYP_BYREF, addr, offsetNode);

// We cannot form and GC report an invalid byref, so this must preserve
// its ordering with the null check.
if (addExplicitNullCheck && addr->TypeIs(TYP_BYREF))
{
addr->SetHasOrderingSideEffect();
}
}
#endif

Expand All @@ -5168,6 +5190,13 @@ GenTree* Compiler::fgMorphExpandInstanceField(GenTree* tree, MorphAddrContext* m
{
addr = gtNewOperNode(GT_ADD, (objRefType == TYP_I_IMPL) ? TYP_I_IMPL : TYP_BYREF, addr,
gtNewIconNode(fieldOffset, fieldSeq));

// We cannot form and GC report an invalid byref, so this must preserve
// its ordering with the null check.
if (addExplicitNullCheck && addr->TypeIs(TYP_BYREF))
{
addr->SetHasOrderingSideEffect();
}
}

if (addExplicitNullCheck)
Expand Down Expand Up @@ -8937,17 +8966,18 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
if (tree->OperIsIndir()) // TODO-CQ: add more operators here (e. g. atomics).
{
// Communicate to FIELD_ADDR morphing that the parent is an indirection.
mac = &indMac;
indMac.Consumer = tree->AsIndir();
mac = &indMac;
}
// For additions, if we already have a context, keep track of whether all offsets added
// to the address are constant, and their sum does not overflow.
else if ((mac != nullptr) && tree->OperIs(GT_ADD) && op2->IsCnsIntOrI())
{
ClrSafeInt<size_t> offset(mac->m_totalOffset);
ClrSafeInt<size_t> offset(mac->TotalOffset);
offset += op2->AsIntCon()->IconValue();
if (!offset.IsOverflow())
{
mac->m_totalOffset = offset.Value();
mac->TotalOffset = offset.Value();
}
else
{
Expand All @@ -8961,13 +8991,6 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA

tree->AsOp()->gtOp1 = op1 = fgMorphTree(op1, mac);

if ((mac != nullptr) && mac->m_used && tree->OperIsIndir())
{
// This context was used to elide an explicit null check on a FIELD_ADDR, with the expectation that
// this indirection will now be responsible for null-checking (implicitly).
tree->gtFlags &= ~GTF_IND_NONFAULTING;
}

// If we are exiting the "then" part of a Qmark-Colon we must
// save the state of the current copy assignment table
// so that we can merge this state with the "else" part exit
Expand Down