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Revert potential UB due to aliasing + more WB removals #111733

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Merged
EgorBo merged 3 commits into from
Jan 26, 2025
Merged

Revert potential UB due to aliasing + more WB removals #111733

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3787478
Revert potential UB due to aliasing + more WB removals
EgorBo Jan 23, 2025
43cead8
Address feedback
EgorBo Jan 23, 2025
0505951
fix regressions
EgorBo Jan 23, 2025
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24 changes: 0 additions & 24 deletions src/coreclr/jit/assertionprop.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5258,30 +5258,6 @@ static GCInfo::WriteBarrierForm GetWriteBarrierForm(Compiler* comp, ValueNum vn)
return GetWriteBarrierForm(comp, funcApp.m_args[0]);
}
}
if (funcApp.m_func == VNF_InitVal)
{
unsigned lclNum = vnStore->CoercedConstantValue<unsigned>(funcApp.m_args[0]);
assert(lclNum != BAD_VAR_NUM);
CORINFO_CLASS_HANDLE srcCls = NO_CLASS_HANDLE;

if (comp->compMethodHasRetVal() && (lclNum == comp->info.compRetBuffArg))
{
// See if the address is in current method's return buffer
// while the return type is a byref-like type.
srcCls = comp->info.compMethodInfo->args.retTypeClass;
}
else if (lclNum == comp->info.compThisArg)
{
// Same for implicit "this" parameter
assert(!comp->info.compIsStatic);
srcCls = comp->info.compClassHnd;
}

if ((srcCls != NO_CLASS_HANDLE) && comp->eeIsByrefLike(srcCls))
{
return GCInfo::WriteBarrierForm::WBF_NoBarrier;
}
}
}
return GCInfo::WriteBarrierForm::WBF_BarrierUnknown;
}
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15 changes: 15 additions & 0 deletions src/coreclr/jit/importer.cpp
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Expand Up @@ -9548,6 +9548,21 @@ void Compiler::impImportBlockCode(BasicBlock* block)
{
indirFlags |= GTF_IND_TGT_HEAP;
}
else if ((lclTyp == TYP_STRUCT) && (fieldInfo.structType != NO_CLASS_HANDLE) &&
eeIsByrefLike(fieldInfo.structType))
{
// Field's type is a byref-like struct -> address is not on the heap.
indirFlags |= GTF_IND_TGT_NOT_HEAP;
}
else
{
// Field's owner is a byref-like struct -> address is not on the heap.
CORINFO_CLASS_HANDLE fldOwner = info.compCompHnd->getFieldClass(resolvedToken.hField);
if ((fldOwner != NO_CLASS_HANDLE) && eeIsByrefLike(fldOwner))
{
indirFlags |= GTF_IND_TGT_NOT_HEAP;
}
}

assert(varTypeIsI(op1));
op1 = (lclTyp == TYP_STRUCT) ? gtNewStoreBlkNode(layout, op1, op2, indirFlags)->AsIndir()
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7 changes: 4 additions & 3 deletions src/coreclr/jit/promotiondecomposition.cpp
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Expand Up @@ -523,16 +523,17 @@ class DecompositionPlan
target_ssize_t addrBaseOffs = 0;
FieldSeq* addrBaseOffsFldSeq = nullptr;
GenTreeFlags indirFlags = GTF_EMPTY;

GenTreeFlags flagsToPropagate = GTF_IND_COPYABLE_FLAGS;
if (m_store->OperIs(GT_STORE_BLK))
{
flagsToPropagate |= GTF_IND_TGT_NOT_HEAP | GTF_IND_TGT_HEAP;
addr = m_store->AsIndir()->Addr();
indirFlags = m_store->gtFlags & GTF_IND_COPYABLE_FLAGS;
indirFlags = m_store->gtFlags & flagsToPropagate;
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@jakobbotsch jakobbotsch Jan 23, 2025

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Is there any benefit to adding something like

if (m_store->AsBlk()->GetLayout()->IsStackOnly())
  indirFlags |= GTF_IND_TGT_NOT_HEAP;

here (and in morphblock.cpp)? Or will m_store already have this flag set for this case?

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@EgorBo EgorBo Jan 23, 2025

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@jakobbotsch I don't see diffs, but this PR already produces too many missing contexts 🙂
Presumably, this is not enough, because some GT_STORE_BLK have this flag without its layout being IsStackOnly. E.g. when we store a non-byreflike struct to byreflike-struct's field

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@jakobbotsch jakobbotsch Jan 23, 2025

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Yeah, it makes sense to me to propagate the flags, but it also makes sense to me to set the flags anew here, since the decomposition is "losing" the information at this point. I will leave it up to you.

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@EgorBo EgorBo Jan 23, 2025

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Added. Looks like MihuBot found a few diffs with it

}
else if (m_src->OperIs(GT_BLK))
{
addr = m_src->AsIndir()->Addr();
indirFlags = m_src->gtFlags & GTF_IND_COPYABLE_FLAGS;
indirFlags = m_src->gtFlags & flagsToPropagate;
}

int numAddrUses = 0;
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