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Fix value numbering of field assignments #61113

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Merged
jakobbotsch merged 4 commits into from
Nov 8, 2021
Merged

Fix value numbering of field assignments #61113

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a6c7492
Fix value numbering of field assignments
SingleAccretion Oct 29, 2021
0a4c6ae
Add an optimization
SingleAccretion Nov 2, 2021
3744a29
Fix formatting
SingleAccretion Nov 2, 2021
352acf4
Go back to typing the "first field map" as a field
SingleAccretion Nov 2, 2021
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Add an optimization 
It was confusing in the dumps to look at unused results of VNForMapSelect,
so just avoid looking for the first field's value if we do not need it.
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@SingleAccretion
SingleAccretion committed Nov 6, 2021
commit 0a4c6aebebe56130b8cdc1d7b883a5cdd02a99e0
32 changes: 21 additions & 11 deletions src/coreclr/jit/valuenum.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7808,22 +7808,32 @@ void Compiler::fgValueNumberAssignment(GenTreeOp* tree)
firstFieldValueSelectorVN = vnStore->VNLiberalNormalValue(staticOffset->gtVNPair);
}

// Construct the ValueNumber for fldMap[obj/offset]. This
// map represents the specific field we're looking to store to.
ValueNum firstFieldValueVN = vnStore->VNForMapSelect(VNK_Liberal, firstFieldType, fldMapVN,
firstFieldValueSelectorVN);

// Now construct the maps updating the rest of the
// fields in the sequence (of which there could be none).
ValueNum newFirstFieldValueVN = vnStore->VNApplySelectorsAssign(VNK_Liberal,
firstFieldValueVN,
fldSeq->m_next,
storeVal, indType);
ValueNum newFirstFieldValueVN = ValueNumStore::NoVN;
// Optimization: avoid traversting the maps for the value of the first field if
// we do not need it, which is the case if the rest of the field sequence is empty.
if (fldSeq->m_next == nullptr)
{
newFirstFieldValueVN = vnStore->VNApplySelectorsAssignTypeCoerce(storeVal, indType);
}
else
{
// Construct the ValueNumber for fldMap[obj/offset]. This (struct)
// map represents the specific field we're looking to store to.
ValueNum firstFieldValueVN = vnStore->VNForMapSelect(VNK_Liberal, firstFieldType,
fldMapVN,
firstFieldValueSelectorVN);

// Construct the maps updating the rest of the fields in the sequence.
newFirstFieldValueVN = vnStore->VNApplySelectorsAssign(VNK_Liberal, firstFieldValueVN,
fldSeq->m_next, storeVal,
indType);
}

// Finally, construct the new field map...
ValueNum newFldMapVN = vnStore->VNForMapStore(vnStore->TypeOfVN(fldMapVN), fldMapVN,
firstFieldValueSelectorVN,
newFirstFieldValueVN);

// ...and a new value for the heap.
newHeapVN = vnStore->VNForMapStore(TYP_REF, fgCurMemoryVN[GcHeap],
firstFieldSelectorVN, newFldMapVN);
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