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Fix value numbering of field assignments (#61113)
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When value numbering an assignment to a field, VNApplySelectorsAssign
was called twice, first for the field sequence to find the exact
value, then for the heap VN update. This is not correct as the method
expects to be called only for sequences that will end up updating a
map with exact values, as it type checks the store with the helper
VNApplySelectorsAssignTypeCoerce. Usage of VNApplySelectorsAssign
to update the heap ended up meaning that any stores to struct fields
ended up with casts for maps, blocking traversal in VNForMapSelect.

A handful of positive diffs for this commit resulting from more CSEs
and redundant branch optimizations, due to more precise liberal VNs.
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@SingleAccretion
SingleAccretion committed Nov 8, 2021
1 parent ff361bd commit 39ece73
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Showing 2 changed files with 111 additions and 100 deletions.
207 changes: 107 additions & 100 deletions src/coreclr/jit/valuenum.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2495,6 +2495,52 @@ ValueNum ValueNumStore::VNForMapSelectWork(
}
}

//------------------------------------------------------------------------
// VNForFieldSelector: A specialized version (with logging) of VNForHandle
// that is used for field handle selectors.
//
// Arguments:
// fieldHnd - handle of the field in question
// pFieldType - [out] parameter for the field's type
// pStructHnd - optional [out] parameter for the struct handle,
// populated if the field is of a struct type
//
// Return Value:
// Value number corresponding to the given field handle.
//
ValueNum ValueNumStore::VNForFieldSelector(CORINFO_FIELD_HANDLE fieldHnd,
var_types* pFieldType,
CORINFO_CLASS_HANDLE* pStructHnd)
{
CORINFO_CLASS_HANDLE structHnd = NO_CLASS_HANDLE;
ValueNum fldHndVN = VNForHandle(ssize_t(fieldHnd), GTF_ICON_FIELD_HDL);

CorInfoType fieldCit = m_pComp->info.compCompHnd->getFieldType(fieldHnd, &structHnd);
var_types fieldType = JITtype2varType(fieldCit);

#ifdef DEBUG
if (m_pComp->verbose)
{
const char* modName;
const char* fldName = m_pComp->eeGetFieldName(fieldHnd, &modName);
printf(" VNForHandle(%s) is " FMT_VN ", fieldType is %s", fldName, fldHndVN, varTypeName(fieldType));
if (varTypeIsStruct(fieldType))
{
printf(", size = %u", m_pComp->info.compCompHnd->getClassSize(structHnd));
}
printf("\n");
}
#endif

if (pStructHnd != nullptr)
{
*pStructHnd = structHnd;
}
*pFieldType = fieldType;

return fldHndVN;
}

ValueNum ValueNumStore::EvalFuncForConstantArgs(var_types typ, VNFunc func, ValueNum arg0VN)
{
assert(CanEvalForConstantArgs(func));
Expand Down Expand Up @@ -3812,12 +3858,11 @@ ValueNum ValueNumStore::VNApplySelectors(ValueNumKind vnk,

assert(field != FieldSeqStore::NotAField());

CORINFO_FIELD_HANDLE fldHnd = field->m_fieldHnd;
CORINFO_CLASS_HANDLE structHnd = NO_CLASS_HANDLE;
ValueNum fldHndVN = VNForHandle(ssize_t(fldHnd), GTF_ICON_FIELD_HDL);
noway_assert(fldHnd != nullptr);
CorInfoType fieldCit = m_pComp->info.compCompHnd->getFieldType(fldHnd, &structHnd);
var_types fieldType = JITtype2varType(fieldCit);
JITDUMP(" VNApplySelectors:\n");
var_types fieldType;
CORINFO_CLASS_HANDLE structHnd;
CORINFO_FIELD_HANDLE fldHnd = field->GetFieldHandle();
ValueNum fldHndVN = VNForFieldSelector(fldHnd, &fieldType, &structHnd);

size_t structSize = 0;
if (varTypeIsStruct(fieldType))
Expand All @@ -3835,21 +3880,6 @@ ValueNum ValueNumStore::VNApplySelectors(ValueNumKind vnk,
*wbFinalStructSize = structSize;
}

#ifdef DEBUG
if (m_pComp->verbose)
{
printf(" VNApplySelectors:\n");
const char* modName;
const char* fldName = m_pComp->eeGetFieldName(fldHnd, &modName);
printf(" VNForHandle(%s) is " FMT_VN ", fieldType is %s", fldName, fldHndVN, varTypeName(fieldType));
if (varTypeIsStruct(fieldType))
{
printf(", size = %d", structSize);
}
printf("\n");
}
#endif

map = VNForMapSelect(vnk, fieldType, map, fldHndVN);
}

Expand Down Expand Up @@ -4005,48 +4035,27 @@ ValueNum ValueNumStore::VNApplySelectorsAssign(
return VNApplySelectorsAssign(vnk, map, fieldSeq->m_next, value, dstIndType);
}

if (fieldSeq->m_next == nullptr)
{
JITDUMP(" VNApplySelectorsAssign:\n");
}

// Otherwise, fldHnd is a real field handle.
CORINFO_FIELD_HANDLE fldHnd = fieldSeq->m_fieldHnd;
ValueNum fldHndVN = VNForHandle(ssize_t(fldHnd), GTF_ICON_FIELD_HDL);
noway_assert(fldHnd != nullptr);
CorInfoType fieldCit = m_pComp->info.compCompHnd->getFieldType(fldHnd);
var_types fieldType = JITtype2varType(fieldCit);
var_types fieldType;
ValueNum fldHndVN = VNForFieldSelector(fieldSeq->GetFieldHandle(), &fieldType);

ValueNum valueAfter;
if (fieldSeq->m_next)
if (fieldSeq->m_next != nullptr)
{
#ifdef DEBUG
if (m_pComp->verbose)
{
const char* modName;
const char* fldName = m_pComp->eeGetFieldName(fldHnd, &modName);
printf(" VNForHandle(%s) is " FMT_VN ", fieldType is %s\n", fldName, fldHndVN,
varTypeName(fieldType));
}
#endif
ValueNum fseqMap = VNForMapSelect(vnk, fieldType, map, fldHndVN);
valueAfter = VNApplySelectorsAssign(vnk, fseqMap, fieldSeq->m_next, value, dstIndType);
}
else
{
#ifdef DEBUG
if (m_pComp->verbose)
{
if (fieldSeq->m_next == nullptr)
{
printf(" VNApplySelectorsAssign:\n");
}
const char* modName;
const char* fldName = m_pComp->eeGetFieldName(fldHnd, &modName);
printf(" VNForHandle(%s) is " FMT_VN ", fieldType is %s\n", fldName, fldHndVN,
varTypeName(fieldType));
}
#endif
valueAfter = VNApplySelectorsAssignTypeCoerce(value, dstIndType);
}

ValueNum newMap = VNForMapStore(fieldType, map, fldHndVN, valueAfter);
return newMap;
return VNForMapStore(fieldType, map, fldHndVN, valueAfter);
}
}

Expand Down Expand Up @@ -7768,82 +7777,80 @@ void Compiler::fgValueNumberAssignment(GenTreeOp* tree)
assert(fldSeq != nullptr);
}

// Get a field sequence for just the first field in the sequence
//
FieldSeqNode* firstFieldOnly = GetFieldSeqStore()->CreateSingleton(fldSeq->m_fieldHnd);
// The value number from the rhs of the assignment
ValueNum storeVal = rhsVNPair.GetLiberal();
ValueNum newHeapVN = ValueNumStore::NoVN;

// The final field in the sequence will need to match the 'indType'
// We will check that the final field in the sequence matches 'indType'.
var_types indType = lhs->TypeGet();
ValueNum fldMapVN =
vnStore->VNApplySelectors(VNK_Liberal, fgCurMemoryVN[GcHeap], firstFieldOnly);

// The type of the field is "struct" if there are more fields in the sequence,
// otherwise it is the type returned from VNApplySelectors above.
var_types firstFieldType = vnStore->TypeOfVN(fldMapVN);

// The value number from the rhs of the assignment
ValueNum storeVal = rhsVNPair.GetLiberal();
ValueNum newFldMapVN = ValueNumStore::NoVN;

// when (obj != nullptr) we have an instance field, otherwise a static field
// when (staticOffset != nullptr) it represents a offset into a static or the call to
// Shared Static Base
if ((obj != nullptr) || (staticOffset != nullptr))
{
ValueNum valAtAddr = fldMapVN;
ValueNum normVal = ValueNumStore::NoVN;
var_types firstFieldType;
ValueNum firstFieldSelectorVN =
vnStore->VNForFieldSelector(fldSeq->GetFieldHandle(), &firstFieldType);

// Construct the "field map" VN. It represents memory state of the first field
// of all objects on the heap. This is our primary map.
ValueNum fldMapVN = vnStore->VNForMapSelect(VNK_Liberal, firstFieldType,
fgCurMemoryVN[GcHeap], firstFieldSelectorVN);

ValueNum firstFieldValueSelectorVN = ValueNumStore::NoVN;
if (obj != nullptr)
{
// Unpack, Norm,Exc for 'obj'
ValueNum vnObjExcSet;
vnStore->VNUnpackExc(obj->gtVNPair.GetLiberal(), &normVal, &vnObjExcSet);
vnExcSet = vnStore->VNExcSetUnion(vnExcSet, vnObjExcSet);

// construct the ValueNumber for 'fldMap at obj'
valAtAddr = vnStore->VNForMapSelect(VNK_Liberal, firstFieldType, fldMapVN, normVal);
firstFieldValueSelectorVN = vnStore->VNLiberalNormalValue(obj->gtVNPair);
}
else // (staticOffset != nullptr)
{
// construct the ValueNumber for 'fldMap at staticOffset'
normVal = vnStore->VNLiberalNormalValue(staticOffset->gtVNPair);
valAtAddr = vnStore->VNForMapSelect(VNK_Liberal, firstFieldType, fldMapVN, normVal);
firstFieldValueSelectorVN = vnStore->VNLiberalNormalValue(staticOffset->gtVNPair);
}
// Now get rid of any remaining struct field dereferences. (if they exist)
if (fldSeq->m_next)

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)
{
storeVal = vnStore->VNApplySelectorsAssign(VNK_Liberal, valAtAddr, fldSeq->m_next,
storeVal, indType);
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);
}

// From which we can construct the new ValueNumber for 'fldMap at normVal'
newFldMapVN =
vnStore->VNForMapStore(vnStore->TypeOfVN(fldMapVN), fldMapVN, normVal, storeVal);
// 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);
}
else
{
// plain static field

// Now get rid of any remaining struct field dereferences. (if they exist)
if (fldSeq->m_next)
{
storeVal = vnStore->VNApplySelectorsAssign(VNK_Liberal, fldMapVN, fldSeq->m_next,
storeVal, indType);
}

newFldMapVN = vnStore->VNApplySelectorsAssign(VNK_Liberal, fgCurMemoryVN[GcHeap], fldSeq,
storeVal, indType);
// Plain static field.
newHeapVN = vnStore->VNApplySelectorsAssign(VNK_Liberal, fgCurMemoryVN[GcHeap], fldSeq,
storeVal, indType);
}

// It is not strictly necessary to set the lhs value number,
// but the dumps read better with it set to the 'storeVal' that we just computed
lhs->gtVNPair.SetBoth(storeVal);

// Update the field map for firstField in GcHeap to this new value.
ValueNum heapVN = vnStore->VNApplySelectorsAssign(VNK_Liberal, fgCurMemoryVN[GcHeap],
firstFieldOnly, newFldMapVN, indType);

recordGcHeapStore(tree, heapVN DEBUGARG("StoreField"));
// Update the GcHeap value.
recordGcHeapStore(tree, newHeapVN DEBUGARG("StoreField"));
}
}
else
Expand Down
4 changes: 4 additions & 0 deletions src/coreclr/jit/valuenum.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -590,6 +590,10 @@ class ValueNumStore
// A specialized version of VNForFunc that is used for VNF_MapStore and provides some logging when verbose is set
ValueNum VNForMapStore(var_types type, ValueNum map, ValueNum index, ValueNum value);

ValueNum VNForFieldSelector(CORINFO_FIELD_HANDLE fieldHnd,
var_types* pFieldType,
CORINFO_CLASS_HANDLE* pStructHnd = nullptr);

// These functions parallel the ones above, except that they take liberal/conservative VN pairs
// as arguments, and return such a pair (the pair of the function applied to the liberal args, and
// the function applied to the conservative args).
Expand Down

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