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JIT: Disallow SCEV analysis of non-values #108603

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Oct 8, 2024
Merged

JIT: Disallow SCEV analysis of non-values #108603

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4 changes: 2 additions & 2 deletions src/coreclr/jit/inductionvariableopts.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -779,7 +779,7 @@ bool Compiler::optWidenIVs(ScalarEvolutionContext& scevContext,
JITDUMP("\n");
DISPSTMT(stmt);

Scev* scev = scevContext.Analyze(loop->GetHeader(), stmt->GetRootNode());
Scev* scev = scevContext.Analyze(loop->GetHeader(), stmt->GetRootNode()->AsLclVarCommon()->Data());
if (scev == nullptr)
{
JITDUMP(" Could not analyze header PHI\n");
Expand Down Expand Up @@ -1417,7 +1417,7 @@ bool StrengthReductionContext::TryStrengthReduce()
DISPSTMT(stmt);

GenTreeLclVarCommon* primaryIVLcl = stmt->GetRootNode()->AsLclVarCommon();
Scev* candidate = m_scevContext.Analyze(m_loop->GetHeader(), primaryIVLcl);
Scev* candidate = m_scevContext.Analyze(m_loop->GetHeader(), primaryIVLcl->Data());
if (candidate == nullptr)
{
JITDUMP(" Could not analyze header PHI\n");
Expand Down
62 changes: 38 additions & 24 deletions src/coreclr/jit/scev.cpp
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Expand Up @@ -563,25 +563,18 @@ Scev* ScalarEvolutionContext::AnalyzeNew(BasicBlock* block, GenTree* tree, int d
return nullptr;
}

return Analyze(ssaDsc->GetBlock(), ssaDsc->GetDefNode(), depth + 1);
return Analyze(ssaDsc->GetBlock(), ssaDsc->GetDefNode()->Data(), depth + 1);
}
case GT_STORE_LCL_VAR:
case GT_PHI:
{
GenTreeLclVarCommon* store = tree->AsLclVarCommon();
GenTree* data = store->Data();
if (!data->OperIs(GT_PHI))
{
return Analyze(block, data, depth + 1);
}

if (block != m_loop->GetHeader())
{
return nullptr;
}

// We have a phi def for the current loop. Look for a primary
// induction variable.
GenTreePhi* phi = data->AsPhi();
GenTreePhi* phi = tree->AsPhi();
GenTreePhiArg* enterSsa = nullptr;
GenTreePhiArg* backedgeSsa = nullptr;

Expand All @@ -606,7 +599,7 @@ Scev* ScalarEvolutionContext::AnalyzeNew(BasicBlock* block, GenTree* tree, int d

ScevLocal* enterScev = NewLocal(enterSsa->GetLclNum(), enterSsa->GetSsaNum());

LclVarDsc* dsc = m_comp->lvaGetDesc(store);
LclVarDsc* dsc = m_comp->lvaGetDesc(enterSsa->GetLclNum());
LclSsaVarDsc* ssaDsc = dsc->GetPerSsaData(backedgeSsa->GetSsaNum());

if (ssaDsc->GetDefNode() == nullptr)
Expand All @@ -615,7 +608,7 @@ Scev* ScalarEvolutionContext::AnalyzeNew(BasicBlock* block, GenTree* tree, int d
return nullptr;
}

if (ssaDsc->GetDefNode()->GetLclNum() != store->GetLclNum())
if (ssaDsc->GetDefNode()->GetLclNum() != enterSsa->GetLclNum())
{
assert(dsc->lvIsStructField && ssaDsc->GetDefNode()->GetLclNum() == dsc->lvParentLcl);
return nullptr;
Expand All @@ -625,7 +618,7 @@ Scev* ScalarEvolutionContext::AnalyzeNew(BasicBlock* block, GenTree* tree, int d

// Try simple but most common case first, where we have a direct
// add recurrence like i = i + 1.
Scev* simpleAddRec = CreateSimpleAddRec(store, enterScev, ssaDsc->GetBlock(), ssaDsc->GetDefNode()->Data());
Scev* simpleAddRec = CreateSimpleAddRec(phi, enterScev, ssaDsc->GetBlock(), ssaDsc->GetDefNode()->Data());
if (simpleAddRec != nullptr)
{
return simpleAddRec;
Expand Down Expand Up @@ -670,8 +663,8 @@ Scev* ScalarEvolutionContext::AnalyzeNew(BasicBlock* block, GenTree* tree, int d
// single operand is the recurrence, we can represent it as an add
// recurrence. See MakeAddRecFromRecursiveScev for the details.
//
ScevConstant* symbolicAddRec = NewConstant(data->TypeGet(), 0xdeadbeef);
m_ephemeralCache.Emplace(store, symbolicAddRec);
ScevConstant* symbolicAddRec = NewConstant(phi->TypeGet(), 0xdeadbeef);
m_ephemeralCache.Emplace(phi, symbolicAddRec);

Scev* result;
if (m_usingEphemeralCache)
Expand Down Expand Up @@ -772,18 +765,18 @@ Scev* ScalarEvolutionContext::AnalyzeNew(BasicBlock* block, GenTree* tree, int d
// "i = i + 1".
//
// Parameters:
// headerStore - Phi definition of the candidate primary induction variable
// headerPhi - Phi value of the candidate primary induction variable
// enterScev - SCEV describing start value of the primary induction variable
// stepDefBlock - Block containing the def of the step value
// stepDefData - Value of the def of the step value
//
// Returns:
// SCEV node if this is a simple addrec shape. Otherwise nullptr.
//
Scev* ScalarEvolutionContext::CreateSimpleAddRec(GenTreeLclVarCommon* headerStore,
ScevLocal* enterScev,
BasicBlock* stepDefBlock,
GenTree* stepDefData)
Scev* ScalarEvolutionContext::CreateSimpleAddRec(GenTreePhi* headerPhi,
ScevLocal* enterScev,
BasicBlock* stepDefBlock,
GenTree* stepDefData)
{
if (!stepDefData->OperIs(GT_ADD))
{
Expand All @@ -793,13 +786,34 @@ Scev* ScalarEvolutionContext::CreateSimpleAddRec(GenTreeLclVarCommon* headerStor
GenTree* stepTree;
GenTree* op1 = stepDefData->gtGetOp1();
GenTree* op2 = stepDefData->gtGetOp2();
if (op1->OperIs(GT_LCL_VAR) && (op1->AsLclVar()->GetLclNum() == headerStore->GetLclNum()) &&
(op1->AsLclVar()->GetSsaNum() == headerStore->GetSsaNum()))

auto getUseValue = [this](GenTree* value) -> GenTree* {
if (!value->OperIs(GT_LCL_VAR))
{
return nullptr;
}

GenTreeLclVarCommon* lcl = value->AsLclVarCommon();
if (!lcl->HasSsaName())
{
return nullptr;
}

LclVarDsc* lclDsc = m_comp->lvaGetDesc(lcl);
LclSsaVarDsc* ssaDsc = lclDsc->GetPerSsaData(lcl->GetSsaNum());
if (ssaDsc->GetDefNode() == nullptr)
{
return nullptr;
}

return ssaDsc->GetDefNode()->Data();
};

if (getUseValue(op1) == headerPhi)
{
stepTree = op2;
}
else if (op2->OperIs(GT_LCL_VAR) && (op2->AsLclVar()->GetLclNum() == headerStore->GetLclNum()) &&
(op2->AsLclVar()->GetSsaNum() == headerStore->GetSsaNum()))
else if (getUseValue(op2) == headerPhi)
{
stepTree = op1;
}
Expand Down
5 changes: 1 addition & 4 deletions src/coreclr/jit/scev.h
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Expand Up @@ -230,10 +230,7 @@ class ScalarEvolutionContext

Scev* Analyze(BasicBlock* block, GenTree* tree, int depth);
Scev* AnalyzeNew(BasicBlock* block, GenTree* tree, int depth);
Scev* CreateSimpleAddRec(GenTreeLclVarCommon* headerStore,
ScevLocal* start,
BasicBlock* stepDefBlock,
GenTree* stepDefData);
Scev* CreateSimpleAddRec(GenTreePhi* headerPhi, ScevLocal* start, BasicBlock* stepDefBlock, GenTree* stepDefData);
Scev* MakeAddRecFromRecursiveScev(Scev* start, Scev* scev, Scev* recursiveScev);
Scev* CreateSimpleInvariantScev(GenTree* tree);
Scev* CreateScevForConstant(GenTreeIntConCommon* tree);
Expand Down
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