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Merged
merged 4 commits into from
Feb 20, 2025
Merged

Handle overlapped groups of bounds checks #112660

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d0a0373
Handle overlapped groups of bounds checks
EgorBo Feb 18, 2025
fd5cd2e
Remove unused array length node handling
EgorBo Feb 20, 2025
b11011a
Update src/coreclr/jit/rangecheckcloning.cpp
EgorBo Feb 20, 2025
28c62b5
feedback
EgorBo Feb 20, 2025
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113 changes: 85 additions & 28 deletions src/coreclr/jit/rangecheckcloning.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -48,17 +48,18 @@
// Arguments:
// comp - The compiler instance
// statement - The statement containing the bounds check
// bndChkNode - The bounds check node
// bndChkParentNode - The parent node of the bounds check node (either null or COMMA)
// statementIdx - The index of the statement in the block
// bndChk - The bounds check node (its use edge)
//
// Return Value:
// true if the initialization was successful, false otherwise.
//
bool BoundsCheckInfo::Initialize(const Compiler* comp, Statement* statement, GenTree** bndChk)
bool BoundsCheckInfo::Initialize(const Compiler* comp, Statement* statement, int statementIdx, GenTree** bndChk)
{
assert((bndChk != nullptr) && ((*bndChk) != nullptr));

stmt = statement;
stmtIdx = statementIdx;
bndChkUse = bndChk;
idxVN = comp->vnStore->VNConservativeNormalValue(BndChk()->GetIndex()->gtVNPair);
lenVN = comp->vnStore->VNConservativeNormalValue(BndChk()->GetArrayLength()->gtVNPair);
Expand Down Expand Up @@ -98,16 +99,26 @@ bool BoundsCheckInfo::Initialize(const Compiler* comp, Statement* statement, Gen
// RemoveBoundsChk - Remove the given bounds check from the statement and the block.
//
// Arguments:
// comp - compiler instance
// check - bounds check node to remove
// comma - check's parent node (either null or COMMA)
// stmt - statement containing the bounds check
// comp - compiler instance
// treeUse - the bounds check node to remove (its use edge)
// stmt - the statement containing the bounds check
//
static void RemoveBoundsChk(Compiler* comp, GenTree** treeUse, Statement* stmt)
{
JITDUMP("Before RemoveBoundsChk:\n");
DISPTREE(*treeUse);

// If we deal with GT_ARR_LEN(lcl), we can unmark the array length node
// as having an NRE. Technically, this should be done by the assertion prop,
// but not today, see https://github.com/dotnet/runtime/pull/93531
//
GenTreeBoundsChk* bndsChk = (*treeUse)->AsBoundsChk();
GenTree* arrObj = bndsChk->GetArray();
if ((arrObj != nullptr) && ((arrObj->gtFlags & GTF_ALL_EFFECT) == 0))
{
bndsChk->GetArrayLength()->gtFlags &= ~GTF_EXCEPT;
}
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@jakobbotsch jakobbotsch Feb 20, 2025

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This isn't really correct. The only thing we know here is that the conservative normal VN is the same as the first bounds check's conservative normal VN, but the array length here could still be something like 0 * (1 / 0) + arr.Length (obviously a constructed example) where this code would get rid of the DivisionByZeroException.

Maybe something like

if (bndsChk->GetArrayLength()->OperIs(GT_ARR_LENGTH) &&
    firstBndsChk->GetArrayLength()->OperIs(GT_ARR_LENGTH) &&
    (bndsChk->GetArrayLength()->GetIndirOrArrMetaDataAddr()->gtVNPair.GetConservative() == firstBndsChk->GetArrayLength()->GetIndirOrArrMetaDataAddr()->gtVNPair.GetConservative())
{
  bndsChk->GetArrayLength()->gtFlags |= GTF_IND_NONFAULTING;
  gtUpdateStmtSideEffects(stmt);
}

would get the cases?

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@EgorBo EgorBo Feb 20, 2025

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Actually, even previous code didn't catch anything, so let me just remove this part


GenTree* sideEffList = nullptr;
comp->gtExtractSideEffList(*treeUse, &sideEffList, GTF_SIDE_EFFECT, /*ignoreRoot*/ true);
*treeUse = (sideEffList != nullptr) ? sideEffList : comp->gtNewNothingNode();
Expand Down Expand Up @@ -155,18 +166,21 @@ static void RemoveBoundsChk(Compiler* comp, GenTree** treeUse, Statement* stmt)
// comp - The compiler instance
// block - The block to clone
// bndChkStack - The stack of bounds checks to clone
// lastStmt - The last statement in the block (the block is split after this statement)
//
// Return Value:
// The block containing the fast path.
//
static BasicBlock* optRangeCheckCloning_DoClone(Compiler* comp, BasicBlock* block, BoundsCheckInfoStack* bndChkStack)
static BasicBlock* optRangeCheckCloning_DoClone(Compiler* comp,
BasicBlock* block,
BoundsCheckInfoStack* bndChkStack,
Statement* lastStmt)
{
assert(block != nullptr);
assert(bndChkStack->Height() > 0);

// The bound checks are in the execution order (top of the stack is the last check)
BoundsCheckInfo firstCheck = bndChkStack->Bottom();
BoundsCheckInfo lastCheck = bndChkStack->Top();
BasicBlock* prevBb = block;

// First, split the block at the first bounds check using gtSplitTree (via fgSplitBlockBeforeTree):
Expand All @@ -187,7 +201,7 @@ static BasicBlock* optRangeCheckCloning_DoClone(Compiler* comp, BasicBlock* bloc
// Now split the block at the last bounds check using fgSplitBlockAfterStatement:
// TODO-RangeCheckCloning: call gtSplitTree for lastBndChkStmt as well, to cut off
// the stuff we don't have to clone.
BasicBlock* lastBb = comp->fgSplitBlockAfterStatement(fastpathBb, lastCheck.stmt);
BasicBlock* lastBb = comp->fgSplitBlockAfterStatement(fastpathBb, lastStmt);

DebugInfo debugInfo = fastpathBb->firstStmt()->GetDebugInfo();

Expand Down Expand Up @@ -351,14 +365,15 @@ static BasicBlock* optRangeCheckCloning_DoClone(Compiler* comp, BasicBlock* bloc
assert(BasicBlock::sameEHRegion(prevBb, fallbackBb));
assert(BasicBlock::sameEHRegion(prevBb, lastBb));

return fastpathBb;
return fastpathBb->Prev();
}

// A visitor to record all the bounds checks in a statement in the execution order
class BoundsChecksVisitor final : public GenTreeVisitor<BoundsChecksVisitor>
{
Statement* m_stmt;
ArrayStack<BoundCheckLocation>* m_boundsChks;
int m_stmtIdx;

public:
enum
Expand All @@ -368,10 +383,14 @@ class BoundsChecksVisitor final : public GenTreeVisitor<BoundsChecksVisitor>
UseExecutionOrder = true
};

BoundsChecksVisitor(Compiler* compiler, Statement* stmt, ArrayStack<BoundCheckLocation>* bndChkLocations)
BoundsChecksVisitor(Compiler* compiler,
Statement* stmt,
int stmtIdx,
ArrayStack<BoundCheckLocation>* bndChkLocations)
: GenTreeVisitor(compiler)
, m_stmt(stmt)
, m_boundsChks(bndChkLocations)
, m_stmtIdx(stmtIdx)
{
}

Expand All @@ -389,7 +408,7 @@ class BoundsChecksVisitor final : public GenTreeVisitor<BoundsChecksVisitor>
{
if ((*use)->OperIs(GT_BOUNDS_CHECK))
{
m_boundsChks->Push(BoundCheckLocation(m_stmt, use));
m_boundsChks->Push(BoundCheckLocation(m_stmt, use, m_stmtIdx));
}
return fgWalkResult::WALK_CONTINUE;
}
Expand All @@ -401,6 +420,7 @@ class BoundsChecksVisitor final : public GenTreeVisitor<BoundsChecksVisitor>
// the bounds checks.
//
// Arguments:
// comp - The compiler instance
// bndChks - The stack of bounds checks
//
// Return Value:
Expand Down Expand Up @@ -499,8 +519,10 @@ PhaseStatus Compiler::optRangeCheckCloning()
bndChkLocations.Reset();
bndChkMap.RemoveAll();

int stmtIdx = -1;
for (Statement* const stmt : block->Statements())
{
stmtIdx++;
if (block->HasTerminator() && (stmt == block->lastStmt()))
{
// TODO-RangeCheckCloning: Splitting these blocks at the last statements
Expand All @@ -510,7 +532,7 @@ PhaseStatus Compiler::optRangeCheckCloning()

// Now just record all the bounds checks in the block (in the execution order)
//
BoundsChecksVisitor visitor(this, stmt, &bndChkLocations);
BoundsChecksVisitor visitor(this, stmt, stmtIdx, &bndChkLocations);
visitor.WalkTree(stmt->GetRootNodePointer(), nullptr);
}

Expand All @@ -528,7 +550,7 @@ PhaseStatus Compiler::optRangeCheckCloning()
{
BoundCheckLocation loc = bndChkLocations.Bottom(i);
BoundsCheckInfo bci{};
if (bci.Initialize(this, loc.stmt, loc.bndChkUse))
if (bci.Initialize(this, loc.stmt, loc.stmtIdx, loc.bndChkUse))
{
IdxLenPair key(bci.idxVN, bci.lenVN);
BoundsCheckInfoStack** value = bndChkMap.LookupPointerOrAdd(key, nullptr);
Expand All @@ -552,34 +574,69 @@ PhaseStatus Compiler::optRangeCheckCloning()
}

// Now choose the largest group of bounds checks (the one with the most checks)
BoundsCheckInfoStack* largestGroup = nullptr;
// BoundsCheckInfoStack* largestGroup = nullptr;
ArrayStack<BoundsCheckInfoStack*> groups(getAllocator(CMK_RangeCheckCloning));

for (BoundsCheckInfoMap::Node* keyValuePair : BoundsCheckInfoMap::KeyValueIteration(&bndChkMap))
{
ArrayStack<BoundsCheckInfo>* value = keyValuePair->GetValue();
if ((largestGroup == nullptr) || (value->Height() > largestGroup->Height()))
if ((value->Height() >= MIN_CHECKS_PER_GROUP) && !DoesComplexityExceed(this, value))
{
if (DoesComplexityExceed(this, value))
{
continue;
}
largestGroup = value;
groups.Push(value);
}
}

if (largestGroup == nullptr)
if (groups.Height() == 0)
{
JITDUMP("No suitable group of bounds checks in the block - bail out.\n");
continue;
}

if (largestGroup->Height() < MIN_CHECKS_PER_GROUP)
// We have multiple groups of bounds checks in the block.
// let's pick a group that appears first in the block and the one whose last bounds check
// appears last in the block.
//
BoundsCheckInfoStack* firstGroup = groups.Top();
BoundsCheckInfoStack* lastGroup = groups.Top();
for (int i = 0; i < groups.Height(); i++)
{
JITDUMP("Not enough bounds checks in the largest group - bail out.\n");
continue;
BoundsCheckInfoStack* group = groups.Bottom(i);
int firstStmt = group->Bottom().stmtIdx;
int secondStmt = group->Top().stmtIdx;
if (firstStmt < firstGroup->Bottom().stmtIdx)
{
firstGroup = group;
}
if (secondStmt > lastGroup->Top().stmtIdx)
{
lastGroup = group;
}
}

JITDUMP("Cloning bounds checks in " FMT_BB "\n", block->bbNum);
block = optRangeCheckCloning_DoClone(this, block, largestGroup);
// We're going to clone for the first group.
// But let's see if we can extend the end of the group so future iterations
// can fit more groups in the same block.
//
Statement* lastStmt = firstGroup->Top().stmt;

int firstGroupStarts = firstGroup->Bottom().stmtIdx;
int firstGroupEnds = firstGroup->Top().stmtIdx;
int lastGroupStarts = lastGroup->Bottom().stmtIdx;
int lastGroupEnds = lastGroup->Top().stmtIdx;

// The only requirement is that both groups must overlap - we don't want to
// end up cloning unrelated statements between them (not a correctness issue,
// just a heuristic to avoid cloning too much).
//
if (firstGroupEnds < lastGroupEnds && firstGroupEnds >= lastGroupStarts)
{
lastStmt = lastGroup->Top().stmt;
}

JITDUMP("Cloning bounds checks in " FMT_BB " from " FMT_STMT " to " FMT_STMT "\n", block->bbNum,
firstGroup->Bottom().stmt->GetID(), lastStmt->GetID());

block = optRangeCheckCloning_DoClone(this, block, firstGroup, lastStmt);
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@jakobbotsch jakobbotsch Feb 20, 2025 •
edited
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Is block here guaranteed to be nonnull in the case where we cloned and it returned fastPathBb->Prev()?

Might be a bit clearer to have optRangeCheckCloning_DoClone return the next block to visit

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@EgorBo EgorBo Feb 20, 2025

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Addressed

modified = true;
}

Expand Down
9 changes: 7 additions & 2 deletions src/coreclr/jit/rangecheckcloning.h
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Original file line number Diff line number Diff line change
Expand Up @@ -22,15 +22,18 @@ struct BoundCheckLocation
{
Statement* stmt;
GenTree** bndChkUse;
int stmtIdx;

BoundCheckLocation(Statement* stmt, GenTree** bndChkUse)
BoundCheckLocation(Statement* stmt, GenTree** bndChkUse, int stmtIdx)
: stmt(stmt)
, bndChkUse(bndChkUse)
, stmtIdx(stmtIdx)
{
assert(stmt != nullptr);
assert((bndChkUse != nullptr));
assert((*bndChkUse) != nullptr);
assert((*bndChkUse)->OperIs(GT_BOUNDS_CHECK));
assert(stmtIdx >= 0);
}
};

Expand All @@ -41,17 +44,19 @@ struct BoundsCheckInfo
ValueNum lenVN;
ValueNum idxVN;
int offset;
int stmtIdx;

BoundsCheckInfo()
: stmt(nullptr)
, bndChkUse(nullptr)
, lenVN(ValueNumStore::NoVN)
, idxVN(ValueNumStore::NoVN)
, offset(0)
, stmtIdx(0)
{
}

bool Initialize(const Compiler* comp, Statement* statement, GenTree** bndChkUse);
bool Initialize(const Compiler* comp, Statement* statement, int statementIdx, GenTree** bndChkUse);

GenTreeBoundsChk* BndChk() const
{
Expand Down
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