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Handle overlapped groups of bounds checks #112660

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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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105 changes: 77 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 @@ -98,10 +99,9 @@ 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)
{
Expand Down Expand Up @@ -155,18 +155,21 @@ 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.
// The next block to visit after the cloning.
//
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 +190,7 @@ 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 @@ -359,6 +362,7 @@ class BoundsChecksVisitor final : public GenTreeVisitor<BoundsChecksVisitor>
{
Statement* m_stmt;
ArrayStack<BoundCheckLocation>* m_boundsChks;
int m_stmtIdx;

public:
enum
Expand All @@ -368,10 +372,14 @@ 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 +397,7 @@ 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 +409,7 @@ 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 +508,10 @@ 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 +521,7 @@ 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 +539,7 @@ 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 +563,72 @@ PhaseStatus Compiler::optRangeCheckCloning()
}

// Now choose the largest group of bounds checks (the one with the most checks)
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;
}
}

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

BasicBlock* nextBbToVisit = optRangeCheckCloning_DoClone(this, block, firstGroup, lastStmt);
assert(nextBbToVisit != nullptr);
// optRangeCheckCloning_DoClone wants us to visit nextBbToVisit next
block = nextBbToVisit->Prev();
assert(block != nullptr);
Comment on lines +627 to +631
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Another way you could do this without requiring the asserts would be:

BasicBlock* next;
for (BasicBlock* block = fgFirstBB; block != nullptr; block = next)
{
  next = block->Next();
  ...
  next = optRangeCheckCloning_DoClone(...);
}

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Ah, makes sense, I was thinking about goto 😄 I'll change in a follow up to avoid spinning CI

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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