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JIT: Use successor edges instead of block targets for BBJ_EHFINALLYRET (
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#98563)

Part of #93020. This is a first step in a broader effort to replace BasicBlock's jump targets (bbTarget, bbFalseTarget, etc.) with successor flow edges. This PR also adds overloaded implementations for commonly used edge maintenance methods (fgReplacePred, fgRemoveRefPred, etc.) that can take advantage of the cheap access to successor edges (i.e. without calling fgGetPredForBlock -- hopefully we'll be able to get rid of that at some point).
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@amanasifkhalid
amanasifkhalid committed Feb 19, 2024
1 parent b313138 commit 5e1caf1
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Showing 9 changed files with 250 additions and 92 deletions.
12 changes: 6 additions & 6 deletions src/coreclr/jit/block.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -658,12 +658,12 @@ void BasicBlock::dspKind() const
}
else
{
const unsigned jumpCnt = bbEhfTargets->bbeCount;
BasicBlock** const jumpTab = bbEhfTargets->bbeSuccs;
const unsigned jumpCnt = bbEhfTargets->bbeCount;
FlowEdge** const jumpTab = bbEhfTargets->bbeSuccs;

for (unsigned i = 0; i < jumpCnt; i++)
{
printf("%c%s", (i == 0) ? ' ' : ',', dspBlockNum(jumpTab[i]));
printf("%c%s", (i == 0) ? ' ' : ',', dspBlockNum(jumpTab[i]->getDestinationBlock()));
}
}

Expand Down Expand Up @@ -1214,7 +1214,7 @@ BasicBlock* BasicBlock::GetSucc(unsigned i) const
}

case BBJ_EHFINALLYRET:
return bbEhfTargets->bbeSuccs[i];
return bbEhfTargets->bbeSuccs[i]->getDestinationBlock();

case BBJ_SWITCH:
return bbSwtTargets->bbsDstTab[i];
Expand Down Expand Up @@ -1315,7 +1315,7 @@ BasicBlock* BasicBlock::GetSucc(unsigned i, Compiler* comp)
case BBJ_EHFINALLYRET:
assert(bbEhfTargets != nullptr);
assert(i < bbEhfTargets->bbeCount);
return bbEhfTargets->bbeSuccs[i];
return bbEhfTargets->bbeSuccs[i]->getDestinationBlock();

case BBJ_CALLFINALLY:
case BBJ_CALLFINALLYRET:
Expand Down Expand Up @@ -1792,7 +1792,7 @@ BBehfDesc::BBehfDesc(Compiler* comp, const BBehfDesc* other) : bbeCount(other->b
{
// Allocate and fill in a new dst tab
//
bbeSuccs = new (comp, CMK_BasicBlock) BasicBlock*[bbeCount];
bbeSuccs = new (comp, CMK_FlowEdge) FlowEdge*[bbeCount];
for (unsigned i = 0; i < bbeCount; i++)
{
bbeSuccs[i] = other->bbeSuccs[i];
Expand Down
78 changes: 60 additions & 18 deletions src/coreclr/jit/block.h
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Original file line number Diff line number Diff line change
Expand Up @@ -314,21 +314,27 @@ class PredBlockList
//
class BBArrayIterator
{
BasicBlock* const* m_bbEntry;
// Quirk: Some BasicBlock kinds refer to their successors with BasicBlock pointers,
// while others use FlowEdge pointers. Eventually, every type will use FlowEdge pointers.
// For now, support iterating with both types.
union {
BasicBlock* const* m_bbEntry;
FlowEdge* const* m_edgeEntry;
};

bool iterateEdges;

public:
BBArrayIterator(BasicBlock* const* bbEntry) : m_bbEntry(bbEntry)
BBArrayIterator(BasicBlock* const* bbEntry) : m_bbEntry(bbEntry), iterateEdges(false)
{
}

BasicBlock* operator*() const
BBArrayIterator(FlowEdge* const* edgeEntry) : m_edgeEntry(edgeEntry), iterateEdges(true)
{
assert(m_bbEntry != nullptr);
BasicBlock* bTarget = *m_bbEntry;
assert(bTarget != nullptr);
return bTarget;
}

BasicBlock* operator*() const;

BBArrayIterator& operator++()
{
assert(m_bbEntry != nullptr);
Expand Down Expand Up @@ -1570,9 +1576,22 @@ struct BasicBlock : private LIR::Range
// need to call a function or execute another `switch` to get them. Also, pre-compute the begin and end
// points of the iteration, for use by BBArrayIterator. `m_begin` and `m_end` will either point at
// `m_succs` or at the switch table successor array.
BasicBlock* m_succs[2];
BasicBlock* const* m_begin;
BasicBlock* const* m_end;
BasicBlock* m_succs[2];

// Quirk: Some BasicBlock kinds refer to their successors with BasicBlock pointers,
// while others use FlowEdge pointers. Eventually, every type will use FlowEdge pointers.
// For now, support iterating with both types.
union {
BasicBlock* const* m_begin;
FlowEdge* const* m_beginEdge;
};

union {
BasicBlock* const* m_end;
FlowEdge* const* m_endEdge;
};

bool iterateEdges;

public:
BBSuccList(const BasicBlock* block);
Expand Down Expand Up @@ -1879,8 +1898,8 @@ inline BBArrayIterator BBSwitchTargetList::end() const
//
struct BBehfDesc
{
BasicBlock** bbeSuccs; // array of `BasicBlock*` pointing to BBJ_EHFINALLYRET block successors
unsigned bbeCount; // size of `bbeSuccs` array
FlowEdge** bbeSuccs; // array of `FlowEdge*` pointing to BBJ_EHFINALLYRET block successors
unsigned bbeCount; // size of `bbeSuccs` array

BBehfDesc() : bbeSuccs(nullptr), bbeCount(0)
{
Expand Down Expand Up @@ -1913,6 +1932,8 @@ inline BBArrayIterator BBEhfSuccList::end() const
inline BasicBlock::BBSuccList::BBSuccList(const BasicBlock* block)
{
assert(block != nullptr);
iterateEdges = false;

switch (block->bbKind)
{
case BBJ_THROW:
Expand Down Expand Up @@ -1957,14 +1978,16 @@ inline BasicBlock::BBSuccList::BBSuccList(const BasicBlock* block)
// been computed.
if (block->GetEhfTargets() == nullptr)
{
m_begin = nullptr;
m_end = nullptr;
m_beginEdge = nullptr;
m_endEdge = nullptr;
}
else
{
m_begin = block->GetEhfTargets()->bbeSuccs;
m_end = block->GetEhfTargets()->bbeSuccs + block->GetEhfTargets()->bbeCount;
m_beginEdge = block->GetEhfTargets()->bbeSuccs;
m_endEdge = block->GetEhfTargets()->bbeSuccs + block->GetEhfTargets()->bbeCount;
}

iterateEdges = true;
break;

case BBJ_SWITCH:
Expand All @@ -1984,12 +2007,12 @@ inline BasicBlock::BBSuccList::BBSuccList(const BasicBlock* block)

inline BBArrayIterator BasicBlock::BBSuccList::begin() const
{
return BBArrayIterator(m_begin);
return (iterateEdges ? BBArrayIterator(m_beginEdge) : BBArrayIterator(m_begin));
}

inline BBArrayIterator BasicBlock::BBSuccList::end() const
{
return BBArrayIterator(m_end);
return (iterateEdges ? BBArrayIterator(m_endEdge) : BBArrayIterator(m_end));
}

// We have a simpler struct, BasicBlockList, which is simply a singly-linked
Expand Down Expand Up @@ -2192,6 +2215,25 @@ struct FlowEdge
}
};

// BasicBlock iterator implementations (that are required to be defined after the declaration of FlowEdge)

inline BasicBlock* BBArrayIterator::operator*() const
{
if (iterateEdges)
{
assert(m_edgeEntry != nullptr);
FlowEdge* edgeTarget = *m_edgeEntry;
assert(edgeTarget != nullptr);
assert(edgeTarget->getDestinationBlock() != nullptr);
return edgeTarget->getDestinationBlock();
}

assert(m_bbEntry != nullptr);
BasicBlock* bTarget = *m_bbEntry;
assert(bTarget != nullptr);
return bTarget;
}

// Pred list iterator implementations (that are required to be defined after the declaration of BasicBlock and FlowEdge)

inline PredEdgeList::iterator::iterator(FlowEdge* pred) : m_pred(pred)
Expand Down
8 changes: 7 additions & 1 deletion src/coreclr/jit/compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5883,6 +5883,8 @@ class Compiler

FlowEdge* fgRemoveRefPred(BasicBlock* block, BasicBlock* blockPred);

void fgRemoveRefPred(FlowEdge* edge);

FlowEdge* fgRemoveAllRefPreds(BasicBlock* block, BasicBlock* blockPred);

void fgRemoveBlockAsPred(BasicBlock* block);
Expand All @@ -5893,12 +5895,16 @@ class Compiler

void fgReplaceEhfSuccessor(BasicBlock* block, BasicBlock* oldSucc, BasicBlock* newSucc);

void fgRemoveEhfSuccessor(BasicBlock* block, BasicBlock* succ);
void fgRemoveEhfSuccessor(BasicBlock* block, const unsigned succIndex);

void fgRemoveEhfSuccessor(FlowEdge* succEdge);

void fgReplaceJumpTarget(BasicBlock* block, BasicBlock* oldTarget, BasicBlock* newTarget);

void fgReplacePred(BasicBlock* block, BasicBlock* oldPred, BasicBlock* newPred);

void fgReplacePred(FlowEdge* edge, BasicBlock* const newPred);

// initializingPreds is only 'true' when we are computing preds in fgLinkBasicBlocks()
template <bool initializingPreds = false>
FlowEdge* fgAddRefPred(BasicBlock* block, BasicBlock* blockPred, FlowEdge* oldEdge = nullptr);
Expand Down
4 changes: 2 additions & 2 deletions src/coreclr/jit/compiler.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -657,7 +657,7 @@ BasicBlockVisit BasicBlock::VisitAllSuccs(Compiler* comp, TFunc func)
{
for (unsigned i = 0; i < bbEhfTargets->bbeCount; i++)
{
RETURN_ON_ABORT(func(bbEhfTargets->bbeSuccs[i]));
RETURN_ON_ABORT(func(bbEhfTargets->bbeSuccs[i]->getDestinationBlock()));
}
}

Expand Down Expand Up @@ -732,7 +732,7 @@ BasicBlockVisit BasicBlock::VisitRegularSuccs(Compiler* comp, TFunc func)
{
for (unsigned i = 0; i < bbEhfTargets->bbeCount; i++)
{
RETURN_ON_ABORT(func(bbEhfTargets->bbeSuccs[i]));
RETURN_ON_ABORT(func(bbEhfTargets->bbeSuccs[i]->getDestinationBlock()));
}
}

Expand Down
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