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JIT: Tail-merge don't produce empty blocks #129092

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JIT: Tail-merge don't produce empty blocks #129092

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55 changes: 48 additions & 7 deletions src/coreclr/jit/fgopt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5212,6 +5212,23 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)

fgUnlinkStmt(predBlock, stmt);

bool canRemove =
predBlock->isEmpty() && !predBlock->HasFlag(BBF_DONT_REMOVE) && predBlock != fgFirstBB;
if (canRemove)
{
for (BasicBlock* const pred : predBlock->PredBlocksEditing())
{
fgReplaceJumpTarget(pred, predBlock, commSucc);
}

fgRemoveBlock(predBlock, true);

if (commSucc->hasProfileWeight())
{
commSucc->increaseBBProfileWeight(predBlock->bbWeight);
}
}

// Add one of the matching stmts to block, and
// update its flags.
//
Expand Down Expand Up @@ -5344,15 +5361,32 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)

// Fix up the flow.
//
if (commSucc != nullptr)
bool canRemove = predBlock->isEmpty() && !predBlock->HasFlag(BBF_DONT_REMOVE) && predBlock != fgFirstBB;
if (canRemove)
{
assert(predBlock->KindIs(BBJ_ALWAYS));
fgRedirectEdge(predBlock->TargetEdgeRef(), crossJumpTarget);
for (BasicBlock* const pred : predBlock->PredBlocksEditing())
{
fgReplaceJumpTarget(pred, predBlock, crossJumpTarget);
}
fgRemoveBlock(predBlock, true);

if (commSucc != nullptr && commSucc->hasProfileWeight())
{
commSucc->increaseBBProfileWeight(predBlock->bbWeight);
}
}
else
{
FlowEdge* const newEdge = fgAddRefPred(crossJumpTarget, predBlock);
predBlock->SetKindAndTargetEdge(BBJ_ALWAYS, newEdge);
if (commSucc != nullptr)
{
assert(predBlock->KindIs(BBJ_ALWAYS));
fgRedirectEdge(predBlock->TargetEdgeRef(), crossJumpTarget);
}
else
{
FlowEdge* const newEdge = fgAddRefPred(crossJumpTarget, predBlock);
predBlock->SetKindAndTargetEdge(BBJ_ALWAYS, newEdge);
}
}

// For tail merge we have a common successor of predBlock and
Expand Down Expand Up @@ -5402,6 +5436,13 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)
continue;
}

// If this block was already processed, skip it
//
if (predBlock->isEmpty())
{
continue;
}

Statement* lastStmt = predBlock->lastStmt();

// Block might be empty.
Expand Down Expand Up @@ -5498,9 +5539,9 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)
predInfo.Reset();
for (BasicBlock* const block : retOrThrowBlocks.BottomUpOrder())
{
// If this block was already merged, skip it
// If this block was already processed, skip it
//
if (!block->KindIs(BBJ_RETURN, BBJ_THROW))
if (!block->KindIs(BBJ_RETURN, BBJ_THROW) || block->isEmpty())
{
continue;
}
Expand Down
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