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Merged
AndyAyersMS merged 1 commit into from
Nov 11, 2024
Merged

JIT: enable tail merge for try exits #109661

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45 changes: 31 additions & 14 deletions src/coreclr/jit/fgopt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6200,9 +6200,20 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)
{
matchedPredInfo.Reset();
matchedPredInfo.Emplace(predInfo.TopRef(i));
Statement* const baseStmt = predInfo.TopRef(i).m_stmt;
Statement* const baseStmt = predInfo.TopRef(i).m_stmt;
BasicBlock* const baseBlock = predInfo.TopRef(i).m_block;

for (int j = i + 1; j < predInfo.Height(); j++)
{
BasicBlock* const otherBlock = predInfo.TopRef(j).m_block;

// Consider: bypass this for statements that can't cause exceptions.
//
if (!BasicBlock::sameEHRegion(baseBlock, otherBlock))
{
continue;
}

Statement* const otherStmt = predInfo.TopRef(j).m_stmt;

// Consider: compute and cache hashes to make this faster
Expand All @@ -6220,12 +6231,18 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)
continue;
}

// We have some number of preds that have identical last statements.
// If all preds of block have a matching last stmt, move that statement to the start of block.
// We can move the identical last statements to commSucc, if it exists,
// and all preds have matching last statements, and we're not changing EH behavior.
//
if ((commSucc != nullptr) && (matchedPredInfo.Height() == (int)commSucc->countOfInEdges()))
bool const hasCommSucc = (commSucc != nullptr);
bool const predsInSameEHRegionAsSucc = hasCommSucc && BasicBlock::sameEHRegion(baseBlock, commSucc);
bool const canMergeAllPreds = hasCommSucc && (matchedPredInfo.Height() == (int)commSucc->countOfInEdges());
bool const canMergeIntoSucc = predsInSameEHRegionAsSucc && canMergeAllPreds;

if (canMergeIntoSucc)
{
JITDUMP("All preds of " FMT_BB " end with the same tree, moving\n", commSucc->bbNum);
JITDUMP("All %d preds of " FMT_BB " end with the same tree, moving\n", matchedPredInfo.Height(),
commSucc->bbNum);
JITDUMPEXEC(gtDispStmt(matchedPredInfo.TopRef(0).m_stmt));

for (int j = 0; j < matchedPredInfo.Height(); j++)
Expand Down Expand Up @@ -6253,15 +6270,20 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)
return true;
}

// A subset of preds have matching last stmt, we will cross-jump.
// Pick one block as the victim -- preferably a block with just one
// All or a subset of preds have matching last stmt, we will cross-jump.
// Pick one pred block as the victim -- preferably a block with just one
// statement or one that falls through to block (or both).
//
if (commSucc != nullptr)
if (predsInSameEHRegionAsSucc)
{
JITDUMP("A set of %d preds of " FMT_BB " end with the same tree\n", matchedPredInfo.Height(),
JITDUMP("A subset of %d preds of " FMT_BB " end with the same tree\n", matchedPredInfo.Height(),
commSucc->bbNum);
}
else if (commSucc != nullptr)
{
JITDUMP("%s %d preds of " FMT_BB " end with the same tree but are in a different EH region\n",
canMergeAllPreds ? "All" : "A subset of", matchedPredInfo.Height(), commSucc->bbNum);
}
else
{
JITDUMP("A set of %d return blocks end with the same tree\n", matchedPredInfo.Height());
Expand Down Expand Up @@ -6416,11 +6438,6 @@ PhaseStatus Compiler::fgHeadTailMerge(bool early)
continue;
}

if (!BasicBlock::sameEHRegion(block, predBlock))
{
continue;
}

Statement* lastStmt = predBlock->lastStmt();

// Block might be empty.
Expand Down