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JIT: Remove switch recognition fallthrough quirk #109796

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Merged
amanasifkhalid merged 1 commit into from
Nov 19, 2024
Merged

JIT: Remove switch recognition fallthrough quirk #109796

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35 changes: 1 addition & 34 deletions src/coreclr/jit/switchrecognition.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -370,40 +370,10 @@ bool Compiler::optSwitchConvert(
assert((jumpCount > 0) && (jumpCount <= SWITCH_MAX_DISTANCE + 1));
FlowEdge** jmpTab = new (this, CMK_FlowEdge) FlowEdge*[jumpCount + 1 /*default case*/];

// Quirk: lastBlock's false target may have diverged from bbNext. If the false target is behind firstBlock,
// we may create a cycle in the BasicBlock list by setting firstBlock->bbNext to it.
// Add a new BBJ_ALWAYS to the false target to avoid this.
// (We only need this if the false target is behind firstBlock,
// but it's cheaper to just check if the false target has diverged)
// TODO-NoFallThrough: Revisit this quirk?
bool skipPredRemoval = false;
if (!lastBlock->FalseTargetIs(lastBlock->Next()))
{
if (isReversed)
{
assert(lastBlock->FalseTargetIs(blockIfTrue));
fgRemoveRefPred(trueEdge);
BasicBlock* targetBlock = blockIfTrue;
blockIfTrue = fgNewBBafter(BBJ_ALWAYS, firstBlock, true);
FlowEdge* const newEdge = fgAddRefPred(targetBlock, blockIfTrue);
skipPredRemoval = true;
blockIfTrue->SetTargetEdge(newEdge);
}
else
{
assert(lastBlock->FalseTargetIs(blockIfFalse));
BasicBlock* targetBlock = blockIfFalse;
blockIfFalse = fgNewBBafter(BBJ_ALWAYS, firstBlock, true);
FlowEdge* const newEdge = fgAddRefPred(targetBlock, blockIfFalse);
blockIfFalse->SetTargetEdge(newEdge);
}
}

fgHasSwitch = true;
firstBlock->GetSwitchTargets()->bbsCount = jumpCount + 1;
firstBlock->GetSwitchTargets()->bbsHasDefault = true;
firstBlock->GetSwitchTargets()->bbsDstTab = jmpTab;
firstBlock->SetNext(isReversed ? blockIfTrue : blockIfFalse);

// Splitting doesn't work well with jump-tables currently
opts.compProcedureSplitting = false;
Expand All @@ -418,10 +388,7 @@ bool Compiler::optSwitchConvert(
}

// Unlink blockIfTrue from firstBlock, we're going to link it again in the loop below.
if (!skipPredRemoval)
{
fgRemoveRefPred(trueEdge);
}
fgRemoveRefPred(trueEdge);

FlowEdge* switchTrueEdge = nullptr;

Expand Down