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[BranchFolding] Add a hook to override tail merge size #99025

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Merged
merged 1 commit into from
Jul 22, 2024
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[BranchFolding] Add a hook to override tail merge size #99025

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6 changes: 6 additions & 0 deletions llvm/include/llvm/CodeGen/TargetInstrInfo.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2226,6 +2226,12 @@ class TargetInstrInfo : public MCInstrInfo {
return OptLevel >= CodeGenOptLevel::Aggressive ? 4 : 2;
}

/// Returns the target-specific default value for tail merging.
/// This value will be used if the tail-merge-size argument is not provided.
virtual unsigned getTailMergeSize(const MachineFunction &MF) const {
return 3;
}

/// Returns the callee operand from the given \p MI.
virtual const MachineOperand &getCalleeOperand(const MachineInstr &MI) const {
return MI.getOperand(0);
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9 changes: 6 additions & 3 deletions llvm/lib/CodeGen/BranchFolding.cpp
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Expand Up @@ -80,7 +80,6 @@ TailMergeThreshold("tail-merge-threshold",
cl::init(150), cl::Hidden);

// Heuristic for tail merging (and, inversely, tail duplication).
// TODO: This should be replaced with a target query.
static cl::opt<unsigned>
TailMergeSize("tail-merge-size",
cl::desc("Min number of instructions to consider tail merging"),
Expand Down Expand Up @@ -145,8 +144,6 @@ BranchFolder::BranchFolder(bool DefaultEnableTailMerge, bool CommonHoist,
ProfileSummaryInfo *PSI, unsigned MinTailLength)
: EnableHoistCommonCode(CommonHoist), MinCommonTailLength(MinTailLength),
MBBFreqInfo(FreqInfo), MBPI(ProbInfo), PSI(PSI) {
if (MinCommonTailLength == 0)
MinCommonTailLength = TailMergeSize;
switch (FlagEnableTailMerge) {
case cl::BOU_UNSET:
EnableTailMerge = DefaultEnableTailMerge;
Expand Down Expand Up @@ -195,6 +192,12 @@ bool BranchFolder::OptimizeFunction(MachineFunction &MF,
MLI = mli;
this->MRI = &MRI;

if (MinCommonTailLength == 0) {
MinCommonTailLength = TailMergeSize.getNumOccurrences() > 0
? TailMergeSize
: TII->getTailMergeSize(MF);
}

UpdateLiveIns = MRI.tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF);
if (!UpdateLiveIns)
MRI.invalidateLiveness();
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