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[CalcSpillWeights] Simplify copy hint register collection. NFC. #114236

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merged 1 commit into from
Nov 7, 2024
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[CalcSpillWeights] Simplify copy hint register collection. NFC. #114236

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37 changes: 16 additions & 21 deletions llvm/lib/CodeGen/CalcSpillWeights.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -209,8 +209,8 @@ float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start,

// CopyHint is a sortable hint derived from a COPY instruction.
struct CopyHint {
const Register Reg;
const float Weight;
Register Reg;
float Weight;
CopyHint(Register R, float W) : Reg(R), Weight(W) {}
bool operator<(const CopyHint &Rhs) const {
// Always prefer any physreg hint.
Expand All @@ -223,8 +223,7 @@ float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start,
};

bool IsExiting = false;
std::set<CopyHint> CopyHints;
SmallDenseMap<unsigned, float, 8> Hint;
SmallDenseMap<Register, float, 8> Hint;
for (MachineRegisterInfo::reg_instr_nodbg_iterator
I = MRI.reg_instr_nodbg_begin(LI.reg()),
E = MRI.reg_instr_nodbg_end();
Expand Down Expand Up @@ -260,8 +259,7 @@ float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start,
return -1.0f;
}

// Force Weight onto the stack so that x86 doesn't add hidden precision,
// similar to HWeight below.
// Force Weight onto the stack so that x86 doesn't add hidden precision.
stack_float_t Weight = 1.0f;
if (IsSpillable) {
// Get loop info for mi.
Expand All @@ -287,29 +285,26 @@ float VirtRegAuxInfo::weightCalcHelper(LiveInterval &LI, SlotIndex *Start,
if (!TII.isCopyInstr(*MI))
continue;
Register HintReg = copyHint(MI, LI.reg(), TRI, MRI);
if (!HintReg)
continue;
// Force HWeight onto the stack so that x86 doesn't add hidden precision,
// making the comparison incorrectly pass (i.e., 1 > 1 == true??).
stack_float_t HWeight = Hint[HintReg] += Weight;
if (HintReg.isVirtual() || MRI.isAllocatable(HintReg))
CopyHints.insert(CopyHint(HintReg, HWeight));
if (HintReg && (HintReg.isVirtual() || MRI.isAllocatable(HintReg)))
Hint[HintReg] += Weight;
}

// Pass all the sorted copy hints to mri.
if (ShouldUpdateLI && CopyHints.size()) {
if (ShouldUpdateLI && Hint.size()) {
// Remove a generic hint if previously added by target.
if (TargetHint.first == 0 && TargetHint.second)
MRI.clearSimpleHint(LI.reg());

SmallSet<Register, 4> HintedRegs;
for (const auto &Hint : CopyHints) {
if (!HintedRegs.insert(Hint.Reg).second ||
(TargetHint.first != 0 && Hint.Reg == TargetHint.second))
// Don't add the same reg twice or the target-type hint again.
continue;
MRI.addRegAllocationHint(LI.reg(), Hint.Reg);
// Don't add the target-type hint again.
Register SkipReg = TargetHint.first != 0 ? TargetHint.second : Register();
SmallVector<CopyHint, 8> RegHints;
for (const auto &[Reg, Weight] : Hint) {
if (Reg != SkipReg)
RegHints.emplace_back(Reg, Weight);
}
sort(RegHints);
for (const auto &[Reg, Weight] : RegHints)
MRI.addRegAllocationHint(LI.reg(), Reg);

// Weakly boost the spill weight of hinted registers.
TotalWeight *= 1.01F;
Expand Down
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