//===- lib/CodeGen/CalcSpillWeights.h ---------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_CALCSPILLWEIGHTS_H
#define LLVM_CODEGEN_CALCSPILLWEIGHTS_H
#include "llvm/CodeGen/SlotIndexes.h"
namespace llvm {
class LiveInterval;
class LiveIntervals;
class MachineBlockFrequencyInfo;
class MachineFunction;
class MachineLoopInfo;
class VirtRegMap;
/// Normalize the spill weight of a live interval
///
/// The spill weight of a live interval is computed as:
///
/// (sum(use freq) + sum(def freq)) / (K + size)
///
/// @param UseDefFreq Expected number of executed use and def instructions
/// per function call. Derived from block frequencies.
/// @param Size Size of live interval as returnexd by getSize()
/// @param NumInstr Number of instructions using this live interval
static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size,
unsigned NumInstr) {
// The constant 25 instructions is added to avoid depending too much on
// accidental SlotIndex gaps for small intervals. The effect is that small
// intervals have a spill weight that is mostly proportional to the number
// of uses, while large intervals get a spill weight that is closer to a use
// density.
return UseDefFreq / (Size + 25*SlotIndex::InstrDist);
}
/// Calculate auxiliary information for a virtual register such as its
/// spill weight and allocation hint.
class VirtRegAuxInfo {
MachineFunction &MF;
LiveIntervals &LIS;
const VirtRegMap &VRM;
const MachineLoopInfo &Loops;
const MachineBlockFrequencyInfo &MBFI;
/// Returns true if Reg of live interval LI is used in instruction with many
/// operands like STATEPOINT.
bool isLiveAtStatepointVarArg(LiveInterval &LI);
public:
VirtRegAuxInfo(MachineFunction &MF, LiveIntervals &LIS,
const VirtRegMap &VRM, const MachineLoopInfo &Loops,
const MachineBlockFrequencyInfo &MBFI)
: MF(MF), LIS(LIS), VRM(VRM), Loops(Loops), MBFI(MBFI) {}
virtual ~VirtRegAuxInfo() = default;
/// (re)compute li's spill weight and allocation hint.
void calculateSpillWeightAndHint(LiveInterval &LI);
/// Compute spill weights and allocation hints for all virtual register
/// live intervals.
void calculateSpillWeightsAndHints();
/// Return the preferred allocation register for reg, given a COPY
/// instruction.
static Register copyHint(const MachineInstr *MI, unsigned Reg,
const TargetRegisterInfo &TRI,
const MachineRegisterInfo &MRI);
/// Determine if all values in LI are rematerializable.
static bool isRematerializable(const LiveInterval &LI,
const LiveIntervals &LIS,
const VirtRegMap &VRM,
const TargetInstrInfo &TII);
protected:
/// Helper function for weight calculations.
/// (Re)compute LI's spill weight and allocation hint, or, for non null
/// start and end - compute future expected spill weight of a split
/// artifact of LI that will span between start and end slot indexes.
/// \param LI The live interval for which to compute the weight.
/// \param Start The expected beginning of the split artifact. Instructions
/// before start will not affect the weight. Relevant for
/// weight calculation of future split artifact.
/// \param End The expected end of the split artifact. Instructions
/// after end will not affect the weight. Relevant for
/// weight calculation of future split artifact.
/// \return The spill weight. Returns negative weight for unspillable LI.
float weightCalcHelper(LiveInterval &LI, SlotIndex *Start = nullptr,
SlotIndex *End = nullptr);
/// Weight normalization function.
virtual float normalize(float UseDefFreq, unsigned Size,
unsigned NumInstr) {
return normalizeSpillWeight(UseDefFreq, Size, NumInstr);
}
};
} // end namespace llvm
#endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H