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| //===- 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/ADT/DenseMap.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 {
public:
using NormalizingFn = float (*)(float, unsigned, unsigned);
private:
MachineFunction &MF;
LiveIntervals &LIS;
VirtRegMap *VRM;
const MachineLoopInfo &Loops;
const MachineBlockFrequencyInfo &MBFI;
DenseMap<unsigned, float> Hint;
NormalizingFn normalize;
public:
VirtRegAuxInfo(MachineFunction &mf, LiveIntervals &lis,
VirtRegMap *vrm, const MachineLoopInfo &loops,
const MachineBlockFrequencyInfo &mbfi,
NormalizingFn norm = normalizeSpillWeight)
: MF(mf), LIS(lis), VRM(vrm), Loops(loops), MBFI(mbfi), normalize(norm) {}
/// (re)compute li's spill weight and allocation hint.
void calculateSpillWeightAndHint(LiveInterval &li);
/// 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 to be split.
/// \param start The expected begining of the split artifact. Instructions
/// before start will not affect the weight.
/// \param end The expected end of the split artifact. Instructions
/// after end will not affect the weight.
/// \return The expected spill weight of the split artifact. Returns
/// negative weight for unspillable li.
float futureWeight(LiveInterval &li, SlotIndex start, SlotIndex end);
/// 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 begining 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);
};
/// Compute spill weights and allocation hints for all virtual register
/// live intervals.
void calculateSpillWeightsAndHints(LiveIntervals &LIS, MachineFunction &MF,
VirtRegMap *VRM,
const MachineLoopInfo &MLI,
const MachineBlockFrequencyInfo &MBFI,
VirtRegAuxInfo::NormalizingFn norm =
normalizeSpillWeight);
} // end namespace llvm
#endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H
|