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108 lines
4.7 KiB
C++
108 lines
4.7 KiB
C++
//===- lib/CodeGen/CalcSpillWeights.h ---------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_CALCSPILLWEIGHTS_H
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#define LLVM_CODEGEN_CALCSPILLWEIGHTS_H
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/CodeGen/SlotIndexes.h"
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namespace llvm {
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class LiveInterval;
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class LiveIntervals;
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class MachineBlockFrequencyInfo;
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class MachineFunction;
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class MachineLoopInfo;
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class VirtRegMap;
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/// Normalize the spill weight of a live interval
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///
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/// The spill weight of a live interval is computed as:
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///
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/// (sum(use freq) + sum(def freq)) / (K + size)
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///
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/// @param UseDefFreq Expected number of executed use and def instructions
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/// per function call. Derived from block frequencies.
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/// @param Size Size of live interval as returnexd by getSize()
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/// @param NumInstr Number of instructions using this live interval
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static inline float normalizeSpillWeight(float UseDefFreq, unsigned Size,
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unsigned NumInstr) {
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// The constant 25 instructions is added to avoid depending too much on
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// accidental SlotIndex gaps for small intervals. The effect is that small
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// intervals have a spill weight that is mostly proportional to the number
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// of uses, while large intervals get a spill weight that is closer to a use
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// density.
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return UseDefFreq / (Size + 25*SlotIndex::InstrDist);
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}
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/// Calculate auxiliary information for a virtual register such as its
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/// spill weight and allocation hint.
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class VirtRegAuxInfo {
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public:
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using NormalizingFn = float (*)(float, unsigned, unsigned);
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private:
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MachineFunction &MF;
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LiveIntervals &LIS;
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VirtRegMap *VRM;
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const MachineLoopInfo &Loops;
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const MachineBlockFrequencyInfo &MBFI;
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DenseMap<unsigned, float> Hint;
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NormalizingFn normalize;
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public:
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VirtRegAuxInfo(MachineFunction &mf, LiveIntervals &lis,
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VirtRegMap *vrm, const MachineLoopInfo &loops,
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const MachineBlockFrequencyInfo &mbfi,
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NormalizingFn norm = normalizeSpillWeight)
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: MF(mf), LIS(lis), VRM(vrm), Loops(loops), MBFI(mbfi), normalize(norm) {}
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/// (re)compute li's spill weight and allocation hint.
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void calculateSpillWeightAndHint(LiveInterval &li);
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/// Compute future expected spill weight of a split artifact of li
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/// that will span between start and end slot indexes.
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/// \param li The live interval to be split.
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/// \param start The expected begining of the split artifact. Instructions
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/// before start will not affect the weight.
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/// \param end The expected end of the split artifact. Instructions
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/// after end will not affect the weight.
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/// \return The expected spill weight of the split artifact. Returns
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/// negative weight for unspillable li.
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float futureWeight(LiveInterval &li, SlotIndex start, SlotIndex end);
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/// Helper function for weight calculations.
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/// (Re)compute li's spill weight and allocation hint, or, for non null
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/// start and end - compute future expected spill weight of a split
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/// artifact of li that will span between start and end slot indexes.
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/// \param li The live interval for which to compute the weight.
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/// \param start The expected begining of the split artifact. Instructions
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/// before start will not affect the weight. Relevant for
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/// weight calculation of future split artifact.
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/// \param end The expected end of the split artifact. Instructions
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/// after end will not affect the weight. Relevant for
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/// weight calculation of future split artifact.
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/// \return The spill weight. Returns negative weight for unspillable li.
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float weightCalcHelper(LiveInterval &li, SlotIndex *start = nullptr,
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SlotIndex *end = nullptr);
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};
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/// Compute spill weights and allocation hints for all virtual register
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/// live intervals.
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void calculateSpillWeightsAndHints(LiveIntervals &LIS, MachineFunction &MF,
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VirtRegMap *VRM,
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const MachineLoopInfo &MLI,
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const MachineBlockFrequencyInfo &MBFI,
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VirtRegAuxInfo::NormalizingFn norm =
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normalizeSpillWeight);
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} // end namespace llvm
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#endif // LLVM_CODEGEN_CALCSPILLWEIGHTS_H
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