| //===- CalcSpillWeights.cpp -----------------------------------------------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/CodeGen/CalcSpillWeights.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/CodeGen/LiveInterval.h" |
| #include "llvm/CodeGen/LiveIntervals.h" |
| #include "llvm/CodeGen/MachineFunction.h" |
| #include "llvm/CodeGen/MachineInstr.h" |
| #include "llvm/CodeGen/MachineLoopInfo.h" |
| #include "llvm/CodeGen/MachineOperand.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/CodeGen/TargetInstrInfo.h" |
| #include "llvm/CodeGen/TargetRegisterInfo.h" |
| #include "llvm/CodeGen/TargetSubtargetInfo.h" |
| #include "llvm/CodeGen/VirtRegMap.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <cassert> |
| #include <tuple> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "calcspillweights" |
| |
| void llvm::calculateSpillWeightsAndHints(LiveIntervals &LIS, |
| MachineFunction &MF, |
| VirtRegMap *VRM, |
| const MachineLoopInfo &MLI, |
| const MachineBlockFrequencyInfo &MBFI, |
| VirtRegAuxInfo::NormalizingFn norm) { |
| LLVM_DEBUG(dbgs() << "********** Compute Spill Weights **********\n" |
| << "********** Function: " << MF.getName() << '\n'); |
| |
| MachineRegisterInfo &MRI = MF.getRegInfo(); |
| VirtRegAuxInfo VRAI(MF, LIS, VRM, MLI, MBFI, norm); |
| for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) { |
| unsigned Reg = TargetRegisterInfo::index2VirtReg(i); |
| if (MRI.reg_nodbg_empty(Reg)) |
| continue; |
| VRAI.calculateSpillWeightAndHint(LIS.getInterval(Reg)); |
| } |
| } |
| |
| // Return the preferred allocation register for reg, given a COPY instruction. |
| static unsigned copyHint(const MachineInstr *mi, unsigned reg, |
| const TargetRegisterInfo &tri, |
| const MachineRegisterInfo &mri) { |
| unsigned sub, hreg, hsub; |
| if (mi->getOperand(0).getReg() == reg) { |
| sub = mi->getOperand(0).getSubReg(); |
| hreg = mi->getOperand(1).getReg(); |
| hsub = mi->getOperand(1).getSubReg(); |
| } else { |
| sub = mi->getOperand(1).getSubReg(); |
| hreg = mi->getOperand(0).getReg(); |
| hsub = mi->getOperand(0).getSubReg(); |
| } |
| |
| if (!hreg) |
| return 0; |
| |
| if (TargetRegisterInfo::isVirtualRegister(hreg)) |
| return sub == hsub ? hreg : 0; |
| |
| const TargetRegisterClass *rc = mri.getRegClass(reg); |
| unsigned CopiedPReg = (hsub ? tri.getSubReg(hreg, hsub) : hreg); |
| if (rc->contains(CopiedPReg)) |
| return CopiedPReg; |
| |
| // Check if reg:sub matches so that a super register could be hinted. |
| if (sub) |
| return tri.getMatchingSuperReg(CopiedPReg, sub, rc); |
| |
| return 0; |
| } |
| |
| // Check if all values in LI are rematerializable |
| static bool isRematerializable(const LiveInterval &LI, |
| const LiveIntervals &LIS, |
| VirtRegMap *VRM, |
| const TargetInstrInfo &TII) { |
| unsigned Reg = LI.reg; |
| unsigned Original = VRM ? VRM->getOriginal(Reg) : 0; |
| for (LiveInterval::const_vni_iterator I = LI.vni_begin(), E = LI.vni_end(); |
| I != E; ++I) { |
| const VNInfo *VNI = *I; |
| if (VNI->isUnused()) |
| continue; |
| if (VNI->isPHIDef()) |
| return false; |
| |
| MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def); |
| assert(MI && "Dead valno in interval"); |
| |
| // Trace copies introduced by live range splitting. The inline |
| // spiller can rematerialize through these copies, so the spill |
| // weight must reflect this. |
| if (VRM) { |
| while (MI->isFullCopy()) { |
| // The copy destination must match the interval register. |
| if (MI->getOperand(0).getReg() != Reg) |
| return false; |
| |
| // Get the source register. |
| Reg = MI->getOperand(1).getReg(); |
| |
| // If the original (pre-splitting) registers match this |
| // copy came from a split. |
| if (!TargetRegisterInfo::isVirtualRegister(Reg) || |
| VRM->getOriginal(Reg) != Original) |
| return false; |
| |
| // Follow the copy live-in value. |
| const LiveInterval &SrcLI = LIS.getInterval(Reg); |
| LiveQueryResult SrcQ = SrcLI.Query(VNI->def); |
| VNI = SrcQ.valueIn(); |
| assert(VNI && "Copy from non-existing value"); |
| if (VNI->isPHIDef()) |
| return false; |
| MI = LIS.getInstructionFromIndex(VNI->def); |
| assert(MI && "Dead valno in interval"); |
| } |
| } |
| |
| if (!TII.isTriviallyReMaterializable(*MI, LIS.getAliasAnalysis())) |
| return false; |
| } |
| return true; |
| } |
| |
| void VirtRegAuxInfo::calculateSpillWeightAndHint(LiveInterval &li) { |
| float weight = weightCalcHelper(li); |
| // Check if unspillable. |
| if (weight < 0) |
| return; |
| li.weight = weight; |
| } |
| |
| float VirtRegAuxInfo::futureWeight(LiveInterval &li, SlotIndex start, |
| SlotIndex end) { |
| return weightCalcHelper(li, &start, &end); |
| } |
| |
| float VirtRegAuxInfo::weightCalcHelper(LiveInterval &li, SlotIndex *start, |
| SlotIndex *end) { |
| MachineRegisterInfo &mri = MF.getRegInfo(); |
| const TargetRegisterInfo &tri = *MF.getSubtarget().getRegisterInfo(); |
| MachineBasicBlock *mbb = nullptr; |
| MachineLoop *loop = nullptr; |
| bool isExiting = false; |
| float totalWeight = 0; |
| unsigned numInstr = 0; // Number of instructions using li |
| SmallPtrSet<MachineInstr*, 8> visited; |
| |
| std::pair<unsigned, unsigned> TargetHint = mri.getRegAllocationHint(li.reg); |
| |
| // Don't recompute spill weight for an unspillable register. |
| bool Spillable = li.isSpillable(); |
| |
| bool localSplitArtifact = start && end; |
| |
| // Do not update future local split artifacts. |
| bool updateLI = !localSplitArtifact; |
| |
| if (localSplitArtifact) { |
| MachineBasicBlock *localMBB = LIS.getMBBFromIndex(*end); |
| assert(localMBB == LIS.getMBBFromIndex(*start) && |
| "start and end are expected to be in the same basic block"); |
| |
| // Local split artifact will have 2 additional copy instructions and they |
| // will be in the same BB. |
| // localLI = COPY other |
| // ... |
| // other = COPY localLI |
| totalWeight += LiveIntervals::getSpillWeight(true, false, &MBFI, localMBB); |
| totalWeight += LiveIntervals::getSpillWeight(false, true, &MBFI, localMBB); |
| |
| numInstr += 2; |
| } |
| |
| // CopyHint is a sortable hint derived from a COPY instruction. |
| struct CopyHint { |
| unsigned Reg; |
| float Weight; |
| bool IsPhys; |
| CopyHint(unsigned R, float W, bool P) : |
| Reg(R), Weight(W), IsPhys(P) {} |
| bool operator<(const CopyHint &rhs) const { |
| // Always prefer any physreg hint. |
| if (IsPhys != rhs.IsPhys) |
| return (IsPhys && !rhs.IsPhys); |
| if (Weight != rhs.Weight) |
| return (Weight > rhs.Weight); |
| return Reg < rhs.Reg; // Tie-breaker. |
| } |
| }; |
| std::set<CopyHint> CopyHints; |
| |
| for (MachineRegisterInfo::reg_instr_iterator |
| I = mri.reg_instr_begin(li.reg), E = mri.reg_instr_end(); |
| I != E; ) { |
| MachineInstr *mi = &*(I++); |
| |
| // For local split artifacts, we are interested only in instructions between |
| // the expected start and end of the range. |
| SlotIndex si = LIS.getInstructionIndex(*mi); |
| if (localSplitArtifact && ((si < *start) || (si > *end))) |
| continue; |
| |
| numInstr++; |
| if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugInstr()) |
| continue; |
| if (!visited.insert(mi).second) |
| continue; |
| |
| float weight = 1.0f; |
| if (Spillable) { |
| // Get loop info for mi. |
| if (mi->getParent() != mbb) { |
| mbb = mi->getParent(); |
| loop = Loops.getLoopFor(mbb); |
| isExiting = loop ? loop->isLoopExiting(mbb) : false; |
| } |
| |
| // Calculate instr weight. |
| bool reads, writes; |
| std::tie(reads, writes) = mi->readsWritesVirtualRegister(li.reg); |
| weight = LiveIntervals::getSpillWeight(writes, reads, &MBFI, *mi); |
| |
| // Give extra weight to what looks like a loop induction variable update. |
| if (writes && isExiting && LIS.isLiveOutOfMBB(li, mbb)) |
| weight *= 3; |
| |
| totalWeight += weight; |
| } |
| |
| // Get allocation hints from copies. |
| if (!mi->isCopy()) |
| continue; |
| unsigned hint = copyHint(mi, li.reg, tri, mri); |
| if (!hint) |
| continue; |
| // Force hweight onto the stack so that x86 doesn't add hidden precision, |
| // making the comparison incorrectly pass (i.e., 1 > 1 == true??). |
| // |
| // FIXME: we probably shouldn't use floats at all. |
| volatile float hweight = Hint[hint] += weight; |
| if (TargetRegisterInfo::isVirtualRegister(hint) || mri.isAllocatable(hint)) |
| CopyHints.insert(CopyHint(hint, hweight, tri.isPhysicalRegister(hint))); |
| } |
| |
| Hint.clear(); |
| |
| // Pass all the sorted copy hints to mri. |
| if (updateLI && CopyHints.size()) { |
| // Remove a generic hint if previously added by target. |
| if (TargetHint.first == 0 && TargetHint.second) |
| mri.clearSimpleHint(li.reg); |
| |
| std::set<unsigned> HintedRegs; |
| for (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); |
| } |
| |
| // Weakly boost the spill weight of hinted registers. |
| totalWeight *= 1.01F; |
| } |
| |
| // If the live interval was already unspillable, leave it that way. |
| if (!Spillable) |
| return -1.0; |
| |
| // Mark li as unspillable if all live ranges are tiny and the interval |
| // is not live at any reg mask. If the interval is live at a reg mask |
| // spilling may be required. |
| if (updateLI && li.isZeroLength(LIS.getSlotIndexes()) && |
| !li.isLiveAtIndexes(LIS.getRegMaskSlots())) { |
| li.markNotSpillable(); |
| return -1.0; |
| } |
| |
| // If all of the definitions of the interval are re-materializable, |
| // it is a preferred candidate for spilling. |
| // FIXME: this gets much more complicated once we support non-trivial |
| // re-materialization. |
| if (isRematerializable(li, LIS, VRM, *MF.getSubtarget().getInstrInfo())) |
| totalWeight *= 0.5F; |
| |
| if (localSplitArtifact) |
| return normalize(totalWeight, start->distance(*end), numInstr); |
| return normalize(totalWeight, li.getSize(), numInstr); |
| } |