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This is slightly more interesting than the previous batch of changes. Specifically: 1. We refactor getSpillWeight to take a MachineBlockFrequencyInfo (MBFI) object. This enables us to completely encapsulate the actual manner we use the MachineBlockFrequencyInfo to get our spill weights. This yields cleaner code since one does not need to fetch the actual block frequency before getting the spill weight if all one wants it the spill weight. It also gives us access to entry frequency which we need for our computation. 2. Instead of having getSpillWeight take a MachineBasicBlock (as one might think) to look up the block frequency via the MBFI object, we instead take in a MachineInstr object. The reason for this is that the method is supposed to return the spill weight for an instruction according to the comments around the function. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197296 91177308-0d34-0410-b5e6-96231b3b80d8
188 lines
6.0 KiB
C++
188 lines
6.0 KiB
C++
//===------------------------ CalcSpillWeights.cpp ------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "calcspillweights"
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#include "llvm/CodeGen/CalcSpillWeights.h"
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#include "llvm/CodeGen/LiveIntervalAnalysis.h"
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#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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using namespace llvm;
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void llvm::calculateSpillWeightsAndHints(LiveIntervals &LIS,
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MachineFunction &MF,
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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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DEBUG(dbgs() << "********** Compute Spill Weights **********\n"
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<< "********** Function: " << MF.getName() << '\n');
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MachineRegisterInfo &MRI = MF.getRegInfo();
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VirtRegAuxInfo VRAI(MF, LIS, MLI, MBFI, norm);
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for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) {
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unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
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if (MRI.reg_nodbg_empty(Reg))
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continue;
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VRAI.calculateSpillWeightAndHint(LIS.getInterval(Reg));
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}
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}
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// Return the preferred allocation register for reg, given a COPY instruction.
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static unsigned copyHint(const MachineInstr *mi, unsigned reg,
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const TargetRegisterInfo &tri,
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const MachineRegisterInfo &mri) {
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unsigned sub, hreg, hsub;
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if (mi->getOperand(0).getReg() == reg) {
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sub = mi->getOperand(0).getSubReg();
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hreg = mi->getOperand(1).getReg();
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hsub = mi->getOperand(1).getSubReg();
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} else {
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sub = mi->getOperand(1).getSubReg();
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hreg = mi->getOperand(0).getReg();
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hsub = mi->getOperand(0).getSubReg();
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}
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if (!hreg)
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return 0;
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if (TargetRegisterInfo::isVirtualRegister(hreg))
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return sub == hsub ? hreg : 0;
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const TargetRegisterClass *rc = mri.getRegClass(reg);
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// Only allow physreg hints in rc.
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if (sub == 0)
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return rc->contains(hreg) ? hreg : 0;
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// reg:sub should match the physreg hreg.
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return tri.getMatchingSuperReg(hreg, sub, rc);
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}
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// Check if all values in LI are rematerializable
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static bool isRematerializable(const LiveInterval &LI,
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const LiveIntervals &LIS,
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const TargetInstrInfo &TII) {
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for (LiveInterval::const_vni_iterator I = LI.vni_begin(), E = LI.vni_end();
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I != E; ++I) {
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const VNInfo *VNI = *I;
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if (VNI->isUnused())
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continue;
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if (VNI->isPHIDef())
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return false;
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MachineInstr *MI = LIS.getInstructionFromIndex(VNI->def);
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assert(MI && "Dead valno in interval");
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if (!TII.isTriviallyReMaterializable(MI, LIS.getAliasAnalysis()))
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return false;
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}
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return true;
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}
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void
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VirtRegAuxInfo::calculateSpillWeightAndHint(LiveInterval &li) {
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MachineRegisterInfo &mri = MF.getRegInfo();
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const TargetRegisterInfo &tri = *MF.getTarget().getRegisterInfo();
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MachineBasicBlock *mbb = 0;
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MachineLoop *loop = 0;
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bool isExiting = false;
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float totalWeight = 0;
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SmallPtrSet<MachineInstr*, 8> visited;
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// Find the best physreg hint and the best virtreg hint.
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float bestPhys = 0, bestVirt = 0;
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unsigned hintPhys = 0, hintVirt = 0;
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// Don't recompute a target specific hint.
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bool noHint = mri.getRegAllocationHint(li.reg).first != 0;
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// Don't recompute spill weight for an unspillable register.
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bool Spillable = li.isSpillable();
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for (MachineRegisterInfo::reg_iterator I = mri.reg_begin(li.reg);
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MachineInstr *mi = I.skipInstruction();) {
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if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugValue())
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continue;
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if (!visited.insert(mi))
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continue;
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float weight = 1.0f;
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if (Spillable) {
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// Get loop info for mi.
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if (mi->getParent() != mbb) {
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mbb = mi->getParent();
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loop = Loops.getLoopFor(mbb);
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isExiting = loop ? loop->isLoopExiting(mbb) : false;
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}
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// Calculate instr weight.
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bool reads, writes;
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tie(reads, writes) = mi->readsWritesVirtualRegister(li.reg);
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weight = LiveIntervals::getSpillWeight(
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writes, reads, &MBFI, mi);
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// Give extra weight to what looks like a loop induction variable update.
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if (writes && isExiting && LIS.isLiveOutOfMBB(li, mbb))
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weight *= 3;
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totalWeight += weight;
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}
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// Get allocation hints from copies.
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if (noHint || !mi->isCopy())
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continue;
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unsigned hint = copyHint(mi, li.reg, tri, mri);
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if (!hint)
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continue;
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float hweight = Hint[hint] += weight;
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if (TargetRegisterInfo::isPhysicalRegister(hint)) {
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if (hweight > bestPhys && mri.isAllocatable(hint))
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bestPhys = hweight, hintPhys = hint;
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} else {
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if (hweight > bestVirt)
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bestVirt = hweight, hintVirt = hint;
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}
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}
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Hint.clear();
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// Always prefer the physreg hint.
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if (unsigned hint = hintPhys ? hintPhys : hintVirt) {
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mri.setRegAllocationHint(li.reg, 0, hint);
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// Weakly boost the spill weight of hinted registers.
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totalWeight *= 1.01F;
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}
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// If the live interval was already unspillable, leave it that way.
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if (!Spillable)
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return;
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// Mark li as unspillable if all live ranges are tiny.
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if (li.isZeroLength(LIS.getSlotIndexes())) {
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li.markNotSpillable();
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return;
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}
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// If all of the definitions of the interval are re-materializable,
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// it is a preferred candidate for spilling.
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// FIXME: this gets much more complicated once we support non-trivial
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// re-materialization.
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if (isRematerializable(li, LIS, *MF.getTarget().getInstrInfo()))
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totalWeight *= 0.5F;
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li.weight = normalize(totalWeight, li.getSize());
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}
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