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shorter/easier and have the DAG use that to do the same lookup. This can be used in the future for TargetMachine based caching lookups from the MachineFunction easily. Update the MIPS subtarget switching machinery to update this pointer at the same time it runs. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214838 91177308-0d34-0410-b5e6-96231b3b80d8
195 lines
6.3 KiB
C++
195 lines
6.3 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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#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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#include "llvm/Target/TargetSubtargetInfo.h"
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using namespace llvm;
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#define DEBUG_TYPE "calcspillweights"
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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.getSubtarget().getRegisterInfo();
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MachineBasicBlock *mbb = nullptr;
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MachineLoop *loop = nullptr;
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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_instr_iterator
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I = mri.reg_instr_begin(li.reg), E = mri.reg_instr_end();
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I != E; ) {
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MachineInstr *mi = &*(I++);
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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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std::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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// Force hweight onto the stack so that x86 doesn't add hidden precision,
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// making the comparison incorrectly pass (i.e., 1 > 1 == true??).
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//
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// FIXME: we probably shouldn't use floats at all.
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volatile 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.getSubtarget().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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