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//===------------------------ CalcSpillWeights.cpp ------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
using namespace llvm;
#define DEBUG_TYPE "calcspillweights"
void llvm::calculateSpillWeightsAndHints(LiveIntervals &LIS,
MachineFunction &MF,
const MachineLoopInfo &MLI,
const MachineBlockFrequencyInfo &MBFI,
VirtRegAuxInfo::NormalizingFn norm) {
DEBUG(dbgs() << "********** Compute Spill Weights **********\n"
<< "********** Function: " << MF.getName() << '\n');
MachineRegisterInfo &MRI = MF.getRegInfo();
VirtRegAuxInfo VRAI(MF, LIS, 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);
// Only allow physreg hints in rc.
if (sub == 0)
return rc->contains(hreg) ? hreg : 0;
// reg:sub should match the physreg hreg.
return tri.getMatchingSuperReg(hreg, sub, rc);
}
// Check if all values in LI are rematerializable
static bool isRematerializable(const LiveInterval &LI,
const LiveIntervals &LIS,
const TargetInstrInfo &TII) {
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");
if (!TII.isTriviallyReMaterializable(MI, LIS.getAliasAnalysis()))
return false;
}
return true;
}
void
VirtRegAuxInfo::calculateSpillWeightAndHint(LiveInterval &li) {
MachineRegisterInfo &mri = MF.getRegInfo();
const TargetRegisterInfo &tri = *MF.getTarget().getRegisterInfo();
MachineBasicBlock *mbb = nullptr;
MachineLoop *loop = nullptr;
bool isExiting = false;
float totalWeight = 0;
SmallPtrSet<MachineInstr*, 8> visited;
// Find the best physreg hint and the best virtreg hint.
float bestPhys = 0, bestVirt = 0;
unsigned hintPhys = 0, hintVirt = 0;
// Don't recompute a target specific hint.
bool noHint = mri.getRegAllocationHint(li.reg).first != 0;
// Don't recompute spill weight for an unspillable register.
bool Spillable = li.isSpillable();
for (MachineRegisterInfo::reg_instr_iterator
I = mri.reg_instr_begin(li.reg), E = mri.reg_instr_end();
I != E; ) {
MachineInstr *mi = &*(I++);
if (mi->isIdentityCopy() || mi->isImplicitDef() || mi->isDebugValue())
continue;
if (!visited.insert(mi))
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 (noHint || !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::isPhysicalRegister(hint)) {
if (hweight > bestPhys && mri.isAllocatable(hint))
bestPhys = hweight, hintPhys = hint;
} else {
if (hweight > bestVirt)
bestVirt = hweight, hintVirt = hint;
}
}
Hint.clear();
// Always prefer the physreg hint.
if (unsigned hint = hintPhys ? hintPhys : hintVirt) {
mri.setRegAllocationHint(li.reg, 0, hint);
// 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;
// Mark li as unspillable if all live ranges are tiny.
if (li.isZeroLength(LIS.getSlotIndexes())) {
li.markNotSpillable();
return;
}
// 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, *MF.getTarget().getInstrInfo()))
totalWeight *= 0.5F;
li.weight = normalize(totalWeight, li.getSize());
}
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