+
+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());
+}