+/// \brief Collect the hint info for \p Reg.
+/// The results are stored into \p Out.
+/// \p Out is not cleared before being populated.
+void RAGreedy::collectHintInfo(unsigned Reg, HintsInfo &Out) {
+ for (const MachineInstr &Instr : MRI->reg_nodbg_instructions(Reg)) {
+ if (!Instr.isFullCopy())
+ continue;
+ // Look for the other end of the copy.
+ unsigned OtherReg = Instr.getOperand(0).getReg();
+ if (OtherReg == Reg) {
+ OtherReg = Instr.getOperand(1).getReg();
+ if (OtherReg == Reg)
+ continue;
+ }
+ // Get the current assignment.
+ unsigned OtherPhysReg = TargetRegisterInfo::isPhysicalRegister(OtherReg)
+ ? OtherReg
+ : VRM->getPhys(OtherReg);
+ // Push the collected information.
+ Out.push_back(HintInfo(MBFI->getBlockFreq(Instr.getParent()), OtherReg,
+ OtherPhysReg));
+ }
+}
+
+/// \brief Using the given \p List, compute the cost of the broken hints if
+/// \p PhysReg was used.
+/// \return The cost of \p List for \p PhysReg.
+BlockFrequency RAGreedy::getBrokenHintFreq(const HintsInfo &List,
+ unsigned PhysReg) {
+ BlockFrequency Cost = 0;
+ for (const HintInfo &Info : List) {
+ if (Info.PhysReg != PhysReg)
+ Cost += Info.Freq;
+ }
+ return Cost;
+}
+
+/// \brief Using the register assigned to \p VirtReg, try to recolor
+/// all the live ranges that are copy-related with \p VirtReg.
+/// The recoloring is then propagated to all the live-ranges that have
+/// been recolored and so on, until no more copies can be coalesced or
+/// it is not profitable.
+/// For a given live range, profitability is determined by the sum of the
+/// frequencies of the non-identity copies it would introduce with the old
+/// and new register.
+void RAGreedy::tryHintRecoloring(LiveInterval &VirtReg) {
+ // We have a broken hint, check if it is possible to fix it by
+ // reusing PhysReg for the copy-related live-ranges. Indeed, we evicted
+ // some register and PhysReg may be available for the other live-ranges.
+ SmallSet<unsigned, 4> Visited;
+ SmallVector<unsigned, 2> RecoloringCandidates;
+ HintsInfo Info;
+ unsigned Reg = VirtReg.reg;
+ unsigned PhysReg = VRM->getPhys(Reg);
+ // Start the recoloring algorithm from the input live-interval, then
+ // it will propagate to the ones that are copy-related with it.
+ Visited.insert(Reg);
+ RecoloringCandidates.push_back(Reg);
+
+ DEBUG(dbgs() << "Trying to reconcile hints for: " << PrintReg(Reg, TRI) << '('
+ << PrintReg(PhysReg, TRI) << ")\n");
+
+ do {
+ Reg = RecoloringCandidates.pop_back_val();
+
+ // We cannot recolor physcal register.
+ if (TargetRegisterInfo::isPhysicalRegister(Reg))
+ continue;
+
+ assert(VRM->hasPhys(Reg) && "We have unallocated variable!!");
+
+ // Get the live interval mapped with this virtual register to be able
+ // to check for the interference with the new color.
+ LiveInterval &LI = LIS->getInterval(Reg);
+ unsigned CurrPhys = VRM->getPhys(Reg);
+ // Check that the new color matches the register class constraints and
+ // that it is free for this live range.
+ if (CurrPhys != PhysReg && (!MRI->getRegClass(Reg)->contains(PhysReg) ||
+ Matrix->checkInterference(LI, PhysReg)))
+ continue;
+
+ DEBUG(dbgs() << PrintReg(Reg, TRI) << '(' << PrintReg(CurrPhys, TRI)
+ << ") is recolorable.\n");
+
+ // Gather the hint info.
+ Info.clear();
+ collectHintInfo(Reg, Info);
+ // Check if recoloring the live-range will increase the cost of the
+ // non-identity copies.
+ if (CurrPhys != PhysReg) {
+ DEBUG(dbgs() << "Checking profitability:\n");
+ BlockFrequency OldCopiesCost = getBrokenHintFreq(Info, CurrPhys);
+ BlockFrequency NewCopiesCost = getBrokenHintFreq(Info, PhysReg);
+ DEBUG(dbgs() << "Old Cost: " << OldCopiesCost.getFrequency()
+ << "\nNew Cost: " << NewCopiesCost.getFrequency() << '\n');
+ if (OldCopiesCost < NewCopiesCost) {
+ DEBUG(dbgs() << "=> Not profitable.\n");
+ continue;
+ }
+ // At this point, the cost is either cheaper or equal. If it is
+ // equal, we consider this is profitable because it may expose
+ // more recoloring opportunities.
+ DEBUG(dbgs() << "=> Profitable.\n");
+ // Recolor the live-range.
+ Matrix->unassign(LI);
+ Matrix->assign(LI, PhysReg);
+ }
+ // Push all copy-related live-ranges to keep reconciling the broken
+ // hints.
+ for (const HintInfo &HI : Info) {
+ if (Visited.insert(HI.Reg).second)
+ RecoloringCandidates.push_back(HI.Reg);
+ }
+ } while (!RecoloringCandidates.empty());
+}
+
+/// \brief Try to recolor broken hints.
+/// Broken hints may be repaired by recoloring when an evicted variable
+/// freed up a register for a larger live-range.
+/// Consider the following example:
+/// BB1:
+/// a =
+/// b =
+/// BB2:
+/// ...
+/// = b
+/// = a
+/// Let us assume b gets split:
+/// BB1:
+/// a =
+/// b =
+/// BB2:
+/// c = b
+/// ...
+/// d = c
+/// = d
+/// = a
+/// Because of how the allocation work, b, c, and d may be assigned different
+/// colors. Now, if a gets evicted later:
+/// BB1:
+/// a =
+/// st a, SpillSlot
+/// b =
+/// BB2:
+/// c = b
+/// ...
+/// d = c
+/// = d
+/// e = ld SpillSlot
+/// = e
+/// This is likely that we can assign the same register for b, c, and d,
+/// getting rid of 2 copies.
+void RAGreedy::tryHintsRecoloring() {
+ for (LiveInterval *LI : SetOfBrokenHints) {
+ assert(TargetRegisterInfo::isVirtualRegister(LI->reg) &&
+ "Recoloring is possible only for virtual registers");
+ // Some dead defs may be around (e.g., because of debug uses).
+ // Ignore those.
+ if (!VRM->hasPhys(LI->reg))
+ continue;
+ tryHintRecoloring(*LI);
+ }
+}
+