forked from OSchip/llvm-project
[RegBankSelect] Refactor the code to split the repairing and mapping of
an instruction. Use the previously introduced RepairingPlacement class to split the code computing the repairing placement from the code doing the actual placement. That way, we will be able to consider different placement and then, only apply the best one. llvm-svn: 270168
This commit is contained in:
Quentin Colombet
parent
5565075418
commit
d84d00baf1
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@ -468,31 +468,60 @@ private:
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bool &OnlyAssign) const;
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/// Insert repairing code for \p Reg as specified by \p ValMapping.
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/// The repairing code is inserted before \p DefUseMI if \p IsDef is false
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/// and after otherwise.
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/// The repairing placement is specified by \p RepairPt.
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/// \p NewVRegs contains all the registers required to remap \p Reg.
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/// In other words, the number of registers in NewVRegs must be equal
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/// to ValMapping.BreakDown.size().
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///
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/// The transformation could be sketched as:
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/// \code
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/// ... = op Reg
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/// \endcode
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/// Becomes
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/// \code
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/// <returned reg> = COPY Reg
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/// <NewRegs> = COPY or extract Reg
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/// ... = op Reg
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/// \endcode
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///
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/// \note This is the responsability of the caller to replace \p Reg
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/// by the returned register.
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/// and
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/// \code
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/// Reg = op ...
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/// \endcode
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/// Becomes
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/// \code
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/// Reg = op ...
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/// Reg = COPY or build_sequence <NewRegs>
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/// \endcode
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///
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/// \return The register of the properly mapped value.
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unsigned repairReg(unsigned Reg,
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const RegisterBankInfo::ValueMapping &ValMapping,
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MachineInstr &DefUseMI, bool IsDef);
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/// \pre NewVRegs.size() == ValMapping.BreakDown.size()
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///
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/// \note The caller is supposed to do the rewriting of op if need be.
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/// I.e., Reg = op ... => <NewRegs> = NewOp ...
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void repairReg(
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MachineOperand &MO, const RegisterBankInfo::ValueMapping &ValMapping,
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RegBankSelect::RepairingPlacement &RepairPt,
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const iterator_range<SmallVectorImpl<unsigned>::iterator> &NewVRegs);
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/// Set the insertion point of the MIRBuilder to a safe point
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/// to insert instructions before (\p Before == true) or after
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/// \p InsertPt.
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void setSafeInsertionPoint(MachineInstr &InsertPt, bool Before);
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/// Compute the cost of mapping \p MI with \p InstrMapping and
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/// compute the repairing placement for such mapping in \p
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/// RepairPts.
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MappingCost
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computeMapping(MachineInstr &MI,
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const RegisterBankInfo::InstructionMapping &InstrMapping,
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SmallVectorImpl<RepairingPlacement> &RepairPts);
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/// Apply \p Mapping to \p MI. \p RepairPts represents the different
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/// mapping action that need to happen for the mapping to be
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/// applied.
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void applyMapping(MachineInstr &MI,
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const RegisterBankInfo::InstructionMapping &InstrMapping,
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SmallVectorImpl<RepairingPlacement> &RepairPts);
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public:
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// Ctor, nothing fancy.
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RegBankSelect();
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@ -65,76 +65,51 @@ bool RegBankSelect::assignmentMatch(
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return CurRegBank == DesiredRegBrank;
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}
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unsigned
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RegBankSelect::repairReg(unsigned Reg,
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const RegisterBankInfo::ValueMapping &ValMapping,
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MachineInstr &DefUseMI, bool IsDef) {
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assert(ValMapping.BreakDown.size() == 1 &&
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"Support for complex break down not supported yet");
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const RegisterBankInfo::PartialMapping &PartialMap = ValMapping.BreakDown[0];
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assert(PartialMap.Length ==
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(TargetRegisterInfo::isPhysicalRegister(Reg)
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? TRI->getMinimalPhysRegClass(Reg)->getSize() * 8
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: MRI->getSize(Reg)) &&
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"Repairing other than copy not implemented yet");
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// If the MIRBuilder is configured to insert somewhere else than
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// DefUseMI, we may not use this function like was it first
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// internded (local repairing), so make sure we pay attention before
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// we remove the assert.
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// In particular, it is likely that we will have to properly save
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// the insertion point of the MIRBuilder and restore it at the end
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// of this method.
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assert(&DefUseMI == &(*MIRBuilder.getInsertPt()) &&
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"Need to save and restore the insertion point");
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// For use, we will add a copy just in front of the instruction.
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// For def, we will add a copy just after the instruction.
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// In either case, the insertion point must be valid. In particular,
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// make sure we do not insert in the middle of terminators or phis.
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bool Before = !IsDef;
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setSafeInsertionPoint(DefUseMI, Before);
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if (DefUseMI.isTerminator() && Before) {
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// Check that the insertion point does not happen
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// before the definition of Reg.
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// This can happen if Reg is defined by a terminator
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// and used by another one.
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// In that case the repairing code is actually more involved
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// because we have to split the block.
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void RegBankSelect::repairReg(
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MachineOperand &MO, const RegisterBankInfo::ValueMapping &ValMapping,
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RegBankSelect::RepairingPlacement &RepairPt,
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const iterator_range<SmallVectorImpl<unsigned>::iterator> &NewVRegs) {
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assert(ValMapping.BreakDown.size() == 1 && "Not yet implemented");
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// Assume we are repairing a use and thus, the original reg will be
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// the source of the repairing.
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unsigned Src = MO.getReg();
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unsigned Dst = *NewVRegs.begin();
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if (ValMapping.BreakDown.size() == 1)
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MO.setReg(Dst);
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// Assert that this is not a physical register.
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// The target independent code does not insert physical registers
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// on terminators, so if we end up in this situation, this is
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// likely a bug in the target.
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assert(!TargetRegisterInfo::isPhysicalRegister(Reg) &&
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"Check for physical register not implemented");
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const MachineInstr *RegDef = MRI->getVRegDef(Reg);
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assert(RegDef && "Reg has more than one definition?");
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// Assert to make the code more readable; Reg is used by DefUseMI, i.e.,
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// (Before == !IsDef == true), so DefUseMI != RegDef otherwise we have
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// a use (that is not a PHI) that is not dominated by its def.
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assert(&DefUseMI != RegDef && "Def does not dominate all of its uses");
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if (RegDef->isTerminator() && RegDef->getParent() == DefUseMI.getParent())
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// By construction, the repairing should happen between two
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// terminators: RegDef and DefUseMI.
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// This is not implemented.
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report_fatal_error("Repairing between terminators not implemented yet");
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}
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// Create a new temporary to hold the repaired value.
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unsigned NewReg = MRI->createGenericVirtualRegister(PartialMap.Length);
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// Set the registers for the source and destination of the copy.
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unsigned Src = Reg, Dst = NewReg;
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// If this is a definition that we repair, the copy will be
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// inverted.
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if (IsDef)
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// If we repair a definition, swap the source and destination for
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// the repairing.
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if (MO.isDef())
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std::swap(Src, Dst);
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(void)MIRBuilder.buildInstr(TargetOpcode::COPY, Dst, Src);
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DEBUG(dbgs() << "Repair: " << PrintReg(Reg) << " with: "
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<< PrintReg(NewReg) << '\n');
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assert((RepairPt.getNumInsertPoints() == 1 ||
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TargetRegisterInfo::isPhysicalRegister(Dst)) &&
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"We are about to create several defs for Dst");
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// Restore the insertion point of the MIRBuilder.
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MIRBuilder.setInstr(DefUseMI, Before);
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return NewReg;
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// Build the instruction used to repair, then clone it at the right places.
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MachineInstr *MI = MIRBuilder.buildInstr(TargetOpcode::COPY, Dst, Src);
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MI->removeFromParent();
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DEBUG(dbgs() << "Copy: " << PrintReg(Src) << " to: " << PrintReg(Dst)
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<< '\n');
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// TODO:
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// Check if MI is legal. if not, we need to legalize all the
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// instructions we are going to insert.
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std::unique_ptr<MachineInstr *[]> NewInstrs(
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new MachineInstr *[RepairPt.getNumInsertPoints()]);
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bool IsFirst = true;
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unsigned Idx = 0;
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for (const std::unique_ptr<InsertPoint> &InsertPt : RepairPt) {
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MachineInstr *CurMI;
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if (IsFirst)
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CurMI = MI;
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else
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CurMI = MIRBuilder.getMF().CloneMachineInstr(MI);
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InsertPt->insert(*CurMI);
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NewInstrs[Idx++] = CurMI;
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IsFirst = false;
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}
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// TODO:
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// Legalize NewInstrs if need be.
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}
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void RegBankSelect::setSafeInsertionPoint(MachineInstr &InsertPt, bool Before) {
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@ -171,81 +146,180 @@ void RegBankSelect::setSafeInsertionPoint(MachineInstr &InsertPt, bool Before) {
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MIRBuilder.setInstr(InsertPt, /*Before*/ Before);
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}
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void RegBankSelect::assignInstr(MachineInstr &MI) {
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DEBUG(dbgs() << "Assign: " << MI);
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const RegisterBankInfo::InstructionMapping DefaultMapping =
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RBI->getInstrMapping(MI);
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// Make sure the mapping is valid for MI.
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assert(DefaultMapping.verify(MI) && "Invalid instruction mapping");
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RegBankSelect::MappingCost RegBankSelect::computeMapping(
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MachineInstr &MI, const RegisterBankInfo::InstructionMapping &InstrMapping,
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SmallVectorImpl<RepairingPlacement> &RepairPts) {
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DEBUG(dbgs() << "Mapping: " << DefaultMapping << '\n');
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// Set the insertion point before MI.
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// This is where we are going to insert the repairing code if any.
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MIRBuilder.setInstr(MI, /*Before*/ true);
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// For now, do not look for alternative mappings.
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// Alternative mapping may require to rewrite MI and we do not support
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// that yet.
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// Walk the operands and assign then to the chosen mapping, possibly with
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// the insertion of repair code for uses.
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for (unsigned OpIdx = 0, EndIdx = MI.getNumOperands(); OpIdx != EndIdx;
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// If mapped with InstrMapping, MI will have the recorded cost.
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MappingCost Cost(1);
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bool Saturated = Cost.addLocalCost(InstrMapping.getCost());
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assert(!Saturated && "Possible mapping saturated the cost");
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DEBUG(dbgs() << "Evaluating mapping cost for: " << MI);
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DEBUG(dbgs() << "With: " << InstrMapping << '\n');
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RepairPts.clear();
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// Moreover, to realize this mapping, the register bank of each operand must
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// match this mapping. In other words, we may need to locally reassign the
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// register banks. Account for that repairing cost as well.
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// In this context, local means in the surrounding of MI.
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for (unsigned OpIdx = 0, EndOpIdx = MI.getNumOperands(); OpIdx != EndOpIdx;
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++OpIdx) {
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MachineOperand &MO = MI.getOperand(OpIdx);
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// Nothing to be done for non-register operands.
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const MachineOperand &MO = MI.getOperand(OpIdx);
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if (!MO.isReg())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg)
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continue;
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DEBUG(dbgs() << "Opd" << OpIdx);
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const RegisterBankInfo::ValueMapping &ValMapping =
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DefaultMapping.getOperandMapping(OpIdx);
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// If Reg is already properly mapped, move on.
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bool OnlyAssign;
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if (assignmentMatch(Reg, ValMapping, OnlyAssign))
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InstrMapping.getOperandMapping(OpIdx);
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// If Reg is already properly mapped, this is free.
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bool Assign;
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if (assignmentMatch(Reg, ValMapping, Assign)) {
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DEBUG(dbgs() << " is free (match).\n");
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continue;
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}
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if (Assign) {
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DEBUG(dbgs() << " is free (simple assignment).\n");
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RepairPts.emplace_back(RepairingPlacement(MI, OpIdx, *TRI, *this,
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RepairingPlacement::Reassign));
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continue;
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// For uses, we may need to create a new temporary.
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// Indeed, if Reg is already assigned a register bank, at this
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// point, we know it is different from the one defined by the
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// chosen mapping, we need to adjust for that.
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// For definitions, changing the register bank will affect all
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// its uses, and in particular the ones we already visited.
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// Although this is correct, since with the RPO traversal of the
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// basic blocks the only uses that we already visisted for this
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// definition are PHIs (i.e., copies), this may not be the best
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// solution according to the cost model.
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// Therefore, create a new temporary for Reg.
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assert(ValMapping.BreakDown.size() == 1 &&
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"Support for complex break down not supported yet");
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if (!OnlyAssign) {
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if (!MO.isDef() && MI.isPHI()) {
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// Phis are already copies, so there is nothing to repair.
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// Note: This will not hold when we support break downs with
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// more than one segment.
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DEBUG(dbgs() << "Skip PHI use\n");
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continue;
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}
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// If MO is a definition, since repairing after a terminator is
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// painful, do not repair. Indeed, this is probably not worse
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// saving the move in the PHIs that will get reassigned.
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if (!MO.isDef() || !MI.isTerminator())
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Reg = repairReg(Reg, ValMapping, MI, MO.isDef());
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}
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// If we end up here, MO should be free of encoding constraints,
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// i.e., we do not have to constrained the RegBank of Reg to
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// the requirement of the operands.
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// If that is not the case, this means the code was broken before
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// hands because we should have found that the assignment match.
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// This will not hold when we will consider alternative mappings.
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DEBUG(dbgs() << "Assign: " << *ValMapping.BreakDown[0].RegBank << " to "
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<< PrintReg(Reg) << '\n');
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// TODO:
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// Ask the repairing module how much it would cost to get this mapping.
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// Use: NewSources <- Val.
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// Same size: copy.
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// Different size: Src1, Src2, ... =
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// extract_value Val, Src1Begin, Src1Len, Src2Begin, Src2Len, ...
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// Def: Val <- NewDefs
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// Same size: copy
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// Different size: Val = build_sequence Defs1, Defs2, ...
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// We should remember that this value is available somewhere else to
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// coalesce the value.
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MRI->setRegBank(Reg, *ValMapping.BreakDown[0].RegBank);
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MO.setReg(Reg);
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// Find the insertion point for the repairing code.
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RepairPts.emplace_back(
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RepairingPlacement(MI, OpIdx, *TRI, *this, RepairingPlacement::Insert));
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RepairingPlacement &RepairPt = RepairPts.back();
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// Check that the materialization of the repairing is possible.
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if (!RepairPt.canMaterialize())
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return MappingCost::ImpossibleCost();
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// Account for the split cost and repair cost.
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// Unless the cost is already saturated.
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if (Saturated)
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continue;
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// Sums up the repairing cost of at each insertion point.
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// TODO: Get the actual repairing cost.
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uint64_t RepairCost = 1;
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// Bias used for splitting: 5%.
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const uint64_t PercentageForBias = 5;
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uint64_t Bias = (RepairCost * PercentageForBias + 99) / 100;
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// We should not need more than a couple of instructions to repair
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// an assignment. In other words, the computation should not
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// overflow because the repairing cost is free of basic block
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// frequency.
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assert(((RepairCost < RepairCost * PercentageForBias) &&
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(RepairCost * PercentageForBias <
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RepairCost * PercentageForBias + 99)) &&
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"Repairing involves more than a billion of instructions?!");
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for (const std::unique_ptr<InsertPoint> &InsertPt : RepairPt) {
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assert(InsertPt->canMaterialize() && "We should not have made it here");
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// We will applied some basic block frequency and those uses uint64_t.
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if (!InsertPt->isSplit())
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Saturated = Cost.addLocalCost(RepairCost);
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else {
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uint64_t CostForInsertPt = RepairCost;
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// Again we shouldn't overflow here givent that
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// CostForInsertPt is frequency free at this point.
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assert(CostForInsertPt + Bias > CostForInsertPt &&
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"Repairing + split bias overflows");
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CostForInsertPt += Bias;
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uint64_t PtCost = InsertPt->frequency(*this) * CostForInsertPt;
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// Check if we just overflowed.
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if ((Saturated = PtCost < CostForInsertPt))
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Cost.saturate();
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else
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Saturated = Cost.addNonLocalCost(PtCost);
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}
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// No need to accumulate more cost information.
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// We need to still gather the repairing information though.
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if (Saturated)
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break;
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}
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}
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return Cost;
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}
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void RegBankSelect::applyMapping(
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MachineInstr &MI, const RegisterBankInfo::InstructionMapping &InstrMapping,
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SmallVectorImpl<RegBankSelect::RepairingPlacement> &RepairPts) {
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assert(InstrMapping.getID() == RegisterBankInfo::DefaultMappingID &&
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"Rewriting of MI not implemented yet");
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// First, place the repairing code.
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bool NeedRewrite = false;
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SmallVector<unsigned, 8> NewVRegs;
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for (RepairingPlacement &RepairPt : RepairPts) {
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assert(RepairPt.canMaterialize() &&
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RepairPt.getKind() != RepairingPlacement::Impossible &&
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"This mapping is impossible");
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assert(RepairPt.getKind() != RepairingPlacement::None &&
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"This should not make its way in the list");
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unsigned OpIdx = RepairPt.getOpIdx();
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MachineOperand &MO = MI.getOperand(OpIdx);
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const RegisterBankInfo::ValueMapping &ValMapping =
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InstrMapping.getOperandMapping(OpIdx);
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unsigned BreakDownSize = ValMapping.BreakDown.size();
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unsigned Reg = MO.getReg();
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NeedRewrite = BreakDownSize != 1;
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switch (RepairPt.getKind()) {
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case RepairingPlacement::Reassign:
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assert(BreakDownSize == 1 &&
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"Reassignment should only be for simple mapping");
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MRI->setRegBank(Reg, *ValMapping.BreakDown[0].RegBank);
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break;
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case RepairingPlacement::Insert:
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// We need as many new virtual registers as the number of partial mapping.
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for (const RegisterBankInfo::PartialMapping &PartMap :
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ValMapping.BreakDown) {
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unsigned Tmp = MRI->createGenericVirtualRegister(PartMap.Length);
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MRI->setRegBank(Tmp, *PartMap.RegBank);
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NewVRegs.push_back(Tmp);
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}
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repairReg(MO, ValMapping, RepairPt,
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make_range(NewVRegs.end() - BreakDownSize, NewVRegs.end()));
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break;
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default:
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llvm_unreachable("Other kind should not happen");
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}
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}
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// Second, rewrite the instruction.
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(void)NeedRewrite;
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assert(!NeedRewrite && "Not implemented yet");
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}
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void RegBankSelect::assignInstr(MachineInstr &MI) {
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DEBUG(dbgs() << "Assign: " << MI);
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RegisterBankInfo::InstructionMapping DefaultMapping =
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RBI->getInstrMapping(MI);
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// Remember the repairing placement for all the operands.
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SmallVector<RepairingPlacement, 4> RepairPts;
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MappingCost DefaultCost = computeMapping(MI, DefaultMapping, RepairPts);
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(void)DefaultCost;
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assert(DefaultCost != MappingCost::ImpossibleCost() &&
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||||
"Default mapping is not suited");
|
||||
|
||||
// Make sure the mapping is valid for MI.
|
||||
assert(DefaultMapping.verify(MI) && "Invalid instruction mapping");
|
||||
|
||||
DEBUG(dbgs() << "Mapping: " << DefaultMapping << '\n');
|
||||
|
||||
applyMapping(MI, DefaultMapping, RepairPts);
|
||||
|
||||
DEBUG(dbgs() << "Assigned: " << MI);
|
||||
}
|
||||
|
||||
|
|
@ -256,9 +330,13 @@ bool RegBankSelect::runOnMachineFunction(MachineFunction &MF) {
|
|||
// Use a RPOT to make sure all registers are assigned before we choose
|
||||
// the best mapping of the current instruction.
|
||||
ReversePostOrderTraversal<MachineFunction*> RPOT(&MF);
|
||||
for (MachineBasicBlock *MBB : RPOT)
|
||||
for (MachineBasicBlock *MBB : RPOT) {
|
||||
// Set a sensible insertion point so that subsequent calls to
|
||||
// MIRBuilder.
|
||||
MIRBuilder.setMBB(*MBB);
|
||||
for (MachineInstr &MI : *MBB)
|
||||
assignInstr(MI);
|
||||
}
|
||||
return false;
|
||||
}
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue