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Diffstat (limited to 'lib/CodeGen/RegAllocPBQP.cpp')
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diff --git a/lib/CodeGen/RegAllocPBQP.cpp b/lib/CodeGen/RegAllocPBQP.cpp new file mode 100644 index 0000000..ee82f63 --- /dev/null +++ b/lib/CodeGen/RegAllocPBQP.cpp @@ -0,0 +1,529 @@ +//===------ RegAllocPBQP.cpp ---- PBQP Register Allocator -------*- C++ -*-===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This file contains a Partitioned Boolean Quadratic Programming (PBQP) based +// register allocator for LLVM. This allocator works by constructing a PBQP +// problem representing the register allocation problem under consideration, +// solving this using a PBQP solver, and mapping the solution back to a +// register assignment. If any variables are selected for spilling then spill +// code is inserted and the process repeated. +// +// The PBQP solver (pbqp.c) provided for this allocator uses a heuristic tuned +// for register allocation. For more information on PBQP for register +// allocation see the following papers: +// +// (1) Hames, L. and Scholz, B. 2006. Nearly optimal register allocation with +// PBQP. In Proceedings of the 7th Joint Modular Languages Conference +// (JMLC'06). LNCS, vol. 4228. Springer, New York, NY, USA. 346-361. +// +// (2) Scholz, B., Eckstein, E. 2002. Register allocation for irregular +// architectures. In Proceedings of the Joint Conference on Languages, +// Compilers and Tools for Embedded Systems (LCTES'02), ACM Press, New York, +// NY, USA, 139-148. +// +// Author: Lang Hames +// Email: lhames@gmail.com +// +//===----------------------------------------------------------------------===// + +// TODO: +// +// * Use of std::set in constructPBQPProblem destroys allocation order preference. +// Switch to an order preserving container. +// +// * Coalescing support. + +#define DEBUG_TYPE "regalloc" + +#include "PBQP.h" +#include "VirtRegMap.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/RegAllocRegistry.h" +#include "llvm/CodeGen/LiveIntervalAnalysis.h" +#include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/CodeGen/MachineLoopInfo.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Target/TargetInstrInfo.h" +#include "llvm/Support/Debug.h" +#include <memory> +#include <map> +#include <set> +#include <vector> +#include <limits> + +using namespace llvm; + +static RegisterRegAlloc +registerPBQPRepAlloc("pbqp", " PBQP register allocator", + createPBQPRegisterAllocator); + + +namespace { + + //! + //! PBQP based allocators solve the register allocation problem by mapping + //! register allocation problems to Partitioned Boolean Quadratic + //! Programming problems. + class VISIBILITY_HIDDEN PBQPRegAlloc : public MachineFunctionPass { + public: + + static char ID; + + //! Construct a PBQP register allocator. + PBQPRegAlloc() : MachineFunctionPass((intptr_t)&ID) {} + + //! Return the pass name. + virtual const char* getPassName() const throw() { + return "PBQP Register Allocator"; + } + + //! PBQP analysis usage. + virtual void getAnalysisUsage(AnalysisUsage &au) const { + au.addRequired<LiveIntervals>(); + au.addRequired<MachineLoopInfo>(); + MachineFunctionPass::getAnalysisUsage(au); + } + + //! Perform register allocation + virtual bool runOnMachineFunction(MachineFunction &MF); + + private: + typedef std::map<const LiveInterval*, unsigned> LI2NodeMap; + typedef std::vector<const LiveInterval*> Node2LIMap; + typedef std::vector<unsigned> AllowedSet; + typedef std::vector<AllowedSet> AllowedSetMap; + typedef std::set<unsigned> IgnoreSet; + + MachineFunction *mf; + const TargetMachine *tm; + const TargetRegisterInfo *tri; + const TargetInstrInfo *tii; + const MachineLoopInfo *loopInfo; + MachineRegisterInfo *mri; + + LiveIntervals *li; + VirtRegMap *vrm; + + LI2NodeMap li2Node; + Node2LIMap node2LI; + AllowedSetMap allowedSets; + IgnoreSet ignoreSet; + + //! Builds a PBQP cost vector. + template <typename Container> + PBQPVector* buildCostVector(const Container &allowed, + PBQPNum spillCost) const; + + //! \brief Builds a PBQP interfernce matrix. + //! + //! @return Either a pointer to a non-zero PBQP matrix representing the + //! allocation option costs, or a null pointer for a zero matrix. + //! + //! Expects allowed sets for two interfering LiveIntervals. These allowed + //! sets should contain only allocable registers from the LiveInterval's + //! register class, with any interfering pre-colored registers removed. + template <typename Container> + PBQPMatrix* buildInterferenceMatrix(const Container &allowed1, + const Container &allowed2) const; + + //! + //! Expects allowed sets for two potentially coalescable LiveIntervals, + //! and an estimated benefit due to coalescing. The allowed sets should + //! contain only allocable registers from the LiveInterval's register + //! classes, with any interfering pre-colored registers removed. + template <typename Container> + PBQPMatrix* buildCoalescingMatrix(const Container &allowed1, + const Container &allowed2, + PBQPNum cBenefit) const; + + //! \brief Helper functior for constructInitialPBQPProblem(). + //! + //! This function iterates over the Function we are about to allocate for + //! and computes spill costs. + void calcSpillCosts(); + + //! \brief Scans the MachineFunction being allocated to find coalescing + // opportunities. + void findCoalescingOpportunities(); + + //! \brief Constructs a PBQP problem representation of the register + //! allocation problem for this function. + //! + //! @return a PBQP solver object for the register allocation problem. + pbqp* constructPBQPProblem(); + + //! \brief Given a solved PBQP problem maps this solution back to a register + //! assignment. + bool mapPBQPToRegAlloc(pbqp *problem); + + }; + + char PBQPRegAlloc::ID = 0; +} + + +template <typename Container> +PBQPVector* PBQPRegAlloc::buildCostVector(const Container &allowed, + PBQPNum spillCost) const { + + // Allocate vector. Additional element (0th) used for spill option + PBQPVector *v = new PBQPVector(allowed.size() + 1); + + (*v)[0] = spillCost; + + return v; +} + +template <typename Container> +PBQPMatrix* PBQPRegAlloc::buildInterferenceMatrix( + const Container &allowed1, const Container &allowed2) const { + + typedef typename Container::const_iterator ContainerIterator; + + // Construct a PBQP matrix representing the cost of allocation options. The + // rows and columns correspond to the allocation options for the two live + // intervals. Elements will be infinite where corresponding registers alias, + // since we cannot allocate aliasing registers to interfering live intervals. + // All other elements (non-aliasing combinations) will have zero cost. Note + // that the spill option (element 0,0) has zero cost, since we can allocate + // both intervals to memory safely (the cost for each individual allocation + // to memory is accounted for by the cost vectors for each live interval). + PBQPMatrix *m = new PBQPMatrix(allowed1.size() + 1, allowed2.size() + 1); + + // Assume this is a zero matrix until proven otherwise. Zero matrices occur + // between interfering live ranges with non-overlapping register sets (e.g. + // non-overlapping reg classes, or disjoint sets of allowed regs within the + // same class). The term "overlapping" is used advisedly: sets which do not + // intersect, but contain registers which alias, will have non-zero matrices. + // We optimize zero matrices away to improve solver speed. + bool isZeroMatrix = true; + + + // Row index. Starts at 1, since the 0th row is for the spill option, which + // is always zero. + unsigned ri = 1; + + // Iterate over allowed sets, insert infinities where required. + for (ContainerIterator a1Itr = allowed1.begin(), a1End = allowed1.end(); + a1Itr != a1End; ++a1Itr) { + + // Column index, starts at 1 as for row index. + unsigned ci = 1; + unsigned reg1 = *a1Itr; + + for (ContainerIterator a2Itr = allowed2.begin(), a2End = allowed2.end(); + a2Itr != a2End; ++a2Itr) { + + unsigned reg2 = *a2Itr; + + // If the row/column regs are identical or alias insert an infinity. + if ((reg1 == reg2) || tri->areAliases(reg1, reg2)) { + (*m)[ri][ci] = std::numeric_limits<PBQPNum>::infinity(); + isZeroMatrix = false; + } + + ++ci; + } + + ++ri; + } + + // If this turns out to be a zero matrix... + if (isZeroMatrix) { + // free it and return null. + delete m; + return 0; + } + + // ...otherwise return the cost matrix. + return m; +} + +void PBQPRegAlloc::calcSpillCosts() { + + // Calculate the spill cost for each live interval by iterating over the + // function counting loads and stores, with loop depth taken into account. + for (MachineFunction::const_iterator bbItr = mf->begin(), bbEnd = mf->end(); + bbItr != bbEnd; ++bbItr) { + + const MachineBasicBlock *mbb = &*bbItr; + float loopDepth = loopInfo->getLoopDepth(mbb); + + for (MachineBasicBlock::const_iterator + iItr = mbb->begin(), iEnd = mbb->end(); iItr != iEnd; ++iItr) { + + const MachineInstr *instr = &*iItr; + + for (unsigned opNo = 0; opNo < instr->getNumOperands(); ++opNo) { + + const MachineOperand &mo = instr->getOperand(opNo); + + // We're not interested in non-registers... + if (!mo.isRegister()) + continue; + + unsigned moReg = mo.getReg(); + + // ...Or invalid registers... + if (moReg == 0) + continue; + + // ...Or physical registers... + if (TargetRegisterInfo::isPhysicalRegister(moReg)) + continue; + + assert ((mo.isUse() || mo.isDef()) && + "Not a use, not a def, what is it?"); + + //... Just the virtual registers. We treat loads and stores as equal. + li->getInterval(moReg).weight += powf(10.0f, loopDepth); + } + + } + + } + +} + +pbqp* PBQPRegAlloc::constructPBQPProblem() { + + typedef std::vector<const LiveInterval*> LIVector; + typedef std::set<unsigned> RegSet; + + // These will store the physical & virtual intervals, respectively. + LIVector physIntervals, virtIntervals; + + // Start by clearing the old node <-> live interval mappings & allowed sets + li2Node.clear(); + node2LI.clear(); + allowedSets.clear(); + + // Iterate over intervals classifying them as physical or virtual, and + // constructing live interval <-> node number mappings. + for (LiveIntervals::iterator itr = li->begin(), end = li->end(); + itr != end; ++itr) { + + if (itr->second->getNumValNums() != 0) { + DOUT << "Live range has " << itr->second->getNumValNums() << ": " << itr->second << "\n"; + } + + if (TargetRegisterInfo::isPhysicalRegister(itr->first)) { + physIntervals.push_back(itr->second); + mri->setPhysRegUsed(itr->second->reg); + } + else { + + // If we've allocated this virtual register interval a stack slot on a + // previous round then it's not an allocation candidate + if (ignoreSet.find(itr->first) != ignoreSet.end()) + continue; + + li2Node[itr->second] = node2LI.size(); + node2LI.push_back(itr->second); + virtIntervals.push_back(itr->second); + } + } + + // Early out if there's no regs to allocate for. + if (virtIntervals.empty()) + return 0; + + // Construct a PBQP solver for this problem + pbqp *solver = alloc_pbqp(virtIntervals.size()); + + // Resize allowedSets container appropriately. + allowedSets.resize(virtIntervals.size()); + + // Iterate over virtual register intervals to compute allowed sets... + for (unsigned node = 0; node < node2LI.size(); ++node) { + + // Grab pointers to the interval and its register class. + const LiveInterval *li = node2LI[node]; + const TargetRegisterClass *liRC = mri->getRegClass(li->reg); + + // Start by assuming all allocable registers in the class are allowed... + RegSet liAllowed(liRC->allocation_order_begin(*mf), + liRC->allocation_order_end(*mf)); + + // If this range is non-empty then eliminate the physical registers which + // overlap with this range, along with all their aliases. + if (!li->empty()) { + for (LIVector::iterator pItr = physIntervals.begin(), + pEnd = physIntervals.end(); pItr != pEnd; ++pItr) { + + if (li->overlaps(**pItr)) { + + unsigned pReg = (*pItr)->reg; + + // Remove the overlapping reg... + liAllowed.erase(pReg); + + const unsigned *aliasItr = tri->getAliasSet(pReg); + + if (aliasItr != 0) { + // ...and its aliases. + for (; *aliasItr != 0; ++aliasItr) { + liAllowed.erase(*aliasItr); + } + + } + + } + + } + + } + + // Copy the allowed set into a member vector for use when constructing cost + // vectors & matrices, and mapping PBQP solutions back to assignments. + allowedSets[node] = AllowedSet(liAllowed.begin(), liAllowed.end()); + + // Set the spill cost to the interval weight, or epsilon if the + // interval weight is zero + PBQPNum spillCost = (li->weight != 0.0) ? + li->weight : std::numeric_limits<PBQPNum>::min(); + + // Build a cost vector for this interval. + add_pbqp_nodecosts(solver, node, + buildCostVector(allowedSets[node], spillCost)); + + } + + // Now add the cost matrices... + for (unsigned node1 = 0; node1 < node2LI.size(); ++node1) { + + const LiveInterval *li = node2LI[node1]; + + if (li->empty()) + continue; + + // Test for live range overlaps and insert interference matrices. + for (unsigned node2 = node1 + 1; node2 < node2LI.size(); ++node2) { + const LiveInterval *li2 = node2LI[node2]; + + if (li2->empty()) + continue; + + if (li->overlaps(*li2)) { + PBQPMatrix *m = + buildInterferenceMatrix(allowedSets[node1], allowedSets[node2]); + + if (m != 0) { + add_pbqp_edgecosts(solver, node1, node2, m); + delete m; + } + } + } + } + + // We're done, PBQP problem constructed - return it. + return solver; +} + +bool PBQPRegAlloc::mapPBQPToRegAlloc(pbqp *problem) { + + // Set to true if we have any spills + bool anotherRoundNeeded = false; + + // Clear the existing allocation. + vrm->clearAllVirt(); + + // Iterate over the nodes mapping the PBQP solution to a register assignment. + for (unsigned node = 0; node < node2LI.size(); ++node) { + unsigned symReg = node2LI[node]->reg, + allocSelection = get_pbqp_solution(problem, node); + + // If the PBQP solution is non-zero it's a physical register... + if (allocSelection != 0) { + // Get the physical reg, subtracting 1 to account for the spill option. + unsigned physReg = allowedSets[node][allocSelection - 1]; + + // Add to the virt reg map and update the used phys regs. + vrm->assignVirt2Phys(symReg, physReg); + mri->setPhysRegUsed(physReg); + } + // ...Otherwise it's a spill. + else { + + // Make sure we ignore this virtual reg on the next round + // of allocation + ignoreSet.insert(node2LI[node]->reg); + + float SSWeight; + + // Insert spill ranges for this live range + SmallVector<LiveInterval*, 8> spillIs; + std::vector<LiveInterval*> newSpills = + li->addIntervalsForSpills(*node2LI[node], spillIs, loopInfo, *vrm, + SSWeight); + + // We need another round if spill intervals were added. + anotherRoundNeeded |= !newSpills.empty(); + } + } + + return !anotherRoundNeeded; +} + +bool PBQPRegAlloc::runOnMachineFunction(MachineFunction &MF) { + + mf = &MF; + tm = &mf->getTarget(); + tri = tm->getRegisterInfo(); + mri = &mf->getRegInfo(); + + li = &getAnalysis<LiveIntervals>(); + loopInfo = &getAnalysis<MachineLoopInfo>(); + + std::auto_ptr<VirtRegMap> vrmAutoPtr(new VirtRegMap(*mf)); + vrm = vrmAutoPtr.get(); + + // Allocator main loop: + // + // * Map current regalloc problem to a PBQP problem + // * Solve the PBQP problem + // * Map the solution back to a register allocation + // * Spill if necessary + // + // This process is continued till no more spills are generated. + + bool regallocComplete = false; + + // Calculate spill costs for intervals + calcSpillCosts(); + + while (!regallocComplete) { + pbqp *problem = constructPBQPProblem(); + + // Fast out if there's no problem to solve. + if (problem == 0) + return true; + + solve_pbqp(problem); + + regallocComplete = mapPBQPToRegAlloc(problem); + + free_pbqp(problem); + } + + ignoreSet.clear(); + + std::auto_ptr<Spiller> spiller(createSpiller()); + + spiller->runOnMachineFunction(*mf, *vrm); + + return true; +} + +FunctionPass* llvm::createPBQPRegisterAllocator() { + return new PBQPRegAlloc(); +} + + +#undef DEBUG_TYPE |