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592 lines
21 KiB
C++
592 lines
21 KiB
C++
//===-- RegAllocBasic.cpp - basic register allocator ----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the RABasic function pass, which provides a minimal
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// implementation of the basic register allocator.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "regalloc"
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#include "RegAllocBase.h"
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#include "LiveDebugVariables.h"
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#include "LiveIntervalUnion.h"
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#include "LiveRangeEdit.h"
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#include "RenderMachineFunction.h"
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#include "Spiller.h"
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#include "VirtRegMap.h"
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#include "llvm/ADT/OwningPtr.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Function.h"
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#include "llvm/PassAnalysisSupport.h"
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#include "llvm/CodeGen/CalcSpillWeights.h"
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#include "llvm/CodeGen/LiveIntervalAnalysis.h"
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#include "llvm/CodeGen/LiveStackAnalysis.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineLoopInfo.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/RegAllocRegistry.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetOptions.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#ifndef NDEBUG
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#include "llvm/ADT/SparseBitVector.h"
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#endif
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Support/Timer.h"
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#include <cstdlib>
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#include <queue>
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using namespace llvm;
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STATISTIC(NumAssigned , "Number of registers assigned");
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STATISTIC(NumUnassigned , "Number of registers unassigned");
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STATISTIC(NumNewQueued , "Number of new live ranges queued");
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static RegisterRegAlloc basicRegAlloc("basic", "basic register allocator",
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createBasicRegisterAllocator);
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// Temporary verification option until we can put verification inside
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// MachineVerifier.
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static cl::opt<bool, true>
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VerifyRegAlloc("verify-regalloc", cl::location(RegAllocBase::VerifyEnabled),
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cl::desc("Verify during register allocation"));
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const char *RegAllocBase::TimerGroupName = "Register Allocation";
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bool RegAllocBase::VerifyEnabled = false;
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namespace {
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struct CompSpillWeight {
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bool operator()(LiveInterval *A, LiveInterval *B) const {
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return A->weight < B->weight;
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}
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};
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}
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namespace {
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/// RABasic provides a minimal implementation of the basic register allocation
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/// algorithm. It prioritizes live virtual registers by spill weight and spills
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/// whenever a register is unavailable. This is not practical in production but
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/// provides a useful baseline both for measuring other allocators and comparing
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/// the speed of the basic algorithm against other styles of allocators.
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class RABasic : public MachineFunctionPass, public RegAllocBase
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{
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// context
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MachineFunction *MF;
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// analyses
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LiveStacks *LS;
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RenderMachineFunction *RMF;
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// state
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std::auto_ptr<Spiller> SpillerInstance;
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std::priority_queue<LiveInterval*, std::vector<LiveInterval*>,
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CompSpillWeight> Queue;
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public:
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RABasic();
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/// Return the pass name.
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virtual const char* getPassName() const {
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return "Basic Register Allocator";
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}
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/// RABasic analysis usage.
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virtual void getAnalysisUsage(AnalysisUsage &AU) const;
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virtual void releaseMemory();
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virtual Spiller &spiller() { return *SpillerInstance; }
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virtual float getPriority(LiveInterval *LI) { return LI->weight; }
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virtual void enqueue(LiveInterval *LI) {
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Queue.push(LI);
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}
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virtual LiveInterval *dequeue() {
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if (Queue.empty())
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return 0;
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LiveInterval *LI = Queue.top();
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Queue.pop();
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return LI;
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}
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virtual unsigned selectOrSplit(LiveInterval &VirtReg,
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SmallVectorImpl<LiveInterval*> &SplitVRegs);
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/// Perform register allocation.
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virtual bool runOnMachineFunction(MachineFunction &mf);
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static char ID;
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};
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char RABasic::ID = 0;
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} // end anonymous namespace
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RABasic::RABasic(): MachineFunctionPass(ID) {
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initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
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initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
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initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
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initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
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initializeRegisterCoalescerPass(*PassRegistry::getPassRegistry());
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initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
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initializeLiveStacksPass(*PassRegistry::getPassRegistry());
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initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
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initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
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initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
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initializeRenderMachineFunctionPass(*PassRegistry::getPassRegistry());
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}
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void RABasic::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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AU.addRequired<AliasAnalysis>();
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AU.addPreserved<AliasAnalysis>();
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AU.addRequired<LiveIntervals>();
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AU.addPreserved<SlotIndexes>();
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AU.addRequired<LiveDebugVariables>();
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AU.addPreserved<LiveDebugVariables>();
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if (StrongPHIElim)
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AU.addRequiredID(StrongPHIEliminationID);
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AU.addRequiredTransitiveID(RegisterCoalescerPassID);
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AU.addRequired<CalculateSpillWeights>();
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AU.addRequired<LiveStacks>();
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AU.addPreserved<LiveStacks>();
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AU.addRequiredID(MachineDominatorsID);
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AU.addPreservedID(MachineDominatorsID);
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AU.addRequired<MachineLoopInfo>();
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AU.addPreserved<MachineLoopInfo>();
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AU.addRequired<VirtRegMap>();
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AU.addPreserved<VirtRegMap>();
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DEBUG(AU.addRequired<RenderMachineFunction>());
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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void RABasic::releaseMemory() {
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SpillerInstance.reset(0);
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RegAllocBase::releaseMemory();
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}
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#ifndef NDEBUG
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// Verify each LiveIntervalUnion.
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void RegAllocBase::verify() {
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LiveVirtRegBitSet VisitedVRegs;
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OwningArrayPtr<LiveVirtRegBitSet>
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unionVRegs(new LiveVirtRegBitSet[PhysReg2LiveUnion.numRegs()]);
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// Verify disjoint unions.
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for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
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DEBUG(PhysReg2LiveUnion[PhysReg].print(dbgs(), TRI));
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LiveVirtRegBitSet &VRegs = unionVRegs[PhysReg];
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PhysReg2LiveUnion[PhysReg].verify(VRegs);
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// Union + intersection test could be done efficiently in one pass, but
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// don't add a method to SparseBitVector unless we really need it.
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assert(!VisitedVRegs.intersects(VRegs) && "vreg in multiple unions");
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VisitedVRegs |= VRegs;
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}
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// Verify vreg coverage.
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for (LiveIntervals::iterator liItr = LIS->begin(), liEnd = LIS->end();
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liItr != liEnd; ++liItr) {
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unsigned reg = liItr->first;
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if (TargetRegisterInfo::isPhysicalRegister(reg)) continue;
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if (!VRM->hasPhys(reg)) continue; // spilled?
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unsigned PhysReg = VRM->getPhys(reg);
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if (!unionVRegs[PhysReg].test(reg)) {
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dbgs() << "LiveVirtReg " << reg << " not in union " <<
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TRI->getName(PhysReg) << "\n";
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llvm_unreachable("unallocated live vreg");
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}
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}
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// FIXME: I'm not sure how to verify spilled intervals.
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}
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#endif //!NDEBUG
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//===----------------------------------------------------------------------===//
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// RegAllocBase Implementation
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//===----------------------------------------------------------------------===//
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// Instantiate a LiveIntervalUnion for each physical register.
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void RegAllocBase::LiveUnionArray::init(LiveIntervalUnion::Allocator &allocator,
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unsigned NRegs) {
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NumRegs = NRegs;
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Array =
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static_cast<LiveIntervalUnion*>(malloc(sizeof(LiveIntervalUnion)*NRegs));
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for (unsigned r = 0; r != NRegs; ++r)
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new(Array + r) LiveIntervalUnion(r, allocator);
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}
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void RegAllocBase::init(VirtRegMap &vrm, LiveIntervals &lis) {
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NamedRegionTimer T("Initialize", TimerGroupName, TimePassesIsEnabled);
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TRI = &vrm.getTargetRegInfo();
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MRI = &vrm.getRegInfo();
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VRM = &vrm;
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LIS = &lis;
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RegClassInfo.runOnMachineFunction(vrm.getMachineFunction());
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const unsigned NumRegs = TRI->getNumRegs();
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if (NumRegs != PhysReg2LiveUnion.numRegs()) {
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PhysReg2LiveUnion.init(UnionAllocator, NumRegs);
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// Cache an interferece query for each physical reg
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Queries.reset(new LiveIntervalUnion::Query[PhysReg2LiveUnion.numRegs()]);
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}
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}
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void RegAllocBase::LiveUnionArray::clear() {
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if (!Array)
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return;
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for (unsigned r = 0; r != NumRegs; ++r)
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Array[r].~LiveIntervalUnion();
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free(Array);
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NumRegs = 0;
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Array = 0;
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}
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void RegAllocBase::releaseMemory() {
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for (unsigned r = 0, e = PhysReg2LiveUnion.numRegs(); r != e; ++r)
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PhysReg2LiveUnion[r].clear();
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}
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// Visit all the live registers. If they are already assigned to a physical
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// register, unify them with the corresponding LiveIntervalUnion, otherwise push
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// them on the priority queue for later assignment.
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void RegAllocBase::seedLiveRegs() {
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NamedRegionTimer T("Seed Live Regs", TimerGroupName, TimePassesIsEnabled);
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for (LiveIntervals::iterator I = LIS->begin(), E = LIS->end(); I != E; ++I) {
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unsigned RegNum = I->first;
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LiveInterval &VirtReg = *I->second;
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if (TargetRegisterInfo::isPhysicalRegister(RegNum))
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PhysReg2LiveUnion[RegNum].unify(VirtReg);
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else
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enqueue(&VirtReg);
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}
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}
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void RegAllocBase::assign(LiveInterval &VirtReg, unsigned PhysReg) {
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DEBUG(dbgs() << "assigning " << PrintReg(VirtReg.reg, TRI)
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<< " to " << PrintReg(PhysReg, TRI) << '\n');
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assert(!VRM->hasPhys(VirtReg.reg) && "Duplicate VirtReg assignment");
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VRM->assignVirt2Phys(VirtReg.reg, PhysReg);
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MRI->setPhysRegUsed(PhysReg);
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PhysReg2LiveUnion[PhysReg].unify(VirtReg);
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++NumAssigned;
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}
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void RegAllocBase::unassign(LiveInterval &VirtReg, unsigned PhysReg) {
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DEBUG(dbgs() << "unassigning " << PrintReg(VirtReg.reg, TRI)
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<< " from " << PrintReg(PhysReg, TRI) << '\n');
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assert(VRM->getPhys(VirtReg.reg) == PhysReg && "Inconsistent unassign");
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PhysReg2LiveUnion[PhysReg].extract(VirtReg);
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VRM->clearVirt(VirtReg.reg);
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++NumUnassigned;
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}
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// Top-level driver to manage the queue of unassigned VirtRegs and call the
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// selectOrSplit implementation.
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void RegAllocBase::allocatePhysRegs() {
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seedLiveRegs();
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// Continue assigning vregs one at a time to available physical registers.
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while (LiveInterval *VirtReg = dequeue()) {
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assert(!VRM->hasPhys(VirtReg->reg) && "Register already assigned");
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// Unused registers can appear when the spiller coalesces snippets.
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if (MRI->reg_nodbg_empty(VirtReg->reg)) {
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DEBUG(dbgs() << "Dropping unused " << *VirtReg << '\n');
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LIS->removeInterval(VirtReg->reg);
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continue;
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}
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// Invalidate all interference queries, live ranges could have changed.
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invalidateVirtRegs();
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// selectOrSplit requests the allocator to return an available physical
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// register if possible and populate a list of new live intervals that
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// result from splitting.
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DEBUG(dbgs() << "\nselectOrSplit "
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<< MRI->getRegClass(VirtReg->reg)->getName()
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<< ':' << *VirtReg << '\n');
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typedef SmallVector<LiveInterval*, 4> VirtRegVec;
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VirtRegVec SplitVRegs;
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unsigned AvailablePhysReg = selectOrSplit(*VirtReg, SplitVRegs);
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if (AvailablePhysReg == ~0u) {
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// selectOrSplit failed to find a register!
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const char *Msg = "ran out of registers during register allocation";
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// Probably caused by an inline asm.
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MachineInstr *MI;
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for (MachineRegisterInfo::reg_iterator I = MRI->reg_begin(VirtReg->reg);
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(MI = I.skipInstruction());)
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if (MI->isInlineAsm())
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break;
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if (MI)
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MI->emitError(Msg);
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else
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report_fatal_error(Msg);
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// Keep going after reporting the error.
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VRM->assignVirt2Phys(VirtReg->reg,
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RegClassInfo.getOrder(MRI->getRegClass(VirtReg->reg)).front());
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continue;
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}
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if (AvailablePhysReg)
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assign(*VirtReg, AvailablePhysReg);
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for (VirtRegVec::iterator I = SplitVRegs.begin(), E = SplitVRegs.end();
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I != E; ++I) {
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LiveInterval *SplitVirtReg = *I;
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assert(!VRM->hasPhys(SplitVirtReg->reg) && "Register already assigned");
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if (MRI->reg_nodbg_empty(SplitVirtReg->reg)) {
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DEBUG(dbgs() << "not queueing unused " << *SplitVirtReg << '\n');
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LIS->removeInterval(SplitVirtReg->reg);
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continue;
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}
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DEBUG(dbgs() << "queuing new interval: " << *SplitVirtReg << "\n");
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assert(TargetRegisterInfo::isVirtualRegister(SplitVirtReg->reg) &&
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"expect split value in virtual register");
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enqueue(SplitVirtReg);
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++NumNewQueued;
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}
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}
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}
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// Check if this live virtual register interferes with a physical register. If
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// not, then check for interference on each register that aliases with the
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// physical register. Return the interfering register.
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unsigned RegAllocBase::checkPhysRegInterference(LiveInterval &VirtReg,
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unsigned PhysReg) {
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for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI)
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if (query(VirtReg, *AliasI).checkInterference())
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return *AliasI;
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return 0;
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}
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// Helper for spillInteferences() that spills all interfering vregs currently
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// assigned to this physical register.
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void RegAllocBase::spillReg(LiveInterval& VirtReg, unsigned PhysReg,
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SmallVectorImpl<LiveInterval*> &SplitVRegs) {
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LiveIntervalUnion::Query &Q = query(VirtReg, PhysReg);
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assert(Q.seenAllInterferences() && "need collectInterferences()");
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const SmallVectorImpl<LiveInterval*> &PendingSpills = Q.interferingVRegs();
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for (SmallVectorImpl<LiveInterval*>::const_iterator I = PendingSpills.begin(),
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E = PendingSpills.end(); I != E; ++I) {
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LiveInterval &SpilledVReg = **I;
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DEBUG(dbgs() << "extracting from " <<
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TRI->getName(PhysReg) << " " << SpilledVReg << '\n');
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// Deallocate the interfering vreg by removing it from the union.
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// A LiveInterval instance may not be in a union during modification!
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unassign(SpilledVReg, PhysReg);
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// Spill the extracted interval.
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LiveRangeEdit LRE(SpilledVReg, SplitVRegs, 0, &PendingSpills);
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spiller().spill(LRE);
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}
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// After extracting segments, the query's results are invalid. But keep the
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// contents valid until we're done accessing pendingSpills.
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Q.clear();
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}
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// Spill or split all live virtual registers currently unified under PhysReg
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// that interfere with VirtReg. The newly spilled or split live intervals are
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// returned by appending them to SplitVRegs.
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bool
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RegAllocBase::spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
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SmallVectorImpl<LiveInterval*> &SplitVRegs) {
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// Record each interference and determine if all are spillable before mutating
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// either the union or live intervals.
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unsigned NumInterferences = 0;
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// Collect interferences assigned to any alias of the physical register.
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for (const unsigned *asI = TRI->getOverlaps(PhysReg); *asI; ++asI) {
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LiveIntervalUnion::Query &QAlias = query(VirtReg, *asI);
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NumInterferences += QAlias.collectInterferingVRegs();
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if (QAlias.seenUnspillableVReg()) {
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return false;
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}
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}
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DEBUG(dbgs() << "spilling " << TRI->getName(PhysReg) <<
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" interferences with " << VirtReg << "\n");
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assert(NumInterferences > 0 && "expect interference");
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// Spill each interfering vreg allocated to PhysReg or an alias.
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for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI)
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spillReg(VirtReg, *AliasI, SplitVRegs);
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return true;
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}
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// Add newly allocated physical registers to the MBB live in sets.
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void RegAllocBase::addMBBLiveIns(MachineFunction *MF) {
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NamedRegionTimer T("MBB Live Ins", TimerGroupName, TimePassesIsEnabled);
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SlotIndexes *Indexes = LIS->getSlotIndexes();
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if (MF->size() <= 1)
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return;
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LiveIntervalUnion::SegmentIter SI;
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for (unsigned PhysReg = 0; PhysReg < PhysReg2LiveUnion.numRegs(); ++PhysReg) {
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LiveIntervalUnion &LiveUnion = PhysReg2LiveUnion[PhysReg];
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if (LiveUnion.empty())
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continue;
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DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " live-in:");
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MachineFunction::iterator MBB = llvm::next(MF->begin());
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MachineFunction::iterator MFE = MF->end();
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SlotIndex Start, Stop;
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tie(Start, Stop) = Indexes->getMBBRange(MBB);
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SI.setMap(LiveUnion.getMap());
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SI.find(Start);
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while (SI.valid()) {
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if (SI.start() <= Start) {
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if (!MBB->isLiveIn(PhysReg))
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MBB->addLiveIn(PhysReg);
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DEBUG(dbgs() << "\tBB#" << MBB->getNumber() << ':'
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<< PrintReg(SI.value()->reg, TRI));
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} else if (SI.start() > Stop)
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MBB = Indexes->getMBBFromIndex(SI.start().getPrevIndex());
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if (++MBB == MFE)
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break;
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tie(Start, Stop) = Indexes->getMBBRange(MBB);
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SI.advanceTo(Start);
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}
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DEBUG(dbgs() << '\n');
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}
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}
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//===----------------------------------------------------------------------===//
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// RABasic Implementation
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//===----------------------------------------------------------------------===//
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// Driver for the register assignment and splitting heuristics.
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// Manages iteration over the LiveIntervalUnions.
|
|
//
|
|
// This is a minimal implementation of register assignment and splitting that
|
|
// spills whenever we run out of registers.
|
|
//
|
|
// selectOrSplit can only be called once per live virtual register. We then do a
|
|
// single interference test for each register the correct class until we find an
|
|
// available register. So, the number of interference tests in the worst case is
|
|
// |vregs| * |machineregs|. And since the number of interference tests is
|
|
// minimal, there is no value in caching them outside the scope of
|
|
// selectOrSplit().
|
|
unsigned RABasic::selectOrSplit(LiveInterval &VirtReg,
|
|
SmallVectorImpl<LiveInterval*> &SplitVRegs) {
|
|
// Populate a list of physical register spill candidates.
|
|
SmallVector<unsigned, 8> PhysRegSpillCands;
|
|
|
|
// Check for an available register in this class.
|
|
ArrayRef<unsigned> Order =
|
|
RegClassInfo.getOrder(MRI->getRegClass(VirtReg.reg));
|
|
for (ArrayRef<unsigned>::iterator I = Order.begin(), E = Order.end(); I != E;
|
|
++I) {
|
|
unsigned PhysReg = *I;
|
|
|
|
// Check interference and as a side effect, intialize queries for this
|
|
// VirtReg and its aliases.
|
|
unsigned interfReg = checkPhysRegInterference(VirtReg, PhysReg);
|
|
if (interfReg == 0) {
|
|
// Found an available register.
|
|
return PhysReg;
|
|
}
|
|
Queries[interfReg].collectInterferingVRegs(1);
|
|
LiveInterval *interferingVirtReg =
|
|
Queries[interfReg].interferingVRegs().front();
|
|
|
|
// The current VirtReg must either be spillable, or one of its interferences
|
|
// must have less spill weight.
|
|
if (interferingVirtReg->weight < VirtReg.weight ) {
|
|
PhysRegSpillCands.push_back(PhysReg);
|
|
}
|
|
}
|
|
// Try to spill another interfering reg with less spill weight.
|
|
for (SmallVectorImpl<unsigned>::iterator PhysRegI = PhysRegSpillCands.begin(),
|
|
PhysRegE = PhysRegSpillCands.end(); PhysRegI != PhysRegE; ++PhysRegI) {
|
|
|
|
if (!spillInterferences(VirtReg, *PhysRegI, SplitVRegs)) continue;
|
|
|
|
assert(checkPhysRegInterference(VirtReg, *PhysRegI) == 0 &&
|
|
"Interference after spill.");
|
|
// Tell the caller to allocate to this newly freed physical register.
|
|
return *PhysRegI;
|
|
}
|
|
|
|
// No other spill candidates were found, so spill the current VirtReg.
|
|
DEBUG(dbgs() << "spilling: " << VirtReg << '\n');
|
|
if (!VirtReg.isSpillable())
|
|
return ~0u;
|
|
LiveRangeEdit LRE(VirtReg, SplitVRegs);
|
|
spiller().spill(LRE);
|
|
|
|
// The live virtual register requesting allocation was spilled, so tell
|
|
// the caller not to allocate anything during this round.
|
|
return 0;
|
|
}
|
|
|
|
bool RABasic::runOnMachineFunction(MachineFunction &mf) {
|
|
DEBUG(dbgs() << "********** BASIC REGISTER ALLOCATION **********\n"
|
|
<< "********** Function: "
|
|
<< ((Value*)mf.getFunction())->getName() << '\n');
|
|
|
|
MF = &mf;
|
|
DEBUG(RMF = &getAnalysis<RenderMachineFunction>());
|
|
|
|
RegAllocBase::init(getAnalysis<VirtRegMap>(), getAnalysis<LiveIntervals>());
|
|
SpillerInstance.reset(createInlineSpiller(*this, *MF, *VRM));
|
|
|
|
allocatePhysRegs();
|
|
|
|
addMBBLiveIns(MF);
|
|
|
|
// Diagnostic output before rewriting
|
|
DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *VRM << "\n");
|
|
|
|
// optional HTML output
|
|
DEBUG(RMF->renderMachineFunction("After basic register allocation.", VRM));
|
|
|
|
// FIXME: Verification currently must run before VirtRegRewriter. We should
|
|
// make the rewriter a separate pass and override verifyAnalysis instead. When
|
|
// that happens, verification naturally falls under VerifyMachineCode.
|
|
#ifndef NDEBUG
|
|
if (VerifyEnabled) {
|
|
// Verify accuracy of LiveIntervals. The standard machine code verifier
|
|
// ensures that each LiveIntervals covers all uses of the virtual reg.
|
|
|
|
// FIXME: MachineVerifier is badly broken when using the standard
|
|
// spiller. Always use -spiller=inline with -verify-regalloc. Even with the
|
|
// inline spiller, some tests fail to verify because the coalescer does not
|
|
// always generate verifiable code.
|
|
MF->verify(this, "In RABasic::verify");
|
|
|
|
// Verify that LiveIntervals are partitioned into unions and disjoint within
|
|
// the unions.
|
|
verify();
|
|
}
|
|
#endif // !NDEBUG
|
|
|
|
// Run rewriter
|
|
VRM->rewrite(LIS->getSlotIndexes());
|
|
|
|
// Write out new DBG_VALUE instructions.
|
|
getAnalysis<LiveDebugVariables>().emitDebugValues(VRM);
|
|
|
|
// The pass output is in VirtRegMap. Release all the transient data.
|
|
releaseMemory();
|
|
|
|
return true;
|
|
}
|
|
|
|
FunctionPass* llvm::createBasicRegisterAllocator()
|
|
{
|
|
return new RABasic();
|
|
}
|