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The main advantages here are way better heuristics, taking into account not just loop depth but also __builtin_expect and other static heuristics and will eventually learn how to use profile info. Most of the work in this patch is pushing the MachineBlockFrequencyInfo analysis into the right places. This is good for a 5% speedup on zlib's deflate (x86_64), there were some very unfortunate spilling decisions in its hottest loop in longest_match(). Other benchmarks I tried were mostly neutral. This changes register allocation in subtle ways, update the tests for it. 2012-02-20-MachineCPBug.ll was deleted as it's very fragile and the instruction it looked for was gone already (but the FileCheck pattern picked up unrelated stuff). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184105 91177308-0d34-0410-b5e6-96231b3b80d8
297 lines
10 KiB
C++
297 lines
10 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 "llvm/CodeGen/Passes.h"
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#include "AllocationOrder.h"
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#include "LiveDebugVariables.h"
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#include "RegAllocBase.h"
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#include "Spiller.h"
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#include "llvm/Analysis/AliasAnalysis.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/LiveRangeEdit.h"
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#include "llvm/CodeGen/LiveRegMatrix.h"
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#include "llvm/CodeGen/LiveStackAnalysis.h"
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#include "llvm/CodeGen/MachineBlockFrequencyInfo.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/RegAllocRegistry.h"
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#include "llvm/CodeGen/VirtRegMap.h"
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#include "llvm/PassAnalysisSupport.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include <cstdlib>
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#include <queue>
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using namespace llvm;
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static RegisterRegAlloc basicRegAlloc("basic", "basic register allocator",
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createBasicRegisterAllocator);
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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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// state
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OwningPtr<Spiller> SpillerInstance;
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std::priority_queue<LiveInterval*, std::vector<LiveInterval*>,
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CompSpillWeight> Queue;
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// Scratch space. Allocated here to avoid repeated malloc calls in
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// selectOrSplit().
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BitVector UsableRegs;
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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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// Helper for spilling all live virtual registers currently unified under preg
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// that interfere with the most recently queried lvr. Return true if spilling
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// was successful, and append any new spilled/split intervals to splitLVRs.
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bool spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
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SmallVectorImpl<LiveInterval*> &SplitVRegs);
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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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initializeRegisterCoalescerPass(*PassRegistry::getPassRegistry());
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initializeMachineSchedulerPass(*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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initializeLiveRegMatrixPass(*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<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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AU.addRequired<CalculateSpillWeights>();
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AU.addRequired<LiveStacks>();
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AU.addPreserved<LiveStacks>();
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AU.addRequired<MachineBlockFrequencyInfo>();
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AU.addPreserved<MachineBlockFrequencyInfo>();
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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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AU.addRequired<LiveRegMatrix>();
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AU.addPreserved<LiveRegMatrix>();
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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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}
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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 RABasic::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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SmallVector<LiveInterval*, 8> Intfs;
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// Collect interferences assigned to any alias of the physical register.
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for (MCRegUnitIterator Units(PhysReg, TRI); Units.isValid(); ++Units) {
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LiveIntervalUnion::Query &Q = Matrix->query(VirtReg, *Units);
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Q.collectInterferingVRegs();
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if (Q.seenUnspillableVReg())
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return false;
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for (unsigned i = Q.interferingVRegs().size(); i; --i) {
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LiveInterval *Intf = Q.interferingVRegs()[i - 1];
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if (!Intf->isSpillable() || Intf->weight > VirtReg.weight)
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return false;
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Intfs.push_back(Intf);
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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(!Intfs.empty() && "expected interference");
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// Spill each interfering vreg allocated to PhysReg or an alias.
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for (unsigned i = 0, e = Intfs.size(); i != e; ++i) {
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LiveInterval &Spill = *Intfs[i];
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// Skip duplicates.
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if (!VRM->hasPhys(Spill.reg))
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continue;
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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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Matrix->unassign(Spill);
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// Spill the extracted interval.
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LiveRangeEdit LRE(&Spill, SplitVRegs, *MF, *LIS, VRM);
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spiller().spill(LRE);
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}
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return true;
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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.
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//
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// This is a minimal implementation of register assignment and splitting that
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// spills whenever we run out of registers.
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//
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// selectOrSplit can only be called once per live virtual register. We then do a
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// single interference test for each register the correct class until we find an
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// available register. So, the number of interference tests in the worst case is
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// |vregs| * |machineregs|. And since the number of interference tests is
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// minimal, there is no value in caching them outside the scope of
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// selectOrSplit().
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unsigned RABasic::selectOrSplit(LiveInterval &VirtReg,
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SmallVectorImpl<LiveInterval*> &SplitVRegs) {
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// Populate a list of physical register spill candidates.
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SmallVector<unsigned, 8> PhysRegSpillCands;
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// Check for an available register in this class.
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AllocationOrder Order(VirtReg.reg, *VRM, RegClassInfo);
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while (unsigned PhysReg = Order.next()) {
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// Check for interference in PhysReg
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switch (Matrix->checkInterference(VirtReg, PhysReg)) {
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case LiveRegMatrix::IK_Free:
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// PhysReg is available, allocate it.
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return PhysReg;
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case LiveRegMatrix::IK_VirtReg:
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// Only virtual registers in the way, we may be able to spill them.
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PhysRegSpillCands.push_back(PhysReg);
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continue;
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default:
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// RegMask or RegUnit interference.
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continue;
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}
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}
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// Try to spill another interfering reg with less spill weight.
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for (SmallVectorImpl<unsigned>::iterator PhysRegI = PhysRegSpillCands.begin(),
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PhysRegE = PhysRegSpillCands.end(); PhysRegI != PhysRegE; ++PhysRegI) {
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if (!spillInterferences(VirtReg, *PhysRegI, SplitVRegs))
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continue;
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assert(!Matrix->checkInterference(VirtReg, *PhysRegI) &&
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"Interference after spill.");
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// Tell the caller to allocate to this newly freed physical register.
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return *PhysRegI;
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}
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// No other spill candidates were found, so spill the current VirtReg.
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DEBUG(dbgs() << "spilling: " << VirtReg << '\n');
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if (!VirtReg.isSpillable())
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return ~0u;
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LiveRangeEdit LRE(&VirtReg, SplitVRegs, *MF, *LIS, VRM);
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spiller().spill(LRE);
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// The live virtual register requesting allocation was spilled, so tell
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// the caller not to allocate anything during this round.
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return 0;
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}
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bool RABasic::runOnMachineFunction(MachineFunction &mf) {
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DEBUG(dbgs() << "********** BASIC REGISTER ALLOCATION **********\n"
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<< "********** Function: "
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<< mf.getName() << '\n');
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MF = &mf;
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RegAllocBase::init(getAnalysis<VirtRegMap>(),
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getAnalysis<LiveIntervals>(),
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getAnalysis<LiveRegMatrix>());
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SpillerInstance.reset(createInlineSpiller(*this, *MF, *VRM));
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allocatePhysRegs();
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// Diagnostic output before rewriting
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DEBUG(dbgs() << "Post alloc VirtRegMap:\n" << *VRM << "\n");
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releaseMemory();
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return true;
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}
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FunctionPass* llvm::createBasicRegisterAllocator()
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{
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return new RABasic();
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}
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