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a92f4c62f1
two fixes with one about error verify-regalloc reported, and another about live range update of phi after rematerialization. r265547: Replace analyzeSiblingValues with new algorithm to fix its compile time issue. The patch is to solve PR17409 and its duplicates. analyzeSiblingValues is a N x N complexity algorithm where N is the number of siblings generated by reg splitting. Although it causes siginificant compile time issue when N is large, it is also important for performance since it removes redundent spills and enables rematerialization. To solve the compile time issue, the patch removes analyzeSiblingValues and replaces it with lower cost alternatives containing two parts. The first part creates a new spill hoisting method in postOptimization of register allocation. It does spill hoisting at once after all the spills are generated instead of inside every instance of selectOrSplit. The second part queries the define expr of the original register for rematerializaiton and keep it always available during register allocation even if it is already dead. It deletes those dead instructions only in postOptimization. With the two parts in the patch, it can remove analyzeSiblingValues without sacrificing performance. Patches on top of r265547: r265610 "Fix the compare-clang diff error introduced by r265547." r265639 "Fix the sanitizer bootstrap error in r265547." r265657 "InlineSpiller.cpp: Escap \@ in r265547. [-Wdocumentation]" Differential Revision: http://reviews.llvm.org/D15302 Differential Revision: http://reviews.llvm.org/D18934 Differential Revision: http://reviews.llvm.org/D18935 Differential Revision: http://reviews.llvm.org/D18936 llvm-svn: 266162
299 lines
10 KiB
C++
299 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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#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/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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#define DEBUG_TYPE "regalloc"
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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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std::unique_ptr<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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const char* getPassName() const override {
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return "Basic Register Allocator";
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}
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/// RABasic analysis usage.
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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void releaseMemory() override;
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Spiller &spiller() override { return *SpillerInstance; }
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void enqueue(LiveInterval *LI) override {
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Queue.push(LI);
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}
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LiveInterval *dequeue() override {
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if (Queue.empty())
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return nullptr;
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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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unsigned selectOrSplit(LiveInterval &VirtReg,
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SmallVectorImpl<unsigned> &SplitVRegs) override;
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/// Perform register allocation.
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bool runOnMachineFunction(MachineFunction &mf) override;
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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<unsigned> &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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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<AAResultsWrapperPass>();
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AU.addPreserved<AAResultsWrapperPass>();
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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<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();
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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<unsigned> &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, nullptr, &DeadRemats);
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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<unsigned> &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, Matrix);
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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, nullptr, &DeadRemats);
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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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calculateSpillWeightsAndHints(*LIS, *MF, VRM,
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getAnalysis<MachineLoopInfo>(),
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getAnalysis<MachineBlockFrequencyInfo>());
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SpillerInstance.reset(createInlineSpiller(*this, *MF, *VRM));
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allocatePhysRegs();
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postOptimization();
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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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