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//===-- RegAllocBasic.cpp - Basic Register Allocator ----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the RABasic function pass, which provides a minimal
// implementation of the basic register allocator.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "RegAllocBase.h"
#include "LiveDebugVariables.h"
#include "RenderMachineFunction.h"
#include "Spiller.h"
#include "VirtRegMap.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Function.h"
#include "llvm/PassAnalysisSupport.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <cstdlib>
#include <queue>
using namespace llvm;
static RegisterRegAlloc basicRegAlloc("basic", "basic register allocator",
createBasicRegisterAllocator);
namespace {
struct CompSpillWeight {
bool operator()(LiveInterval *A, LiveInterval *B) const {
return A->weight < B->weight;
}
};
}
namespace {
/// RABasic provides a minimal implementation of the basic register allocation
/// algorithm. It prioritizes live virtual registers by spill weight and spills
/// whenever a register is unavailable. This is not practical in production but
/// provides a useful baseline both for measuring other allocators and comparing
/// the speed of the basic algorithm against other styles of allocators.
class RABasic : public MachineFunctionPass, public RegAllocBase
{
// context
MachineFunction *MF;
// analyses
LiveStacks *LS;
RenderMachineFunction *RMF;
// state
std::auto_ptr<Spiller> SpillerInstance;
std::priority_queue<LiveInterval*, std::vector<LiveInterval*>,
CompSpillWeight> Queue;
// Scratch space. Allocated here to avoid repeated malloc calls in
// selectOrSplit().
BitVector UsableRegs;
public:
RABasic();
/// Return the pass name.
virtual const char* getPassName() const {
return "Basic Register Allocator";
}
/// RABasic analysis usage.
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual void releaseMemory();
virtual Spiller &spiller() { return *SpillerInstance; }
virtual float getPriority(LiveInterval *LI) { return LI->weight; }
virtual void enqueue(LiveInterval *LI) {
Queue.push(LI);
}
virtual LiveInterval *dequeue() {
if (Queue.empty())
return 0;
LiveInterval *LI = Queue.top();
Queue.pop();
return LI;
}
virtual unsigned selectOrSplit(LiveInterval &VirtReg,
SmallVectorImpl<LiveInterval*> &SplitVRegs);
/// Perform register allocation.
virtual bool runOnMachineFunction(MachineFunction &mf);
// Helper for spilling all live virtual registers currently unified under preg
// that interfere with the most recently queried lvr. Return true if spilling
// was successful, and append any new spilled/split intervals to splitLVRs.
bool spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
SmallVectorImpl<LiveInterval*> &SplitVRegs);
void spillReg(LiveInterval &VirtReg, unsigned PhysReg,
SmallVectorImpl<LiveInterval*> &SplitVRegs);
static char ID;
};
char RABasic::ID = 0;
} // end anonymous namespace
RABasic::RABasic(): MachineFunctionPass(ID) {
initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
initializeRegisterCoalescerPass(*PassRegistry::getPassRegistry());
initializeMachineSchedulerPass(*PassRegistry::getPassRegistry());
initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
initializeLiveStacksPass(*PassRegistry::getPassRegistry());
initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
initializeRenderMachineFunctionPass(*PassRegistry::getPassRegistry());
}
void RABasic::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AliasAnalysis>();
AU.addPreserved<AliasAnalysis>();
AU.addRequired<LiveIntervals>();
AU.addPreserved<SlotIndexes>();
AU.addRequired<LiveDebugVariables>();
AU.addPreserved<LiveDebugVariables>();
AU.addRequired<CalculateSpillWeights>();
AU.addRequired<LiveStacks>();
AU.addPreserved<LiveStacks>();
AU.addRequiredID(MachineDominatorsID);
AU.addPreservedID(MachineDominatorsID);
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addRequired<VirtRegMap>();
AU.addPreserved<VirtRegMap>();
DEBUG(AU.addRequired<RenderMachineFunction>());
MachineFunctionPass::getAnalysisUsage(AU);
}
void RABasic::releaseMemory() {
SpillerInstance.reset(0);
RegAllocBase::releaseMemory();
}
// Helper for spillInterferences() that spills all interfering vregs currently
// assigned to this physical register.
void RABasic::spillReg(LiveInterval& VirtReg, unsigned PhysReg,
SmallVectorImpl<LiveInterval*> &SplitVRegs) {
LiveIntervalUnion::Query &Q = query(VirtReg, PhysReg);
assert(Q.seenAllInterferences() && "need collectInterferences()");
const SmallVectorImpl<LiveInterval*> &PendingSpills = Q.interferingVRegs();
for (SmallVectorImpl<LiveInterval*>::const_iterator I = PendingSpills.begin(),
E = PendingSpills.end(); I != E; ++I) {
LiveInterval &SpilledVReg = **I;
DEBUG(dbgs() << "extracting from " <<
TRI->getName(PhysReg) << " " << SpilledVReg << '\n');
// Deallocate the interfering vreg by removing it from the union.
// A LiveInterval instance may not be in a union during modification!
unassign(SpilledVReg, PhysReg);
// Spill the extracted interval.
LiveRangeEdit LRE(SpilledVReg, SplitVRegs, *MF, *LIS, VRM);
spiller().spill(LRE);
}
// After extracting segments, the query's results are invalid. But keep the
// contents valid until we're done accessing pendingSpills.
Q.clear();
}
// Spill or split all live virtual registers currently unified under PhysReg
// that interfere with VirtReg. The newly spilled or split live intervals are
// returned by appending them to SplitVRegs.
bool RABasic::spillInterferences(LiveInterval &VirtReg, unsigned PhysReg,
SmallVectorImpl<LiveInterval*> &SplitVRegs) {
// Record each interference and determine if all are spillable before mutating
// either the union or live intervals.
unsigned NumInterferences = 0;
// Collect interferences assigned to any alias of the physical register.
for (const uint16_t *asI = TRI->getOverlaps(PhysReg); *asI; ++asI) {
LiveIntervalUnion::Query &QAlias = query(VirtReg, *asI);
NumInterferences += QAlias.collectInterferingVRegs();
if (QAlias.seenUnspillableVReg()) {
return false;
}
}
DEBUG(dbgs() << "spilling " << TRI->getName(PhysReg) <<
" interferences with " << VirtReg << "\n");
assert(NumInterferences > 0 && "expect interference");
// Spill each interfering vreg allocated to PhysReg or an alias.
for (const uint16_t *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI)
spillReg(VirtReg, *AliasI, SplitVRegs);
return true;
}
// Driver for the register assignment and splitting heuristics.
// 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) {
// Check for register mask interference. When live ranges cross calls, the
// set of usable registers is reduced to the callee-saved ones.
bool CrossRegMasks = LIS->checkRegMaskInterference(VirtReg, UsableRegs);
// 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;
// If PhysReg is clobbered by a register mask, it isn't useful for
// allocation or spilling.
if (CrossRegMasks && !UsableRegs.test(PhysReg))
continue;
// 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;
}
LiveIntervalUnion::Query &IntfQ = query(VirtReg, interfReg);
IntfQ.collectInterferingVRegs(1);
LiveInterval *interferingVirtReg = IntfQ.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, *MF, *LIS, VRM);
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);
// All machine operands and other references to virtual registers have been
// replaced. Remove the virtual registers and release all the transient data.
VRM->clearAllVirt();
MRI->clearVirtRegs();
releaseMemory();
return true;
}
FunctionPass* llvm::createBasicRegisterAllocator()
{
return new RABasic();
}