210fc62a91
VirtRegMap keeps track of allocations so it knows what's not used. As a horrible hack, the stack coloring can color spill slots with *free* registers. That is, it replace reload and spills with copies from and to the free register. It unfold instructions that load and store the spill slot and replace them with register using variants. Not yet enabled. This is part 1. More coming. llvm-svn: 70787
568 lines
19 KiB
C++
568 lines
19 KiB
C++
//===-- StackSlotColoring.cpp - Stack slot coloring pass. -----------------===//
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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 implements the stack slot coloring pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "stackcoloring"
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#include "VirtRegMap.h"
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#include "llvm/CodeGen/Passes.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/MachineFrameInfo.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/PseudoSourceValue.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/ADT/BitVector.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include <vector>
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using namespace llvm;
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static cl::opt<bool>
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DisableSharing("no-stack-slot-sharing",
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cl::init(false), cl::Hidden,
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cl::desc("Suppress slot sharing during stack coloring"));
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static cl::opt<bool>
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ColorWithRegs("-color-ss-with-regs",
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cl::init(false), cl::Hidden,
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cl::desc("Color stack slots with free registers"));
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static cl::opt<int> DCELimit("ssc-dce-limit", cl::init(-1), cl::Hidden);
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STATISTIC(NumEliminated, "Number of stack slots eliminated due to coloring");
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STATISTIC(NumDead, "Number of trivially dead stack accesses eliminated");
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STATISTIC(NumRegRepl, "Number of stack slot refs replaced with reg refs");
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namespace {
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class VISIBILITY_HIDDEN StackSlotColoring : public MachineFunctionPass {
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LiveStacks* LS;
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VirtRegMap* VRM;
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MachineFrameInfo *MFI;
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MachineRegisterInfo *MRI;
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const TargetInstrInfo *TII;
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const TargetRegisterInfo *TRI;
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const MachineLoopInfo *loopInfo;
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// SSIntervals - Spill slot intervals.
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std::vector<LiveInterval*> SSIntervals;
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// SSRefs - Keep a list of frame index references for each spill slot.
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SmallVector<SmallVector<MachineInstr*, 8>, 16> SSRefs;
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// OrigAlignments - Alignments of stack objects before coloring.
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SmallVector<unsigned, 16> OrigAlignments;
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// OrigSizes - Sizess of stack objects before coloring.
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SmallVector<unsigned, 16> OrigSizes;
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// AllColors - If index is set, it's a spill slot, i.e. color.
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// FIXME: This assumes PEI locate spill slot with smaller indices
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// closest to stack pointer / frame pointer. Therefore, smaller
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// index == better color.
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BitVector AllColors;
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// NextColor - Next "color" that's not yet used.
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int NextColor;
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// UsedColors - "Colors" that have been assigned.
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BitVector UsedColors;
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// Assignments - Color to intervals mapping.
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SmallVector<SmallVector<LiveInterval*,4>, 16> Assignments;
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public:
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static char ID; // Pass identification
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StackSlotColoring() : MachineFunctionPass(&ID), NextColor(-1) {}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LiveStacks>();
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AU.addRequired<VirtRegMap>();
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AU.addPreserved<VirtRegMap>();
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AU.addRequired<MachineLoopInfo>();
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AU.addPreserved<MachineLoopInfo>();
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AU.addPreservedID(MachineDominatorsID);
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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virtual bool runOnMachineFunction(MachineFunction &MF);
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virtual const char* getPassName() const {
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return "Stack Slot Coloring";
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}
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private:
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void InitializeSlots();
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void ScanForSpillSlotRefs(MachineFunction &MF);
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bool OverlapWithAssignments(LiveInterval *li, int Color) const;
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int ColorSlot(LiveInterval *li);
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bool ColorSlots(MachineFunction &MF);
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bool ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
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SmallVector<SmallVector<int, 4>, 16> &RevMap,
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BitVector &SlotIsReg);
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void RewriteInstruction(MachineInstr *MI, int OldFI, int NewFI,
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MachineFunction &MF);
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void UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
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unsigned Reg, MachineFunction &MF);
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bool AllMemRefsCanBeUnfolded(int SS);
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bool RemoveDeadStores(MachineBasicBlock* MBB);
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};
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} // end anonymous namespace
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char StackSlotColoring::ID = 0;
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static RegisterPass<StackSlotColoring>
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X("stack-slot-coloring", "Stack Slot Coloring");
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FunctionPass *llvm::createStackSlotColoringPass() {
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return new StackSlotColoring();
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}
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namespace {
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// IntervalSorter - Comparison predicate that sort live intervals by
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// their weight.
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struct IntervalSorter {
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bool operator()(LiveInterval* LHS, LiveInterval* RHS) const {
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return LHS->weight > RHS->weight;
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}
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};
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}
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/// ScanForSpillSlotRefs - Scan all the machine instructions for spill slot
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/// references and update spill slot weights.
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void StackSlotColoring::ScanForSpillSlotRefs(MachineFunction &MF) {
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SSRefs.resize(MFI->getObjectIndexEnd());
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// FIXME: Need the equivalent of MachineRegisterInfo for frameindex operands.
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for (MachineFunction::iterator MBBI = MF.begin(), E = MF.end();
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MBBI != E; ++MBBI) {
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MachineBasicBlock *MBB = &*MBBI;
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unsigned loopDepth = loopInfo->getLoopDepth(MBB);
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for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
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MII != EE; ++MII) {
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MachineInstr *MI = &*MII;
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (!MO.isFI())
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continue;
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int FI = MO.getIndex();
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if (FI < 0)
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continue;
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if (!LS->hasInterval(FI))
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continue;
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LiveInterval &li = LS->getInterval(FI);
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li.weight += LiveIntervals::getSpillWeight(false, true, loopDepth);
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SSRefs[FI].push_back(MI);
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}
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}
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}
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}
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/// InitializeSlots - Process all spill stack slot liveintervals and add them
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/// to a sorted (by weight) list.
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void StackSlotColoring::InitializeSlots() {
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int LastFI = MFI->getObjectIndexEnd();
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OrigAlignments.resize(LastFI);
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OrigSizes.resize(LastFI);
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AllColors.resize(LastFI);
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UsedColors.resize(LastFI);
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Assignments.resize(LastFI);
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// Gather all spill slots into a list.
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DOUT << "Spill slot intervals:\n";
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for (LiveStacks::iterator i = LS->begin(), e = LS->end(); i != e; ++i) {
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LiveInterval &li = i->second;
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DEBUG(li.dump());
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int FI = li.getStackSlotIndex();
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if (MFI->isDeadObjectIndex(FI))
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continue;
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SSIntervals.push_back(&li);
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OrigAlignments[FI] = MFI->getObjectAlignment(FI);
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OrigSizes[FI] = MFI->getObjectSize(FI);
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AllColors.set(FI);
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}
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DOUT << '\n';
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// Sort them by weight.
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std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
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// Get first "color".
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NextColor = AllColors.find_first();
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}
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/// OverlapWithAssignments - Return true if LiveInterval overlaps with any
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/// LiveIntervals that have already been assigned to the specified color.
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bool
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StackSlotColoring::OverlapWithAssignments(LiveInterval *li, int Color) const {
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const SmallVector<LiveInterval*,4> &OtherLIs = Assignments[Color];
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for (unsigned i = 0, e = OtherLIs.size(); i != e; ++i) {
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LiveInterval *OtherLI = OtherLIs[i];
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if (OtherLI->overlaps(*li))
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return true;
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}
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return false;
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}
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/// ColorSlotsWithFreeRegs - If there are any free registers available, try
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/// replacing spill slots references with registers instead.
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bool
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StackSlotColoring::ColorSlotsWithFreeRegs(SmallVector<int, 16> &SlotMapping,
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SmallVector<SmallVector<int, 4>, 16> &RevMap,
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BitVector &SlotIsReg) {
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if (!ColorWithRegs || !VRM->HasUnusedRegisters())
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return false;
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bool Changed = false;
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DOUT << "Assigning unused registers to spill slots:\n";
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for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
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LiveInterval *li = SSIntervals[i];
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int SS = li->getStackSlotIndex();
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if (!UsedColors[SS])
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continue;
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// Get the largest common sub- register class of all the stack slots that
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// are colored to this stack slot.
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const TargetRegisterClass *RC = 0;
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for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
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int RSS = RevMap[SS][j];
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const TargetRegisterClass *RRC = LS->getIntervalRegClass(RSS);
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if (!RC)
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RC = RRC;
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else
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RC = getCommonSubClass(RC, RRC);
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}
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// If it's not colored to another stack slot, try coloring it
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// to a "free" register.
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if (!RC)
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continue;
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unsigned Reg = VRM->getFirstUnusedRegister(RC);
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if (!Reg)
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continue;
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bool IsSafe = true;
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for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
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int RSS = RevMap[SS][j];
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if (!AllMemRefsCanBeUnfolded(RSS)) {
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IsSafe = false;
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break;
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}
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}
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if (!IsSafe)
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// Try color the next spill slot.
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continue;
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DOUT << "Assigning fi#" << SS << " to " << TRI->getName(Reg)
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<< ", which in turn means...\n";
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// Register and its sub-registers are no longer free.
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VRM->setRegisterUsed(Reg);
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// If reg is a callee-saved register, it will have to be spilled in
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// the prologue.
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MRI->setPhysRegUsed(Reg);
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for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
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VRM->setRegisterUsed(*AS);
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MRI->setPhysRegUsed(*AS);
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}
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// This spill slot is dead after the rewrites
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MFI->RemoveStackObject(SS);
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// Remember all these FI references will have to be unfolded.
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for (unsigned j = 0, ee = RevMap[SS].size(); j != ee; ++j) {
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int RSS = RevMap[SS][j];
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DOUT << " Assigning fi#" << RSS << " to " << TRI->getName(Reg) << '\n';
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SlotMapping[RSS] = Reg;
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SlotIsReg.set(RSS);
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}
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++NumEliminated;
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Changed = true;
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}
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DOUT << '\n';
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return Changed;
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}
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/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
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///
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int StackSlotColoring::ColorSlot(LiveInterval *li) {
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int Color = -1;
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bool Share = false;
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if (!DisableSharing) {
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// Check if it's possible to reuse any of the used colors.
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Color = UsedColors.find_first();
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while (Color != -1) {
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if (!OverlapWithAssignments(li, Color)) {
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Share = true;
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++NumEliminated;
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break;
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}
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Color = UsedColors.find_next(Color);
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}
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}
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// Assign it to the first available color (assumed to be the best) if it's
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// not possible to share a used color with other objects.
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if (!Share) {
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assert(NextColor != -1 && "No more spill slots?");
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Color = NextColor;
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UsedColors.set(Color);
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NextColor = AllColors.find_next(NextColor);
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}
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// Record the assignment.
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Assignments[Color].push_back(li);
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int FI = li->getStackSlotIndex();
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DOUT << "Assigning fi#" << FI << " to fi#" << Color << "\n";
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// Change size and alignment of the allocated slot. If there are multiple
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// objects sharing the same slot, then make sure the size and alignment
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// are large enough for all.
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unsigned Align = OrigAlignments[FI];
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if (!Share || Align > MFI->getObjectAlignment(Color))
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MFI->setObjectAlignment(Color, Align);
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int64_t Size = OrigSizes[FI];
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if (!Share || Size > MFI->getObjectSize(Color))
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MFI->setObjectSize(Color, Size);
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return Color;
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}
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/// Colorslots - Color all spill stack slots and rewrite all frameindex machine
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/// operands in the function.
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bool StackSlotColoring::ColorSlots(MachineFunction &MF) {
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unsigned NumObjs = MFI->getObjectIndexEnd();
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SmallVector<int, 16> SlotMapping(NumObjs, -1);
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SmallVector<float, 16> SlotWeights(NumObjs, 0.0);
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SmallVector<SmallVector<int, 4>, 16> RevMap(NumObjs);
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BitVector SlotIsReg(NumObjs);
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BitVector UsedColors(NumObjs);
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DOUT << "Color spill slot intervals:\n";
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bool Changed = false;
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for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
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LiveInterval *li = SSIntervals[i];
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int SS = li->getStackSlotIndex();
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int NewSS = ColorSlot(li);
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assert(NewSS >= 0 && "Stack coloring failed?");
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SlotMapping[SS] = NewSS;
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RevMap[NewSS].push_back(SS);
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SlotWeights[NewSS] += li->weight;
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UsedColors.set(NewSS);
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Changed |= (SS != NewSS);
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}
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DOUT << "\nSpill slots after coloring:\n";
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for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i) {
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LiveInterval *li = SSIntervals[i];
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int SS = li->getStackSlotIndex();
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li->weight = SlotWeights[SS];
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}
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// Sort them by new weight.
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std::stable_sort(SSIntervals.begin(), SSIntervals.end(), IntervalSorter());
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#ifndef NDEBUG
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for (unsigned i = 0, e = SSIntervals.size(); i != e; ++i)
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DEBUG(SSIntervals[i]->dump());
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DOUT << '\n';
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#endif
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// Can we "color" a stack slot with a unused register?
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Changed |= ColorSlotsWithFreeRegs(SlotMapping, RevMap, SlotIsReg);
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if (!Changed)
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return false;
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// Rewrite all MO_FrameIndex operands.
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for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
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bool isReg = SlotIsReg[SS];
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int NewFI = SlotMapping[SS];
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if (NewFI == -1 || (NewFI == (int)SS && !isReg))
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continue;
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SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
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for (unsigned i = 0, e = RefMIs.size(); i != e; ++i)
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if (isReg)
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// Rewrite to use a register instead.
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UnfoldAndRewriteInstruction(RefMIs[i], SS, NewFI, MF);
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else
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RewriteInstruction(RefMIs[i], SS, NewFI, MF);
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}
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// Delete unused stack slots.
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while (NextColor != -1) {
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DOUT << "Removing unused stack object fi#" << NextColor << "\n";
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MFI->RemoveStackObject(NextColor);
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NextColor = AllColors.find_next(NextColor);
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}
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return true;
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}
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/// AllMemRefsCanBeUnfolded - Return true if all references of the specified
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/// spill slot index can be unfolded.
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bool StackSlotColoring::AllMemRefsCanBeUnfolded(int SS) {
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SmallVector<MachineInstr*, 8> &RefMIs = SSRefs[SS];
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for (unsigned i = 0, e = RefMIs.size(); i != e; ++i) {
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MachineInstr *MI = RefMIs[i];
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if (!TII->getOpcodeAfterMemoryUnfold(MI->getOpcode(), false, false))
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return false;
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for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
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MachineOperand &MO = MI->getOperand(j);
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if (MO.isFI() && MO.getIndex() != SS)
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// If it uses another frameindex, we can, currently* unfold it.
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return false;
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}
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}
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return true;
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}
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/// RewriteInstruction - Rewrite specified instruction by replacing references
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/// to old frame index with new one.
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void StackSlotColoring::RewriteInstruction(MachineInstr *MI, int OldFI,
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int NewFI, MachineFunction &MF) {
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for (unsigned i = 0, ee = MI->getNumOperands(); i != ee; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (!MO.isFI())
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continue;
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int FI = MO.getIndex();
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if (FI != OldFI)
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continue;
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MO.setIndex(NewFI);
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}
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// Update the MachineMemOperand for the new memory location.
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// FIXME: We need a better method of managing these too.
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SmallVector<MachineMemOperand, 2> MMOs(MI->memoperands_begin(),
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MI->memoperands_end());
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MI->clearMemOperands(MF);
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const Value *OldSV = PseudoSourceValue::getFixedStack(OldFI);
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for (unsigned i = 0, ee = MMOs.size(); i != ee; ++i) {
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if (MMOs[i].getValue() != OldSV)
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MI->addMemOperand(MF, MMOs[i]);
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else {
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MachineMemOperand MMO(PseudoSourceValue::getFixedStack(NewFI),
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MMOs[i].getFlags(), MMOs[i].getOffset(),
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MMOs[i].getSize(), MMOs[i].getAlignment());
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MI->addMemOperand(MF, MMO);
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}
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}
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}
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/// UnfoldAndRewriteInstruction - Rewrite specified instruction by unfolding
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/// folded memory references and replacing those references with register
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/// references instead.
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void StackSlotColoring::UnfoldAndRewriteInstruction(MachineInstr *MI, int OldFI,
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unsigned Reg,
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MachineFunction &MF) {
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MachineBasicBlock *MBB = MI->getParent();
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SmallVector<MachineInstr*, 4> NewMIs;
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bool Success = TII->unfoldMemoryOperand(MF, MI, Reg, false, false, NewMIs);
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assert(Success && "Failed to unfold!");
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MBB->insert(MI, NewMIs[0]);
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MBB->erase(MI);
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++NumRegRepl;
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}
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/// RemoveDeadStores - Scan through a basic block and look for loads followed
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/// by stores. If they're both using the same stack slot, then the store is
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/// definitely dead. This could obviously be much more aggressive (consider
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|
/// pairs with instructions between them), but such extensions might have a
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|
/// considerable compile time impact.
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|
bool StackSlotColoring::RemoveDeadStores(MachineBasicBlock* MBB) {
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// FIXME: This could be much more aggressive, but we need to investigate
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|
// the compile time impact of doing so.
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|
bool changed = false;
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|
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|
SmallVector<MachineInstr*, 4> toErase;
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|
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for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
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|
I != E; ++I) {
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|
if (DCELimit != -1 && (int)NumDead >= DCELimit)
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|
break;
|
|
|
|
MachineBasicBlock::iterator NextMI = next(I);
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|
if (NextMI == MBB->end()) continue;
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|
|
|
int FirstSS, SecondSS;
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|
unsigned LoadReg = 0;
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|
unsigned StoreReg = 0;
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|
if (!(LoadReg = TII->isLoadFromStackSlot(I, FirstSS))) continue;
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|
if (!(StoreReg = TII->isStoreToStackSlot(NextMI, SecondSS))) continue;
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|
if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1) continue;
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|
|
|
++NumDead;
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|
changed = true;
|
|
|
|
if (NextMI->findRegisterUseOperandIdx(LoadReg, true, 0) != -1) {
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|
++NumDead;
|
|
toErase.push_back(I);
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|
}
|
|
|
|
toErase.push_back(NextMI);
|
|
++I;
|
|
}
|
|
|
|
for (SmallVector<MachineInstr*, 4>::iterator I = toErase.begin(),
|
|
E = toErase.end(); I != E; ++I)
|
|
(*I)->eraseFromParent();
|
|
|
|
return changed;
|
|
}
|
|
|
|
|
|
bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
|
|
DOUT << "********** Stack Slot Coloring **********\n";
|
|
|
|
MFI = MF.getFrameInfo();
|
|
MRI = &MF.getRegInfo();
|
|
TII = MF.getTarget().getInstrInfo();
|
|
TRI = MF.getTarget().getRegisterInfo();
|
|
LS = &getAnalysis<LiveStacks>();
|
|
VRM = &getAnalysis<VirtRegMap>();
|
|
loopInfo = &getAnalysis<MachineLoopInfo>();
|
|
|
|
bool Changed = false;
|
|
|
|
unsigned NumSlots = LS->getNumIntervals();
|
|
if (NumSlots < 2) {
|
|
if (NumSlots == 0 || !VRM->HasUnusedRegisters())
|
|
// Nothing to do!
|
|
return false;
|
|
}
|
|
|
|
// Gather spill slot references
|
|
ScanForSpillSlotRefs(MF);
|
|
InitializeSlots();
|
|
Changed = ColorSlots(MF);
|
|
|
|
NextColor = -1;
|
|
SSIntervals.clear();
|
|
for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
|
|
SSRefs[i].clear();
|
|
SSRefs.clear();
|
|
OrigAlignments.clear();
|
|
OrigSizes.clear();
|
|
AllColors.clear();
|
|
UsedColors.clear();
|
|
for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
|
|
Assignments[i].clear();
|
|
Assignments.clear();
|
|
|
|
if (Changed) {
|
|
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
|
|
Changed |= RemoveDeadStores(I);
|
|
}
|
|
|
|
return Changed;
|
|
}
|