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The order of this container was needed at one point - so, at that point create a temporary array of pointers, sort those, then iterate them. This keeps lookup efficient (& the lesser issue, of allowing the use of emplace... ), object identity preserved, and ordered iteration in the one place that requires it. While this has no functional change, I realize it does mean allocating an extra data structure and performing a sort - so if this looks suspect to anyone regarding perf characteristics, I'm all ears. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231189 91177308-0d34-0410-b5e6-96231b3b80d8
471 lines
15 KiB
C++
471 lines
15 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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#include "llvm/CodeGen/Passes.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 "llvm/CodeGen/LiveIntervalAnalysis.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/MachineFrameInfo.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineMemOperand.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/IR/Module.h"
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#include "llvm/Support/CommandLine.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/TargetInstrInfo.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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#include <vector>
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using namespace llvm;
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#define DEBUG_TYPE "stackslotcoloring"
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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<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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namespace {
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class StackSlotColoring : public MachineFunctionPass {
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LiveStacks* LS;
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MachineFrameInfo *MFI;
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const TargetInstrInfo *TII;
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const MachineBlockFrequencyInfo *MBFI;
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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 MachineMemOperands for each spill slot.
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// MachineMemOperands can be shared between instructions, so we need
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// to be careful that renames like [FI0, FI1] -> [FI1, FI2] do not
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// become FI0 -> FI1 -> FI2.
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SmallVector<SmallVector<MachineMemOperand *, 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() :
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MachineFunctionPass(ID), NextColor(-1) {
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initializeStackSlotColoringPass(*PassRegistry::getPassRegistry());
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<SlotIndexes>();
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AU.addPreserved<SlotIndexes>();
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AU.addRequired<LiveStacks>();
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AU.addRequired<MachineBlockFrequencyInfo>();
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AU.addPreserved<MachineBlockFrequencyInfo>();
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AU.addPreservedID(MachineDominatorsID);
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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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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void RewriteInstruction(MachineInstr *MI, SmallVectorImpl<int> &SlotMapping,
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MachineFunction &MF);
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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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char &llvm::StackSlotColoringID = StackSlotColoring::ID;
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INITIALIZE_PASS_BEGIN(StackSlotColoring, "stack-slot-coloring",
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"Stack Slot Coloring", false, false)
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INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
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INITIALIZE_PASS_DEPENDENCY(LiveStacks)
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INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
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INITIALIZE_PASS_END(StackSlotColoring, "stack-slot-coloring",
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"Stack Slot Coloring", false, false)
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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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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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if (!MI->isDebugValue())
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li.weight += LiveIntervals::getSpillWeight(false, true, MBFI, MI);
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}
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for (MachineInstr::mmo_iterator MMOI = MI->memoperands_begin(),
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EE = MI->memoperands_end(); MMOI != EE; ++MMOI) {
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MachineMemOperand *MMO = *MMOI;
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if (const FixedStackPseudoSourceValue *FSV =
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dyn_cast_or_null<FixedStackPseudoSourceValue>(
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MMO->getPseudoValue())) {
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int FI = FSV->getFrameIndex();
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if (FI >= 0)
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SSRefs[FI].push_back(MMO);
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}
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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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typedef std::iterator_traits<LiveStacks::iterator>::value_type Pair;
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SmallVector<Pair *, 16> Intervals;
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Intervals.reserve(LS->getNumIntervals());
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for (auto &I : *LS)
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Intervals.push_back(&I);
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std::sort(Intervals.begin(), Intervals.end(),
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[](Pair *LHS, Pair *RHS) { return LHS->first < RHS->first; });
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// Gather all spill slots into a list.
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DEBUG(dbgs() << "Spill slot intervals:\n");
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for (auto *I : Intervals) {
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LiveInterval &li = I->second;
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DEBUG(li.dump());
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int FI = TargetRegisterInfo::stackSlot2Index(li.reg);
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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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DEBUG(dbgs() << '\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 SmallVectorImpl<LiveInterval *> &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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/// 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 = TargetRegisterInfo::stackSlot2Index(li->reg);
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DEBUG(dbgs() << "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 UsedColors(NumObjs);
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DEBUG(dbgs() << "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 = TargetRegisterInfo::stackSlot2Index(li->reg);
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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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DEBUG(dbgs() << "\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 = TargetRegisterInfo::stackSlot2Index(li->reg);
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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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DEBUG(dbgs() << '\n');
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#endif
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if (!Changed)
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return false;
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// Rewrite all MachineMemOperands.
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for (unsigned SS = 0, SE = SSRefs.size(); SS != SE; ++SS) {
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int NewFI = SlotMapping[SS];
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if (NewFI == -1 || (NewFI == (int)SS))
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continue;
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const PseudoSourceValue *NewSV = PseudoSourceValue::getFixedStack(NewFI);
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SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
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for (unsigned i = 0, e = RefMMOs.size(); i != e; ++i)
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RefMMOs[i]->setValue(NewSV);
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}
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// Rewrite all MO_FrameIndex operands. Look for dead stores.
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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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for (MachineBasicBlock::iterator MII = MBB->begin(), EE = MBB->end();
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MII != EE; ++MII)
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RewriteInstruction(MII, SlotMapping, MF);
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RemoveDeadStores(MBB);
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}
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// Delete unused stack slots.
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while (NextColor != -1) {
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DEBUG(dbgs() << "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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/// 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,
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SmallVectorImpl<int> &SlotMapping,
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MachineFunction &MF) {
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// Update the operands.
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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 OldFI = MO.getIndex();
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if (OldFI < 0)
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continue;
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int NewFI = SlotMapping[OldFI];
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if (NewFI == -1 || NewFI == OldFI)
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continue;
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MO.setIndex(NewFI);
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}
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// The MachineMemOperands have already been updated.
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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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SmallVector<MachineInstr*, 4> toErase;
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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;
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int FirstSS, SecondSS;
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if (TII->isStackSlotCopy(I, FirstSS, SecondSS) &&
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FirstSS == SecondSS &&
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FirstSS != -1) {
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++NumDead;
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changed = true;
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toErase.push_back(I);
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continue;
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}
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MachineBasicBlock::iterator NextMI = std::next(I);
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if (NextMI == MBB->end()) continue;
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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;
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if (NextMI->findRegisterUseOperandIdx(LoadReg, true, nullptr) != -1) {
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++NumDead;
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toErase.push_back(I);
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}
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toErase.push_back(NextMI);
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++I;
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}
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for (SmallVectorImpl<MachineInstr *>::iterator I = toErase.begin(),
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E = toErase.end(); I != E; ++I)
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(*I)->eraseFromParent();
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return changed;
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}
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bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
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DEBUG({
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dbgs() << "********** Stack Slot Coloring **********\n"
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<< "********** Function: " << MF.getName() << '\n';
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});
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MFI = MF.getFrameInfo();
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TII = MF.getSubtarget().getInstrInfo();
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LS = &getAnalysis<LiveStacks>();
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MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
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bool Changed = false;
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unsigned NumSlots = LS->getNumIntervals();
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if (NumSlots == 0)
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// Nothing to do!
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return false;
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// If there are calls to setjmp or sigsetjmp, don't perform stack slot
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// coloring. The stack could be modified before the longjmp is executed,
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// resulting in the wrong value being used afterwards. (See
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// <rdar://problem/8007500>.)
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if (MF.exposesReturnsTwice())
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return false;
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// Gather spill slot references
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ScanForSpillSlotRefs(MF);
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InitializeSlots();
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Changed = ColorSlots(MF);
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NextColor = -1;
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SSIntervals.clear();
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for (unsigned i = 0, e = SSRefs.size(); i != e; ++i)
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SSRefs[i].clear();
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SSRefs.clear();
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OrigAlignments.clear();
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OrigSizes.clear();
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AllColors.clear();
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UsedColors.clear();
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for (unsigned i = 0, e = Assignments.size(); i != e; ++i)
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Assignments[i].clear();
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Assignments.clear();
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return Changed;
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}
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