d9b4bdbff5
The existing analysis was already a pimpl wrapper. I have extracted legacy pass logic to a LDVImpl wrapper named `LiveDebugVariables` which is the analysis::Result now. This controls whether to activate the LDV (depending on `-live-debug-variables` and DIsubprogram) itself. The legacy and new analysis only construct the LiveDebugVariables. VirtRegRewriter will test this.
562 lines
18 KiB
C++
562 lines
18 KiB
C++
//===- StackSlotColoring.cpp - Stack slot coloring pass. ------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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/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/LiveDebugVariables.h"
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#include "llvm/CodeGen/LiveInterval.h"
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#include "llvm/CodeGen/LiveIntervalUnion.h"
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#include "llvm/CodeGen/LiveIntervals.h"
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#include "llvm/CodeGen/LiveStacks.h"
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#include "llvm/CodeGen/MachineBasicBlock.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/MachineFunction.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/MachineMemOperand.h"
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#include "llvm/CodeGen/MachineOperand.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/PseudoSourceValue.h"
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#include "llvm/CodeGen/PseudoSourceValueManager.h"
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#include "llvm/CodeGen/SlotIndexes.h"
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#include "llvm/CodeGen/TargetInstrInfo.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.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 <cassert>
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#include <cstdint>
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#include <iterator>
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#include <vector>
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using namespace llvm;
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#define DEBUG_TYPE "stack-slot-coloring"
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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 = nullptr;
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MachineFrameInfo *MFI = nullptr;
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const TargetInstrInfo *TII = nullptr;
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const MachineBlockFrequencyInfo *MBFI = nullptr;
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SlotIndexes *Indexes = nullptr;
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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<Align, 16> OrigAlignments;
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// OrigSizes - Sizes 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. This is per stack ID.
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SmallVector<BitVector, 2> AllColors;
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// NextColor - Next "color" that's not yet used. This is per stack ID.
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SmallVector<int, 2> NextColors = { -1 };
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// UsedColors - "Colors" that have been assigned. This is per stack ID
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SmallVector<BitVector, 2> UsedColors;
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// Join all intervals sharing one color into a single LiveIntervalUnion to
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// speedup range overlap test.
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class ColorAssignmentInfo {
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// Single liverange (used to avoid creation of LiveIntervalUnion).
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LiveInterval *SingleLI = nullptr;
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// LiveIntervalUnion to perform overlap test.
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LiveIntervalUnion *LIU = nullptr;
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// LiveIntervalUnion has a parameter in its constructor so doing this
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// dirty magic.
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uint8_t LIUPad[sizeof(LiveIntervalUnion)];
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public:
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~ColorAssignmentInfo() {
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if (LIU)
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LIU->~LiveIntervalUnion(); // Dirty magic again.
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}
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// Return true if LiveInterval overlaps with any
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// intervals that have already been assigned to this color.
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bool overlaps(LiveInterval *LI) const {
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if (LIU)
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return LiveIntervalUnion::Query(*LI, *LIU).checkInterference();
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return SingleLI ? SingleLI->overlaps(*LI) : false;
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}
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// Add new LiveInterval to this color.
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void add(LiveInterval *LI, LiveIntervalUnion::Allocator &Alloc) {
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assert(!overlaps(LI));
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if (LIU) {
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LIU->unify(*LI, *LI);
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} else if (SingleLI) {
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LIU = new (LIUPad) LiveIntervalUnion(Alloc);
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LIU->unify(*SingleLI, *SingleLI);
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LIU->unify(*LI, *LI);
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SingleLI = nullptr;
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} else
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SingleLI = LI;
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}
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};
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LiveIntervalUnion::Allocator LIUAlloc;
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// Assignments - Color to intervals mapping.
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SmallVector<ColorAssignmentInfo, 16> Assignments;
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public:
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static char ID; // Pass identification
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StackSlotColoring() : MachineFunctionPass(ID) {
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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<SlotIndexesWrapperPass>();
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AU.addPreserved<SlotIndexesWrapperPass>();
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AU.addRequired<LiveStacks>();
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AU.addRequired<MachineBlockFrequencyInfoWrapperPass>();
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AU.addPreserved<MachineBlockFrequencyInfoWrapperPass>();
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AU.addPreservedID(MachineDominatorsID);
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// In some Target's pipeline, register allocation (RA) might be
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// split into multiple phases based on register class. So, this pass
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// may be invoked multiple times requiring it to save these analyses to be
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// used by RA later.
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AU.addPreserved<LiveIntervalsWrapperPass>();
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AU.addPreserved<LiveDebugVariablesWrapperLegacy>();
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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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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, DEBUG_TYPE,
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"Stack Slot Coloring", false, false)
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INITIALIZE_PASS_DEPENDENCY(SlotIndexesWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LiveStacks)
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INITIALIZE_PASS_DEPENDENCY(MachineLoopInfoWrapperPass)
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INITIALIZE_PASS_END(StackSlotColoring, DEBUG_TYPE,
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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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} // end anonymous namespace
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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 (MachineBasicBlock &MBB : MF) {
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for (MachineInstr &MI : MBB) {
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for (const MachineOperand &MO : MI.operands()) {
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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.isDebugInstr())
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li.incrementWeight(
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LiveIntervals::getSpillWeight(false, true, MBFI, MI));
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}
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for (MachineMemOperand *MMO : MI.memoperands()) {
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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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// There is always at least one stack ID.
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AllColors.resize(1);
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UsedColors.resize(1);
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OrigAlignments.resize(LastFI);
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OrigSizes.resize(LastFI);
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AllColors[0].resize(LastFI);
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UsedColors[0].resize(LastFI);
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Assignments.resize(LastFI);
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using Pair = std::iterator_traits<LiveStacks::iterator>::value_type;
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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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llvm::sort(Intervals,
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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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LLVM_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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LLVM_DEBUG(li.dump());
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int FI = Register::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->getObjectAlign(FI);
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OrigSizes[FI] = MFI->getObjectSize(FI);
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auto StackID = MFI->getStackID(FI);
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if (StackID != 0) {
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AllColors.resize(StackID + 1);
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UsedColors.resize(StackID + 1);
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AllColors[StackID].resize(LastFI);
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UsedColors[StackID].resize(LastFI);
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}
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AllColors[StackID].set(FI);
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}
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LLVM_DEBUG(dbgs() << '\n');
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// Sort them by weight.
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llvm::stable_sort(SSIntervals, IntervalSorter());
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NextColors.resize(AllColors.size());
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// Get first "color".
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for (unsigned I = 0, E = AllColors.size(); I != E; ++I)
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NextColors[I] = AllColors[I].find_first();
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}
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/// ColorSlot - Assign a "color" (stack slot) to the specified stack slot.
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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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int FI = Register::stackSlot2Index(li->reg());
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uint8_t StackID = MFI->getStackID(FI);
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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[StackID].find_first();
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while (Color != -1) {
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if (!Assignments[Color].overlaps(li)) {
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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[StackID].find_next(Color);
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}
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}
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if (Color != -1 && MFI->getStackID(Color) != MFI->getStackID(FI)) {
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LLVM_DEBUG(dbgs() << "cannot share FIs with different stack IDs\n");
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Share = false;
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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(NextColors[StackID] != -1 && "No more spill slots?");
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Color = NextColors[StackID];
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UsedColors[StackID].set(Color);
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NextColors[StackID] = AllColors[StackID].find_next(NextColors[StackID]);
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}
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assert(MFI->getStackID(Color) == MFI->getStackID(FI));
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// Record the assignment.
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Assignments[Color].add(li, LIUAlloc);
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LLVM_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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Align Alignment = OrigAlignments[FI];
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if (!Share || Alignment > MFI->getObjectAlign(Color))
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MFI->setObjectAlignment(Color, Alignment);
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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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LLVM_DEBUG(dbgs() << "Color spill slot intervals:\n");
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bool Changed = false;
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for (LiveInterval *li : SSIntervals) {
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int SS = Register::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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LLVM_DEBUG(dbgs() << "\nSpill slots after coloring:\n");
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for (LiveInterval *li : SSIntervals) {
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int SS = Register::stackSlot2Index(li->reg());
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li->setWeight(SlotWeights[SS]);
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}
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// Sort them by new weight.
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llvm::stable_sort(SSIntervals, IntervalSorter());
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#ifndef NDEBUG
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for (LiveInterval *li : SSIntervals)
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LLVM_DEBUG(li->dump());
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LLVM_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 = MF.getPSVManager().getFixedStack(NewFI);
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SmallVectorImpl<MachineMemOperand *> &RefMMOs = SSRefs[SS];
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for (MachineMemOperand *MMO : RefMMOs)
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MMO->setValue(NewSV);
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}
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// Rewrite all MO_FrameIndex operands. Look for dead stores.
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for (MachineBasicBlock &MBB : MF) {
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for (MachineInstr &MI : MBB)
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RewriteInstruction(MI, SlotMapping, MF);
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RemoveDeadStores(&MBB);
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}
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// Delete unused stack slots.
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for (int StackID = 0, E = AllColors.size(); StackID != E; ++StackID) {
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int NextColor = NextColors[StackID];
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while (NextColor != -1) {
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LLVM_DEBUG(dbgs() << "Removing unused stack object fi#" << NextColor << "\n");
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MFI->RemoveStackObject(NextColor);
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NextColor = AllColors[StackID].find_next(NextColor);
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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,
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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 (MachineOperand &MO : MI.operands()) {
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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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assert(MFI->getStackID(OldFI) == MFI->getStackID(NewFI));
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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) && 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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MachineBasicBlock::iterator ProbableLoadMI = I;
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Register LoadReg;
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Register StoreReg;
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unsigned LoadSize = 0;
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unsigned StoreSize = 0;
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if (!(LoadReg = TII->isLoadFromStackSlot(*I, FirstSS, LoadSize)))
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continue;
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// Skip the ...pseudo debugging... instructions between a load and store.
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while ((NextMI != E) && NextMI->isDebugInstr()) {
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++NextMI;
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++I;
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}
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if (NextMI == E) continue;
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if (!(StoreReg = TII->isStoreToStackSlot(*NextMI, SecondSS, StoreSize)))
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|
continue;
|
|
if (FirstSS != SecondSS || LoadReg != StoreReg || FirstSS == -1 ||
|
|
LoadSize != StoreSize || !MFI->isSpillSlotObjectIndex(FirstSS))
|
|
continue;
|
|
|
|
++NumDead;
|
|
changed = true;
|
|
|
|
if (NextMI->findRegisterUseOperandIdx(LoadReg, /*TRI=*/nullptr, true) !=
|
|
-1) {
|
|
++NumDead;
|
|
toErase.push_back(&*ProbableLoadMI);
|
|
}
|
|
|
|
toErase.push_back(&*NextMI);
|
|
++I;
|
|
}
|
|
|
|
for (MachineInstr *MI : toErase) {
|
|
if (Indexes)
|
|
Indexes->removeMachineInstrFromMaps(*MI);
|
|
MI->eraseFromParent();
|
|
}
|
|
|
|
return changed;
|
|
}
|
|
|
|
bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
|
|
LLVM_DEBUG({
|
|
dbgs() << "********** Stack Slot Coloring **********\n"
|
|
<< "********** Function: " << MF.getName() << '\n';
|
|
});
|
|
|
|
if (skipFunction(MF.getFunction()))
|
|
return false;
|
|
|
|
MFI = &MF.getFrameInfo();
|
|
TII = MF.getSubtarget().getInstrInfo();
|
|
LS = &getAnalysis<LiveStacks>();
|
|
MBFI = &getAnalysis<MachineBlockFrequencyInfoWrapperPass>().getMBFI();
|
|
Indexes = &getAnalysis<SlotIndexesWrapperPass>().getSI();
|
|
|
|
bool Changed = false;
|
|
|
|
unsigned NumSlots = LS->getNumIntervals();
|
|
if (NumSlots == 0)
|
|
// Nothing to do!
|
|
return false;
|
|
|
|
// If there are calls to setjmp or sigsetjmp, don't perform stack slot
|
|
// coloring. The stack could be modified before the longjmp is executed,
|
|
// resulting in the wrong value being used afterwards.
|
|
if (MF.exposesReturnsTwice())
|
|
return false;
|
|
|
|
// Gather spill slot references
|
|
ScanForSpillSlotRefs(MF);
|
|
InitializeSlots();
|
|
Changed = ColorSlots(MF);
|
|
|
|
for (int &Next : NextColors)
|
|
Next = -1;
|
|
|
|
SSIntervals.clear();
|
|
for (auto &RefMMOs : SSRefs)
|
|
RefMMOs.clear();
|
|
SSRefs.clear();
|
|
OrigAlignments.clear();
|
|
OrigSizes.clear();
|
|
AllColors.clear();
|
|
UsedColors.clear();
|
|
Assignments.clear();
|
|
|
|
return Changed;
|
|
}
|