StackMapLivenessAnalysis.cpp revision 360784 
1//===-- StackMapLivenessAnalysis.cpp - StackMap live Out Analysis ----------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the StackMap Liveness analysis pass. The pass calculates
10// the liveness for each basic block in a function and attaches the register
11// live-out information to a stackmap or patchpoint intrinsic if present.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/ADT/Statistic.h"
16#include "llvm/CodeGen/LivePhysRegs.h"
17#include "llvm/CodeGen/MachineFrameInfo.h"
18#include "llvm/CodeGen/MachineFunction.h"
19#include "llvm/CodeGen/MachineFunctionPass.h"
20#include "llvm/CodeGen/Passes.h"
21#include "llvm/CodeGen/TargetSubtargetInfo.h"
22#include "llvm/InitializePasses.h"
23#include "llvm/Support/CommandLine.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/raw_ostream.h"
26
27using namespace llvm;
28
29#define DEBUG_TYPE "stackmaps"
30
31static cl::opt<bool> EnablePatchPointLiveness(
32    "enable-patchpoint-liveness", cl::Hidden, cl::init(true),
33    cl::desc("Enable PatchPoint Liveness Analysis Pass"));
34
35STATISTIC(NumStackMapFuncVisited, "Number of functions visited");
36STATISTIC(NumStackMapFuncSkipped, "Number of functions skipped");
37STATISTIC(NumBBsVisited,          "Number of basic blocks visited");
38STATISTIC(NumBBsHaveNoStackmap,   "Number of basic blocks with no stackmap");
39STATISTIC(NumStackMaps,           "Number of StackMaps visited");
40
41namespace {
42/// This pass calculates the liveness information for each basic block in
43/// a function and attaches the register live-out information to a patchpoint
44/// intrinsic if present.
45///
46/// This pass can be disabled via the -enable-patchpoint-liveness=false flag.
47/// The pass skips functions that don't have any patchpoint intrinsics. The
48/// information provided by this pass is optional and not required by the
49/// aformentioned intrinsic to function.
50class StackMapLiveness : public MachineFunctionPass {
51  const TargetRegisterInfo *TRI;
52  LivePhysRegs LiveRegs;
53
54public:
55  static char ID;
56
57  /// Default construct and initialize the pass.
58  StackMapLiveness();
59
60  /// Tell the pass manager which passes we depend on and what
61  /// information we preserve.
62  void getAnalysisUsage(AnalysisUsage &AU) const override;
63
64  MachineFunctionProperties getRequiredProperties() const override {
65    return MachineFunctionProperties().set(
66        MachineFunctionProperties::Property::NoVRegs);
67  }
68
69  /// Calculate the liveness information for the given machine function.
70  bool runOnMachineFunction(MachineFunction &MF) override;
71
72private:
73  /// Performs the actual liveness calculation for the function.
74  bool calculateLiveness(MachineFunction &MF);
75
76  /// Add the current register live set to the instruction.
77  void addLiveOutSetToMI(MachineFunction &MF, MachineInstr &MI);
78
79  /// Create a register mask and initialize it with the registers from
80  /// the register live set.
81  uint32_t *createRegisterMask(MachineFunction &MF) const;
82};
83} // namespace
84
85char StackMapLiveness::ID = 0;
86char &llvm::StackMapLivenessID = StackMapLiveness::ID;
87INITIALIZE_PASS(StackMapLiveness, "stackmap-liveness",
88                "StackMap Liveness Analysis", false, false)
89
90/// Default construct and initialize the pass.
91StackMapLiveness::StackMapLiveness() : MachineFunctionPass(ID) {
92  initializeStackMapLivenessPass(*PassRegistry::getPassRegistry());
93}
94
95/// Tell the pass manager which passes we depend on and what information we
96/// preserve.
97void StackMapLiveness::getAnalysisUsage(AnalysisUsage &AU) const {
98  // We preserve all information.
99  AU.setPreservesAll();
100  AU.setPreservesCFG();
101  MachineFunctionPass::getAnalysisUsage(AU);
102}
103
104/// Calculate the liveness information for the given machine function.
105bool StackMapLiveness::runOnMachineFunction(MachineFunction &MF) {
106  if (!EnablePatchPointLiveness)
107    return false;
108
109  LLVM_DEBUG(dbgs() << "********** COMPUTING STACKMAP LIVENESS: "
110                    << MF.getName() << " **********\n");
111  TRI = MF.getSubtarget().getRegisterInfo();
112  ++NumStackMapFuncVisited;
113
114  // Skip this function if there are no patchpoints to process.
115  if (!MF.getFrameInfo().hasPatchPoint()) {
116    ++NumStackMapFuncSkipped;
117    return false;
118  }
119  return calculateLiveness(MF);
120}
121
122/// Performs the actual liveness calculation for the function.
123bool StackMapLiveness::calculateLiveness(MachineFunction &MF) {
124  bool HasChanged = false;
125  // For all basic blocks in the function.
126  for (auto &MBB : MF) {
127    LLVM_DEBUG(dbgs() << "****** BB " << MBB.getName() << " ******\n");
128    LiveRegs.init(*TRI);
129    // FIXME: This should probably be addLiveOuts().
130    LiveRegs.addLiveOutsNoPristines(MBB);
131    bool HasStackMap = false;
132    // Reverse iterate over all instructions and add the current live register
133    // set to an instruction if we encounter a patchpoint instruction.
134    for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) {
135      if (I->getOpcode() == TargetOpcode::PATCHPOINT) {
136        addLiveOutSetToMI(MF, *I);
137        HasChanged = true;
138        HasStackMap = true;
139        ++NumStackMaps;
140      }
141      LLVM_DEBUG(dbgs() << "   " << LiveRegs << "   " << *I);
142      LiveRegs.stepBackward(*I);
143    }
144    ++NumBBsVisited;
145    if (!HasStackMap)
146      ++NumBBsHaveNoStackmap;
147  }
148  return HasChanged;
149}
150
151/// Add the current register live set to the instruction.
152void StackMapLiveness::addLiveOutSetToMI(MachineFunction &MF,
153                                         MachineInstr &MI) {
154  uint32_t *Mask = createRegisterMask(MF);
155  MachineOperand MO = MachineOperand::CreateRegLiveOut(Mask);
156  MI.addOperand(MF, MO);
157}
158
159/// Create a register mask and initialize it with the registers from the
160/// register live set.
161uint32_t *StackMapLiveness::createRegisterMask(MachineFunction &MF) const {
162  // The mask is owned and cleaned up by the Machine Function.
163  uint32_t *Mask = MF.allocateRegMask();
164  for (auto Reg : LiveRegs)
165    Mask[Reg / 32] |= 1U << (Reg % 32);
166
167  // Give the target a chance to adjust the mask.
168  TRI->adjustStackMapLiveOutMask(Mask);
169
170  return Mask;
171}
172