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