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      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   MachineFunctionPass::getAnalysisUsage(AU);
     98 }
     99 
    100 /// Calculate the liveness information for the given machine function.
    101 bool StackMapLiveness::runOnMachineFunction(MachineFunction &MF) {
    102   if (!EnablePatchPointLiveness)
    103     return false;
    104 
    105   DEBUG(dbgs() << "********** COMPUTING STACKMAP LIVENESS: " << MF.getName()
    106                << " **********\n");
    107   TRI = MF.getSubtarget().getRegisterInfo();
    108   ++NumStackMapFuncVisited;
    109 
    110   // Skip this function if there are no patchpoints to process.
    111   if (!MF.getFrameInfo()->hasPatchPoint()) {
    112     ++NumStackMapFuncSkipped;
    113     return false;
    114   }
    115   return calculateLiveness(MF);
    116 }
    117 
    118 /// Performs the actual liveness calculation for the function.
    119 bool StackMapLiveness::calculateLiveness(MachineFunction &MF) {
    120   bool HasChanged = false;
    121   // For all basic blocks in the function.
    122   for (auto &MBB : MF) {
    123     DEBUG(dbgs() << "****** BB " << MBB.getName() << " ******\n");
    124     LiveRegs.init(TRI);
    125     LiveRegs.addLiveOuts(&MBB);
    126     bool HasStackMap = false;
    127     // Reverse iterate over all instructions and add the current live register
    128     // set to an instruction if we encounter a patchpoint instruction.
    129     for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) {
    130       if (I->getOpcode() == TargetOpcode::PATCHPOINT) {
    131         addLiveOutSetToMI(MF, *I);
    132         HasChanged = true;
    133         HasStackMap = true;
    134         ++NumStackMaps;
    135       }
    136       DEBUG(dbgs() << "   " << LiveRegs << "   " << *I);
    137       LiveRegs.stepBackward(*I);
    138     }
    139     ++NumBBsVisited;
    140     if (!HasStackMap)
    141       ++NumBBsHaveNoStackmap;
    142   }
    143   return HasChanged;
    144 }
    145 
    146 /// Add the current register live set to the instruction.
    147 void StackMapLiveness::addLiveOutSetToMI(MachineFunction &MF,
    148                                          MachineInstr &MI) {
    149   uint32_t *Mask = createRegisterMask(MF);
    150   MachineOperand MO = MachineOperand::CreateRegLiveOut(Mask);
    151   MI.addOperand(MF, MO);
    152 }
    153 
    154 /// Create a register mask and initialize it with the registers from the
    155 /// register live set.
    156 uint32_t *StackMapLiveness::createRegisterMask(MachineFunction &MF) const {
    157   // The mask is owned and cleaned up by the Machine Function.
    158   uint32_t *Mask = MF.allocateRegisterMask(TRI->getNumRegs());
    159   for (auto Reg : LiveRegs)
    160     Mask[Reg / 32] |= 1U << (Reg % 32);
    161 
    162   // Give the target a chance to adjust the mask.
    163   TRI->adjustStackMapLiveOutMask(Mask);
    164 
    165   return Mask;
    166 }
    167