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      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 
     27 using namespace llvm;
     28 
     29 #define DEBUG_TYPE "stackmaps"
     30 
     31 static cl::opt<bool> EnablePatchPointLiveness(
     32     "enable-patchpoint-liveness", cl::Hidden, cl::init(true),
     33     cl::desc("Enable PatchPoint Liveness Analysis Pass"));
     34 
     35 STATISTIC(NumStackMapFuncVisited, "Number of functions visited");
     36 STATISTIC(NumStackMapFuncSkipped, "Number of functions skipped");
     37 STATISTIC(NumBBsVisited,          "Number of basic blocks visited");
     38 STATISTIC(NumBBsHaveNoStackmap,   "Number of basic blocks with no stackmap");
     39 STATISTIC(NumStackMaps,           "Number of StackMaps visited");
     40 
     41 namespace {
     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.
     50 class StackMapLiveness : public MachineFunctionPass {
     51   const TargetRegisterInfo *TRI;
     52   LivePhysRegs LiveRegs;
     53 
     54 public:
     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 
     72 private:
     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 
     85 char StackMapLiveness::ID = 0;
     86 char &llvm::StackMapLivenessID = StackMapLiveness::ID;
     87 INITIALIZE_PASS(StackMapLiveness, "stackmap-liveness",
     88                 "StackMap Liveness Analysis", false, false)
     89 
     90 /// Default construct and initialize the pass.
     91 StackMapLiveness::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.
     97 void 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.
    105 bool 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.
    123 bool 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.
    152 void 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.
    161 uint32_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