llvm/lib/CodeGen/StackMapLivenessAnalysis.cpp

   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/TargetSubtargetInfo.h"
  21 #include "llvm/InitializePasses.h"
  22 #include "llvm/Pass.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 = nullptr;
  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   TRI = MF.getSubtarget().getRegisterInfo();
 110   ++NumStackMapFuncVisited;
 111
 112   // Skip this function if there are no patchpoints to process.
 113   if (!MF.getFrameInfo().hasPatchPoint()) {
 114     ++NumStackMapFuncSkipped;
 115     return false;
 116   }
 117   return calculateLiveness(MF);
 118 }
 119
 120 /// Performs the actual liveness calculation for the function.
 121 bool StackMapLiveness::calculateLiveness(MachineFunction &MF) {
 122   LLVM_DEBUG(dbgs() << "********** COMPUTING STACKMAP LIVENESS: "
 123                     << MF.getName() << " **********\n");
 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     LiveRegs.addLiveOuts(MBB);
 130     bool HasStackMap = false;
 131     // Reverse iterate over all instructions and add the current live register
 132     // set to an instruction if we encounter a patchpoint instruction.
 133     for (MachineInstr &MI : llvm::reverse(MBB)) {
 134       if (MI.getOpcode() == TargetOpcode::PATCHPOINT) {
 135         addLiveOutSetToMI(MF, MI);
 136         HasChanged = true;
 137         HasStackMap = true;
 138         ++NumStackMaps;
 139       }
 140       LLVM_DEBUG(dbgs() << "   " << LiveRegs << "   " << MI);
 141       LiveRegs.stepBackward(MI);
 142     }
 143     ++NumBBsVisited;
 144     if (!HasStackMap)
 145       ++NumBBsHaveNoStackmap;
 146   }
 147   return HasChanged;
 148 }
 149
 150 /// Add the current register live set to the instruction.
 151 void StackMapLiveness::addLiveOutSetToMI(MachineFunction &MF,
 152                                          MachineInstr &MI) {
 153   uint32_t *Mask = createRegisterMask(MF);
 154   MachineOperand MO = MachineOperand::CreateRegLiveOut(Mask);
 155   MI.addOperand(MF, MO);
 156 }
 157
 158 /// Create a register mask and initialize it with the registers from the
 159 /// register live set.
 160 uint32_t *StackMapLiveness::createRegisterMask(MachineFunction &MF) const {
 161   // The mask is owned and cleaned up by the Machine Function.
 162   uint32_t *Mask = MF.allocateRegMask();
 163   for (auto Reg : LiveRegs)
 164     Mask[Reg / 32] |= 1U << (Reg % 32);
 165
 166   // Give the target a chance to adjust the mask.
 167   TRI->adjustStackMapLiveOutMask(Mask);
 168
 169   return Mask;
 170 }