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
getRequiredProperties() const64 MachineFunctionProperties getRequiredProperties() const override {
65 return MachineFunctionProperties().setNoVRegs();
66 }
67
68 /// Calculate the liveness information for the given machine function.
69 bool runOnMachineFunction(MachineFunction &MF) override;
70
71 private:
72 /// Performs the actual liveness calculation for the function.
73 bool calculateLiveness(MachineFunction &MF);
74
75 /// Add the current register live set to the instruction.
76 void addLiveOutSetToMI(MachineFunction &MF, MachineInstr &MI);
77
78 /// Create a register mask and initialize it with the registers from
79 /// the register live set.
80 uint32_t *createRegisterMask(MachineFunction &MF) const;
81 };
82 } // namespace
83
84 char StackMapLiveness::ID = 0;
85 char &llvm::StackMapLivenessID = StackMapLiveness::ID;
86 INITIALIZE_PASS(StackMapLiveness, "stackmap-liveness",
87 "StackMap Liveness Analysis", false, false)
88
89 /// Default construct and initialize the pass.
StackMapLiveness()90 StackMapLiveness::StackMapLiveness() : MachineFunctionPass(ID) {
91 initializeStackMapLivenessPass(*PassRegistry::getPassRegistry());
92 }
93
94 /// Tell the pass manager which passes we depend on and what information we
95 /// preserve.
getAnalysisUsage(AnalysisUsage & AU) const96 void StackMapLiveness::getAnalysisUsage(AnalysisUsage &AU) const {
97 // We preserve all information.
98 AU.setPreservesAll();
99 AU.setPreservesCFG();
100 MachineFunctionPass::getAnalysisUsage(AU);
101 }
102
103 /// Calculate the liveness information for the given machine function.
runOnMachineFunction(MachineFunction & MF)104 bool StackMapLiveness::runOnMachineFunction(MachineFunction &MF) {
105 if (!EnablePatchPointLiveness)
106 return false;
107
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.
calculateLiveness(MachineFunction & MF)120 bool StackMapLiveness::calculateLiveness(MachineFunction &MF) {
121 LLVM_DEBUG(dbgs() << "********** COMPUTING STACKMAP LIVENESS: "
122 << MF.getName() << " **********\n");
123 bool HasChanged = false;
124 // For all basic blocks in the function.
125 for (auto &MBB : MF) {
126 LLVM_DEBUG(dbgs() << "****** BB " << MBB.getName() << " ******\n");
127 LiveRegs.init(*TRI);
128 LiveRegs.addLiveOuts(MBB);
129 bool HasStackMap = false;
130 // Reverse iterate over all instructions and add the current live register
131 // set to an instruction if we encounter a patchpoint instruction.
132 for (MachineInstr &MI : llvm::reverse(MBB)) {
133 if (MI.getOpcode() == TargetOpcode::PATCHPOINT) {
134 addLiveOutSetToMI(MF, MI);
135 HasChanged = true;
136 HasStackMap = true;
137 ++NumStackMaps;
138 }
139 LLVM_DEBUG(dbgs() << " " << LiveRegs << " " << MI);
140 LiveRegs.stepBackward(MI);
141 }
142 ++NumBBsVisited;
143 if (!HasStackMap)
144 ++NumBBsHaveNoStackmap;
145 }
146 return HasChanged;
147 }
148
149 /// Add the current register live set to the instruction.
addLiveOutSetToMI(MachineFunction & MF,MachineInstr & MI)150 void StackMapLiveness::addLiveOutSetToMI(MachineFunction &MF,
151 MachineInstr &MI) {
152 uint32_t *Mask = createRegisterMask(MF);
153 MachineOperand MO = MachineOperand::CreateRegLiveOut(Mask);
154 MI.addOperand(MF, MO);
155 }
156
157 /// Create a register mask and initialize it with the registers from the
158 /// register live set.
createRegisterMask(MachineFunction & MF) const159 uint32_t *StackMapLiveness::createRegisterMask(MachineFunction &MF) const {
160 // The mask is owned and cleaned up by the Machine Function.
161 uint32_t *Mask = MF.allocateRegMask();
162 for (auto Reg : LiveRegs)
163 Mask[Reg / 32] |= 1U << (Reg % 32);
164
165 // Give the target a chance to adjust the mask.
166 TRI->adjustStackMapLiveOutMask(Mask);
167
168 return Mask;
169 }
170