1 //===- LiveDebugValues.cpp - Tracking Debug Value MIs ---------------------===//
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 #include "LiveDebugValues.h"
10 
11 #include "llvm/CodeGen/MachineDominators.h"
12 #include "llvm/CodeGen/MachineFunction.h"
13 #include "llvm/CodeGen/MachineFunctionPass.h"
14 #include "llvm/CodeGen/Passes.h"
15 #include "llvm/CodeGen/TargetPassConfig.h"
16 #include "llvm/InitializePasses.h"
17 #include "llvm/Pass.h"
18 #include "llvm/PassRegistry.h"
19 #include "llvm/Support/CommandLine.h"
20 #include "llvm/Target/TargetMachine.h"
21 #include "llvm/TargetParser/Triple.h"
22 
23 /// \file LiveDebugValues.cpp
24 ///
25 /// The LiveDebugValues pass extends the range of variable locations
26 /// (specified by DBG_VALUE instructions) from single blocks to successors
27 /// and any other code locations where the variable location is valid.
28 /// There are currently two implementations: the "VarLoc" implementation
29 /// explicitly tracks the location of a variable, while the "InstrRef"
30 /// implementation tracks the values defined by instructions through locations.
31 ///
32 /// This file implements neither; it merely registers the pass, allows the
33 /// user to pick which implementation will be used to propagate variable
34 /// locations.
35 
36 #define DEBUG_TYPE "livedebugvalues"
37 
38 using namespace llvm;
39 
40 static cl::opt<bool>
41     ForceInstrRefLDV("force-instr-ref-livedebugvalues", cl::Hidden,
42                      cl::desc("Use instruction-ref based LiveDebugValues with "
43                               "normal DBG_VALUE inputs"),
44                      cl::init(false));
45 
46 static cl::opt<cl::boolOrDefault> ValueTrackingVariableLocations(
47     "experimental-debug-variable-locations",
48     cl::desc("Use experimental new value-tracking variable locations"));
49 
50 // Options to prevent pathological compile-time behavior. If InputBBLimit and
51 // InputDbgValueLimit are both exceeded, range extension is disabled.
52 static cl::opt<unsigned> InputBBLimit(
53     "livedebugvalues-input-bb-limit",
54     cl::desc("Maximum input basic blocks before DBG_VALUE limit applies"),
55     cl::init(10000), cl::Hidden);
56 static cl::opt<unsigned> InputDbgValueLimit(
57     "livedebugvalues-input-dbg-value-limit",
58     cl::desc(
59         "Maximum input DBG_VALUE insts supported by debug range extension"),
60     cl::init(50000), cl::Hidden);
61 
62 namespace {
63 /// Generic LiveDebugValues pass. Calls through to VarLocBasedLDV or
64 /// InstrRefBasedLDV to perform location propagation, via the LDVImpl
65 /// base class.
66 class LiveDebugValues : public MachineFunctionPass {
67 public:
68   static char ID;
69 
70   LiveDebugValues();
71   ~LiveDebugValues() = default;
72 
73   /// Calculate the liveness information for the given machine function.
74   bool runOnMachineFunction(MachineFunction &MF) override;
75 
76   void getAnalysisUsage(AnalysisUsage &AU) const override {
77     AU.setPreservesCFG();
78     MachineFunctionPass::getAnalysisUsage(AU);
79   }
80 
81 private:
82   std::unique_ptr<LDVImpl> InstrRefImpl;
83   std::unique_ptr<LDVImpl> VarLocImpl;
84   TargetPassConfig *TPC = nullptr;
85   MachineDominatorTree MDT;
86 };
87 } // namespace
88 
89 char LiveDebugValues::ID = 0;
90 
91 char &llvm::LiveDebugValuesID = LiveDebugValues::ID;
92 
93 INITIALIZE_PASS(LiveDebugValues, DEBUG_TYPE, "Live DEBUG_VALUE analysis", false,
94                 false)
95 
96 /// Default construct and initialize the pass.
97 LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
98   initializeLiveDebugValuesPass(*PassRegistry::getPassRegistry());
99   InstrRefImpl =
100       std::unique_ptr<LDVImpl>(llvm::makeInstrRefBasedLiveDebugValues());
101   VarLocImpl = std::unique_ptr<LDVImpl>(llvm::makeVarLocBasedLiveDebugValues());
102 }
103 
104 bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
105   // Except for Wasm, all targets should be only using physical register at this
106   // point. Wasm only use virtual registers throught its pipeline, but its
107   // virtual registers don't participate  in this LiveDebugValues analysis; only
108   // its target indices do.
109   assert(MF.getTarget().getTargetTriple().isWasm() ||
110          MF.getProperties().hasProperty(
111              MachineFunctionProperties::Property::NoVRegs));
112 
113   bool InstrRefBased = MF.useDebugInstrRef();
114   // Allow the user to force selection of InstrRef LDV.
115   InstrRefBased |= ForceInstrRefLDV;
116 
117   TPC = getAnalysisIfAvailable<TargetPassConfig>();
118   LDVImpl *TheImpl = &*VarLocImpl;
119 
120   MachineDominatorTree *DomTree = nullptr;
121   if (InstrRefBased) {
122     DomTree = &MDT;
123     MDT.calculate(MF);
124     TheImpl = &*InstrRefImpl;
125   }
126 
127   return TheImpl->ExtendRanges(MF, DomTree, TPC, InputBBLimit,
128                                InputDbgValueLimit);
129 }
130 
131 bool llvm::debuginfoShouldUseDebugInstrRef(const Triple &T) {
132   // Enable by default on x86_64, disable if explicitly turned off on cmdline.
133   if (T.getArch() == llvm::Triple::x86_64 &&
134       ValueTrackingVariableLocations != cl::boolOrDefault::BOU_FALSE)
135     return true;
136 
137   // Enable if explicitly requested on command line.
138   return ValueTrackingVariableLocations == cl::boolOrDefault::BOU_TRUE;
139 }
140