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/ADT/Triple.h"
12 #include "llvm/CodeGen/MachineDominators.h"
13 #include "llvm/CodeGen/MachineFunction.h"
14 #include "llvm/CodeGen/MachineFunctionPass.h"
15 #include "llvm/CodeGen/Passes.h"
16 #include "llvm/CodeGen/TargetPassConfig.h"
17 #include "llvm/InitializePasses.h"
18 #include "llvm/Pass.h"
19 #include "llvm/PassRegistry.h"
20 #include "llvm/Support/CommandLine.h"
21 
22 /// \file LiveDebugValues.cpp
23 ///
24 /// The LiveDebugValues pass extends the range of variable locations
25 /// (specified by DBG_VALUE instructions) from single blocks to successors
26 /// and any other code locations where the variable location is valid.
27 /// There are currently two implementations: the "VarLoc" implementation
28 /// explicitly tracks the location of a variable, while the "InstrRef"
29 /// implementation tracks the values defined by instructions through locations.
30 ///
31 /// This file implements neither; it merely registers the pass, allows the
32 /// user to pick which implementation will be used to propagate variable
33 /// locations.
34 
35 #define DEBUG_TYPE "livedebugvalues"
36 
37 using namespace llvm;
38 
39 static cl::opt<bool>
40     ForceInstrRefLDV("force-instr-ref-livedebugvalues", cl::Hidden,
41                      cl::desc("Use instruction-ref based LiveDebugValues with "
42                               "normal DBG_VALUE inputs"),
43                      cl::init(false));
44 
45 static cl::opt<cl::boolOrDefault> ValueTrackingVariableLocations(
46     "experimental-debug-variable-locations",
47     cl::desc("Use experimental new value-tracking variable locations"));
48 
49 // Options to prevent pathological compile-time behavior. If InputBBLimit and
50 // InputDbgValueLimit are both exceeded, range extension is disabled.
51 static cl::opt<unsigned> InputBBLimit(
52     "livedebugvalues-input-bb-limit",
53     cl::desc("Maximum input basic blocks before DBG_VALUE limit applies"),
54     cl::init(10000), cl::Hidden);
55 static cl::opt<unsigned> InputDbgValueLimit(
56     "livedebugvalues-input-dbg-value-limit",
57     cl::desc(
58         "Maximum input DBG_VALUE insts supported by debug range extension"),
59     cl::init(50000), cl::Hidden);
60 
61 namespace {
62 /// Generic LiveDebugValues pass. Calls through to VarLocBasedLDV or
63 /// InstrRefBasedLDV to perform location propagation, via the LDVImpl
64 /// base class.
65 class LiveDebugValues : public MachineFunctionPass {
66 public:
67   static char ID;
68 
69   LiveDebugValues();
70   ~LiveDebugValues() = default;
71 
72   /// Calculate the liveness information for the given machine function.
73   bool runOnMachineFunction(MachineFunction &MF) override;
74 
75   MachineFunctionProperties getRequiredProperties() const override {
76     return MachineFunctionProperties().set(
77         MachineFunctionProperties::Property::NoVRegs);
78   }
79 
80   void getAnalysisUsage(AnalysisUsage &AU) const override {
81     AU.setPreservesCFG();
82     MachineFunctionPass::getAnalysisUsage(AU);
83   }
84 
85 private:
86   std::unique_ptr<LDVImpl> InstrRefImpl;
87   std::unique_ptr<LDVImpl> VarLocImpl;
88   TargetPassConfig *TPC;
89   MachineDominatorTree MDT;
90 };
91 } // namespace
92 
93 char LiveDebugValues::ID = 0;
94 
95 char &llvm::LiveDebugValuesID = LiveDebugValues::ID;
96 
97 INITIALIZE_PASS(LiveDebugValues, DEBUG_TYPE, "Live DEBUG_VALUE analysis", false,
98                 false)
99 
100 /// Default construct and initialize the pass.
101 LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
102   initializeLiveDebugValuesPass(*PassRegistry::getPassRegistry());
103   InstrRefImpl =
104       std::unique_ptr<LDVImpl>(llvm::makeInstrRefBasedLiveDebugValues());
105   VarLocImpl = std::unique_ptr<LDVImpl>(llvm::makeVarLocBasedLiveDebugValues());
106 }
107 
108 bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
109   bool InstrRefBased = MF.useDebugInstrRef();
110   // Allow the user to force selection of InstrRef LDV.
111   InstrRefBased |= ForceInstrRefLDV;
112 
113   TPC = getAnalysisIfAvailable<TargetPassConfig>();
114   LDVImpl *TheImpl = &*VarLocImpl;
115 
116   MachineDominatorTree *DomTree = nullptr;
117   if (InstrRefBased) {
118     DomTree = &MDT;
119     MDT.calculate(MF);
120     TheImpl = &*InstrRefImpl;
121   }
122 
123   return TheImpl->ExtendRanges(MF, DomTree, TPC, InputBBLimit,
124                                InputDbgValueLimit);
125 }
126 
127 bool llvm::debuginfoShouldUseDebugInstrRef(const Triple &T) {
128   // Enable by default on x86_64, disable if explicitly turned off on cmdline.
129   if (T.getArch() == llvm::Triple::x86_64 &&
130       ValueTrackingVariableLocations != cl::boolOrDefault::BOU_FALSE)
131     return true;
132 
133   // Enable if explicitly requested on command line.
134   return ValueTrackingVariableLocations == cl::boolOrDefault::BOU_TRUE;
135 }
136