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