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
38using namespace llvm;
39
40static 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(Val: false));
45
46static 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.
52static cl::opt<unsigned> InputBBLimit(
53 "livedebugvalues-input-bb-limit",
54 cl::desc("Maximum input basic blocks before DBG_VALUE limit applies"),
55 cl::init(Val: 10000), cl::Hidden);
56static 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(Val: 50000), cl::Hidden);
61
62namespace {
63/// Generic LiveDebugValues pass. Calls through to VarLocBasedLDV or
64/// InstrRefBasedLDV to perform location propagation, via the LDVImpl
65/// base class.
66class LiveDebugValues : public MachineFunctionPass {
67public:
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
81private:
82 std::unique_ptr<LDVImpl> InstrRefImpl;
83 std::unique_ptr<LDVImpl> VarLocImpl;
84 TargetPassConfig *TPC = nullptr;
85 MachineDominatorTree MDT;
86};
87} // namespace
88
89char LiveDebugValues::ID = 0;
90
91char &llvm::LiveDebugValuesID = LiveDebugValues::ID;
92
93INITIALIZE_PASS(LiveDebugValues, DEBUG_TYPE, "Live DEBUG_VALUE analysis", false,
94 false)
95
96/// Default construct and initialize the pass.
97LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
98 initializeLiveDebugValuesPass(Registry&: *PassRegistry::getPassRegistry());
99 InstrRefImpl =
100 std::unique_ptr<LDVImpl>(llvm::makeInstrRefBasedLiveDebugValues());
101 VarLocImpl = std::unique_ptr<LDVImpl>(llvm::makeVarLocBasedLiveDebugValues());
102}
103
104bool 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(F&: MF);
124 TheImpl = &*InstrRefImpl;
125 }
126
127 return TheImpl->ExtendRanges(MF, DomTree, TPC, InputBBLimit,
128 InputDbgValLimit: InputDbgValueLimit);
129}
130
131bool 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