1//===- MachineDebugify.cpp - Attach synthetic debug info to everything ----===//
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/// \file This pass attaches synthetic debug info to everything. It can be used
10/// to create targeted tests for debug info preservation, or test for CodeGen
11/// differences with vs. without debug info.
12///
13/// This isn't intended to have feature parity with Debugify.
14//===----------------------------------------------------------------------===//
15
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/SmallSet.h"
18#include "llvm/ADT/SmallVector.h"
19#include "llvm/CodeGen/MachineInstrBuilder.h"
20#include "llvm/CodeGen/MachineModuleInfo.h"
21#include "llvm/CodeGen/Passes.h"
22#include "llvm/CodeGen/TargetInstrInfo.h"
23#include "llvm/CodeGen/TargetSubtargetInfo.h"
24#include "llvm/IR/IntrinsicInst.h"
25#include "llvm/InitializePasses.h"
26#include "llvm/Transforms/Utils/Debugify.h"
27
28#define DEBUG_TYPE "mir-debugify"
29
30using namespace llvm;
31
32namespace {
33bool applyDebugifyMetadataToMachineFunction(MachineModuleInfo &MMI,
34 DIBuilder &DIB, Function &F) {
35 MachineFunction *MaybeMF = MMI.getMachineFunction(F);
36 if (!MaybeMF)
37 return false;
38 MachineFunction &MF = *MaybeMF;
39 const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
40
41 DISubprogram *SP = F.getSubprogram();
42 assert(SP && "IR Debugify just created it?");
43
44 Module &M = *F.getParent();
45 LLVMContext &Ctx = M.getContext();
46
47 unsigned NextLine = SP->getLine();
48 for (MachineBasicBlock &MBB : MF) {
49 for (MachineInstr &MI : MBB) {
50 // This will likely emit line numbers beyond the end of the imagined
51 // source function and into subsequent ones. We don't do anything about
52 // that as it doesn't really matter to the compiler where the line is in
53 // the imaginary source code.
54 MI.setDebugLoc(DILocation::get(Context&: Ctx, Line: NextLine++, Column: 1, Scope: SP));
55 }
56 }
57
58 // Find local variables defined by debugify. No attempt is made to match up
59 // MIR-level regs to the 'correct' IR-level variables: there isn't a simple
60 // way to do that, and it isn't necessary to find interesting CodeGen bugs.
61 // Instead, simply keep track of one variable per line. Later, we can insert
62 // DBG_VALUE insts that point to these local variables. Emitting DBG_VALUEs
63 // which cover a wide range of lines can help stress the debug info passes:
64 // if we can't do that, fall back to using the local variable which precedes
65 // all the others.
66 Function *DbgValF = M.getFunction(Name: "llvm.dbg.value");
67 DbgValueInst *EarliestDVI = nullptr;
68 DenseMap<unsigned, DILocalVariable *> Line2Var;
69 DIExpression *Expr = nullptr;
70 if (DbgValF) {
71 for (const Use &U : DbgValF->uses()) {
72 auto *DVI = dyn_cast<DbgValueInst>(Val: U.getUser());
73 if (!DVI || DVI->getFunction() != &F)
74 continue;
75 unsigned Line = DVI->getDebugLoc().getLine();
76 assert(Line != 0 && "debugify should not insert line 0 locations");
77 Line2Var[Line] = DVI->getVariable();
78 if (!EarliestDVI || Line < EarliestDVI->getDebugLoc().getLine())
79 EarliestDVI = DVI;
80 Expr = DVI->getExpression();
81 }
82 }
83 if (Line2Var.empty())
84 return true;
85
86 // Now, try to insert a DBG_VALUE instruction after each real instruction.
87 // Do this by introducing debug uses of each register definition. If that is
88 // not possible (e.g. we have a phi or a meta instruction), emit a constant.
89 uint64_t NextImm = 0;
90 SmallSet<DILocalVariable *, 16> VarSet;
91 const MCInstrDesc &DbgValDesc = TII.get(Opcode: TargetOpcode::DBG_VALUE);
92 for (MachineBasicBlock &MBB : MF) {
93 MachineBasicBlock::iterator FirstNonPHIIt = MBB.getFirstNonPHI();
94 for (auto I = MBB.begin(), E = MBB.end(); I != E;) {
95 MachineInstr &MI = *I;
96 ++I;
97
98 // `I` may point to a DBG_VALUE created in the previous loop iteration.
99 if (MI.isDebugInstr())
100 continue;
101
102 // It's not allowed to insert DBG_VALUEs after a terminator.
103 if (MI.isTerminator())
104 continue;
105
106 // Find a suitable insertion point for the DBG_VALUE.
107 auto InsertBeforeIt = MI.isPHI() ? FirstNonPHIIt : I;
108
109 // Find a suitable local variable for the DBG_VALUE.
110 unsigned Line = MI.getDebugLoc().getLine();
111 if (!Line2Var.count(Val: Line))
112 Line = EarliestDVI->getDebugLoc().getLine();
113 DILocalVariable *LocalVar = Line2Var[Line];
114 assert(LocalVar && "No variable for current line?");
115 VarSet.insert(Ptr: LocalVar);
116
117 // Emit DBG_VALUEs for register definitions.
118 SmallVector<MachineOperand *, 4> RegDefs;
119 for (MachineOperand &MO : MI.all_defs())
120 if (MO.getReg())
121 RegDefs.push_back(Elt: &MO);
122 for (MachineOperand *MO : RegDefs)
123 BuildMI(BB&: MBB, I: InsertBeforeIt, DL: MI.getDebugLoc(), MCID: DbgValDesc,
124 /*IsIndirect=*/false, MOs: *MO, Variable: LocalVar, Expr);
125
126 // OK, failing that, emit a constant DBG_VALUE.
127 if (RegDefs.empty()) {
128 auto ImmOp = MachineOperand::CreateImm(Val: NextImm++);
129 BuildMI(BB&: MBB, I: InsertBeforeIt, DL: MI.getDebugLoc(), MCID: DbgValDesc,
130 /*IsIndirect=*/false, MOs: ImmOp, Variable: LocalVar, Expr);
131 }
132 }
133 }
134
135 // Here we save the number of lines and variables into "llvm.mir.debugify".
136 // It is useful for mir-check-debugify.
137 NamedMDNode *NMD = M.getNamedMetadata(Name: "llvm.mir.debugify");
138 IntegerType *Int32Ty = Type::getInt32Ty(C&: Ctx);
139 if (!NMD) {
140 NMD = M.getOrInsertNamedMetadata(Name: "llvm.mir.debugify");
141 auto addDebugifyOperand = [&](unsigned N) {
142 NMD->addOperand(M: MDNode::get(
143 Context&: Ctx, MDs: ValueAsMetadata::getConstant(C: ConstantInt::get(Ty: Int32Ty, V: N))));
144 };
145 // Add number of lines.
146 addDebugifyOperand(NextLine - 1);
147 // Add number of variables.
148 addDebugifyOperand(VarSet.size());
149 } else {
150 assert(NMD->getNumOperands() == 2 &&
151 "llvm.mir.debugify should have exactly 2 operands!");
152 auto setDebugifyOperand = [&](unsigned Idx, unsigned N) {
153 NMD->setOperand(I: Idx, New: MDNode::get(Context&: Ctx, MDs: ValueAsMetadata::getConstant(
154 C: ConstantInt::get(Ty: Int32Ty, V: N))));
155 };
156 auto getDebugifyOperand = [&](unsigned Idx) {
157 return mdconst::extract<ConstantInt>(MD: NMD->getOperand(i: Idx)->getOperand(I: 0))
158 ->getZExtValue();
159 };
160 // Set number of lines.
161 setDebugifyOperand(0, NextLine - 1);
162 // Set number of variables.
163 auto OldNumVars = getDebugifyOperand(1);
164 setDebugifyOperand(1, OldNumVars + VarSet.size());
165 }
166
167 return true;
168}
169
170/// ModulePass for attaching synthetic debug info to everything, used with the
171/// legacy module pass manager.
172struct DebugifyMachineModule : public ModulePass {
173 bool runOnModule(Module &M) override {
174 // We will insert new debugify metadata, so erasing the old one.
175 assert(!M.getNamedMetadata("llvm.mir.debugify") &&
176 "llvm.mir.debugify metadata already exists! Strip it first");
177 MachineModuleInfo &MMI =
178 getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
179 return applyDebugifyMetadata(
180 M, Functions: M.functions(),
181 Banner: "ModuleDebugify: ", ApplyToMF: [&](DIBuilder &DIB, Function &F) -> bool {
182 return applyDebugifyMetadataToMachineFunction(MMI, DIB, F);
183 });
184 }
185
186 DebugifyMachineModule() : ModulePass(ID) {}
187
188 void getAnalysisUsage(AnalysisUsage &AU) const override {
189 AU.addRequired<MachineModuleInfoWrapperPass>();
190 AU.addPreserved<MachineModuleInfoWrapperPass>();
191 AU.setPreservesCFG();
192 }
193
194 static char ID; // Pass identification.
195};
196char DebugifyMachineModule::ID = 0;
197
198} // end anonymous namespace
199
200INITIALIZE_PASS_BEGIN(DebugifyMachineModule, DEBUG_TYPE,
201 "Machine Debugify Module", false, false)
202INITIALIZE_PASS_END(DebugifyMachineModule, DEBUG_TYPE,
203 "Machine Debugify Module", false, false)
204
205ModulePass *llvm::createDebugifyMachineModulePass() {
206 return new DebugifyMachineModule();
207}
208

source code of llvm/lib/CodeGen/MachineDebugify.cpp