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/CodeGen/MachineDebugify.h"
17#include "llvm/ADT/DenseMap.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
32bool llvm::applyDebugifyMetadataToMachineFunction(
33 DIBuilder &DIB, Function &F,
34 llvm::function_ref<MachineFunction *(Function &)> GetMF) {
35 MachineFunction *MaybeMF = GetMF(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 DbgVariableRecord *EarliestDVR = nullptr;
67 DenseMap<unsigned, DILocalVariable *> Line2Var;
68 DIExpression *Expr = nullptr;
69 for (BasicBlock &BB : F) {
70 for (Instruction &I : BB) {
71 for (DbgVariableRecord &DVR : filterDbgVars(R: I.getDbgRecordRange())) {
72 if (!DVR.isDbgValue())
73 continue;
74 unsigned Line = DVR.getDebugLoc().getLine();
75 assert(Line != 0 && "debugify should not insert line 0 locations");
76 Line2Var[Line] = DVR.getVariable();
77 if (!EarliestDVR || Line < EarliestDVR->getDebugLoc().getLine())
78 EarliestDVR = &DVR;
79 Expr = DVR.getExpression();
80 }
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 SmallPtrSet<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 auto It = Line2Var.find(Val: Line);
112 if (It == Line2Var.end()) {
113 Line = EarliestDVR->getDebugLoc().getLine();
114 It = Line2Var.find(Val: Line);
115 assert(It != Line2Var.end());
116 }
117 DILocalVariable *LocalVar = It->second;
118 assert(LocalVar && "No variable for current line?");
119 VarSet.insert(Ptr: LocalVar);
120
121 // Emit DBG_VALUEs for register definitions.
122 SmallVector<MachineOperand *, 4> RegDefs;
123 for (MachineOperand &MO : MI.all_defs())
124 if (MO.getReg())
125 RegDefs.push_back(Elt: &MO);
126 for (MachineOperand *MO : RegDefs)
127 BuildMI(BB&: MBB, I: InsertBeforeIt, DL: MI.getDebugLoc(), MCID: DbgValDesc,
128 /*IsIndirect=*/false, MOs: *MO, Variable: LocalVar, Expr);
129
130 // OK, failing that, emit a constant DBG_VALUE.
131 if (RegDefs.empty()) {
132 auto ImmOp = MachineOperand::CreateImm(Val: NextImm++);
133 BuildMI(BB&: MBB, I: InsertBeforeIt, DL: MI.getDebugLoc(), MCID: DbgValDesc,
134 /*IsIndirect=*/false, MOs: ImmOp, Variable: LocalVar, Expr);
135 }
136 }
137 }
138
139 // Here we save the number of lines and variables into "llvm.mir.debugify".
140 // It is useful for mir-check-debugify.
141 NamedMDNode *NMD = M.getNamedMetadata(Name: "llvm.mir.debugify");
142 IntegerType *Int32Ty = Type::getInt32Ty(C&: Ctx);
143 if (!NMD) {
144 NMD = M.getOrInsertNamedMetadata(Name: "llvm.mir.debugify");
145 auto addDebugifyOperand = [&](unsigned N) {
146 NMD->addOperand(M: MDNode::get(
147 Context&: Ctx, MDs: ValueAsMetadata::getConstant(C: ConstantInt::get(Ty: Int32Ty, V: N))));
148 };
149 // Add number of lines.
150 addDebugifyOperand(NextLine - 1);
151 // Add number of variables.
152 addDebugifyOperand(VarSet.size());
153 } else {
154 assert(NMD->getNumOperands() == 2 &&
155 "llvm.mir.debugify should have exactly 2 operands!");
156 auto setDebugifyOperand = [&](unsigned Idx, unsigned N) {
157 NMD->setOperand(I: Idx, New: MDNode::get(Context&: Ctx, MDs: ValueAsMetadata::getConstant(
158 C: ConstantInt::get(Ty: Int32Ty, V: N))));
159 };
160 auto getDebugifyOperand = [&](unsigned Idx) {
161 return mdconst::extract<ConstantInt>(MD: NMD->getOperand(i: Idx)->getOperand(I: 0))
162 ->getZExtValue();
163 };
164 // Set number of lines.
165 setDebugifyOperand(0, NextLine - 1);
166 // Set number of variables.
167 auto OldNumVars = getDebugifyOperand(1);
168 setDebugifyOperand(1, OldNumVars + VarSet.size());
169 }
170
171 return true;
172}
173
174namespace {
175
176/// ModulePass for attaching synthetic debug info to everything, used with the
177/// legacy module pass manager.
178struct DebugifyMachineModule : public ModulePass {
179 bool runOnModule(Module &M) override {
180 // We will insert new debugify metadata, so erasing the old one.
181 assert(!M.getNamedMetadata("llvm.mir.debugify") &&
182 "llvm.mir.debugify metadata already exists! Strip it first");
183 MachineModuleInfo &MMI =
184 getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
185 return applyDebugifyMetadata(
186 M, Functions: M.functions(),
187 Banner: "ModuleDebugify: ", ApplyToMF: [&](DIBuilder &DIB, Function &F) -> bool {
188 return applyDebugifyMetadataToMachineFunction(
189 DIB, F, GetMF: [&MMI](Function &F) -> MachineFunction * {
190 return MMI.getMachineFunction(F);
191 });
192 });
193 }
194
195 DebugifyMachineModule() : ModulePass(ID) {}
196
197 void getAnalysisUsage(AnalysisUsage &AU) const override {
198 AU.addRequired<MachineModuleInfoWrapperPass>();
199 AU.addPreserved<MachineModuleInfoWrapperPass>();
200 AU.setPreservesCFG();
201 }
202
203 static char ID; // Pass identification.
204};
205char DebugifyMachineModule::ID = 0;
206
207} // end anonymous namespace
208
209INITIALIZE_PASS_BEGIN(DebugifyMachineModule, DEBUG_TYPE,
210 "Machine Debugify Module", false, false)
211INITIALIZE_PASS_END(DebugifyMachineModule, DEBUG_TYPE,
212 "Machine Debugify Module", false, false)
213
214ModulePass *llvm::createDebugifyMachineModulePass() {
215 return new DebugifyMachineModule();
216}
217