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 
30 using namespace llvm;
31 
32 namespace {
33 bool 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(Ctx, NextLine++, 1, 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("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>(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(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(Line))
112         Line = EarliestDVI->getDebugLoc().getLine();
113       DILocalVariable *LocalVar = Line2Var[Line];
114       assert(LocalVar && "No variable for current line?");
115       VarSet.insert(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(&MO);
122       for (MachineOperand *MO : RegDefs)
123         BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
124                 /*IsIndirect=*/false, *MO, LocalVar, Expr);
125 
126       // OK, failing that, emit a constant DBG_VALUE.
127       if (RegDefs.empty()) {
128         auto ImmOp = MachineOperand::CreateImm(NextImm++);
129         BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
130                 /*IsIndirect=*/false, ImmOp, 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("llvm.mir.debugify");
138   IntegerType *Int32Ty = Type::getInt32Ty(Ctx);
139   if (!NMD) {
140     NMD = M.getOrInsertNamedMetadata("llvm.mir.debugify");
141     auto addDebugifyOperand = [&](unsigned N) {
142       NMD->addOperand(MDNode::get(
143           Ctx, ValueAsMetadata::getConstant(ConstantInt::get(Int32Ty, 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(Idx, MDNode::get(Ctx, ValueAsMetadata::getConstant(
154                                                 ConstantInt::get(Int32Ty, N))));
155     };
156     auto getDebugifyOperand = [&](unsigned Idx) {
157       return mdconst::extract<ConstantInt>(NMD->getOperand(Idx)->getOperand(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.
172 struct 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, M.functions(),
181         "ModuleDebugify: ", [&](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 };
196 char DebugifyMachineModule::ID = 0;
197 
198 } // end anonymous namespace
199 
200 INITIALIZE_PASS_BEGIN(DebugifyMachineModule, DEBUG_TYPE,
201                       "Machine Debugify Module", false, false)
202 INITIALIZE_PASS_END(DebugifyMachineModule, DEBUG_TYPE,
203                     "Machine Debugify Module", false, false)
204 
205 ModulePass *llvm::createDebugifyMachineModulePass() {
206   return new DebugifyMachineModule();
207 }
208