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/SmallVector.h"
18 #include "llvm/CodeGen/MachineFunctionPass.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/DIBuilder.h"
25 #include "llvm/IR/DebugInfo.h"
26 #include "llvm/IR/IntrinsicInst.h"
27 #include "llvm/InitializePasses.h"
28 #include "llvm/Transforms/Utils/Debugify.h"
29 
30 #define DEBUG_TYPE "mir-debugify"
31 
32 using namespace llvm;
33 
34 namespace {
35 bool applyDebugifyMetadataToMachineFunction(MachineModuleInfo &MMI,
36                                             DIBuilder &DIB, Function &F) {
37   MachineFunction *MaybeMF = MMI.getMachineFunction(F);
38   if (!MaybeMF)
39     return false;
40   MachineFunction &MF = *MaybeMF;
41   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
42 
43   DISubprogram *SP = F.getSubprogram();
44   assert(SP && "IR Debugify just created it?");
45 
46   Module &M = *F.getParent();
47   LLVMContext &Ctx = M.getContext();
48 
49   unsigned NextLine = SP->getLine();
50   for (MachineBasicBlock &MBB : MF) {
51     for (MachineInstr &MI : MBB) {
52       // This will likely emit line numbers beyond the end of the imagined
53       // source function and into subsequent ones. We don't do anything about
54       // that as it doesn't really matter to the compiler where the line is in
55       // the imaginary source code.
56       MI.setDebugLoc(DILocation::get(Ctx, NextLine++, 1, SP));
57     }
58   }
59 
60   // Find local variables defined by debugify. No attempt is made to match up
61   // MIR-level regs to the 'correct' IR-level variables: there isn't a simple
62   // way to do that, and it isn't necessary to find interesting CodeGen bugs.
63   // Instead, simply keep track of one variable per line. Later, we can insert
64   // DBG_VALUE insts that point to these local variables. Emitting DBG_VALUEs
65   // which cover a wide range of lines can help stress the debug info passes:
66   // if we can't do that, fall back to using the local variable which precedes
67   // all the others.
68   Function *DbgValF = M.getFunction("llvm.dbg.value");
69   DbgValueInst *EarliestDVI = nullptr;
70   DenseMap<unsigned, DILocalVariable *> Line2Var;
71   DIExpression *Expr = nullptr;
72   if (DbgValF) {
73     for (const Use &U : DbgValF->uses()) {
74       auto *DVI = dyn_cast<DbgValueInst>(U.getUser());
75       if (!DVI || DVI->getFunction() != &F)
76         continue;
77       unsigned Line = DVI->getDebugLoc().getLine();
78       assert(Line != 0 && "debugify should not insert line 0 locations");
79       Line2Var[Line] = DVI->getVariable();
80       if (!EarliestDVI || Line < EarliestDVI->getDebugLoc().getLine())
81         EarliestDVI = DVI;
82       Expr = DVI->getExpression();
83     }
84   }
85   if (Line2Var.empty())
86     return true;
87 
88   // Now, try to insert a DBG_VALUE instruction after each real instruction.
89   // Do this by introducing debug uses of each register definition. If that is
90   // not possible (e.g. we have a phi or a meta instruction), emit a constant.
91   uint64_t NextImm = 0;
92   const MCInstrDesc &DbgValDesc = TII.get(TargetOpcode::DBG_VALUE);
93   for (MachineBasicBlock &MBB : MF) {
94     MachineBasicBlock::iterator FirstNonPHIIt = MBB.getFirstNonPHI();
95     for (auto I = MBB.begin(), E = MBB.end(); I != E; ) {
96       MachineInstr &MI = *I;
97       ++I;
98 
99       // `I` may point to a DBG_VALUE created in the previous loop iteration.
100       if (MI.isDebugInstr())
101         continue;
102 
103       // It's not allowed to insert DBG_VALUEs after a terminator.
104       if (MI.isTerminator())
105         continue;
106 
107       // Find a suitable insertion point for the DBG_VALUE.
108       auto InsertBeforeIt = MI.isPHI() ? FirstNonPHIIt : I;
109 
110       // Find a suitable local variable for the DBG_VALUE.
111       unsigned Line = MI.getDebugLoc().getLine();
112       if (!Line2Var.count(Line))
113         Line = EarliestDVI->getDebugLoc().getLine();
114       DILocalVariable *LocalVar = Line2Var[Line];
115       assert(LocalVar && "No variable for current line?");
116 
117       // Emit DBG_VALUEs for register definitions.
118       SmallVector<MachineOperand *, 4> RegDefs;
119       for (MachineOperand &MO : MI.operands())
120         if (MO.isReg() && MO.isDef() && 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   return true;
136 }
137 
138 /// ModulePass for attaching synthetic debug info to everything, used with the
139 /// legacy module pass manager.
140 struct DebugifyMachineModule : public ModulePass {
141   bool runOnModule(Module &M) override {
142     MachineModuleInfo &MMI =
143         getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
144     return applyDebugifyMetadata(
145         M, M.functions(),
146         "ModuleDebugify: ", [&](DIBuilder &DIB, Function &F) -> bool {
147           return applyDebugifyMetadataToMachineFunction(MMI, DIB, F);
148         });
149   }
150 
151   DebugifyMachineModule() : ModulePass(ID) {}
152 
153   void getAnalysisUsage(AnalysisUsage &AU) const override {
154     AU.addRequired<MachineModuleInfoWrapperPass>();
155     AU.addPreserved<MachineModuleInfoWrapperPass>();
156     AU.setPreservesCFG();
157   }
158 
159   static char ID; // Pass identification.
160 };
161 char DebugifyMachineModule::ID = 0;
162 
163 } // end anonymous namespace
164 
165 INITIALIZE_PASS_BEGIN(DebugifyMachineModule, DEBUG_TYPE,
166                       "Machine Debugify Module", false, false)
167 INITIALIZE_PASS_END(DebugifyMachineModule, DEBUG_TYPE,
168                     "Machine Debugify Module", false, false)
169 
170 ModulePass *llvm::createDebugifyMachineModulePass() {
171   return new DebugifyMachineModule();
172 }
173