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 {
applyDebugifyMetadataToMachineFunction(MachineModuleInfo & MMI,DIBuilder & DIB,Function & F)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 DbgVariableRecord *EarliestDVR = nullptr;
69 DenseMap<unsigned, DILocalVariable *> Line2Var;
70 DIExpression *Expr = nullptr;
71 if (DbgValF) {
72 for (const Use &U : DbgValF->uses()) {
73 auto *DVI = dyn_cast<DbgValueInst>(U.getUser());
74 if (!DVI || DVI->getFunction() != &F)
75 continue;
76 unsigned Line = DVI->getDebugLoc().getLine();
77 assert(Line != 0 && "debugify should not insert line 0 locations");
78 Line2Var[Line] = DVI->getVariable();
79 if (!EarliestDVI || Line < EarliestDVI->getDebugLoc().getLine())
80 EarliestDVI = DVI;
81 Expr = DVI->getExpression();
82 }
83 }
84 for (BasicBlock &BB : F) {
85 for (Instruction &I : BB) {
86 for (DbgVariableRecord &DVR : filterDbgVars(I.getDbgRecordRange())) {
87 if (!DVR.isDbgValue())
88 continue;
89 unsigned Line = DVR.getDebugLoc().getLine();
90 assert(Line != 0 && "debugify should not insert line 0 locations");
91 Line2Var[Line] = DVR.getVariable();
92 if (!EarliestDVR || Line < EarliestDVR->getDebugLoc().getLine())
93 EarliestDVR = &DVR;
94 Expr = DVR.getExpression();
95 }
96 }
97 }
98 if (Line2Var.empty())
99 return true;
100
101 // Now, try to insert a DBG_VALUE instruction after each real instruction.
102 // Do this by introducing debug uses of each register definition. If that is
103 // not possible (e.g. we have a phi or a meta instruction), emit a constant.
104 uint64_t NextImm = 0;
105 SmallSet<DILocalVariable *, 16> VarSet;
106 const MCInstrDesc &DbgValDesc = TII.get(TargetOpcode::DBG_VALUE);
107 for (MachineBasicBlock &MBB : MF) {
108 MachineBasicBlock::iterator FirstNonPHIIt = MBB.getFirstNonPHI();
109 for (auto I = MBB.begin(), E = MBB.end(); I != E;) {
110 MachineInstr &MI = *I;
111 ++I;
112
113 // `I` may point to a DBG_VALUE created in the previous loop iteration.
114 if (MI.isDebugInstr())
115 continue;
116
117 // It's not allowed to insert DBG_VALUEs after a terminator.
118 if (MI.isTerminator())
119 continue;
120
121 // Find a suitable insertion point for the DBG_VALUE.
122 auto InsertBeforeIt = MI.isPHI() ? FirstNonPHIIt : I;
123
124 // Find a suitable local variable for the DBG_VALUE.
125 unsigned Line = MI.getDebugLoc().getLine();
126 if (!Line2Var.count(Line))
127 Line = EarliestDVI ? EarliestDVI->getDebugLoc().getLine()
128 : EarliestDVR->getDebugLoc().getLine();
129 DILocalVariable *LocalVar = Line2Var[Line];
130 assert(LocalVar && "No variable for current line?");
131 VarSet.insert(LocalVar);
132
133 // Emit DBG_VALUEs for register definitions.
134 SmallVector<MachineOperand *, 4> RegDefs;
135 for (MachineOperand &MO : MI.all_defs())
136 if (MO.getReg())
137 RegDefs.push_back(&MO);
138 for (MachineOperand *MO : RegDefs)
139 BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
140 /*IsIndirect=*/false, *MO, LocalVar, Expr);
141
142 // OK, failing that, emit a constant DBG_VALUE.
143 if (RegDefs.empty()) {
144 auto ImmOp = MachineOperand::CreateImm(NextImm++);
145 BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
146 /*IsIndirect=*/false, ImmOp, LocalVar, Expr);
147 }
148 }
149 }
150
151 // Here we save the number of lines and variables into "llvm.mir.debugify".
152 // It is useful for mir-check-debugify.
153 NamedMDNode *NMD = M.getNamedMetadata("llvm.mir.debugify");
154 IntegerType *Int32Ty = Type::getInt32Ty(Ctx);
155 if (!NMD) {
156 NMD = M.getOrInsertNamedMetadata("llvm.mir.debugify");
157 auto addDebugifyOperand = [&](unsigned N) {
158 NMD->addOperand(MDNode::get(
159 Ctx, ValueAsMetadata::getConstant(ConstantInt::get(Int32Ty, N))));
160 };
161 // Add number of lines.
162 addDebugifyOperand(NextLine - 1);
163 // Add number of variables.
164 addDebugifyOperand(VarSet.size());
165 } else {
166 assert(NMD->getNumOperands() == 2 &&
167 "llvm.mir.debugify should have exactly 2 operands!");
168 auto setDebugifyOperand = [&](unsigned Idx, unsigned N) {
169 NMD->setOperand(Idx, MDNode::get(Ctx, ValueAsMetadata::getConstant(
170 ConstantInt::get(Int32Ty, N))));
171 };
172 auto getDebugifyOperand = [&](unsigned Idx) {
173 return mdconst::extract<ConstantInt>(NMD->getOperand(Idx)->getOperand(0))
174 ->getZExtValue();
175 };
176 // Set number of lines.
177 setDebugifyOperand(0, NextLine - 1);
178 // Set number of variables.
179 auto OldNumVars = getDebugifyOperand(1);
180 setDebugifyOperand(1, OldNumVars + VarSet.size());
181 }
182
183 return true;
184 }
185
186 /// ModulePass for attaching synthetic debug info to everything, used with the
187 /// legacy module pass manager.
188 struct DebugifyMachineModule : public ModulePass {
runOnModule__anon3e55c6380111::DebugifyMachineModule189 bool runOnModule(Module &M) override {
190 // We will insert new debugify metadata, so erasing the old one.
191 assert(!M.getNamedMetadata("llvm.mir.debugify") &&
192 "llvm.mir.debugify metadata already exists! Strip it first");
193 MachineModuleInfo &MMI =
194 getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
195 return applyDebugifyMetadata(
196 M, M.functions(),
197 "ModuleDebugify: ", [&](DIBuilder &DIB, Function &F) -> bool {
198 return applyDebugifyMetadataToMachineFunction(MMI, DIB, F);
199 });
200 }
201
DebugifyMachineModule__anon3e55c6380111::DebugifyMachineModule202 DebugifyMachineModule() : ModulePass(ID) {}
203
getAnalysisUsage__anon3e55c6380111::DebugifyMachineModule204 void getAnalysisUsage(AnalysisUsage &AU) const override {
205 AU.addRequired<MachineModuleInfoWrapperPass>();
206 AU.addPreserved<MachineModuleInfoWrapperPass>();
207 AU.setPreservesCFG();
208 }
209
210 static char ID; // Pass identification.
211 };
212 char DebugifyMachineModule::ID = 0;
213
214 } // end anonymous namespace
215
216 INITIALIZE_PASS_BEGIN(DebugifyMachineModule, DEBUG_TYPE,
217 "Machine Debugify Module", false, false)
218 INITIALIZE_PASS_END(DebugifyMachineModule, DEBUG_TYPE,
219 "Machine Debugify Module", false, false)
220
createDebugifyMachineModulePass()221 ModulePass *llvm::createDebugifyMachineModulePass() {
222 return new DebugifyMachineModule();
223 }
224