llvm/lib/CodeGen/MachineDebugify.cpp

   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/MachineFunctionPass.h"
  20 #include "llvm/CodeGen/MachineInstrBuilder.h"
  21 #include "llvm/CodeGen/MachineModuleInfo.h"
  22 #include "llvm/CodeGen/Passes.h"
  23 #include "llvm/CodeGen/TargetInstrInfo.h"
  24 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  25 #include "llvm/IR/DIBuilder.h"
  26 #include "llvm/IR/DebugInfo.h"
  27 #include "llvm/IR/IntrinsicInst.h"
  28 #include "llvm/InitializePasses.h"
  29 #include "llvm/Transforms/Utils/Debugify.h"
  30
  31 #define DEBUG_TYPE "mir-debugify"
  32
  33 using namespace llvm;
  34
  35 namespace {
  36 bool applyDebugifyMetadataToMachineFunction(MachineModuleInfo &MMI,
  37                                             DIBuilder &DIB, Function &F) {
  38   MachineFunction *MaybeMF = MMI.getMachineFunction(F);
  39   if (!MaybeMF)
  40     return false;
  41   MachineFunction &MF = *MaybeMF;
  42   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
  43
  44   DISubprogram *SP = F.getSubprogram();
  45   assert(SP && "IR Debugify just created it?");
  46
  47   Module &M = *F.getParent();
  48   LLVMContext &Ctx = M.getContext();
  49
  50   unsigned NextLine = SP->getLine();
  51   for (MachineBasicBlock &MBB : MF) {
  52     for (MachineInstr &MI : MBB) {
  53       // This will likely emit line numbers beyond the end of the imagined
  54       // source function and into subsequent ones. We don't do anything about
  55       // that as it doesn't really matter to the compiler where the line is in
  56       // the imaginary source code.
  57       MI.setDebugLoc(DILocation::get(Ctx, NextLine++, 1, SP));
  58     }
  59   }
  60
  61   // Find local variables defined by debugify. No attempt is made to match up
  62   // MIR-level regs to the 'correct' IR-level variables: there isn't a simple
  63   // way to do that, and it isn't necessary to find interesting CodeGen bugs.
  64   // Instead, simply keep track of one variable per line. Later, we can insert
  65   // DBG_VALUE insts that point to these local variables. Emitting DBG_VALUEs
  66   // which cover a wide range of lines can help stress the debug info passes:
  67   // if we can't do that, fall back to using the local variable which precedes
  68   // all the others.
  69   Function *DbgValF = M.getFunction("llvm.dbg.value");
  70   DbgValueInst *EarliestDVI = nullptr;
  71   DenseMap<unsigned, DILocalVariable *> Line2Var;
  72   DIExpression *Expr = nullptr;
  73   if (DbgValF) {
  74     for (const Use &U : DbgValF->uses()) {
  75       auto *DVI = dyn_cast<DbgValueInst>(U.getUser());
  76       if (!DVI || DVI->getFunction() != &F)
  77         continue;
  78       unsigned Line = DVI->getDebugLoc().getLine();
  79       assert(Line != 0 && "debugify should not insert line 0 locations");
  80       Line2Var[Line] = DVI->getVariable();
  81       if (!EarliestDVI || Line < EarliestDVI->getDebugLoc().getLine())
  82         EarliestDVI = DVI;
  83       Expr = DVI->getExpression();
  84     }
  85   }
  86   if (Line2Var.empty())
  87     return true;
  88
  89   // Now, try to insert a DBG_VALUE instruction after each real instruction.
  90   // Do this by introducing debug uses of each register definition. If that is
  91   // not possible (e.g. we have a phi or a meta instruction), emit a constant.
  92   uint64_t NextImm = 0;
  93   SmallSet<DILocalVariable *, 16> VarSet;
  94   const MCInstrDesc &DbgValDesc = TII.get(TargetOpcode::DBG_VALUE);
  95   for (MachineBasicBlock &MBB : MF) {
  96     MachineBasicBlock::iterator FirstNonPHIIt = MBB.getFirstNonPHI();
  97     for (auto I = MBB.begin(), E = MBB.end(); I != E;) {
  98       MachineInstr &MI = *I;
  99       ++I;
 100
 101       // `I` may point to a DBG_VALUE created in the previous loop iteration.
 102       if (MI.isDebugInstr())
 103         continue;
 104
 105       // It's not allowed to insert DBG_VALUEs after a terminator.
 106       if (MI.isTerminator())
 107         continue;
 108
 109       // Find a suitable insertion point for the DBG_VALUE.
 110       auto InsertBeforeIt = MI.isPHI() ? FirstNonPHIIt : I;
 111
 112       // Find a suitable local variable for the DBG_VALUE.
 113       unsigned Line = MI.getDebugLoc().getLine();
 114       if (!Line2Var.count(Line))
 115         Line = EarliestDVI->getDebugLoc().getLine();
 116       DILocalVariable *LocalVar = Line2Var[Line];
 117       assert(LocalVar && "No variable for current line?");
 118       VarSet.insert(LocalVar);
 119
 120       // Emit DBG_VALUEs for register definitions.
 121       SmallVector<MachineOperand *, 4> RegDefs;
 122       for (MachineOperand &MO : MI.operands())
 123         if (MO.isReg() && MO.isDef() && MO.getReg())
 124           RegDefs.push_back(&MO);
 125       for (MachineOperand *MO : RegDefs)
 126         BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
 127                 /*IsIndirect=*/false, *MO, LocalVar, Expr);
 128
 129       // OK, failing that, emit a constant DBG_VALUE.
 130       if (RegDefs.empty()) {
 131         auto ImmOp = MachineOperand::CreateImm(NextImm++);
 132         BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
 133                 /*IsIndirect=*/false, ImmOp, LocalVar, Expr);
 134       }
 135     }
 136   }
 137
 138   // Here we save the number of lines and variables into "llvm.mir.debugify".
 139   // It is useful for mir-check-debugify.
 140   NamedMDNode *NMD = M.getNamedMetadata("llvm.mir.debugify");
 141   IntegerType *Int32Ty = Type::getInt32Ty(Ctx);
 142   if (!NMD) {
 143     NMD = M.getOrInsertNamedMetadata("llvm.mir.debugify");
 144     auto addDebugifyOperand = [&](unsigned N) {
 145       NMD->addOperand(MDNode::get(
 146           Ctx, ValueAsMetadata::getConstant(ConstantInt::get(Int32Ty, N))));
 147     };
 148     // Add number of lines.
 149     addDebugifyOperand(NextLine - 1);
 150     // Add number of variables.
 151     addDebugifyOperand(VarSet.size());
 152   } else {
 153     assert(NMD->getNumOperands() == 2 &&
 154            "llvm.mir.debugify should have exactly 2 operands!");
 155     auto setDebugifyOperand = [&](unsigned Idx, unsigned N) {
 156       NMD->setOperand(Idx, MDNode::get(Ctx, ValueAsMetadata::getConstant(
 157                                                 ConstantInt::get(Int32Ty, N))));
 158     };
 159     // Set number of lines.
 160     setDebugifyOperand(0, NextLine - 1);
 161     // Set number of variables.
 162     setDebugifyOperand(1, VarSet.size());
 163   }
 164
 165   return true;
 166 }
 167
 168 /// ModulePass for attaching synthetic debug info to everything, used with the
 169 /// legacy module pass manager.
 170 struct DebugifyMachineModule : public ModulePass {
 171   bool runOnModule(Module &M) override {
 172     MachineModuleInfo &MMI =
 173         getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
 174     return applyDebugifyMetadata(
 175         M, M.functions(),
 176         "ModuleDebugify: ", [&](DIBuilder &DIB, Function &F) -> bool {
 177           return applyDebugifyMetadataToMachineFunction(MMI, DIB, F);
 178         });
 179   }
 180
 181   DebugifyMachineModule() : ModulePass(ID) {}
 182
 183   void getAnalysisUsage(AnalysisUsage &AU) const override {
 184     AU.addRequired<MachineModuleInfoWrapperPass>();
 185     AU.addPreserved<MachineModuleInfoWrapperPass>();
 186     AU.setPreservesCFG();
 187   }
 188
 189   static char ID; // Pass identification.
 190 };
 191 char DebugifyMachineModule::ID = 0;
 192
 193 } // end anonymous namespace
 194
 195 INITIALIZE_PASS_BEGIN(DebugifyMachineModule, DEBUG_TYPE,
 196                       "Machine Debugify Module", false, false)
 197 INITIALIZE_PASS_END(DebugifyMachineModule, DEBUG_TYPE,
 198                     "Machine Debugify Module", false, false)
 199
 200 ModulePass *llvm::createDebugifyMachineModulePass() {
 201   return new DebugifyMachineModule();
 202 }