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/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 }