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//===- MachineDebugify.cpp - Attach synthetic debug info to everything ----===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file This pass attaches synthetic debug info to everything. It can be used
/// to create targeted tests for debug info preservation, or test for CodeGen
/// differences with vs. without debug info.
/// This isn't intended to have feature parity with Debugify.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/InitializePasses.h"
#include "llvm/Transforms/Utils/Debugify.h"
#define DEBUG_TYPE "mir-debugify"
using namespace llvm;
namespace {
bool applyDebugifyMetadataToMachineFunction(MachineModuleInfo &MMI,
DIBuilder &DIB, Function &F) {
MachineFunction *MaybeMF = MMI.getMachineFunction(F);
if (!MaybeMF)
return false;
MachineFunction &MF = *MaybeMF;
const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
DISubprogram *SP = F.getSubprogram();
assert(SP && "IR Debugify just created it?");
Module &M = *F.getParent();
LLVMContext &Ctx = M.getContext();
unsigned NextLine = SP->getLine();
for (MachineBasicBlock &MBB : MF) {
for (MachineInstr &MI : MBB) {
// This will likely emit line numbers beyond the end of the imagined
// source function and into subsequent ones. We don't do anything about
// that as it doesn't really matter to the compiler where the line is in
// the imaginary source code.
MI.setDebugLoc(DILocation::get(Ctx, NextLine++, 1, SP));
// Find local variables defined by debugify. No attempt is made to match up
// MIR-level regs to the 'correct' IR-level variables: there isn't a simple
// way to do that, and it isn't necessary to find interesting CodeGen bugs.
// Instead, simply keep track of one variable per line. Later, we can insert
// DBG_VALUE insts that point to these local variables. Emitting DBG_VALUEs
// which cover a wide range of lines can help stress the debug info passes:
// if we can't do that, fall back to using the local variable which precedes
// all the others.
Function *DbgValF = M.getFunction("llvm.dbg.value");
DbgValueInst *EarliestDVI = nullptr;
DenseMap<unsigned, DILocalVariable *> Line2Var;
DIExpression *Expr = nullptr;
if (DbgValF) {
for (const Use &U : DbgValF->uses()) {
auto *DVI = dyn_cast<DbgValueInst>(U.getUser());
if (!DVI || DVI->getFunction() != &F)
unsigned Line = DVI->getDebugLoc().getLine();
assert(Line != 0 && "debugify should not insert line 0 locations");
Line2Var[Line] = DVI->getVariable();
if (!EarliestDVI || Line < EarliestDVI->getDebugLoc().getLine())
EarliestDVI = DVI;
Expr = DVI->getExpression();
if (Line2Var.empty())
return true;
// Now, try to insert a DBG_VALUE instruction after each real instruction.
// Do this by introducing debug uses of each register definition. If that is
// not possible (e.g. we have a phi or a meta instruction), emit a constant.
uint64_t NextImm = 0;
SmallSet<DILocalVariable *, 16> VarSet;
const MCInstrDesc &DbgValDesc = TII.get(TargetOpcode::DBG_VALUE);
for (MachineBasicBlock &MBB : MF) {
MachineBasicBlock::iterator FirstNonPHIIt = MBB.getFirstNonPHI();
for (auto I = MBB.begin(), E = MBB.end(); I != E;) {
MachineInstr &MI = *I;
// `I` may point to a DBG_VALUE created in the previous loop iteration.
if (MI.isDebugInstr())
// It's not allowed to insert DBG_VALUEs after a terminator.
if (MI.isTerminator())
// Find a suitable insertion point for the DBG_VALUE.
auto InsertBeforeIt = MI.isPHI() ? FirstNonPHIIt : I;
// Find a suitable local variable for the DBG_VALUE.
unsigned Line = MI.getDebugLoc().getLine();
if (!Line2Var.count(Line))
Line = EarliestDVI->getDebugLoc().getLine();
DILocalVariable *LocalVar = Line2Var[Line];
assert(LocalVar && "No variable for current line?");
// Emit DBG_VALUEs for register definitions.
SmallVector<MachineOperand *, 4> RegDefs;
for (MachineOperand &MO : MI.operands())
if (MO.isReg() && MO.isDef() && MO.getReg())
for (MachineOperand *MO : RegDefs)
BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
/*IsIndirect=*/false, *MO, LocalVar, Expr);
// OK, failing that, emit a constant DBG_VALUE.
if (RegDefs.empty()) {
auto ImmOp = MachineOperand::CreateImm(NextImm++);
BuildMI(MBB, InsertBeforeIt, MI.getDebugLoc(), DbgValDesc,
/*IsIndirect=*/false, ImmOp, LocalVar, Expr);
// Here we save the number of lines and variables into "llvm.mir.debugify".
// It is useful for mir-check-debugify.
NamedMDNode *NMD = M.getNamedMetadata("llvm.mir.debugify");
IntegerType *Int32Ty = Type::getInt32Ty(Ctx);
if (!NMD) {
NMD = M.getOrInsertNamedMetadata("llvm.mir.debugify");
auto addDebugifyOperand = [&](unsigned N) {
Ctx, ValueAsMetadata::getConstant(ConstantInt::get(Int32Ty, N))));
// Add number of lines.
addDebugifyOperand(NextLine - 1);
// Add number of variables.
} else {
assert(NMD->getNumOperands() == 2 &&
"llvm.mir.debugify should have exactly 2 operands!");
auto setDebugifyOperand = [&](unsigned Idx, unsigned N) {
NMD->setOperand(Idx, MDNode::get(Ctx, ValueAsMetadata::getConstant(
ConstantInt::get(Int32Ty, N))));
// Set number of lines.
setDebugifyOperand(0, NextLine - 1);
// Set number of variables.
setDebugifyOperand(1, VarSet.size());
return true;
/// ModulePass for attaching synthetic debug info to everything, used with the
/// legacy module pass manager.
struct DebugifyMachineModule : public ModulePass {
bool runOnModule(Module &M) override {
MachineModuleInfo &MMI =
return applyDebugifyMetadata(
M, M.functions(),
"ModuleDebugify: ", [&](DIBuilder &DIB, Function &F) -> bool {
return applyDebugifyMetadataToMachineFunction(MMI, DIB, F);
DebugifyMachineModule() : ModulePass(ID) {}
void getAnalysisUsage(AnalysisUsage &AU) const override {
static char ID; // Pass identification.
char DebugifyMachineModule::ID = 0;
} // end anonymous namespace
"Machine Debugify Module", false, false)
"Machine Debugify Module", false, false)
ModulePass *llvm::createDebugifyMachineModulePass() {
return new DebugifyMachineModule();