1 files changed, 87 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/MachineDebugify.cpp b/llvm/lib/CodeGen/MachineDebugify.cpp
index bc607ca..bf57ec0 100644
--- a/llvm/lib/CodeGen/MachineDebugify.cpp
+++ b/llvm/lib/CodeGen/MachineDebugify.cpp
@@ -7,16 +7,23 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file This pass attaches synthetic debug info to everything. It can be used
-/// to create targeted tests for debug info preservation.
+/// 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/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"
 
@@ -31,13 +38,15 @@ bool applyDebugifyMetadataToMachineFunction(MachineModuleInfo &MMI,
   if (!MaybeMF)
     return false;
   MachineFunction &MF = *MaybeMF;
+  const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
 
   DISubprogram *SP = F.getSubprogram();
   assert(SP && "IR Debugify just created it?");
 
-  LLVMContext &Ctx = F.getParent()->getContext();
-  unsigned NextLine = SP->getLine();
+  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
@@ -48,6 +57,81 @@ bool applyDebugifyMetadataToMachineFunction(MachineModuleInfo &MMI,
     }
   }
 
+  // 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)
+        continue;
+      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;
+  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;
+
+      // `I` may point to a DBG_VALUE created in the previous loop iteration.
+      if (MI.isDebugInstr())
+        continue;
+
+      // It's not allowed to insert DBG_VALUEs after a terminator.
+      if (MI.isTerminator())
+        continue;
+
+      // 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())
+          RegDefs.push_back(&MO);
+      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);
+      }
+    }
+  }
+
   return true;
 }