Add a verifier check to make sure that DBG_VALUE and DBG_VALUE_LIST always refers to a DILocalVariable.

[rastogishubham]

Summary

The machine verifier never verifies that a DBG_VALUE or DBG_VALUE_LIST refers to a DILocalVariable. This may cause issues in optimization passes.

This patch adds a quick check to make sure a DBG_VALUE or DBG_VALUE_LIST always refers to a DILocalVariable

[aprantl]

Did you forget to git-add the testcase?

llvm/lib/CodeGen/MachineVerifier.cpp

1812

dead code

[rastogishubham]

I cannot seem to create a testcase which returns a null DILocalVariable for a DBG_VALUE or a DBG_VALUE_LIST, so I don't think this patch is necessary

llvm/lib/CodeGen/MachineVerifier.cpp

     Register Def = MI->getOperand(0).getReg();
     if (Def.isVirtual() &&
         !MF->getProperties().hasProperty(
             MachineFunctionProperties::Property::NoPHIs) &&
         std::distance(MRI->use_nodbg_begin(Def), MRI->use_nodbg_end()) > 1)
       report("Unspillable Terminator expected to have at most one use!", MI);
   }
 
-  // A fully-formed DBG_VALUE must have a location. Ignore partially formed
-  // DBG_VALUEs: these are convenient to use in tests, but should never get
-  // generated.
-  if (MI->isDebugValue() && MI->getNumOperands() == 4)
+  // Ignore partially formed DBG_VALUEs: these are convenient to use in tests,
+  // but should never get
+  //  generated.
+  if (MI->isDebugValue() && MI->getNumOperands() == 4) {
+    // A fully-formed DBG_VALUE must have a location.
     if (!MI->getDebugLoc())
       report("Missing DebugLoc for debug instruction", MI);
+    // A fully-formed DBG_VALUE or DBG_VALUE_LIST must have a DILocalvariable
+    // associated with it.
+    if (!MI->getDebugVariable())
+      report("Missing DebugVariable for debug instruction", MI);
+  }
+
+  if (MI->isDebugValue() && MI->getNumOperands() == 4) {
+  }
 
   // Meta instructions should never be the subject of debug value tracking,
   // they don't create a value in the output program at all.
   if (MI->isMetaInstruction() && MI->peekDebugInstrNum())
     report("Metadata instruction should not have a value tracking number", MI);
 
   // Check the MachineMemOperands for basic consistency.
   for (MachineMemOperand *Op : MI->memoperands()) {