[DebugInfo] [NFC] Refactor debug intrinsic copy and delete to instead just move

[Orlando]

Summary

This is in preparation for the assignment tracking changes. Without this change dbg.assign intrinsics are accidentally converted to dbg.values here. A test for the assignment tracking case will be added in a separate patch.

[jryans]

Thanks, looks good to me! 😄

[Orlando]

Thanks :-)

llvm/lib/Transforms/Utils/LoopUtils.cpp

for (auto *Block : L->blocks())
         DeadDebugInst.push_back(DVI);
       }
 
     // After the loop has been deleted all the values defined and modified
     // inside the loop are going to be unavailable.
     // Since debug values in the loop have been deleted, inserting an undef
     // dbg.value truncates the range of any dbg.value before the loop where the
     // loop used to be. This is particularly important for constant values.
-    DIBuilder DIB(*ExitBlock->getModule());
     Instruction *InsertDbgValueBefore = ExitBlock->getFirstNonPHI();
     assert(InsertDbgValueBefore &&
            "There should be a non-PHI instruction in exit block, else these "
            "instructions will have no parent.");
-    for (auto *DVI : DeadDebugInst)
-      DIB.insertDbgValueIntrinsic(UndefValue::get(Builder.getInt32Ty()),
-                                  DVI->getVariable(), DVI->getExpression(),
-                                  DVI->getDebugLoc(), InsertDbgValueBefore);
+    for (auto *DVI : DeadDebugInst) {
+      DVI->setUndef();
+      DVI->moveBefore(InsertDbgValueBefore);
+    }
   }
 
   // Remove the block from the reference counting scheme, so that we can
   // delete it freely later.
   for (auto *Block : L->blocks())
     Block->dropAllReferences();
 
   if (MSSA && VerifyMemorySSA)