[Assignment Tracking][5.1/*] Add deleteAssignmentMarkers function

[Orlando]

Summary

deleteAssignmentMarkers(const Instruction *Inst) does exactly as you'd expect - it deletes any dbg.assign intrinsics linked to Inst.

I'll fold this into the previous patch (D132224) when landing them, but I wanted to keep the review separate as that one has already been accepted.

[Orlando]

note to self: add unittest

[Orlando]

+ Add unittest
+ Fix review title

[jmorse]

LGTM with nit

llvm/include/llvm/IR/DebugInfo.h

222

[Orlando]

I'll fold this into the previous patch (D132224) when landing them

As it happens I forgot to do this. I'll be landing these separately.

[rastogishubham]

I am sorry for reverting this patch, but I have to revert it because I need to revert 171f7024cc82e8702abebdedb699d37b50574be7 due to the cyclic dependency that was introduced in the modules build

[Orlando]

Re-landed in 26382a4412d29e1c31fc3cda5071d5d60832b69c, folded into D132224.

llvm/include/llvm/IR/DebugInfo.h

 /// Iterators invalidated by deleting an intrinsic contained in this range.
 inline AssignmentMarkerRange getAssignmentMarkers(const Instruction *Inst) {
   if (auto *ID = Inst->getMetadata(LLVMContext::MD_DIAssignID))
     return getAssignmentMarkers(cast<DIAssignID>(ID));
   else
     return make_range(Value::user_iterator(), Value::user_iterator());
 }
 
+/// Delete the llvm.dbg.assgin intrinsics linked to \p Inst.
+void deleteAssignmentMarkers(const Instruction *Inst);
+
 /// Replace all uses (and attachments) of \p Old with \p New.
 void RAUW(DIAssignID *Old, DIAssignID *New);
 
 /// Remove all Assignment Tracking related intrinsics and metadata from \p F.
 void deleteAll(Function *F);
 
 /// Helper struct for trackAssignments, below. We don't use the similar
 /// DebugVariable class because trackAssignments doesn't (yet?) understand

llvm/lib/IR/DebugInfo.cpp

AssignmentMarkerRange at::getAssignmentMarkers(DIAssignID *ID) {
   // The ID is only used wrapped in MetadataAsValue(ID), so lets check that
   // one of those already exists first.
   if (!IDAsValue)
     return make_range(Value::user_iterator(), Value::user_iterator());
 
   return make_range(IDAsValue->user_begin(), IDAsValue->user_end());
 }
 
+void at::deleteAssignmentMarkers(const Instruction *Inst) {
+  auto Range = getAssignmentMarkers(Inst);
+  if (Range.empty())
+    return;
+  SmallVector<DbgAssignIntrinsic *> ToDelete(Range.begin(), Range.end());
+  for (auto *DAI : ToDelete)
+    DAI->eraseFromParent();
+}
+
 void at::RAUW(DIAssignID *Old, DIAssignID *New) {
   // Replace MetadataAsValue uses.
   if (auto *OldIDAsValue =
           MetadataAsValue::getIfExists(Old->getContext(), Old)) {
     auto *NewIDAsValue = MetadataAsValue::get(Old->getContext(), New);
     OldIDAsValue->replaceAllUsesWith(NewIDAsValue);
   }