[Assignment Tracking][8/*] Add DIAssignID merging utilities

The Assignment Tracking debug-info feature is outlined in this RFC:

https://discourse.llvm.org/t/
rfc-assignment-tracking-a-better-way-of-specifying-variable-locations-in-ir

Add method:

  Instruction::mergeDIAssignID(
      ArrayRef<const Instruction* > SourceInstructions)

which merges the DIAssignID metadata attachments on `SourceInstructions` and
`this` and replaces uses of the original IDs with the new shared one.

This is used when stores are merged, for example sinking stores out of a
if-diamond CFG or vectorizing contiguous stores.

Reviewed By: jmorse

Differential Revision: https://reviews.llvm.org/D133291

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index e31e691..f3c2371 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2583,6 +2583,9 @@ void llvm::combineMetadata(Instruction *K, const Instruction *J,
         break;
       case LLVMContext::MD_dbg:
         llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
+      case LLVMContext::MD_DIAssignID:
+        K->mergeDIAssignID(J);
+        break;
       case LLVMContext::MD_tbaa:
         K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
         break;