IR: Add 'distinct' MDNodes to bitcode and assembly

Propagate whether `MDNode`s are 'distinct' through the other types of IR
(assembly and bitcode).  This adds the `distinct` keyword to assembly.

Currently, no one actually calls `MDNode::getDistinct()`, so these nodes
only get created for:

  - self-references, which are never uniqued, and
  - nodes whose operands are replaced that hit a uniquing collision.

The concept of distinct nodes is still not quite first-class, since
distinct-ness doesn't yet survive across `MapMetadata()`.

Part of PR22111.

llvm-svn: 225474

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 7c7eebde1df..1792f8b8dd4 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1106,6 +1106,7 @@ std::error_code BitcodeReader::ParseMetadata() {
     // Read a record.
     Record.clear();
     unsigned Code = Stream.readRecord(Entry.ID, Record);
+    bool IsDistinct = false;
     switch (Code) {
     default:  // Default behavior: ignore.
       break;
@@ -1196,12 +1197,17 @@ std::error_code BitcodeReader::ParseMetadata() {
           NextMDValueNo++);
       break;
     }
+    case bitc::METADATA_DISTINCT_NODE:
+      IsDistinct = true;
+      // fallthrough...
     case bitc::METADATA_NODE: {
       SmallVector<Metadata *, 8> Elts;
       Elts.reserve(Record.size());
       for (unsigned ID : Record)
         Elts.push_back(ID ? MDValueList.getValueFwdRef(ID - 1) : nullptr);
-      MDValueList.AssignValue(MDNode::get(Context, Elts), NextMDValueNo++);
+      MDValueList.AssignValue(IsDistinct ? MDNode::getDistinct(Context, Elts)
+                                         : MDNode::get(Context, Elts),
+                              NextMDValueNo++);
       break;
     }
     case bitc::METADATA_STRING: {