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, 6 insertions, 0 deletions

diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 5238fe90d30..0a1c7768d5a 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -2848,6 +2848,12 @@ their operand. For example:
 
     !{ !"test\00", i32 10}
 
+Metadata nodes that aren't uniqued use the ``distinct`` keyword. For example:
+
+.. code-block:: llvm
+
+    !0 = distinct !{!"test\00", i32 10}
+
 A :ref:`named metadata <namedmetadatastructure>` is a collection of
 metadata nodes, which can be looked up in the module symbol table. For
 example: