[PATCH] D29110: LangRef: Document the allowed metadata dropping transforms.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc updated this revision to Diff 85800.
pcc marked an inline comment as done.
pcc added a comment.

- New wording


https://reviews.llvm.org/D29110

Files:
  llvm/docs/LangRef.rst


Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -3941,15 +3941,29 @@
 
     %indvar.next = add i64 %indvar, 1, !dbg !21
 
-Metadata can also be attached to a function definition. Here metadata ``!22``
-is attached to the ``foo`` function using the ``!dbg`` identifier:
+Metadata can also be attached to a function or a global variable. Here metadata
+``!22`` is attached to the ``f1`` and ``f2 functions, and the globals ``g1``
+and ``g2`` using the ``!dbg`` identifier:
 
 .. code-block:: llvm
 
-    define void @foo() !dbg !22 {
+    declare !dbg !22 void @f1()
+    define void @f2() !dbg !22 {
       ret void
     }
 
+    @g1 = global i32 0, !dbg !22
+    @g2 = external global i32, !dbg !22
+
+A transformation is required to drop any metadata attachment that it does not
+know or know it can't preserve. Currently there is an exception for metadata
+attachment to globals for ``!type`` and ``!absolute_symbol`` which can't be
+unconditionally dropped unless the global is itself deleted.
+
+Metadata attached to a module using named metadata may not be dropped. However,
+debug metadata (named metadata with the name ``!llvm.dbg.*``) may always
+be dropped.
+
 More information about specific metadata nodes recognized by the
 optimizers and code generator is found below.
 


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