[PATCH] D106304: [LangRef] Clarify support for multiple metadata attachments with same id

[Teresa Johnson via Phabricator via llvm-commits]

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As discussed on D105251 <https://reviews.llvm.org/D105251>, currently the compiler does not support
multiple metadata attachments on instructions having the same
identifier, whereas it does for global objects. Note this in the
Language Reference manual for clarity.

See D105251 <https://reviews.llvm.org/D105251> for discussions of history behind this divergence, and the
complexities and possible approaches of adding this support to
instructions in the future.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106304

Files:
  llvm/docs/LangRef.rst


Index: llvm/docs/LangRef.rst
===================================================================
--- llvm/docs/LangRef.rst
+++ llvm/docs/LangRef.rst
@@ -5035,8 +5035,8 @@
 Metadata
 ========
 
-LLVM IR allows metadata to be attached to instructions in the program
-that can convey extra information about the code to the optimizers and
+LLVM IR allows metadata to be attached to instructions and global objects in the
+program that can convey extra information about the code to the optimizers and
 code generator. One example application of metadata is source-level
 debug information. There are two metadata primitives: strings and nodes.
 
@@ -5096,6 +5096,9 @@
 
     %indvar.next = add i64 %indvar, 1, !dbg !21
 
+Instructions may not have multiple metadata attachments with the same
+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:
@@ -5110,6 +5113,9 @@
     @g1 = global i32 0, !dbg !22
     @g2 = external global i32, !dbg !22
 
+Unlike instructions, global objects (functions and global variables) may have
+multiple metadata attachments with the same identifier.
+
 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


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