Add llvm.codeview.annotation to implement MSVC __annotation

Summary:
This intrinsic represents a label with a list of associated metadata
strings. It is modelled as reading and writing inaccessible memory so
that it won't be removed as dead code. I think the intention is that the
annotation strings should appear at most once in the debug info, so I
marked it noduplicate. We are allowed to inline code with annotations as
long as we strip the annotation, but that can be done later.

Reviewers: majnemer

Subscribers: eraman, llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D36904

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312569 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 0 deletions

diff --git a/docs/LangRef.rst b/docs/LangRef.rst
index 49ded73aaf6..eb7638fed36 100644
--- a/docs/LangRef.rst
+++ b/docs/LangRef.rst
@@ -13626,6 +13626,27 @@ with arbitrary strings. This can be useful for special purpose
 optimizations that want to look for these annotations. These have no
 other defined use; they are ignored by code generation and optimization.
 
+'``llvm.codeview.annotation``' Intrinsic
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Syntax:
+"""""""
+
+This annotation emits a label at its program point and an associated
+``S_ANNOTATION`` codeview record with some additional string metadata. This is
+used to implement MSVC's ``__annotation`` intrinsic. It is marked
+``noduplicate``, so calls to this intrinsic prevent inlining and should be
+considered expensive.
+
+::
+
+      declare void @llvm.codeview.annotation(metadata)
+
+Arguments:
+""""""""""
+
+The argument should be an MDTuple containing any number of MDStrings.
+
 '``llvm.trap``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^