[pr19844] Add thread local mode to aliases.

This matches gcc's behavior. It also seems natural given that aliases
contain other properties that govern how it is accessed (linkage,
visibility, dll storage).

Clang still has to be updated to expose this feature to C.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209759 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 32 insertions, 19 deletions

diff --git a/docs/LangRef.rst b/docs/LangRef.rst
index fa40363a75..650012e7f9 100644
--- a/docs/LangRef.rst
+++ b/docs/LangRef.rst
@@ -464,6 +464,34 @@ DLL storage class:
     exists for defining a dll interface, the compiler, assembler and linker know
     it is externally referenced and must refrain from deleting the symbol.
 
+.. _tls_model:
+
+Thread Local Storage Models
+---------------------------
+
+A variable may be defined as ``thread_local``, which means that it will
+not be shared by threads (each thread will have a separated copy of the
+variable). Not all targets support thread-local variables. Optionally, a
+TLS model may be specified:
+
+``localdynamic``
+    For variables that are only used within the current shared library.
+``initialexec``
+    For variables in modules that will not be loaded dynamically.
+``localexec``
+    For variables defined in the executable and only used within it.
+
+If no explicit model is given, the "general dynamic" model is used.
+
+The models correspond to the ELF TLS models; see `ELF Handling For
+Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for
+more information on under which circumstances the different models may
+be used. The target may choose a different TLS model if the specified
+model is not supported, or if a better choice of model can be made.
+
+A model can also be specified in a alias, but then it only governs how
+the alias is accessed. It will not have any effect in the aliasee.
+
 .. _namedtypes:
 
 Structure Types
@@ -497,24 +525,6 @@ to be placed in, and may have an optional explicit alignment specified.
 Global variables in other translation units can also be declared, in which
 case they don't have an initializer.
 
-A variable may be defined as ``thread_local``, which means that it will
-not be shared by threads (each thread will have a separated copy of the
-variable). Not all targets support thread-local variables. Optionally, a
-TLS model may be specified:
-
-``localdynamic``
-    For variables that are only used within the current shared library.
-``initialexec``
-    For variables in modules that will not be loaded dynamically.
-``localexec``
-    For variables defined in the executable and only used within it.
-
-The models correspond to the ELF TLS models; see `ELF Handling For
-Thread-Local Storage <http://people.redhat.com/drepper/tls.pdf>`_ for
-more information on under which circumstances the different models may
-be used. The target may choose a different TLS model if the specified
-model is not supported, or if a better choice of model can be made.
-
 A variable may be defined as a global ``constant``, which indicates that
 the contents of the variable will **never** be modified (enabling better
 optimization, allowing the global data to be placed in the read-only
@@ -572,6 +582,9 @@ iteration.
 
 Globals can also have a :ref:`DLL storage class <dllstorageclass>`.
 
+Variables and aliasaes can have a
+:ref:`Thread Local Storage Model <tls_model>`.
+
 Syntax::
 
     [@<GlobalVarName> =] [Linkage] [Visibility] [DLLStorageClass] [ThreadLocal]
@@ -674,7 +687,7 @@ Aliases may have an optional :ref:`linkage type <linkage>`, an optional
 
 Syntax::
 
-    @<Name> = [Visibility] [DLLStorageClass] alias [Linkage] <AliaseeTy> @<Aliasee>
+    @<Name> = [Visibility] [DLLStorageClass] [ThreadLocal] alias [Linkage] <AliaseeTy> @<Aliasee>
 
 The linkage must be one of ``private``, ``internal``, ``linkonce``, ``weak``,
 ``linkonce_odr``, ``weak_odr``, ``external``. Note that some system linkers