Emit section information for extern variables

Update IR generated to retain section information for external declarations.
This is related to https://reviews.llvm.org/D36487

Patch By: eandrews
Differential Revision: https://reviews.llvm.org/D36712

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311459 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/docs/LangRef.rst b/docs/LangRef.rst
index bfc4d90263dfd2898d8da7abec6d49ab609484bd..7fa2ec1c58837598833220903a2010b8521ed601 100644 (file)
--- a/docs/LangRef.rst
+++ b/docs/LangRef.rst
@@ -579,7 +579,9 @@ Global variables in other translation units can also be declared, in which
 case they don't have an initializer.
 
 Either global variable definitions or declarations may have an explicit section
-to be placed in and may have an optional explicit alignment specified.
+to be placed in and may have an optional explicit alignment specified. If there 
+is a mismatch between the explicit or inferred section information for the 
+variable declaration and its definition the resulting behavior is undefined. 
 
 A variable may be defined as a global ``constant``, which indicates that
 the contents of the variable will **never** be modified (enabling better
@@ -622,6 +624,12 @@ target supports it, it will emit globals to the section specified.
 Additionally, the global can placed in a comdat if the target has the necessary
 support.
 
+External declarations may have an explicit section specified. Section 
+information is retained in LLVM IR for targets that make use of this 
+information. Attaching section information to an external declaration is an 
+assertion that its definition is located in the specified section. If the 
+definition is located in a different section, the behavior is undefined.   
+
 By default, global initializers are optimized by assuming that global
 variables defined within the module are not modified from their
 initial values before the start of the global initializer. This is