Clarify common linkage and the requirements on it. Enforce
them in the verifier.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78160 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/LangRef.html b/docs/LangRef.html
index 33fc7d4..52ec978 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -552,19 +552,22 @@
translation unit that uses it. Unreferenced <tt>linkonce</tt> globals are
allowed to be discarded.</dd>
- <dt><tt><b><a name="linkage_common">common</a></b></tt>: </dt>
- <dd>"<tt>common</tt>" linkage is exactly the same as <tt>linkonce</tt>
- linkage, except that unreferenced <tt>common</tt> globals may not be
- discarded. This is used for globals that may be emitted in multiple
- translation units, but that are not guaranteed to be emitted into every
- translation unit that uses them. One example of this is tentative
- definitions in C, such as "<tt>int X;</tt>" at global scope.</dd>
-
<dt><tt><b><a name="linkage_weak">weak</a></b></tt>: </dt>
- <dd>"<tt>weak</tt>" linkage is the same as <tt>common</tt> linkage, except
- that some targets may choose to emit different assembly sequences for them
- for target-dependent reasons. This is used for globals that are declared
- "weak" in C source code.</dd>
+ <dd>"<tt>weak</tt>" linkage has the same merging semantics as
+ <tt>linkonce</tt> linkage, except that unreferenced globals with
+ <tt>weak</tt> linkage may not be discarded. This is used for globals that
+ are declared "weak" in C source code.</dd>
+
+ <dt><tt><b><a name="linkage_common">common</a></b></tt>: </dt>
+ <dd>"<tt>common</tt>" linkage is most similar to "<tt>weak</tt>" linkage, but
+ they are used for tentative definitions in C, such as "<tt>int X;</tt>" at
+ global scope.
+ Symbols with "<tt>common</tt>" linkage are merged in the same way as
+ <tt>weak symbols</tt>, and they may not be deleted if unreferenced.
+ Further, <tt>common</tt> symbols may not have an explicit section, and
+ must have a zero initializer. Functions and aliases may not have common
+ linkage.</dd>
+
<dt><tt><b><a name="linkage_appending">appending</a></b></tt>: </dt>
<dd>"<tt>appending</tt>" linkage may only be applied to global variables of