First step in fixing PR8927:

Add a unnamed_addr bit to global variables and functions. This will be used
to indicate that the address is not significant and therefore the constant
or function can be merged with others.

If an optimization pass can show that an address is not used, it can set this.

Examples of things that can have this set by the FE are globals created to
hold string literals and C++ constructors.

Adding unnamed_addr to a non-const global should have no effect unless
an optimization can transform that global into a constant.

Aliases are not allowed to have unnamed_addr since I couldn't figure
out any use for it.

llvm-svn: 123063

2 files changed, 18 insertions, 2 deletions

diff --git a/llvm/docs/BitCodeFormat.html b/llvm/docs/BitCodeFormat.html
index d8ddc2b6b21..0b8747c261f 100644
--- a/llvm/docs/BitCodeFormat.html
+++ b/llvm/docs/BitCodeFormat.html
@@ -922,6 +922,9 @@ encoding of the visibility of this variable:
 <li><i>threadlocal</i>: If present and non-zero, indicates that the variable
 is <tt>thread_local</tt></li>
 
+<li><i>unnamed_addr</i>: If present and non-zero, indicates that the variable
+has <tt>unnamed_addr<tt></li>
+
 </ul>
 </div>
 
@@ -975,6 +978,10 @@ entries.</li>
 <li><i>gc</i>: If present and nonzero, the 1-based garbage collector
 index in the table of
 <a href="#MODULE_CODE_GCNAME">MODULE_CODE_GCNAME</a> entries.</li>
+
+<li><i>unnamed_addr</i>: If present and non-zero, indicates that the function
+has <tt>unnamed_addr<tt></li>
+
 </ul>
 </div>
 
diff --git a/llvm/docs/LangRef.html b/llvm/docs/LangRef.html
index 21144125b04..2121fc67408 100644
--- a/llvm/docs/LangRef.html
+++ b/llvm/docs/LangRef.html
@@ -846,6 +846,10 @@ define i32 @main() {   <i>; i32()* </i>&nbsp;
    region of memory, and all memory objects in LLVM are accessed through
    pointers.</p>
 
+<p>Global variables can be marked with <tt>unnamed_addr</tt> which indicates
+  that the address is not significant, only the content. Constants marked
+  like this can be merged if they have the same content.</p>
+
 <p>A global variable may be declared to reside in a target-specific numbered
    address space. For targets that support them, address spaces may affect how
    optimizations are performed and/or what target instructions are used to
@@ -885,7 +889,8 @@ define i32 @main() {   <i>; i32()* </i>&nbsp;
 <p>LLVM function definitions consist of the "<tt>define</tt>" keyword, an
    optional <a href="#linkage">linkage type</a>, an optional
    <a href="#visibility">visibility style</a>, an optional
-   <a href="#callingconv">calling convention</a>, a return type, an optional
+   <a href="#callingconv">calling convention</a>,
+   an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
    <a href="#paramattrs">parameter attribute</a> for the return type, a function
    name, a (possibly empty) argument list (each with optional
    <a href="#paramattrs">parameter attributes</a>), optional
@@ -896,7 +901,8 @@ define i32 @main() {   <i>; i32()* </i>&nbsp;
 <p>LLVM function declarations consist of the "<tt>declare</tt>" keyword, an
    optional <a href="#linkage">linkage type</a>, an optional
    <a href="#visibility">visibility style</a>, an optional
-   <a href="#callingconv">calling convention</a>, a return type, an optional
+   <a href="#callingconv">calling convention</a>,
+   an optional <tt>unnamed_addr</tt> attribute, a return type, an optional
    <a href="#paramattrs">parameter attribute</a> for the return type, a function
    name, a possibly empty list of arguments, an optional alignment, and an
    optional <a href="#gc">garbage collector name</a>.</p>
@@ -922,6 +928,9 @@ define i32 @main() {   <i>; i32()* </i>&nbsp;
    specified, the function is forced to have at least that much alignment.  All
    alignments must be a power of 2.</p>
 
+<p>If the <tt>unnamed_addr</tt> attribute is given, the address is know to not
+  be significant and two identical functions can be merged</p>.
+
 <h5>Syntax:</h5>
 <pre class="doc_code">
 define [<a href="#linkage">linkage</a>] [<a href="#visibility">visibility</a>]