diff options
| author | Hans Wennborg <hans@hanshq.net> | 2012-06-23 11:37:03 +0000 |
|---|---|---|
| committer | Hans Wennborg <hans@hanshq.net> | 2012-06-23 11:37:03 +0000 |
| commit | ce718ff9f42c7da092eaa01dd0242e8d5ba84713 (patch) | |
| tree | d3c6b996686af3fc9f47f7b5407c773a86a4f653 /docs/LangRef.html | |
| parent | 47cbc4e0ee6098b7be3c60108000a979f1809949 (diff) | |
| download | llvm-ce718ff9f42c7da092eaa01dd0242e8d5ba84713.tar.gz llvm-ce718ff9f42c7da092eaa01dd0242e8d5ba84713.tar.bz2 llvm-ce718ff9f42c7da092eaa01dd0242e8d5ba84713.tar.xz | |
Extend the IL for selecting TLS models (PR9788)
This allows the user/front-end to specify a model that is better
than what LLVM would choose by default. For example, a variable
might be declared as
@x = thread_local(initialexec) global i32 42
if it will not be used in a shared library that is dlopen'ed.
If the specified model isn't supported by the target, or if LLVM can
make a better choice, a different model may be used.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159077 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/LangRef.html')
| -rw-r--r-- | docs/LangRef.html | 34 |
1 files changed, 32 insertions, 2 deletions
diff --git a/docs/LangRef.html b/docs/LangRef.html index 9cb7e6392a..ba653dbd49 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -838,9 +838,32 @@ define i32 @main() { <i>; i32()* </i> <p>Global variables define regions of memory allocated at compilation time instead of run-time. Global variables may optionally be initialized, may have an explicit section to be placed in, and may have an optional explicit - alignment specified. A variable may be defined as "thread_local", which + alignment specified.</p> + +<p>A variable may be defined as <tt>thread_local</tt>, which means that it will not be shared by threads (each thread will have a - separated copy of the variable). A variable may be defined as a global + separated copy of the variable). Not all targets support thread-local + variables. Optionally, a TLS model may be specified:</p> + +<dl> + <dt><b><tt>localdynamic</tt></b>:</dt> + <dd>For variables that are only used within the current shared library.</dd> + + <dt><b><tt>initialexec</tt></b>:</dt> + <dd>For variables in modules that will not be loaded dynamically.</dd> + + <dt><b><tt>localexec</tt></b>:</dt> + <dd>For variables defined in the executable and only used within it.</dd> +</dl> + +<p>The models correspond to the ELF TLS models; see + <a href="http://people.redhat.com/drepper/tls.pdf">ELF + Handling For Thread-Local Storage</a> 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.</p> + +<p>A variable may be defined as a global "constant," which indicates that the contents of the variable will <b>never</b> be modified (enabling better optimization, allowing the global data to be placed in the read-only section of an executable, etc). @@ -893,6 +916,13 @@ define i32 @main() { <i>; i32()* </i> @G = addrspace(5) constant float 1.0, section "foo", align 4 </pre> +<p>The following example defines a thread-local global with + the <tt>initialexec</tt> TLS model:</p> + +<pre class="doc_code"> +@G = thread_local(initialexec) global i32 0, align 4 +</pre> + </div> |