<ol>
<li><a href="#debug_info_descriptors">Debug information descriptors</a>
<ul>
- <li><a href="#format_anchors">Anchor descriptors</a></li>
<li><a href="#format_compile_units">Compile unit descriptors</a></li>
<li><a href="#format_global_variables">Global variable descriptors</a></li>
<li><a href="#format_subprograms">Subprogram descriptors</a></li>
</div>
-<!-- ======================================================================= -->
-<div class="doc_subsubsection">
- <a name="format_anchors">Anchor descriptors</a>
-</div>
-
-<div class="doc_text">
-
-<div class="doc_code">
-<pre>
-%<a href="#format_anchors">llvm.dbg.anchor.type</a> = type {
- i32, ;; Tag = 0 + <a href="#LLVMDebugVersion">LLVMDebugVersion</a>
- i32 ;; Tag of descriptors grouped by the anchor
-}
-</pre>
-</div>
-
-<p>One important aspect of the LLVM debug representation is that it allows the
- LLVM debugger to efficiently index all of the global objects without having
- to scan the program. To do this, all of the global objects use "anchor"
- descriptors with designated names. All of the global objects of a particular
- type (e.g., compile units) contain a pointer to the anchor. This pointer
- allows a debugger to use def-use chains to find all global objects of that
- type.</p>
-
-<p>The following names are recognized as anchors by LLVM:</p>
-
-<div class="doc_code">
-<pre>
-%<a href="#format_compile_units">llvm.dbg.compile_units</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> {
- i32 0,
- i32 17
-} ;; DW_TAG_compile_unit
-%<a href="#format_global_variables">llvm.dbg.global_variables</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> {
- i32 0,
- i32 52
-} ;; DW_TAG_variable
-%<a href="#format_subprograms">llvm.dbg.subprograms</a> = linkonce constant %<a href="#format_anchors">llvm.dbg.anchor.type</a> {
- i32 0,
- i32 46
-} ;; DW_TAG_subprogram
-</pre>
-</div>
-
-<p>Using anchors in this way (where the compile unit descriptor points to the
- anchors, as opposed to having a list of compile unit descriptors) allows for
- the standard dead global elimination and merging passes to automatically
- remove unused debugging information. If the globals were kept track of
- through lists, there would always be an object pointing to the descriptors,
- thus would never be deleted.</p>
-
-</div>
-
<!-- ======================================================================= -->
<div class="doc_subsubsection">
<a name="format_compile_units">Compile unit descriptors</a>