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Remove debug info anchors - llvm.dbg.compile_units, llvm.dbg.subprograms

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and llvm.dbg.global_variables.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74251 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel
2009-06-26 01:49:18 +00:00
parent 6f8f6066fd
commit 13e16b65dd
6 changed files with 95 additions and 238 deletions
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docs/SourceLevelDebugging.html
-53
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@@ -24,7 +24,6 @@
<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>
@@ -334,58 +333,6 @@ height="369">
</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>