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GarbageCollection.html is expanded to encompass the coming

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capabilities. This is a major rewrite and is easier to read en toto
rather than patchwise.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42414 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Gordon Henriksen 2007-09-27 19:31:36 +00:00
parent 1ed37fdb3b
commit 326e24fff0
4 changed files with 1195 additions and 266 deletions
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@ -30,13 +30,19 @@
</tr>
<tr><th colspan="8"><b>- <a href="#D">D</a> -</b></th></tr>
<tr>
<td><a href="#DAG">DAG</a></td>
<td><a href="#Derived_Pointer">Derived Pointer</a></td>
<td><a href="#DSA">DSA</a></td>
<td><a href="#DSE">DSE</a></td>
</tr>
<tr><th colspan="8"><b>- <a href="#G">G</a> -</b></th></tr>
<td><a href="#GC">GC</a></td>
</tr>
<tr><th colspan="8"><b>- <a href="#I">I</a> -</b></th></tr>
<tr>
<td><a href="#IPA">IPA</a></td>
<td><a href="#IPO">IPO</a></td>
<td><a href="#ISel">ISel</a></td>
</tr>
<tr><th colspan="8"><b>- <a href="#L">L</a> -</b></th></tr>
<tr>
@ -44,6 +50,10 @@
<td><a href="#LICM">LICM</a></td>
<td><a href="#Load-VN">Load-VN</a></td>
</tr>
<tr><th colspan="8"><b>- <a href="#O">O</a> -</b></th></tr>
<tr>
<td><a href="#Object_Pointer">Object Pointer</a></td>
</tr>
<tr><th colspan="8"><b>- <a href="#P">P</a> -</b></th></tr>
<tr>
<td><a href="#PRE">PRE</a></td>
@ -51,13 +61,16 @@
<tr><th colspan="8"><b>- <a href="#R">R</a> -</b></th></tr>
<tr>
<td><a href="#Reassociation">Reassociation</a></td>
<td><a href="#Root">Root</a></td>
</tr>
<tr><th colspan="8"><b>- <a href="#S">S</a> -</b></th></tr>
<tr>
<td><a href="#Safe_Point">Safe Point</a></td>
<td><a href="#SCC">SCC</a></td>
<td><a href="#SCCP">SCCP</a></td>
<td><a href="#SDISel">SDISel</a></td>
<td><a href="#SRoA">SRoA</a></td>
<td><a href="#SSA">SSA</a></td>
<td><a href="#Stack_Map">Stack Map</a></td>
</tr>
</table>
</div>
@ -92,13 +105,23 @@ href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
subexpression compuation. For example <tt>(a+b)*(a+b)</tt> has two
subexpressions that are the same: <tt>(a+b)</tt>. This optimization would
perform the addition only once and then perform the multiply (but only if
its compulationally correct/safe).
it's compulationally correct/safe).
</dl>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="D">- D -</a></div>
<div class="doc_text">
<dl>
<dt><a name="DAG"><b>DAG</b></a></dt>
<dd>Directed Acyclic Graph</dd>
<dt><a name="Derived_Pointer"><b>Derived Pointer</b></a></dt>
<dd>A pointer to the interior of an object, such that a garbage collector
is unable to use the pointer for reachability analysis. While a derived
pointer is live, the corresponding object pointer must be kept in a root,
otherwise the collector might free the referenced object. With copying
collectors, derived pointers pose an additional hazard that they may be
invalidated at any <a href="Safe_Point">safe point</a>. This term is used in
opposition to <a href="#Object_Pointer">object pointer</a>.</dd>
<dt><a name="DSA"><b>DSA</b></a></dt>
<dd>Data Structure Analysis</dd>
<dt><a name="DSE"><b>DSE</b></a></dt>
@ -106,6 +129,24 @@ href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
</dl>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="G">- G -</a></div>
<div class="doc_text">
<dl>
<dt><a name="GC"><b>GC</b></a></dt>
<dd>Garbage Collection. The practice of using reachability analysis instead
of explicit memory management to reclaim unused memory.</dd>
</dl>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="H">- H -</a></div>
<div class="doc_text">
<dl>
<dt><a name="Heap"><b>Heap</b></a></dt>
<dd>In garbage collection, the region of memory which is managed using
reachability analysis.</dd>
</dl>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="I">- I -</a></div>
<div class="doc_text">
<dl>
@ -116,6 +157,8 @@ href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
<dd>Inter-Procedural Optimization. Refers to any variety of code
optimization that occurs between procedures, functions or compilation units
(modules).</dd>
<dt><a name="IPO"><b>ISel</b></a></dt>
<dd>Instruction Selection.</dd>
</dl>
</div>
<!-- _______________________________________________________________________ -->
@ -131,6 +174,17 @@ href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
</dl>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="P">- O -</a></div>
<div class="doc_text">
<dl>
<dt><a name="Object_Pointer"><b>Object Pointer</b></a></dt>
<dd>A pointer to an object such that the garbage collector is able to trace
references contained within the object. This term is used in opposition to
<a href="#Derived_Pointer">derived pointer</a>.</dd>
</dl>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsection"><a name="P">- P -</a></div>
<div class="doc_text">
@ -147,7 +201,12 @@ href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
<dt><a name="Reassociation"><b>Reassociation</b></a></dt> <dd>Rearranging
associative expressions to promote better redundancy elimination and other
optimization. For example, changing (A+B-A) into (B+A-A), permitting it to
be optimized into (B+0) then (B).
be optimized into (B+0) then (B).</dd>
<dt><a name="Root"><b>Root</b></a></dt> <dd>In garbage collection, a
pointer variable lying outside of the <a href="#Heap">heap</a> from which
the collector begins its reachability analysis. In the context of code
generation, "root" almost always refers to a "stack root"&#151;a local or
temporary variable within an executing function.</dd>
</dl>
</div>
@ -155,6 +214,16 @@ href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
<div class="doc_subsection"><a name="S">- S -</a></div>
<div class="doc_text">
<dl>
<dt><a name="SCC"><b>Safe Point</b></a></dt>
<dd>In garbage collection, it is necessary to identify <a href="#Root">stack
roots</a> so that reachability analysis may proceed. It may be infeasible to
provide this information for every instruction, so instead the information
may is calculated only at designated safe points. With a copying collector,
<a href="#Derived_Pointers">derived pointers</a> must not be retained across
safe points and <a href="#Object_Pointers">object pointers</a> must be
reloaded from stack roots.</dd>
<dt><a name="SDISel"><b>SDISel</b></a></dt>
<dd>Selection DAG Instruction Selection.</dd>
<dt><a name="SCC"><b>SCC</b></a></dt>
<dd>Strongly Connected Component</dd>
<dt><a name="SCCP"><b>SCCP</b></a></dt>
@ -163,6 +232,10 @@ href="http://www.program-transformation.org/Transform/BURG">BURG</a> tool.</dd>
<dd>Scalar Replacement of Aggregates</dd>
<dt><a name="SSA"><b>SSA</b></a></dt>
<dd>Static Single Assignment</dd>
<dt><a name="Stack_Map"><b>Stack Map</b></a></dt>
<dd>In garbage collection, metadata emitted by the code generator which
identifies <a href="#Root">roots</a> within the stack frame of an executing
function.</dd>
</dl>
</div>
<!-- *********************************************************************** -->

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TR, TD { border: 2px solid gray; padding: 4pt 4pt 2pt 2pt; }
TH { border: 2px solid gray; font-weight: bold; font-size: 105%;
color: black; background: url("img/lines.gif");
background: url("img/lines.gif");
font-family: "Georgia,Palatino,Times,Roman,SanSerif"; text-align:center;
vertical-align: middle; }
TABLE { text-align: center; border: 2px solid black;

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@ -0,0 +1,5 @@
//===----------------------------------------------------------------------===//
Possible enhancement: If a collection cycle happens and the heap is not
compacted very much (say less than 25% of the allocated memory was freed), the
memory regions should be doubled in size.