[llvm-commits] CVS: llvm/www/docs/ProgrammersManual.html
Chris Lattner
lattner at cs.uiuc.edu
Sun Sep 22 14:39:01 PDT 2002
Changes in directory llvm/www/docs:
ProgrammersManual.html updated: 1.29 -> 1.30
---
Log message:
Add information about the DEBUG() macro and the Statistic template
---
Diffs of the changes:
Index: llvm/www/docs/ProgrammersManual.html
diff -u llvm/www/docs/ProgrammersManual.html:1.29 llvm/www/docs/ProgrammersManual.html:1.30
--- llvm/www/docs/ProgrammersManual.html:1.29 Wed Sep 18 00:14:25 2002
+++ llvm/www/docs/ProgrammersManual.html Sun Sep 22 14:38:40 2002
@@ -12,8 +12,24 @@
<li><a href="#general">General Information</a>
<ul>
<li><a href="#stl">The C++ Standard Template Library</a>
+<!--
+ <li>The <tt>-time-passes</tt> option
+ <li>How to use the LLVM Makefile system
+ <li>How to write a regression test
+-->
+ </ul>
+ <li><a href="#apis">Important and useful LLVM APIs</a>
+ <ul>
<li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt> and
<tt>dyn_cast<></tt> templates</a>
+ <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro &
+ <tt>-debug</tt> option</a>
+ <li><a href="#Statistic">The <tt>Statistic</tt> template &
+ <tt>-stats</tt> option</a>
+<!--
+ <li>The <tt>InstVisitor</tt> template
+ <li>The general graph API
+-->
</ul>
<li><a href="#common">Helpful Hints for Common Operations</a>
<ul>
@@ -48,22 +64,6 @@
<li>
<li>
</ul>
- <li>Useful LLVM APIs
- <ul>
- <li>The general graph API
- <li>The <tt>InstVisitor</tt> template
- <li>The DEBUG() macro
- <li>The <tt>Statistic</tt> template
--->
- </ul>
-<!--
- <li>Useful related topics
- <ul>
- <li>The <tt>-time-passes</tt> option
- <li>How to use the LLVM Makefile system
- <li>How to write a regression test
- <li>
- </ul>
-->
</ul>
<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
@@ -183,6 +183,16 @@
to write maintainable code more than where to put your curly braces.<p>
+<!-- *********************************************************************** -->
+</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
+<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
+<a name="apis">Important and useful LLVM APIs
+</b></font></td></tr></table><ul>
+<!-- *********************************************************************** -->
+
+Here we highlight some LLVM APIs that are generally useful and good to know
+about when writing transformations.<p>
+
<!-- ======================================================================= -->
</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td> </td><td width="100%">
@@ -292,13 +302,145 @@
lots of examples in the LLVM source base.<p>
+<!-- ======================================================================= -->
+</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
+<tr><td> </td><td width="100%">
+<font color="#EEEEFF" face="Georgia,Palatino"><b>
+<a name="DEBUG">The <tt>DEBUG()</tt> macro & <tt>-debug</tt> option</a>
+</b></font></td></tr></table><ul>
+
+Often when working on your pass you will put a bunch of debugging printouts and
+other code into your pass. After you get it working, you want to remove
+it... but you may need it again in the future (to work out new bugs that you run
+across).<p>
+
+Naturally, because of this, you don't want to delete the debug printouts, but
+you don't want them to always be noisy. A standard compromise is to comment
+them out, allowing you to enable them if you need them in the future.<p>
+
+The "<tt><a
+href="/doxygen/StatisticReporter_8h-source.html">StatisticReporter.h</a></tt>"
+file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
+this problem. Basically, you can put arbitrary code into the argument of the
+<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' is run with the
+'<tt>-debug</tt>' command line argument:
+
+<pre>
+ ...
+ DEBUG(std::cerr << "I am here!\n");
+ ...
+</pre><p>
+
+Then you can run your pass like this:<p>
+
+<pre>
+ $ opt < a.bc > /dev/null -mypass
+ <no output>
+ $ opt < a.bc > /dev/null -mypass -debug
+ I am here!
+ $
+</pre><p>
+
+Using the <tt>DEBUG()</tt> macro instead of a home brewed solution allows you to
+now have to create "yet another" command line option for the debug output for
+your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized
+builds, so they do not cause a performance impact at all.<p>
+
+
+<!-- ======================================================================= -->
+</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
+<tr><td> </td><td width="100%">
+<font color="#EEEEFF" face="Georgia,Palatino"><b>
+<a name="Statistic">The <tt>Statistic</tt> template & <tt>-stats</tt>
+option</a>
+</b></font></td></tr></table><ul>
+
+The "<tt><a
+href="/doxygen/StatisticReporter_8h-source.html">StatisticReporter.h</a></tt>"
+file provides a template named <tt>Statistic</tt> that is used as a unified way
+to keeping track of what the LLVM compiler is doing and how effective various
+optimizations are. It is useful to see what optimizations are contributing to
+making a particular program run faster.<p>
+
+Often you may run your pass on some big program, and you're interested to see
+how many times it makes a certain transformation. Although you can do this with
+hand inspection, or some ad-hoc method, this is a real pain and not very useful
+for big programs. Using the <tt>Statistic</tt> template makes it very easy to
+keep track of this information, and the calculated information is presented in a
+uniform manner with the rest of the passes being executed.<p>
+
+There are many examples of <tt>Statistic</tt> users, but this basics of using it
+are as follows:<p>
+
+<ol>
+<li>Define your statistic like this:<p>
+
+<pre>
+static Statistic<> NumXForms("mypassname\t- The # of times I did stuff");
+</pre><p>
+
+The <tt>Statistic</tt> template can emulate just about any data-type, but if you
+do not specify a template argument, it defaults to acting like an unsigned int
+counter (this is usually what you want).<p>
+
+<li>Whenever you make a transformation, bump the counter:<p>
+
+<pre>
+ ++NumXForms; // I did stuff
+</pre><p>
+
+</ol><p>
+
+That's all you have to do. To get '<tt>opt</tt>' to print out the statistics
+gathered, use the '<tt>-stats</tt>' option:<p>
+
+<pre>
+ $ opt -stats -mypassname < program.bc > /dev/null
+ ... statistic output ...
+</pre><p>
+
+When running <tt>gccas</tt> on a C file from the SPEC benchmark suite, it gives
+a report that looks like this:<p>
+
+<pre>
+ 7646 bytecodewriter - Number of normal instructions
+ 725 bytecodewriter - Number of oversized instructions
+ 129996 bytecodewriter - Number of bytecode bytes written
+ 2817 raise - Number of insts DCEd or constprop'd
+ 3213 raise - Number of cast-of-self removed
+ 5046 raise - Number of expression trees converted
+ 75 raise - Number of other getelementptr's formed
+ 138 raise - Number of load/store peepholes
+ 42 deadtypeelim - Number of unused typenames removed from symtab
+ 392 funcresolve - Number of varargs functions resolved
+ 27 globaldce - Number of global variables removed
+ 2 adce - Number of basic blocks removed
+ 134 cee - Number of branches revectored
+ 49 cee - Number of setcc instruction eliminated
+ 532 gcse - Number of loads removed
+ 2919 gcse - Number of instructions removed
+ 86 indvars - Number of cannonical indvars added
+ 87 indvars - Number of aux indvars removed
+ 25 instcombine - Number of dead inst eliminate
+ 434 instcombine - Number of insts combined
+ 248 licm - Number of load insts hoisted
+ 1298 licm - Number of insts hoisted to a loop pre-header
+ 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
+ 75 mem2reg - Number of alloca's promoted
+ 1444 cfgsimplify - Number of blocks simplified
+</pre><p>
+
+Obviously, with so many optimizations, having a unified framework for this stuff
+is very nice. Making your pass fit well into the framework makes it more
+maintainable and useful.<p>
+
<!-- *********************************************************************** -->
</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
<a name="common">Helpful Hints for Common Operations
-</b></font></td></tr></table><ul>
-<!-- *********************************************************************** -->
+</b></font></td></tr></table><ul> <!--
+*********************************************************************** -->
This section describes how to perform some very simple transformations of LLVM
code. This is meant to give examples of common idioms used, showing the
@@ -1616,6 +1758,6 @@
<a href="mailto:sabre at nondot.org">Chris Lattner</a></address>
<!-- Created: Tue Aug 6 15:00:33 CDT 2002 -->
<!-- hhmts start -->
-Last modified: Tue Sep 17 22:16:24 CDT 2002
+Last modified: Sun Sep 22 14:38:05 CDT 2002
<!-- hhmts end -->
</font></body></html>
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